KOVIN ZLITIN - i METALS ALLOYS TECHNOLOGIES ko ^ o o T- O I- lil Izdajatelji / Publishers: Inštitut za kovinske materiale in tehnologije Ljubljana, ACRONI Jesenice, Institut Jožef Štefan Ljubljana, IMPOL Slovenska Bistrica, Kemijski inštitut Ljubljana, Koncem Slovenske železarne, Metal Ravne, Talum Kidričevo, Fakulteta za strojništvo Ljubljana, Slovensko društvo za tribologijo Ljubljana Glavni urednik / Editor: F. Vodopivec, IMT Ljubljana, Slovenija Gostujoči urednik / Guest Editor: M. Jenko, IMT Ljubljana, Slovenija KOVINE LETNIK STEV. STR. LJUBLJANA ZLITINE 31 6 465-608 TEHNOLOGIJE VOLUME NO. P. SLOVENIJA Prosimo avtorje, da pri pripravi rokopisa za objavo članka dosledno upoštevajo naslednja navodila: - Članek mora biti izvirno delo, ki ni bilo v dani obliki še nikjer objavljeno. Deli članka so lahko že bili podani kot referat. - Avtor naj odda članek oz. besedilo napisano na računalnik z urejevalniki besedil: - VVORDSTAR, verzija 4, 5, 6, 7 za DOS - VVORD za DOS ali VVINDOVVS. Če avtor besedila ne more dostaviti v prej naštetih oblikah, naj pošlje besedilo urejeno v ASCII formatu. Prosimo avtorje, da pošljejo disketo z oznako datoteke in računalniškim izpisom te datoteke na papirju. Formule so lahko v datoteki samo naznačene, na izpisu pa ročno izpisane. Celoten rokopis članka obsega: - naslov članka (v slovenskem in angleškem jeziku), - podatke o avtorju, - povzetek (v slovenskem in angleškem jeziku), - ključne besede (v slovenskem in angleškem jeziku), - besedilo članka, - preglednice, tabele, - slike (risbe ali fotografije), - podpise k slikam (v slovenskem in angleškem jeziku), - pregled literature. Članek naj bi bil čim krajši in naj ne bi presegal 5-7 tiskanih strani, pregledni članek 12 strani, prispevek s posvetovanj pa 3-5 tiskanih strani. Obvezna je raba merskih enot, ki jih določa zakon o merskih enotah in merilih, tj. enot mednarodnega sistema SI. Enačbe se označujejo ob desni strani besedila s tekočo številko v okroglih oklepajih. Preglednice (tabele) je treba napisati na posebnih listih in ne med besedilom. V preglednicah naj se - kjer je le mogoče - ne uporabljajo izpisana imena veličin, ampak ustrezni simboli. Slike (risbe ali fotografije) morajo biti priložene posebej in ne vstavljene (ali nalepljene) med besedilom. Risbe naj bodo izdelane praviloma povečane v merilu 2:1. Za vse slike po fotografskih posnetkih je potrebno priložiti izvirne fotografije, ki so ostre, kontrastne in primerno velike. Vsi podpisi k slikam (v slovenskem in angleškem jeziku) naj bodo zbrani na posebnem listu in ne med besedilom. V pregledu literature naj bo vsak vir oštevilčen s tekočo številko v oglatih oklepajih (ki jih uporabljamo tudi med besedilom, kadar se želimo sklicevati na določeni literarni vir). Vsak vir mora biti opremljen s podatki, ki omogočajo bralcu, da ga lahko poišče: knjige: - avtor, naslov knjige, ime založbe in kraj ter leto izdaje (po potrebi tudi določene strani): H. Ibach and H. Luth, Solid State Physics, Springer, Berlin 1991, p. 245 članki: - avtor, naslov članka, ime revije in kraj izhajanja, letnik, leto, številka ter strani: H. J. Grabke, Kovine zlitine tehnologije, 27, 1993,1-2, 9 Avtorji naj rokopisu članka priložijo povzetek v omejenem obsegu do 10 vrstic v slovenskem in angleškem jeziku. Rokopisu morajo biti dodani tudi podatki o avtorju: - ime in priimek, akademski naslov in poklic, ime delovne organizacije v kateri dela, naslov stanovanja, telefonska številka, E-mail in številka fax-a. Uredništvo KZT - odloča o sprejemu članka za objavo, - poskrbi za strokovne ocene in morebitne predloge za krajšanje ali izpopolnitev, - poskrbi za jezikovne korekture. Authors are kindly requested to prepare the manuscripts accord-ing to the follovving instructions: - The paper must be original, unpublished and properly prepared for printing. - Manuscripts should be typed vvith double spacing and wide margins on numbered pages and should be submitted on flop-py disk in form of: - VVORDSTAR, version 4, 5, 6, 7 for DOS, - VVORD for DOS or VVINDOVVS, - ASCII text vvithout formulae, in which čase formulae should be clearly vvritten by hand in the printed copy. Preparation of Manuscript: - the paper title (in English and Slovenian Language)* - author(s) name(s) and affiliation(s) - the text of the Abstract (in English and Slovenian Language)* - key vvords (in English and Slovenian Language)* - the text of the paper (in English and Slovenian Language)* - tables (in English Language) - figures (dravvings or photographs) - captions to figures (in English and Slovenian Language)* - captions to tables (in English) - acknovvledgement - references * The Editorial Board will provide for the translation in Slovenian Language for foreign authors. The length of published papers should not exceed 5-7 journal pages, of revievv papers 12 journal pages and of contributed papers 3-5 journal pages. The international system units (SI) should be used. Equations should be numbered sequentially on the right-hand side in round brackets. Tables should be typed on separate sheets at the end of manuscript. They should have a descriptive caption explaining dis-played data. Figures (dravvings or photographs) should be numbered and their captions listed together at the end of the manuscript. The dravvings for the line figures should be twice the size than in the print. Figures have to be original, sharp and well contrasted, enclosed separately to the text. References must be typed in a separate reference section at the end of the manuscript. vvith items refereed too in the text by numerals in square brackets. References must be presented as follovvs: - books: author(s), title, the publisher, location, year, page num-bers H. Ibach and H. Luth, Solid State Physics, Springer, Berlin 1991, p. 245 - articles: author(s), a journal name, volume, a year, issue number, page H. J. Grabke, Kovine zlitine thenologije, 27, 1993 , 1-2, 9 The abstract (both in English and in Slovenian Language) should not exceed 200 vvords. The title page should contain each author(s) fuli names, affiliation vvith fuli address, E-mail number, telephone and fax number if available. The Editor - will decide if the paper is accepted for publication, - will take care of the refereeing process, - language corrections. The manuscripts of papers accepted for publication are not re-turned. Rokopisi člankov ostanejo v arhivu uredništva Kovine zlitine tehnologije. KOVINE ZLITINE TEHNOLOGIJE METALS ALLOYS TECHNOLOGIES [{2292 8 0 KOVINE ZLITINE TEHNOLOGIJE Izdajatelj (Published for): Inštitut za kovinske materiale in tehnologije Ljubljana Soizdajatelji (Associated Publishers): SŽ ŽJ ACRONI Jesenice, IMPOL Slovenska Bistrica, Institut Jožef Štefan Ljubljana, Kemijski inštitut Ljubljana, Koncem Slovenske Železarne, Metal Ravne, Talum Kidričevo, Fakulteta za strojništvo Ljubljana, Slovensko društvo za tribologijo Ljubljana Izdajanje KOVINE ZLITINE TEHNOLOGIJE sofinancira: Ministrstvo za znanost in tehnologijo Republike Slovenije (Journal METALS ALLOYS TECHNOLOGIES is financialty supported by Ministrstvo za znanost in tehnologijo, Republika Slovenija) Glavni in odgovorni urednik (Editor-in-chief): prof. Franc Vodopivec, Inštitut za kovinske materiale in tehnologije Ljubljana, 1000 Ljubljana, Lepi pot 11, Slovenija Pomočnik glavnega urednika: doc. dr. Monika Jenko Področni uredniki: kovinski materiali (prof. dr. Franc Vodopivec), polimeri (dr. Majda Žigon), keramika (dr. Marija Kosec), vakuumska tehnika (dr. Jože Gasperič) Urednik (Editor): mag. Aleš Lagoja Tehnični urednik (Technical Editor): Jana Jamar Lektorji (Linguistic Advisers): dr. Jože Gasperič in Jana Jamar (slovenski jezik), prof. dr. Andrej Paulin (angleški jezik) Uredniški odbor (Editorial Board): doc. dr. Monika Jenko, prof. Jakob Lamut, prof. Vasilij Prešeren, prof. Drago Kolar, prof. Stane Pejovnik, prof. Jože Vižintin, dipl. ing. Sudradjat Dai, Jana Jamar Mednarodni pridruženi člani uredniškega odbora (International Advisory Board): prof. Hans Jurgen Grabke, Max-Planck-lnstitut fur Eisenforschung, Diisseldorf, Deutschland prof. Thomas Bell, Faculty of Engineering School of Metallurgy and Materials, The University of Birmingham, Birmingham, UK prof. Jožef Zrnik, Technicka Univerzita, Hutnicka fakulteta, Košice, Slovakia prof. Ilija Mamuzič, Sveučilište u Zagrebu, Hrvatska prof. V. Lupine, Istituto per la Technologia dei Materiali Metallici non Tradizionali, Milano, Italia prof. Gunther Petzov, Max-Pianck-lnstitut fur Metallforschung, Stuttgart, Deutschland prof. Hans-Eckart Oechsner, Universitat Darmstadt, Deutschland Izdajateljski svet (Editorial Advisory Board): prof. Marin Gabrovšek, prof. Blaženko Koroušič, prof. Ladislav Kosec, prof. Alojz Križman, prof. Tatjana Malavašič, dr. Tomaž Kosmač, prof. Leopold Vehotrar, prof. Anton Smolej, dr. Boris Ule, doc. dr. Tomaž Kolenko, dr. Jelena Vojvodič-Gvardjančič Članki objavljeni v periodični publikaciji KOVINE ZLITINE TEHNOLOGIJE so indeksirani v mednarodnih sekundarnih virih: (Articles published in journal are indexed in international secondary periodicals and databases): - METALS ABSTRACTS - ENGINEERED MATERIALS ABSTRACTS - BUSINESS ALERT ABSTRACTS (STEELS, NONFERROUS, POLYMERS, CERAMICS, COMPOSITES) - CHEMICAL ABSTRACTS - ALUMINIUM INDUSTRY ABSTRACTS - REFERATIVNYJ ŽURNAL: METALLURGUA Naslov uredništva (Editorial Address): KOVINE ZLITINE TEHNOLOGIJE IMT Ljubljana Lepi pot 11 1000 Ljubljana, Slovenija Telefon: +386 61 125 11 61 Telefax: +386 61 213 780 Žiro račun: 50101-603-50316 IMT pri Agenciji Ljubljana Na INTERNET-u je revija KOVINE ZLrTINE TEHNOLOGIJE dosegljiva na naslovu: http : // www. ctk. si /kovine/ (INTERNET: http://www.ctk.si/kovineO Elektronska pošta (E-mail): cobissimtlj @ ctklj.ctk.si Slika na ovitku: Pogled skozi opazovalno okno v ultra visokovakuumsko analizno posodo na vzorec, elektronsko in ionsko puško ter rentgenski izvir visokoločljivega Augerjevega spektrometra na poljsko emisijo Oblikovanje ovitka: Ignac Kofol Tisk (Print): Tiskarna PLANPRINT, Ljubljana Po mnenju Ministrstva za znanost in tehnologijo Republike Slovenije št, 23-335-92 z dne 09.06. 1992 šteje KOVINE ZLITINE TEHNOLOGIJE med proizvode, za katere se plačuje 5K3dstotni davek od prometa proizvodov. /o6 BESEDA GLAVNEGA UREDNIKA Za vsako revijo, še posebej za revije, ki delajo v majhnem okolju, imajo jubilejne številke poseben pomen. To velja tudi za revijo Kovine Zlitine Tehnologije. Poseben pomen jubilejnih številk pove najmanj dvoje: da v okolju, v katerem revija vrši svoje poslanstvo, seznanja javnost z raziskovalnimi, razvojnimi in tehnološko tehničnimi dosežki posameznikov, ki s kakovostjo in obsegom dovolj izstopajo iz poprečja. Posebne številke so tudi dokaz, da posamezniki z dosežki presegajo lokalni nivo, zato se med govornike, ki pred javnostjo nastopajo v njihovo počastitev, vključijo tudi priznani znanstveniki iz tujine. Organizatorji Konference o materialih in tehnologijah ter uredništvo revije Kovine Zlitine Tehnologije so veseli in ponosni, da sta jubilanta leta 1997 dva eminentna raziskovalca iz področij keramike in vakuuma, ki sodita v delovno področje konference in revije. Prof. dr. Dragu Kolarju lahko brez pretiravanja pripišemo očetovstvo resnega znanstveno raziskovalnega dela na področju elektro in elektronske keramike v Sloveniji. Njegovo ime najdemo med avtorji mnogih publikacij v Sloveniji in tujini, pa tudi med pobudniki in izvajalci razvojnih projektov za industrijska podjetja. Enako pomembno je tudi delo, ki ga je opravil pri vzgoji naslednikov, od katerih mnogi nadaljujejo delo na institutu, drugi pa kariero nadaljujejo v industrijskih podjetjih. Manj opaženo v raziskovalni sferi in javnosti, zato pa nič manj uspešno in koristno, je delo na področju vakuuma opravljal dr. Jože Gasperič, eden od utemeljiteljev vakuuma kot vede, stroke in tehnologije v Sloveniji in bivši Jugoslaviji. Kot pionir se je moral soočati z vrsto problemov, od pridobivanja začetnih znanj, preko visokega vakuuma kot bistvene komponente sodobne elektronike, humanih aplikacij vakuuma, do načrtovanja difuzijskih črpalk. Nekako logično ga najdemo zato tudi med razvijalci elektronskih komponent in tehnologij. V reviji Kovine Zlitine Tehnologije smo še posebej veseli, da zelo uspešno opravlja zahtevno nalogo lektorja slovenskih tekstov. Uredništvo revije in organizatorji Konference o materialih in tehnologijah obema slavljencema čestitajo, jima želijo še vnaprej dobrega zdravja in uspešnega dela, tudi mnogo uspeha pri prenosu znanja in izkušenj na mlade sodelavce. Glavni in odgovorni urednik: Prof. dr. Franc Vodopivec EDITOR'S FOREWORD Jubilee numbers are of special importance for scientific journals, especially those operating in small environments. Also for the journal Metals Alloys Technologies the editor sees at least two arguments supporting this view. The printing of a jubilee number demonstrates that also in the small environment, where the journal fulfils its role of information and education, individuals are found who are above the average by the quality and quantity of research and development performances to a level justifing the celebration. And, what is probably even more important, it is evident, that their work as scientists and engineers meets sufficient interest in the foreign research community and eminent scientists from abroad are ready to speak on the jubilants work or on their honour. The organisers of the Conference on Materials and Technologies and the editors of the journal Metals Alloys Technologies are glad and honoured to celebrate in 1997 the jubilee of Drago Kolar and Jože Gasperič, two eminent scientists and engineers active in the fields of ceramics and vacuum, two research and engineer domains of interest for both, the conference and the journal. It is possible, without exaggeration, to attribute to Drago Kolar the fatherhood of modern research in the field of electronic and electric ceramics in Slovenia. His name is found as author and coauthor in a a great number of scientific paper in domestic and foreign publications, and also betvveen the proposers and performers of research and development projects for industrial companies. At least of equal importance is the work of Drago Kolar by the education of young scientists and engineers, which are continuing and spreading his scientific and engineer activity. Less in public eyes, however with equal success and benefit, was the activity of Jože Gasperič, one of the pioneers of vacuum, as science and technology in Slovenia. As pioneer, he had to deal with many problems, from the acquisition of basic knowledge, over vacuum as vital component of the modern electronics and human vacuum applications, till the development and construction of diffusion vacuum pumps. It seems logical to find him also between the developers of electronic components and technology. The journal Metals Alloys Technologies is honoured to have Jože Gasperič as appreciated assistance as lecturer of manuscripts submitted in slovenian language. The editors of the journal and the organisers of the Conference on Materials and Technologies felicitate both jubilants and wish to both of them good health, productive work continuation, and successful transfer of knowledge and experience to younger colloborators. The editor Prof. dr. Franc Vodopivec 5. KONFERENCA O MATERIALIH IN TEHNOLOGIJAH 1.-3. oktober 1997, Kongresni center Grand hotel Emona, Portorož, Slovenija 50. POSVETOVANJE O METALURGIJI IN KOVINSKIH GRADIVIH 5. POSVETOVANJE O MATERIALIH 17. SLOVENSKO VAKUUMSKO POSVETOVANJE ZBORNIK - 1. DEL Posvetovanje so organizirali: INŠTITUT ZA KOVINSKE MATERIALE IN TEHNOLOGIJE, LJUBLJANA ODDELEK ZA MATERIALE IN METALURGIJO, NTF, UNIVERZA V LJUBLJANI KEMIJSKI INŠTITUT, LJUBLJANA; INŠTITUT JOŽEF ŠTEFAN, LJUBLJANA; SLOVENSKO DRUŠTVO ZA MATERIALE; SLOVENSKO KEMIJSKO DRUŠTVO: SEKCIJI ZA POLIMERE IN KERAMIKO; DRUŠTVO ZA VAKUUMSKO TEHNIKO SLOVENIJE Mednarodni znanstveni odbor H.J. Grabke G. Petzow M. Milim Znanstveni odbor F. Vodopivec M. Jenko J. Lamut S. Ažman F. Grešovnik D. Kolar S. Pejovnik T. Malavašič J. Gasperič Organizacijski odbor M. Jenko F. Vodopivec M. Torkar D. Steiner Petrovič S. Kobe M. Zigon A. Pregelj Mcvc-Planck-Institute for Iron Research, Dsseldorf, Germany Mcvc-Planck-Institute for Metal Research Stuttgart, Germany Institute of Physics, University of Zagreb, Croatia Inštitut za kovinske materiale in tehnologije, Ljubljana Inštitut za kovinske materiale in tehnologije, Ljubljana OMM, NTF, Univerza v Ljubljani SŽ ŽJ ACRONI d.o.o., Jesenice SŽ METAL RAVNE d.o.o., Ravne na Koroškem Fakulteta za kemijo in kemijsko tehnologijo, Univerza v Ljubljani Kemijski inštitut, Ljubljana Kemijski inštitut, Ljubljana Institut Jožef Štefan, Ljubljana Inštitut za kovinske materiale in tehnologije, Ljubljana Inštitut za kovinske materiale in tehnologije, Ljubljana Inštitut za kovinske materiale in tehnologije, Ljubljana Inštitut za kovinske materiale in tehnologije, Ljubljana Institut Jožef Štefan, Ljubljana Kemijski inštitut, Ljubljana Inštitut za elektroniko in vakuumsko tehniko, Ljubljana Posvetovanje je finančno podprlo Ministrstvo za znanost in tehnologijo Republike Slovenije Uredila: M. Jenko in F. Vodopivec, IMT Ljubljana 5th CONFERENCE ON MATERIALS AND TECHNOLOG Y October 1-3, 1997 Convention Centre Grand Hotel Emona, Portorož, Slovenia 50th SYMPOSIUM ON METALLURGY AND METALLIC MATERIALS 5th SYMPOSIUM ON MATERIALS 17th SLOVENIAN VACUUM SYMPOSIUM SELECTED PAPERS - PART 1 The Conference is organized by: INSTITUTE OF METALS AND TECHNOLOGY, LJUBLJANA DEPARTMENT OF MATERIALS AND METALLURGY, NTF, UNIVERSITY OF LJUBLJANA; NATIONAL INSTITUTE OF CHEMISTRY, LJUBLJANA; JOŽEF ŠTEFAN INSTITUTE, LJUBLJANA; SLOVENIAN SOCIETY OF MATERIALS SLOVENIAN CHEMICAL SOCIETY: DIVISIONS OF POLYMERS AND CERAMICS; SLOVENIAN VACUUM SOCIETY International Scientific Committee H.J. Grabke Max-Planck-Institute for Iron Research, Dsseldorf, Germany G. Petzow Max-Planck-Institute for Metal Research Stuttgart, Germany M. Milun Institute of Physics, University of Zagreb, Croatia Scientific Committee F. Vodopivec M.Jenko J. Lamut S. Ažman F. Grešovnik D. Kolar S. Pejovnik T. Malavašič J. Gasperič Institute of Metals and Technology, Ljubljana Institute of Metals and Technology, Ljubljana Dept. of Materials and Metallurgy, University of Ljubljana SŽ ŽJ ACRONI d.o.o., Jesenice SŽ METAL RAVNE d.o.o., Ravne na Koroškem Faculty of Chemistry and Chemical Technology, University of Ljubljana National Institute of Chemistry, Ljubljana National Institute of Chemistry, Ljubljana Jožef Štefan Institute, Ljubljana Organizing Committee M. Jenko Institute of Metals and Technology, Ljubljana F. Vodopivec Institute of Metals and Technology, Ljubljana M. Torkar Institute of Metals and Technology, Ljubljana D. Steiner Petrovič Institute of Metals and Technology, Ljubljana S. Kobe Jožef Štefan Institute, Ljubljana M. Žigon National Institute of Chemistry, Ljubljana A. Pregelj Institute for Electronics and Vacuum Techniques, Ljubljana The Conference is financially supported by Ministrstvo za znanost in tehnologijo, Republika Slovenija. Edited by M. Jenko and F. Vodopivec, IMT Ljubljana Vsebina - Contents IZBRANI PRISPEVKI, predstavljeni na 5. Konferenci o materialih in tehnologijah, Portorož, 1997 -SELECTED PAPERS presented at 5th Conference on Materials and Technology, Portorož 1997 ZNANSTVENI PRISPEVKI - SCIENTIFIC PAPERS I. KOLARJEV DAN - KOLAR'S DAY Anorganski materiali - Inorganic Materials Contemporary Ceramic Research - a Čase Study G. Petzow .......................................................................... 473 Chemistry Controlled Sintering and Microstructural Development in Ceramics Kemijsko nadzorovano sintranje in razvoj mikrostrukture v keramiki D. Kolar ........................................................................... Ali Growth of III-Nitrides Via Sublimation and Metalorganic Vapor Phase Epitaxy Rast III-nitridov s sublimacijo in metalorgansko parno fazno epitaksijo R. F. Daviš, C. M. Balkas, M. D. Bremser, O. H. Nam, W. G. Perry, B. L. Ward, L. Bergman, R. J. Nemanich, Z. Sitar, T. Zheleva, I. K. Shmagin, J. F. Muth, R. M. Kolbas................... 485 Pionieer Years of Electron Probe Microanalysis in Slovenia Pionirsko obdobje elektronske mikroanalize v Sloveniji F. Vodopivec........................................................................ 495 II. GASPERIČEV DAN - GASPERIČ'S DAY Vakuumska tehnika - Vacuum Technique Laudation in Honour of Professor Dr. Jože Gasperič on the Occasion of his 65th Birthday M. Jenko........................................................................... 501 The Proper Operation of the High Vacuum Pumping System Pravilno delovanje visokovakuumskega črpalnega sistema J. Gasperič......................................................................... 503 Ultra Thin Deposited and Segregated Films Ultra tanke nanesene in segregirane plasti M. Jenko........................................................................... 507 The New Research Equipment for Surface Characterisation of Materials at the IMT Ljubljana Nova raziskovalna oprema za raziskave površin trdnih snovi na IMT, Ljubljana M. Jenko........................................................................... 519 III. Kovine - Metals Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching Vpliv dinamike prenosa toplote na porazdelitev trdote po kaljenju B. Liščič........................................................................... 521 Methods for the Validation of Advanced Thin Hard Protective Coatings - an European Program Metoda za validacijo naprednih tankih zaščitnih plasti - evropski program P. Mayr, H. Vetters, A. Schulz.......................................................... 529 As-Rolled Multi-Phase Microalloyed Steel Bars with Improved Properties Valjane večfazne mikrolegirane jeklene palice z izboljšanimi lastnostmi Dj. Drobnjak, A. Koprivica............................................................ 533 471 Two-Way Shape Memory Effect and its Degradation During Thermal Cycles in Ni-Ti Alloys Dvosmerni spominski efekt v Ni-Ti zlitinah in njegova degradacija med toplotnimi cikli H. Scherngell, A. C. Kneissl........................................................... 539 Introduction of Unshaped Refractories in the Wear Lining of Steel Ladles Uporaba neoblikovanega ognjestalnega materiala za obrobno obstojno obzidavo jeklarskih ponovc (Prispevek, predstavljen na 4. Konferenci o materialih in tehnologijah, Portorož 1996) F. Etienne, E. Ziarovski............................................................... 545 Pulse Plasma Nitrocarburising of Gas Shock Absorber Ttibes from Steel W.No. 1.0116 Nitrokarburiranje cevi plinskega blažilca iz jekla W.No. 1.0116 v pulzirajoči plazmi V. Leskovšek, M. Doberšek, A. Rodič.................................................... 551 Possibilities and Perspectives for Development of Metallurgy in the Republic of Macedonia Možnosti in perspektive za razvoj metalurgije v Republiki Makedoniji J. K. Mickovski, N. Nacevski, B. Nikov, S. Milosevski ...................................... 557 Investigation of Kinetics Leaching and Extraction of Vanadiumpentoxyde as a Function of Temperature Raziskave kinetike luženja in ekstrakcije vanadijevega pentoksida v odvisnosti od temperature N. Nacevski, B. Nikov ................................................................ 563 Anorganski materiali - Inorganic Materials The Difference Between the Magneto- Crystalline Anisotropy of Intermetallic Alloy Pr2(Coo.5Feo.5)l7 and Interstitially Modified Pr2(Coo.5Feo.5)l7N3-6 Razlika med magnetno kristalno anizotropijo Pr2(Coo.5Feo.5)l7 in Pr2(Coo.5Feo.5)i7N3-§ M. Komelj, S. Kobe .................................................................. 567 Polimeri - Polymers Model Polymers with Dimethylamine and Sulfozwitterionic End-Groups. Synthesis and Self Assembly in Solution and in Bulk Modelni polimeri z dimetilaminskimi in sulfozwitterionskimi končnimi skupinami N. Hadjichristidis, S Pispas, M. Pitsikalis ............................................... 571 Recent Advances in Synthesis of Monosubstituted Acetylene Polymers Razvoj na področju sinteze monosubstituiranih acetilenskih polimerov J. Vohlidal, J. Sedlaček, M. Žigon ...................................................... 581 Interfacial Phenomena in Thin Polymer Films Studied by Direct Profiling Techniques Študij pojavov na mejnih ploskvah tankih polimernih plasti z direktnimi tehnikami profiliranja A. Budkowski ....................................................................... 587 IV. REDNI PRISPEVKI - REGULAR PAPERS Kovine - Metals Mechanical and Microstructural Properties of Duplex Steel Mikrostruktura in mehanske lastnosti dupleks jekel M. Gojič, L. Kosec, L. Vehovar ...............................................................593 V. Letno kazalo - Index ............................................................. 599 CONTEMPORARY CERAMIC RESEARCH - A ČASE STUDY GUNTHER PETZOW Max-Planck-Institut, Institut fur Metalforschung, Heissenbergstrasse 5, 70569 Stuttgart Mr. Chairman, Ladies and Gentlemen, it is my great pleasure to he here today and to look at many faces so familiar to me. And this is especially true with Drago Kolar, the bright centre of our Kolar' s Day. When I was asked by the organisers of Kolar's Day for the title of my speech I suggested: "Drago Kolar - A Pioneer and Ambassador of Science of Ceramics". But as you can realise from the program the title is printed as "Contemporary Ceramic Research - A Čase Study " since I do not know the reason for the change, I assume it is a printing error. May it be as it is: It does not matter! I simply take as my Čase Study: "Drago Kolar" a short circuit. Because it is evident that "Contemporary Ceramic Research " and Drago Kolar are synonymous. Ladies and Gentlemen, dear Drago, "It is an obvious privilege of age to be able to relieve worldly things of their material focus and gravity and il-luminate them with the inner light of the mind, where they can be seen in a panoramic view". These words were vvritten by Baron Wilhelm von Humboldt, the elder brother of the famous scholar Alex-ander von Humboldt as he turned sixty-five (230 years ago). I should like to preface my laudatory remarks with these words. They convincingly impact a sense of the maturity that results from a fuli life, whichever turns it may have taken. Experience and calmness are expressed with these vvords and, if you will, an independence of špirit, a piece of self -actualisation. Humbaldt's words are eminently suitable for the present occasion. Drago Kolar has been a mover and has achieved much. This vvas not always accomplished at first blush and things may not always have gone according to plan. But setbacks are the spice which brings flavour to suc-cess. And in the ups and downs in Drago's life dealt by fate he has remained ever true to his own self, and that alone matters. The inner light of his ideas - to pick up Humbaldfs thought, the inner light, shines and is reflected in his ac-tions. Today I am honoured to report on them. I shall do so by follovving the chronological progress of his career, but take some liberties in the selection of events because the limitations of this programme do not permit fuli cover-age of his remarkably multifaceted life. Prof. dr. Drago Kolar "Omnium euim reum..." we were taught in school. Ali things begin small - so also little Drago when he en-tered the stage of life on the fifteenth of September, 1932, that is exactly sixty-five years and fifteen days ago. On this platform, he considered a calling in the arts or perhaps in literature - such vvere the career goals of the grovving boy, whose broad spectrum of talents indi-cated a specific inclination for chemistry, but certainly none in the direction of materials science and engineer-ing. However, it appears that Saint Barbara, the patron of the foundryman and metallurgists and more recently of materials scientists too, had an eye on him. Ali things begin small, but if time is used, they grow! And little Drago grew up. He went to school and he vvas an excel-lent schoolboy and then at the University of Ljubljana a very good študent, who passed his final examination vvith great success in 1957. Thereafter he began to work on his Ph.D. thesis. The experimental vvork he did at the highly respectable Jožef Štefan Institute and graduated at the University of Ljubljana. It vvas in 1964, vvhen the doctor's degree of science in chemistry vvas confirmed upon him. This is 7 to 8 years after he has received his master certificate. 7 to 8 years are really an unusual time spent for a gradu- ation. And at first sight one could have the impression of a lazy candidate of poor dynamic, living an unconven-tional life like a bohemian devoted to ali kinds of fun and pleasure. But as we know: the reverse is true! He has made op-timum use of his time besides his Ph.D. activities. From 1957 to 1959 he has been a Research Assistant at the Jožef Štefan Institute. This occupation was interrupted by a one year's military service, which he has completed in the rank of a non-commissioned officer. Obviously he has not had great interest in a military career. At that time it was a must for a young and ambitious scientist to go for a research stay in a top laboratory in USA. Drago Kolar became a research participant at the International Institute for Nuclear Science and Engineering of Ar-gonne National Laboratory, Illinois. He was in the age of 28 then and really enjoyed the stimulating atmosphere in a famous and renovvned laboratory in which well experi-enced, well-known scientists co-operated with highly motivated young colleagues from ali over the world. Drago Kolar became involved in investigations on kinetic processes in solid materials. A topic of great fasci-nation to him and vvhich he took up again and again during his further research work; of course always with improved methods and on the basis of an advanced knovvledge. His special interest was preferably directed to high performance ceramics which at that time became a research topic of highest actuality. Remember, it was the time of beginning of the so called ceramic fever. To-day it is obvious vvith this work he has established him-self in the elite of the Contemporary Ceramic Research. It was in 1961, when Drago Kolar came back home to the Jožef Štefan Institute, where he then ran through a brilliant career form a Research Assistant to a Senior Research Associate and finally, already in 1965 to the Head of the new founded Ceramic Department, vvhich under his leadership has grovvn up to be among the top ceramic research facilities in the vvorld. Beside his busy professional career he found enough time to court a lovely lady študent named Majda, who he married in 1960. In 1964 - the year of his graduation - he also became father of the vvonderful tvvins Jana and Aleš. Good timing! So, again, I vvould like to repeat: The guess, Drago has been a lazy Ph.D. candidate is com-pletely disproved. Also in his spare private hours he was active and successful. In addition he vvrote during this time five papers, vvhich have been published in recognised scientific jour-nals. It is really remarkable! His very first article vvas published 1962 in the March issue of the Journal of the American Ceramic So-ciety, the leading Journal in the field. In his first paper entitled: " Influence of Gas Flovv on DTA curves of UO2.'1, he described the use of Differen-tial Thermal Analysis to study the oxidation behaviour of U02. The resultant conclusions he gave in regard to the oxidation kinetics are stili relevant today. Numerous other publications follovved the first ones. Meanvvhile more than 200 papers are on his list of publi- cations and another more than 200 are published in pro-ceedings, monographs and encyclopaedias. He holds 8 patents, has written two fine textbooks on ceramics and is editor of 5 Proceeding Volumes of International Con-ferences. To underline Dr. Kolar's great scientific poten-tial, one should also mention the high number of invited and introductory lectures on conferences, universities and institutes abroad. I have had the pleasure to hear many of his lectures and I have always been impressed by theirs precision and lucidity. Drago KoIar's first scientific actions have fallen in a prosperous time for the field of materials science, vvhich flourished, and consequently had a strong influx of stu-dents and scientists from traditional disciplines, mainly from physics. It has been a vvonderful stimulating period, full of nevv and exciting possibilities. The electron microscopy, for instance, became introduced to materials investigations and brought a deeper insight into the microstructure. The metal physicists ex-amined the structure of real crystals and established the basic understanding of the influence of structural failures on properties. With the upcoming modern computers, simulations and calculations of complex processes and multicomponent materials of higher order could be han-dled much easier than ever before. In those days generous support to ali fields of science vvas the rule but the outstanding contributions were given to nuclear research and development. Accordingly, nuclear materials have been investigated vvith preference. This has also influenced Drago Kolar's vvork. Synthesis, processing and properties of Uranium containing materials have been mainly his study objects. Hovvever, the period of nuclear euphoria vvas short and even changed to serious non-acceptance by many people, as we knovv. Many of the reactor research centres, vvhich have had grovvn up very fast had to take into account the changing situation and to look for other research topics. No doubt Drago Kolar vvas among those, vvho have easily foreseen this development. As a consequence he fixed another aim for the research activities in his depart-ment and himself. He decided for advanced materials, and more specifically for functional ceramics. BaTi03 based materials became his personal favourite - one can say "his great love". And indeed these substances are multifunctional vvith many facets and suitable for several applications; as disks and multilayer capacitors for instance and microvvave ceramics and others. BaTi03 can really be compared vvith a coquettish, charming, but mysterious and sometimes even a tricky lady vvho never fully opens her heart. Comparable vvith Mona Lisa vvhose mysterious smile has inspired men's fantasy since long. But Drago Kolar took away many secrets from the difficult and brittle lady BaTi03 and clarified utmost complex phase relations of BaTi03 based multicomponent systems. He discovered several ternary compounds vvith perovskite like structures vvhich exhibit good di-electric properties and high temperature stabilities. And he is among those vvho gave the most solid results in this field. With same exactness he studied the exaggerated grain growth, twins formation, processing, and sintering of BaTiOi based materials with the aim of dense materi-als of excellent quality. But of course, BaTiOi was not the only substance in-vestigated by him. More or less ali oxide - nitride and carbide based advanced ceramics have been object of his sophisticated studies. His main scientific interest was al-ways directed to the interrelation between processing, microstructure and properties. Processing mechanism de-termine the microstructural formation. And the microstructure affects many technically important properties and is therefore given considerable attention in science, deveiopment and testing of materials. The higher the de-mands on a material, the more sophisticated the microstructural insight becomes, i.e. the more exacting the re-quirements on the microstructural parameters will be. "Microstructural engineering" or "microstructural design" are the key words that characterise these problems. This scientific strategy is in full accordance with the in-tentions of the Max-Planck Institute for Metals Research at Stuttgart. And this conformitv is the basis for our long-lasting fruitful and pleasant co-operation with pro-fessor Kolar and his wonderful team. For that co-operation I vvould like to express my sincere thanks to you and your co-workers. And I am doing this also on behalf of the board of directors of our institute. I have to bring the greetings and the message: " Dear Drago, you are wel-come in Stuttgart at any time!" It is an extraordinary merit of Drago Kolar that he in ali his scientific efforts has never lost the view for the requirements of application. Drago Kolar took a scientific curiosity and turned it into an engineering material, whose economic utilisation he significantly influenced. Best in ali these activities he never deviated from his high scientific standards. Doubtless he belongs to those pioneers who build bridges from basic research to application, seeking close co-operation with industrial partners. This underlines again his foresight, for today transfer of science and innovation are required more than ever before. It is a precondition for ali support from govern-ments, business and industry. Here I would like to quote some remarks of Gottfried Wilhelm Leibniz, the great philosopher and mathematician who lived three hundreds years ago. He stated in that time already: "The work of science should be application-oriented from the outset. Otherwise government will withdraw its hands for, the ministries vvill soon tire of useless curiosities and not recommend the prices to put much stock in them." Teaching and research were always an inseparable unity to Drago Kolar and it is his ongoing concern that his knovvledge and research skills will pass on to future generations. Numerous diploma and doctoral candidates have con-tributed to his scientific work. Here, it is Drago Kolar, who must be credited for defining the problems, setting quality standards and providing critical guidance to his co-workers. Many of them are present today and will tes-tify to his positive influence on their work. It is indeed impressive how engaged Drago Kolar took over ali the pleasure and burden of an academic teacher beside his extensive duties as head of the Ceramics Department of the Jožef Štefan Institute. Since 1972 he is teaching at the Faculty of Chemistry and Chemical Technology at the University of Ljubljana. The same plače where he had done his first steps into science. What a nicely closed circle! After being assistant profes-sor first, he became a full professor of ceramics and materials science in 1977. He thereby entered a circle of in-dividuals of whom Johann Wolfgang Goethe stood in awe and admiration when he wrote to his father in Octo-ber of 1765: You will not believe what a splendid affair a professor is: I was delighted to observe several of these fellows in their glory." Beyond research and teaching he maintained contacts with many universities and research laboratories and suc-ceeded in bridging research and applications in a most impressive manner. Some of this will become evident in the presentations by several of his road companions, which are to follovv. In acknovvledgement of his extraor-dinary merits in broadening the foundations of materials science and applying this knowledge to the deveiopment of advanced materials he received several honourable in-vitations as a guest professor or a member of advisory boards. I can not mention ali of them. As an example for many others I would like to mention the Keating Cravv-ford distinguished visiting professorship of Metallurgical Engineering and Materials Science of the University of Notre Dame, Indiana. During this period from 1982 to 1983 he had the opportunity to stay in close exchange of ideas and theories with the famous George Kuczynski, one of the bright brains in the science of sintering. The high reputation of Drago Kolar creative power is also underlined by the many awards he has won. I have counted about 25, but vvould like to mention only one, vvhich I think is the one vvhich represents Drago Kolar's life - vvork best. That is the distinction as an ambassador of science of the Republic of Slovenia. And I vvould like to go beyond that and add: he is in addition an impressive ambassador of contemporary ceramics and of science of sintering! Ladies and Gentlemen, there is a saying among chil-dren in our country vvhich is often quoted: "The uncle, who brings a present is much better than the aunt, who plays the piano." And I think since I have not played the laudation piano plentifully, I have to deliver a present. It is a very special one: This sculpture is knovvn as the "Two Particle Man" or "Sinterman". It is the highest distinction that the P/M Committee of the German Materials Society can bestovv. It is only conferred for excep-tional contributions to the field of sintering whereby the recipient is not only critical of his ovvn performance, but also has a sense of humour. The Tvvo-Particle Man con-sists of spherical povvder particles of a particular size distribution, so that in the first sintering stage they form a neck, just as how we understand the tvvo particle sintering theory. The body vvhich represents the particle, and the head vvhich embodies the theory, are equally large. Of course, that is a big compliment to the theoreticians. Drago knows very well: Theory and practice in sintering are like the hare and the tortoise in a race. Whenever the theory - hare breathlessly reaches the next check point he finds the Practice - tortoise already there. The tortoise smiles and explains: I don't know how, but I am already here!" This trophy, a high distinction in a humorous form, is in significance comparable to an Oscar. Up to now it has only been avvarded five times to excellent scientists and practitioners in the field of sintering. And now Drago Kolar; the award of this trophy is in recognition of your extraordinary contribution in densification ceramic povv-ders which has brought many advantages. Here symbol-ised by an alumina bali of full density for bioimplanta-tion. The recognition of your theoretical contribution is symbolised by the 3 particles in your hands, which stand for the 3 particle theory, on which we already had end-less discussions. May you, Drago Kolar, as the youngest prize holder, stay in freshness of your colleagues and friends of the German Povvder Metallurgy Committee. And I may add, it is the desire of ali of us. Ladies and Gentlemen, Drago Kolar is a scientist for whom mental image and practical implementation are not opposites but form a fertile contribution. This I have attempted to demon-strate vvith an account of his professional career. His recognition among peers had led to his engage-ment in numerous extra curricular activities vvhich he took on and continues to take on cheerfully. By the latest count there have been 16 membership in vvorkshops, topical committees, advisory boards, executive councils, revievv committees, editorial boards, and others. In ali of these bodies he is never just a member but an active par-ticipant in word and deed who gets noticed by his crisp language and his spirited involvement in discussions. Again, I will mention only one example, which involves ali fun and trouble of the preparation and realisation in connection vvith committee activities. That is the Yugo-slav - German co-operation on Engineering Materials Science and Technology. This co-operation started in 1972 vvith good financial support of German government and is now continued by bilateral Slovene-German activities. From the beginning this scientific partnership was characterised by a stimulating exchange of scientists in different fields of research. I think it is not exagger-ated to claim, Drago Kolar was a main driving force be-hind the co-operation and pushing the realisation of the regular meetings. He was the first who has contacted us after the disintegration of former Yugoslavia to start vvith the Slovene-German co-operation again. In lune 1992, he vvrote to me: "In the meantime, we are trying here to keep our activities on decent level. It is not easy in changing political situation. We are trying to escape the pitfalls of separation. Hovvever, the priče in economical terms is high. But prospects are great and vvith a little help we may catch the prosperity again. My letter con-cerns possible co-operation ...". And novv, five years after independence, Slovenia is a completely accepted candi-date for the European Union. Novv, of course, Ladies and Gentlemen, no honest human being vvould vvant to stand up and praise his fellovv colleague unless he can claim some affinity vvith him. In this sense, I had no difficulty ansvvering in the affirm-ative vvhen Prof. Stane Pejovnik asked me to present this laudation. Hovvever, the more I dug into Drago Kolar's back-ground the more obvious it became that I had missed a fevv things and that, perhaps, someone else vvould have been better qualified to give the talk. He might have put a different spin on events in his life and surely vvould have illustrated other facts than I did. What I can say is that: vvith the study of his life history, my admiration of Drago Kolar has grovvn greatly. The performance of Drago Kolar can only be explained by personal effort be-yond the call of duty, a sovereign command of the scientific field and the joy of creative work. It goes vvithout saying that one's vvork environment must be supportive, providing outstanding co-workers, good infrastructure and a peaceful home. A vvord about Drago's hobbies: First his vvork on Ba-Ti03, second his vvork on exaggerated grain grovvth, third condensor ceramic and then some gardening in the garden of his vveekend house, bicycle riding and slovv vvalking together vvith his male cat David. Novv Drago Kolar leaves his position as Head of the Ceramics Department. But he vvill not disappear and vvill be present in the department and his partners at the uni-versity and, of course, in the minds and heads of his co-vvorkers and colleagues. And it vvould be vvise to trust furthermore in his experience and advice. In closing, I should like to add a personal note of friendship that brings us full circle to the vvords of Wil-helm von Humboldt vvith vvhich I began. The vvords are borrovved from inscriptions in St. Paul's Cathedral at Baltimore: "Cheerful and calmly accept the council of age. Take leave of things of youth vvith grace. Whatever your vvork and your yearnings may be, maintain peace vvithin your soul, in the noisy bustle of life". Dear Drago, your colleagues and the present assem-bly thank you for your many contributions to our field. We vvish you, your family and your institute the very best for a happy future. Please accept our congratulations and best vvishes on your 65th birthday. CHEMICALLY CONTROLLED SINTERING AND MICROSTRUCTURAL DEVELOPMENT IN CERAMICS KEMIJSKO NADZOROVANO SINTRANJE IN RAZVOJ MIKROSTRUKTURE V KERAMIKI DRAGO KOLAR Fakulteta za kemijo in kemijsko tehnologijo, Murnikova 5a, 1000 Ljubljana in Institut J. Štefan, Ljubljana Faculty of Chemistry & Chemical Engineering, University of Ljubljana, and J. Štefan Institute, Ljubljana Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 The sintering step in manufacturing most ceramic articles is dominated by the chemical reactions which occur during firing. Such chemical reactions may be caused by chemical heterogeneity of the constituents of the ceramic body, small amounts of additives or impurities. Even in chemically equilibrated multicomponent systems the capillary forces may cause dehomogenisation and influence the sintering mechanism. Reaction sintering in the BaTi03-CaZr03-Ti02 system is described as an example of a system where controlled chemical heterogeneity may optimise the electrical properties. Sintering of PbZri-xTix03 ceramic is described as an example of chemical dehomogenisation due to capillary forces. Key words: reaction sintering, ceramic microstructure, barium titanate, lead zirconate-titanate, sintering mechanisms Proces sintranja v proizvodnji večine keramičnih izdelkov določajo kemijske reakcije, ki potekajo med žganjem. Kemijske reakcije lahko povzročajo heterogenost sestavin keramike, majhne količine dodatkov ali nečistoče. Celo v kemijsko uravnoteženih večkomponentnih sistemih lahko kapilarne sile povzročijo dehomogenizacijo in vplivajo na mehanizem sintranja. Delo obravnava reakcijsko sintranje v sistemu BaTi03-Ti02-CaZrC>3 kot primer procesa, pri katerem lahko z nadzorovano kemijsko heterogenostjo optimiziramo električne lastnosti keramike. Sintranje PbZri-xTix03 keramike obravnavamo kot primer sistema, pri katerem se kemijsko homogena trdna raztopina med sintranjem prehodno dehomogenizira. Fenomen vpliva na mehanizem sintranja in električne lastnosti piezokeramike. Ključne besede: reakcijsko sintranje. keramična mikrostruktura. barijev titanat, svinčev cirkonat-titanat, mehanizmi sintranja 1 INTRODUCTION 1.1 SWOT analysis of advanced technical ceramics SWOT analysis (S = strength, W = weakness, O = opportunities, T = threat) is a frequently used method for evaluation of the potential of a particular activity. Such analysis applied to the manufacture of ceramic articles may give the following answers: (Many other arguments may be added). S: Ceramics are the oldest artificial materials invented by mankind. In last 50 or 60 years the applicability of ceramics increased enormously. As a result, the mar-ket grovvth in many segments in recent decades main-tained a level of 8-10 % per year, vvhich is far above many other industrial activities. W: The weaknesses of ceramics are well knovvn: The producers and consumers complain of insufficient re-producibility, insufficient reliability and insufficient cost effectiveness of ceramic products. O: Experts agree on the great yet unexploited technical potential of ceramics. T: There are several obstacles vvhich limit opportunities in the ceramic field. To be competitive and assure high performance products, high investments in knovvledge and manufacturing equipment are neces-sary. In the following, we examine reasons for shortcom-ings of ceramics, listed in "W". In this article, we con-centrate on sintering. Sintering is the final step in the ceramic fabrication process. It decisively influences the properties of products made from povvders by sintering and represents the last chance of optimising the product. Sintering theories are based on physical arguments such as the tendency for reduction in free surface energy and on simplified assumptions such as simple particle shapes (spheres) and simple particle arrangements (two or a limited number of spheres). The general validity of sintering theories developed in pioneertng works by Frenkel1, Ivensen2, Kucyznski3, Kingery4, Coble5, Johnson6 and others was proven by nu-merous experiments. Sintering theories are primarily concerned vvith material transport mechanisms and the kinetics of the sintering process. Knovvledge of both are of fundamental importance for designing a cost effective manufacturing process for ceramic and powder metal articles vvith optimal properties. Hovvever, the value of sintering theories in the manufacturing practice of specific ceramic products is limited due to the fact that theoretical assumptions about sintering processes are not valid in practice7. Fundamental studies assume (I) a pure, a homogeneous, single compo-nent starting povvder, (II) uniform, small, spherical grains, (III) homogeneous body before sintering, and (IV) sintering at constant temperature. In contrast, prac-titioners in industrial produetion deal vvith (I) impure povvders, usually inhomogeneous mixtures, (II) povvders vvith a vvide distribution of particle sizes, aggiomerated to various degree, (III) vvith non-uniform density distri- bution, and (IV) sintering at practically non-isothermal conditions. Among serious inconsistencies between the assump-tions underlying theoretical and basic experimental re-seareh on sintering phenomenon, chemical reactions at sintering temperature among constituents in the sintered body play an important role. Chemical reactions in many ceramic systems occur among the constituents which are not in equilibrium at high temperatures and form new compounds or solid so-lutions. When the sintering process involves purposely chemically heterogeneous mixtures vvhich are supposed to react during the sintering operation, one uses the term "reaction sintering". Examples are BaTi03 capacitor ce-ramics or ZnO based varistor ceramics. Most ceramic products are made of a basic compound vvith a small amount of additives which are intended to accelerate densification, suppress grain growth or modify the physi-cal properties of the fired ceramics. The role of additives was frequently analysed, for example in 8 and 9. In general, the additives may accelerate sintering by forming a liquid phase or control the mierostructure by forming solid second phases which pin grain boundaries and im-pede grain growth. More subtle effects, vvhich, however, profoundly influence the sintering process, are segrega-tion at the grain boundaries, change of lattice defect concentration and diffusion constants when additives form a solid solution vvith the major component and a change in the ratio of grain boundary energy to free surface energy. It is clear that the design of the sintering process, based on theoretical physical arguments only, must be modified by taking into account the possible chemical reactions. In the follovving section, we report the results of re-search conducted in our laboratory on the effects of various aspects of chemical reactions on sintering. Specifi-cally, we report effects of chemical heterogeneity on the sintering process in multicomponent systems. We dem-onstrate that even in single phase systems chemical de-homogenisation/homogenisation takes plače. The aim of the revievv is to stress the importance of knovvledge of chemical phenomena vvhich occur during sintering of ceramics in designing and control]ing the sintering process. 2 REACTION SINTERING IN THE BaTi03-CaZr03-Ti02 SYSTEM The term "reaction sintering" or "reactive sintering" is used to describe a sintering process in vvhich a chemical reaction in the starting povvder mixture and the densification of the ceramic body occur in the same heating operation. Depending on the material system and proc-essing variables (particle size, temperature, pressure, etc.) the two processes, reaction and densification, can occur simultaneously, in sequence or as some mixture of these. Temperature [°CJ Figure 1: Dilatometric curves for BaTi03 - 2 mol % Ti02 (1), BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 (2), BaTi03 - 8 mol % CaZr03 (3) and CaZr03 (4). Slika X: Krivulje krčenja za mešanice BaTi03 - 2 mol % Ti02 (1), BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 (2), BaTi03 - 8 mol % CaZr03 (3) in CaZr03 (4). mol'/. CaZrOj Figure 2: Average grain size vs. composition in BaTi03 - 2 mol % TiC>2 - CaZr03 ceramics sintered 1 hour at 1360°C. Slika 2: Poprečna velikost zrn v odvisnosti od sestave keramike BaTi03 - 2 mol % Ti02 - CaZr03, sintrane 1 uro pri 1360DC. In ceramic fabrication practice, reaction sintering is usually avoided. The complexity of the processes caused by the chemical potential on one hand and the tendency to decrease the surface energy on the other renders the process difficult to control reproducibly. So, for example, in the manufacturing of soft Mn-Zn ferrites, the oxides are first calcined to form spinel solid solutions and then sintered. On the other hand, reactive sintering offers the possibility to optimise the properties of sintered products vvhich are intentionally not in chemical equilibrium. Such is the čase with several types of functional ceramics, for example varistors or high permittivity ceramic capacitors. Frequently used compositions for ceramic capacitors are based on the solid solutions (Bai-xCax)(Tii.yZry)03. If Zr is incorporated into BaTiOi the maximum of the per-mittivity curve (at the Curie point) is shifted from 130°C to room temperature, vvhereas the non-ferroelectric Ca-TiOj broadens this maximum. CaTiOi has only limited solubility in BaTiOj and small undissolved particles of CaTiOj act as grain-growth inhibitors in the ferroelectric matrixl(). (Bai-xCax)(Tii-yZry)03 capacitor ceramic is usually prepared by reaction sintering of BaTi03 - CaZr03 mixed powders. BaTi03 and CaZrOs are not compatible at high temperatures. During sintering, chemical reaction takes plače resulting in formation of (Ba,Ca)(Ti,Zr)03 and (Ca,Ba)Ti03 solid solutions". The sintering kinetics and microstructural development of BaTi03-CaZr03 formu-lations are influenced by the kinetics of the chemical reaction, particularly at lower temperatures, i.e. in the in-itial sintering stage. Research in our laboratory12-13 showed that the par-ticular batch of BaTi03 used started to shrink at around 1100°C and sintered considerably in the temperature re-gion 1300-1350°C (Fig. 1). CaZr03, being more refrac- tory, started to shrink at around 1250°C and sintered to high density in the temperature region 1450-1500°C. A BaTi03 - 8 mol % CaZr03 mixture started to shrink at approximately the same temperature as BaTi03. Hovv-ever, after a few % shrinkage the kinetics slowed down and temperatures higher than 1500°C were needed for densification. The sinterability of the BaTi03-CaZr03 mixture was improved by avoiding solid state diffusion. A small addition of Ti02 (2 mol %), causing the formation of a low melting BaTiOs-BafiTinO^ eutectic at around 1310°C, strongly improved the sinterability of the mixture. Temperatures between 1300-1350°C were sufficient to achieve high density. The microstructures of dense BaTi03 - 2 mol % TiOj and BaTiOs - 10 mol % CaZr03-2 mol % Ti02 ceramics sintered at 1360°C are shown in Fig. 2. The microstructures also show that CaZr03 strongly reduces the exaggerated grain growth vvhich is common phenomenon in BaTi03 - Ti02 ceramics. Comparison of the relative linear shrinkage of BaTiOs - 2 mol % Ti02 and BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 compacts as a function of time for isothermal sintering at 1260°C (Fig. 3) clearly indicated the differ-ences in the sintering mechanism. BaTi03 - 2 mol % Ti02 sintering kinetics in the initial stage can be de-scribed by an equation for first order kinetics Al/l = kt" in vvhich n is constant over the vvhole temperature range of sintering. In contrast, for BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 the graphical representation of ln(Al/l0)vs. In t shovvs a change in slope, indicating tvvo different densification regions vvith different n - values. The densification process is especially disturbed in the first stage of sintering at lovver temperatures (Fig. 4) due to the chemical reaction betvveen BaTi03 and CaZr03. When heated, BaTi03 and CaZr03 react to form a (Ba,Ca)(Ti,Zr)03 solid solution. The equilibrium solid solution limit is ln t [mini Figure 3: Comparison of the relative linear shrinkage of BaTi03 - 2 mol % Ti02 (a) and BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 (b) compacts as a function of time for the isothermal sintering at 1260°C. Slika 3: Primerjava med relativnim skrčkom oblikovancev iz BaTi03 -2 mol % Ti02 (a) in BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 (b) v odvisnosti od časa izotermnega sintranja pri 1260°C. 1300°C ln t [min) Figure 4: The relative linear shrinkage of BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 samples as a function of time for the isothermal sintering temperatures of 1260°C, 128CTC and 1300°C. Slika 4: Relativni linearni skrček oblikovancev iz BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 v odvisnosti od časa pri izotermnem sintranju pri 1260°C, 1280°C in 1300°C. Time [min) Figure 5: Degree of reaction (a) as a function of time for BaTi03 + CaZrOj —> BaZrOj + CaTi03 at various temperatures. Slika 5: Stopnja reakcije (a) v odvisnosti od časa za reakcijo BaTiOj + CaZrOj BaZrOj + CaTi03 pri različnih temperaturah. around 16 mol % CaZr03. Larger amounts of CaZr03 cause formation of barium zirconate phase vvith some Ca and Ti in solid solution and a calcium titanate phase vvith some dissolved BaTi0310''4. In a 1:1 mole ratio BaTi03 -CaZr03 mixture the reaction vvas detectable by XRD analysis after only 1 hour's heating at 1100°C. The tvvo characteristic X-ray reflections of CaTi03 at 2 0 = 59.052 (d = 1.563) and 2 9 = 47.401 (d = 1.918) vvere used for identification of CaTi03 and to determine the amount of CaTi03 formed during the reaction. The degree of reaction a as a function of time for the reaction BaTi03 + CaZr03 BaZr03 + CaTi03 at various temperatures is shovvn in Fig. 5. At lovver temperatures (1100°C) a remains under 20 % even after pro-longed heating. A considerably higher degree of reaction vvas achieved by heating the mixture of BaTi03 and CaZr03 at 1250°C and higher. The relationship a = f(t) at various temperatures has been evaluated using different mathematical expressions, theoretically derived for various models. The best fit vvas achieved vvith Jander's equation15: [1 -(1 - a)"3]2 = kt, vvhich describes three dimensional diffusion16. It may be concluded that the diffusion mechanism is rate con-trolling. The reaction kinetics da/dt vvere compared vvith the sintering kinetics da'/dt. The densification parameter a' (a'= p-po/pih-po) was calculated from dilatometric meas-urements in the temperature region 1200-1300°C (Fig. 6). Comparison of the reaction rates vvith the densification rates at various temperatures confirmed the priority of chemical reaction in the first stage of sintering, and densification in the second stage (at higher temperatures). Sintering conditions have a strong influence on the microstructural development. A slovver heating rate _da' dt Figure 6: Comparison of the reaction rate da/dt and densification rate da'/dt (a=p'-po/p,h-p0) for BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 samples at 1260°C. Slika 6: Primerjava med reakcijsko hitrostjo doc/dt in hitrostjo zgoščevanja daVdt (a'=p'-po/pth-po) oblikovancev iz BaTi03 - 2 mol % TiOi - 8 mol % CaZr03 pri 1260°C. (l°/min) leads to the development of a coarse microstructure vvith a broad grain size distribution, vvhereas more rapid heating (5° or 10°C/min.) results in a ftner microstructure vvith a narrovver grain size distribution. The results may be explained on the basis of the kinetic studies. A fast heating rate favours reaction sintering vvith hindered grain grovvth, vvhereas a slovv heating rate favours chemical reaction vvhich takes plače at lovver temperatures than densification. The heterogeneous structure vvith phase separations in the initial sintering stage favours discontinuous grain grovvth and a broad grain size distribution. Microstructural development also depends on the solid state diffusion rate during heating. A small excess of Ti02, causing a liquid phase eutectic at sintering temperature, promotes grain grovvth, especially at slovv heating rates. When BaTi03 vvith a small excess of BaO vvas used, grain grovvth during sintering vvas considerably hindered, especially vvhen a slovv heating rate vvas used. Coarsening of the microstructure as a result of pro-longed firing is accompanied by dielectric property changes. Different compositions of BaTi03 - CaZr03 based ceramics vvere fired at 1360°C for 15, 60, 480 minutes and the resulting dielectric properties vvere measured (Table 1). Whereas an e value belovv the Curie temperature decreases vvith increasing firing time, the peak at the Curie temperature increases in value and broadens. Changes in the intensity and broadness of the peak are accompanied by coarsening of the microstructure. The coarse microstructure shovvs a more pro-nounced Tc shift and higher permittivity, vvhile the room temperature permittivity is lovvered. Maximum values of permittivity vvere obtained vvith the composition 84 mol % BaTi03 - 16 mol % CaZr03 near to the limit of solid solubility in the system. D. KOLAR: CHEMICALLY CONTROLLED SINTERING Table 1: Dielectric properties of BaZr03 based ceramics vvith 2 mol % TiOi addition vs. soaking rime at 1360°C (at 1 kHz) Composition 90 m/o BaTi03-10 m/o CZ 84 m/o BaTi03-16 m/o CZ 80 m/o BaTi03-20 m/o CZ time (min) 15 60 480 15 60 480 15 60 480 £25°C 4753 4270 2030 4045 7200 10694 2780 3105 5210 tg5.104 107 105 200 79 92 130 45 74 105 Tc(°C) 60 60 70 20 25 35 -20 -15 -10 6350 7820 8960 4600 7200 10767 3820 4650 6619 AC/C (%) / / / -31,0 + 14,0 -48,20 -71,2 +0,7 / / / Chemically inhomogeneous ceramics in metastable ceramic equilibrium make it possible to make, by careful control of firing conditions, the temperature stable dielectric materials. This is ascribed to specific core-shell grain structure17. The relatively flat temperature charac-teristic of dielectric constant of BaTi03-CaZr03 based ceramics is determined by the superposition of the two permittivity/temperature maxima, those of BaTi03 core at - 120°C and (Ca,Zr) doped BaTi03 shell with maxi-mum at lower temperature. Core-shell structure is dis-cernible in TEM micrograph in Fig. 7. In the formation of the shell, reactive liquid phase plays important role, since the shell is formed by precipitation of dissolved matter on BaTiOj nuclei. Prolonged sintering provokes chemical homogenisation by solid state diffusion giving rise to inereased permittivity and inereased temperature dependence of permittivity. 3 SINTERING OF MONOPHASE COMPLEX CERAMICS: SINTERING OF Pb(Zro.5Tio.5)03 (PZT) In analysing sintering phenomena, it is important to realise that chemical reactions may influence the densifi-cation mechanism even in chemically homogenous com-pounds. In recent years, considerable progress in the processing of ceramics has been achieved by improving the quality of povvders. Attention is paid to vvet-chemical methods of povvder preparation, vvhich assure fine particle size, controlled morphology, high purity and high ho-mogeneity. Improved homogeneity is particularly desir-able in complex multicomponent ceramics. It is frequently stressed that vvet chemical methods, such as coprecipitation or sol-gel methods, assure chemical homogeneity "on a molecular" level. Hovvever, this homogeneity may be temporarily lost during the sintering operation due to the very nature of the sintering process. Kuczynski et alls pointed out that the vacancy gradient set up betvveen sintered particles by the sharp curva-ture of the neck betvveen particles can, under favourable conditions, produce considerable segregation in a com-pletely homogenised solid solution. When the diffusion coefficients of constituent atoms in solid solution are different (vvhich is frequently the čase), the neck area be- comes enriched in the faster diffusing atoms, at least in the early stage of sintering vvhen the vacancy gradient due to the smallness of the radius of neck curvature is large. Such segregation must be a transient phenomenon, since segregation gives rise to a chemical potential gradient arising from the concentration gradient betvveen the neck and regions adjacent to the neck, and acts in a di-reetion opposite to the chemical potential gradient due to the neck curvature. When the radius of curvature of the neck inereases, the chemical potential vvhich causes the dehomogenization decreases. With accumulation of faster diffusing atoms in the neck, the concentration gradient also inereases and the maximum segregation is reached. After this, the chemical potential gradient due to the concentration gradient predominates and back diffusion from the neck to other regions occurs. As a result, homogeneity is re-established. Kuczynski et al18 demonstrated segregation in Cu-In and Cu-Ag alloys. Mishra et al19 demonstrated dehomogenization of Au-Ag alloy and concluded that the initial neck grovvth as vvell as segregation take plače by surface Figure 7: TEM photomicrograph of BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 ceramic, sintered 2 hours at 1260°C showing (A) solidified TiOi - rich phase at grain corners and along grain boundaries, (B) Ca-and Zr- modified domain free region and (C) ferroelectric BaTi03 grain core. Slika 7: TEM posnetek keramike iz BaTi03 - 2 mol % Ti02 - 8 mol % CaZr03 keramike, sintrane 2 uri pri 1260°C. Posnetek kaže (A) strjeno talino, bogato na TiO? med zrni in vzdolž zrn, (B) s Ca in Zr bogat rob zrn brez domen in (C) ferroelektrično BaTi03 jedro z domenami. IOOt 90-80- D H 70i (Č 60-50- 40 200 400 600 T(oC) 800 1000 Figure 8: Sintering curve of Pb(Zro.5Ti».5)03 compact in air, pressed at 100 MPa. Heating rate: 10°C/minute. Slika 8: Krivulja zgoščevanja oblikovanca iz PbfZro.sTio.OO,!, stisnjenega s tlakom 100 MPa. Hitrost segrevanja 10°C/min. D H 300 t(min) Figure 9: Density of Pb(Zro.5Tio.5)03 ceramics as a function of temperature and time of isothermal heating runs in an air atmosphere. Slika 9: Gostota Pb(Zro.5Tio.5)03 keramike v odvisnosti od temperature in časa pri izotermnem segrevanju v atmosferi zraka. diffusion, whereas back diffusion occurs by a combina-tion of surface and volume diffusion. It may be expected, due to capillary forces in the early sintering stage, that the dehomogenization effect occurs in complex ceramic systems as well. It should be particularly pronounced in sintering of nanosized pow-ders, where surface diffusion plays an important role. The segregation-homogenisation phenomenon should be reflected in densification curves. To demonstrate the effect, we examined the sintering of fine sol-gel prepared powders of lead zirconate - lead titanate solid solution, Pb(Zr0.5Tio.5)03 (PZT)20. Fig. 8 shows the densification curve of a Pb(Zr0 5Ti().5)03 compact, made of fine powder prepared by alkoxide sol-gel synthesis. The very rapid densification above ~950°C does not support the expected solid state sintering mechanism. Instead, the sudden and steep inerease in sintering rate and the well crystallised grains are indicative of liquid phase sintering. The liquid phase may be the PbO-PZT eutectic above ~840°C; however, the presence of PbO could not be detected by XRD or TEM in the starting powder. The isothermal densification curves, presented in Fig. 9, show anomalous behaviour in the temperature region 750-800°C. The anomaly is an extended "induetion" period in the densification curves at 750 and 800°C. Anomalous densification of PZT in the initial sintering stage may be explained by preferential diffusion of PZT constituents. Accumulation of faster diffusing species in the neeks between the particles, triggered by surface curvature, causes an inereased tendency for backward diffusion, sustained by the concentration gradient. Formation of the thermodynamically nonequilibrium phase and its sub-sequent annihilation interferes with the normal densification process, being reflected as an induetion period. Fur-ther densification commences only after neck curvature decreases and the material homogenises again. At low sintering temperatures, material transport takes plače predominantly by surface diffusion and, when possible. by vapour transport. PZT is known for the high vapour pressure of PbO21. To the author's knovvledge, surface diffusivities of Pb, Zr and Ti ions in PZT have not been reported. Slinkina and Doncov22, using radioactive tracers, measured the effective self-diffu-sion coefficients in polycrystalline 99 % dense Pb(Zro.5Tio.5)03 ceramics. The effective diffusion coeffi-cient of Pb2+ was 5 - 40 times higher than that of O2" and almost two orders of magnitude higher than Dr, and DZr, Figure 10: TEM micrograph of Pb(Zro.5Tio.5)03 ceramic, sintered at 900°C for I hour. Arrow points to Pb-rich inclusion among 3 perovskite grains (Courtesy G. Dražič). Slika 10: TEM posnetek Pb(Zro.5Tio.5)03 keramike, sintrane pri 900°C 1 uro. Puščica kaže vključek, bogat s Pb, med 3 perovskitnimi zrni (posnetek G. Dražič). vvhich were close to each other. Nakamura, Chandratreya and Fulrath21 and Kosec and Kolar24 reported that during the formation of PZT from PbTiO, and PhZrO,, titanium ions diffuse much faster than zirconium ions. The vapour pressure transport of PbO into the necks is also possible. To maintain electrical neutrality, diffusion of cations is accompanied by a simultaneous flow of oxygen ions, or through gas-phase transport. Faster diffusion of Pb and Ti, caused by high neck curvature in the initial sintering stage of fine-grained PZT compacts, causes accumula-tion of Pb and Ti or Zr in the necks, and corresponding depletion of both species in other regions of PZT grains. According to the phase diagram25, PZT may be Pb deft-cient up to 2 mol % PbO; however, PbO does not dis-solve in PZT. The simplified equation derived by Kuczynski et al18, makes it possible to estimate the maxi-mal excess concentration of the faster diffusing species in the neck area. In simplified form, Kuczynski's equation reads: 2yQC Pc ~ AC kT where pc critical neck radius necessary to reverse the neck curvature driven atoms outvvard flow to concentration gradient driven inward flow y surface energy Q mean atomic volume AC/C relative concentration gradient between neck area and grain interior k Baltzman's constant T temperature Neck radius is related to particle diameter (2a) and neck diameter (2x) by expression Assuming surface energy =1 J/m2, mean atomic volume 1029 m3, and kT (at 1000 K) 1,4.10 20 J, one can estimate the maximal excess concentration of the faster diffusing specie in the neck area. With 200 nm size particles and neck diameter 140 nm, the calculated excess concentration is 8 mol %. In view of crudity of assump-tions, the result seems reasonable. The proposed explanation of the PZT sintering anom-aly was supported by the following experimental obser-vations: (1)XRD patterns of PZT after the early sintering stage conftrmed the presence of tetragonal and rhombohe-dral phases, whereas in the starting PZT powder only reflections of the tetragonal phase were present. Pb(ZrxTii-x)03 solid solution exhibits a phase trans-formation from the tetragonal to rhombohedral structure at x - 0.53. The appearance of rhombohedral phase indicates the shift in PZT composition. After prolonged sintering, the rhombohedral phase disap- peared, confirming homogenisation to the initial composition with x = 0.5. (2) After the early sintering stage, PbO inclusions in the microstructure were observed by SEM and TEM ex-aminations (Fig. 10). Enrichment of PbO in the necks as compared with the grain interior was confirmed by quantitative EDX analysis in the transmission elec-tron microscope. On further heating, PbO inclusions redissolved. The findings of the work presented disprove the cor-rectness of solid state sintering models assumed for PZT by several researchers. The transient presence of PbO, vvhich forms a eutectic in the early sintering stage, pro-vokes liquid phase sintering. This has several important consequences, for example that microstructural develop-ment in PZT must be sensitive to the heating schedule. Probably the most important result from this investiga-tion is that the dehomogenization phenomenon vvith the transient existence of metastable phases is likely to be a frequent occurrence in the initial stage of sintering of multicomponent ceramics. It is particularly to be ex-pected in sintering of fine povvders vvith a high driving force for sintering. 4 SUMMARY The critical issues in mastering ceramic processing to assure the reliability and reproducibility of ceramic bod-ies are vvell knovvn. These are (a) appropriate ravv mate-rials (purity, finess, grain size distribution), (b) correct shaping of homogenous bodies vvithout macro defects and (c) suitable sintering parameters (T, t, dT/dt, etc.) But of particular importance for the reliable manufactur-ing process is a knovvledge and control of chemical reac-tions at high temperatures. This in turn demands knovvledge of high temperature phase relations, knovvledge of reaction kinetics and availability of data such as (1) sys-tematic trends in the periodic system, (2) the nature and strength of chemical bonds, (3) thermodynamics (AG,y) and (4) kinetic parameters (diffusion coefficients). In short, to achieve optimal properties of ceramic products and to assure competitiveness demands a high profes-sional knovvledge and appropriate equipment. 5 REFERENCES 'J. Frenkel, J. Phys„ 9 (1945) 5, 385-91 2B. Ya. Pines, J. ofTechn. Phys„ 16 (1946), 737 3 G. C. Kuczynski, Trans. Am. Inst. Mining Met. Eng.. 185, (1949), 169-78 4W. D. Kingery and M. Berg, i. Appl. Phys„ 26 (1955), 1205-12 5 (a) R. L. Coble, J. Appl. Phys„ 32 (1961), 787-92 (b) J. Appl. Phys„ 36 (1965), 2327 6D. L. Johnson, J. Appl. Phys„ 40 (1969) 1, 192-200 7 D. Kolar, Mat. Sci. Pes., 13 (1980), 335 SM. F. Yan, Materials Science and Engineering, 48 (1981), 53 'R. J. Brook, S. P. Howlet, and S. X. Wu. Mat. Sci. Monographs, 14 (1982), 135 10 M. McQuarrie and F. Behke, J. Am. Ceram. Soc., 37 (1954), 539-543 11 H. J. Hagemann, D. Hennings, and R. Wernicke, Philips Tech. Rev., 41 (1983/84), 89-98 12 D. Suvorov and D. Kolar, Sintering and Dielectric Properties in The BaTi03-CaZr0.i System, pp 2.314-2.318 in Euro-Ceramics, Vol. 2, ed. by G. de With, R. A. Tepstra and R. Metselaar, Elsevier, Amsterdam 1989 l3D. Suvorov and D. Kolar, Silicates Industriels, 5-6 (1993), 109-113 14 G. H. Jonker, Philips Tech. Rundschau, 17 (1955), 127-135 15 W. Jander, Z. Anorg. Allg. Chem, 163 (1927), 1-52 l6J. Beretka, J. Amer. Ceram. Soc., 76 (1984), 615-620 17 B. S. Rawal, M. Kahn, and W. R. Buessem, Grain Core - Grain Shell Structure in Barium Titanate-Based Dielectrics, pp 172-88 in Ad-vances in Ceramics, Vol. 1, The American Ceramic Society, Colum-bus, Ohio, 1981 18 G. C. Kuczynski, G. Matsumura, and B. D. Cullity, Acta Metallurgica. 8 (1960), 209-15 19 A. Mishra, F. V. Lenel, and G. S. Ansell, Mat. Sci. Research, 10, Ple-num, New York, 1975, 339-347 20B. Malic, D. Kolar, and M. Kosec, Anomalous Densification of Com-plex Ceramics in the Initial Sintering Stage, pp 69-76 in Sintering Technology, ed. by R. M. German, G. L. Messing and R. G. Cornwall, Marcel Dekker Inc., New York, 1996 21 K. H. Hardtl and H. Rau, Solid State Comm., 1 (1969), 41-45 22 M. V. Slinkina and G. L. Doncov, Izv. Akad. Nauk SSSR Neorgan. Mat., 28 (1992), 567-570 23 Y. Nakamura, S. S. Chandratreya, and R. M. Fulrath, Ceramurgia Int., 6 (1980), 57-60 24M. Kosec and D. Kolar, PZT solid solution formation from PbZr03 and PbTi03, Mater. Sci. Monographs 16: Ceramic Povvders, ed. by P. Vinzenzini, Elsevier, Amsterdam, pp. 421-427, 1983 GROWTH OF III-NITRIDES VIA SUBLIMATION AND METALORGANIC VAPOR PHASE EPITAXY RAST HI-NITRIDOV S SUBLIMACIJO IN METALORGANSKO PARNO FAZNO EPITAKSIJO ROBERT F. DAVIŠ', C. M. BALKAS1, M. D. BREMSER1, O. H. NAM1, W. G. PERRY', B. L. WARD2, Z. SITAR1, T. ZHELEVA1, L. BERGMAN2,1. K. SHMAGIN3, J. F. MUTH3, R. M. KOLBAS3, R. J. NEMANICH2 'Department of Materials Science and Engineering, North Carolina State University, Box 7907 Raleigh, NC, 27695-7907 2Department of Physics, North Carolina State University, Bo\ 8202, Raleigh, NC 27695-8202 3Department of Electrical and Computer Engineering, North Carolina State University, Box 7911, Raleigh, NC 27695-7911 Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Single crystals of GaN < 3 mm in length were grown by sublimation/recondensation of GaN in 760 Torr NH3 at 1100°C. Platelets of A1N < 1 mm thick were similarly grown between 1950 and 2250°C using an Al source. Monocrystalline GaN and AlxGa,.xN(0001) (0.05 < x < 0.96) films were grown via MOVPE on a(6H)-SiC(0001) wafers with and without, respectively, a 1000 A A1N buffer layer. Photoluminescence (PL) spectra of GaN showed bound and free excitonic recombinations. Selective growth of hexagonal pyramid arrays of undoped GaN and Si-doped GaN vvas achieved on 6H-SiC(0001)/AIN/GaN multilayer substrates using a patterned Si02 mask. Field emission of these arrays exhibited a tum-on field of 25 V/(im for an emission current of 10.8 nA at an anode-to-sample distance of 27 jim. Lateral growth and coalescence of GaN have been achieved using stripes oriented along <1100> at 1100°C and a triethylgallium flow rate of 26 mmol/min. Approximately 109 cm"2 dislocations, originating from the underlying GaN/AlN interface, were contained in the GaN grovvn in the vvindovv regions. The overgrovvth regions contained a very low density of dislocations. Key words: gallium nitride, aluminum nitride, single crystals, thin films, photoluminescence, Raman spectroscopy, cathodoluminescence, selective growth, lateral overgrovvth Kristali GaN < 3 mm dolžine so bili izdelani s sublimacijo/rekondenzacijo GaN pri 760 tor. NH3 in 1100°C. Ploščice A1N < 1 mm debeline so bile na podoben način izdelane pri 1950 do 2250°C z uporabo Al kot izvora. Monokristalini filmi GaN in AlxGai.x N(001) z (0.05 S x < 0.96) so bili izdelani z MOVPE na a(6H)-SiC(0001) vaferjih z in brez 1000 A A1N bufer sloja. Fotoluminiscentni (PL) spektri GaN so pokazali vezi in proste excitonske rekombinacije. Selektivna rast združb heksagonalnih piramid nedopiranega GaN in GaN dopiranega s silicijem je bila dosežena na 6H - Si(0001)/AlN/GaN večslojnih substratih z uporabo vzorčastih SiOj mask. Prag polja emisije teh združb je imel jakost 25 V/)jm za emisijski tok 10.8 nA pri razdalji 27 pm med anodo in preizkušancem. Lateralna rast in koalescenca GaN je bila dosežena z uporabo lamel orientiranih vzdolž <1100> pri 1100°C in pretoku trietilgalija 26 mmol/min. V GaN, ki je nastal v področju oken je bilo približno 109 cm"2 dislokacij, ki so izvirale iz mejne površine GaN/AlN. Področja večje rasti so imela majhno gostoto dislokacij. Ključne besede: galijev nitrid, aluminijev nitrid, posamični kristali, tanki filmi, fotoluminiscenca, Raman spektroskopija, katodoluminiscenca, selektivna rast, pospešena lateralna rast 1INTRODUCTION The realization of blue and green light emitting di-odes and blue lasers as well as prototypes of several mi-croelectronic devices produced from GaN-based materials containing copious line and planar defects has been most fortunate. These achievements also indicate that the employment of substrates on which homoepitaxial films can be grovvn would result in marked improvements in the properties of the devices fabricated in these films. At present, very thin films of GaN, A1N and AlxGa|.xN are deposited on foreign substrates as buffer layers on which the device-related III-V nitrides films are grovvn. Aluminum nitride is also a candidate material for selected pie-zoelectric applications and surface acoustic vvave (SAW) devices. Hovvever, the potential of A1N in these and other applications has been hampered by the lack of bulk single crystals, as discussed in several revievv articles'"4. Gallium nitride is a promising material for field emission because of its Iow electron affinity (2.7-3.3eV)5 6, reason-able thermal, chemical and mechanical stability and the ability for controlled n-type doping. Recently, it has been reported6-7 that A1N and Al-rich AlxGa,.xN (x > 0.75) films exhibit a negative electron affinity vvhich suggests that these materials belong to a special class of field emitters. Recent research conducted by the authors and de-scribed in the follovving sections represent important ad-vances in the determination of the process parameters necessary to achieve grovvth of GaN and A1N bulk single crystals via seeded sublimation/recondensation. Addi-tionally, we discuss the employment of a 1000 A, monocrystalline, high-temperature (HT) (1100°C) A1N buffer layer for metalorganic vapor phase epitaxy (MOVPE) thin film deposition vvhich has resulted in subsequently deposited GaN films void of oriented do-main structures and associated lovv-angle grain bounda-ries8 9. Monocrystalline films of AlxGai_xN (0.05 < x < 0.96) of the same quality as GaN vvith a HT-AIN buffer layer have also been achieved directly on 6H-SiC(0001) vvafers at 1100°C. We also report the selective grovvth of GaN and Si-doped GaN hexagonal pyramid arrays on circular patterns etched in Si02 masks deposited on GaN/AlN/6H-SiC(0001) multilayer substrates and the field emission results from these arrays, as well as the deposition, the lateral overgrowth and subsequent coales-cence of the GaN stripes selectively grown in the same manner. 2 EXPERIMENTAL PROCEDURES A. GaN Bulk Growth Growth of individual GaN crystals was achieved by evaporating 0.5" diameter and 0.25" high GaN pellets cold pressed from high purity GaN povvders produced in our laboratory10 in a stream of 99.9999% pure NH, gas. Experiments were conducted in a system that was spe-cifically designed for GaN growth. The growth system consisted of: (1) an outer vacuum chamber that con-tained the heat shields and electrical feed-throughs and (2) a reaction tube containing the source and seed mate-rials. Two independently controlled heaters vvere used to achieve the necessary temperature gradients for sublima-tion growth. Heater temperatures vvere monitored and controlled via the use of thermocouples placed adjacent to each heater. Source and substrate temperatures vvere monitored independently from within the reaction tube. Experiments vvere performed vvithin the source temperature range of 1100-1450°C. The seed heater was main-tained at 1100°C throughout each deposition. Growth pressures of 50-760 torr vvere investigated; hovvever, most experiments vvere conducted at 760 torr. An NH3 flow rate of 50 sccm was used for ali grovvth experi-ments. Blank BN seed holders vvere used as substrates and placed at a distance from the source vvherein the crystals vvith lovv aspect ratios could be obtained. B. AIN Bulk Growth Aluminum nitride sublimation/recondensation ex-periments vvere also conducted in a resistively heated graphite furnace. Bulk AIN (99% dense) blocks produced via sintering vvithout additives vvere used as the source material. The source vvas positioned in the iso-thermal section of the furnace to ensure an essentially constant evaporation rate. Single crystal, 6H-SiC (0001) squares (10 mm x 10 mm) vvere used as seeds in ali ex-periments due to the relatively small lattice mismatch to AIN (0.9%) and high temperature stability. The seed crystals vvere heated in vacuum at =1150°C prior to crys-tal grovvth to desorb the surface oxide, hydrocarbons and any other contaminants. Ali AIN experiments vvere performed under a 100 sccm flow of ultra-high purity N2. The background pressure vvas maintained at 500 Torr by an automatic throttle valve. The temperature ranges of 2100-2250°C and 1950-2050°C vvere investigated consecutively. The lovver temperature range vvas employed primarily be-cause of the degradation of the furnace and the seed crystals at the higher temperatures. In both cases, a temperature difference of 80-150°C vvas employed, depend-ing on the separation distance (1-40 mm) betvveen the source and the seed. The grovvth rate at a separation of 3 mm vvas =30 times higher than at a 15 mm separation. The AIN source vvas repositioned to the desired source height before each experiment. C. Metalorganic Vapor Phase E pitaxy and Selective Area Growth As-received vicinal 6H-SiC(0001) vvafers11 oriented 3°-4° off-axis tovvard <1120> vvere cut into 7 mm squares. These pieces vvere degreased in sequential ultra-sonic baths of trichloroethylene, acetone and methanol and rinsed in deionized vvater. The substrates vvere sub-sequently dipped into a 10% HF solution for 10 minutes to remove the thermally grovvn oxide layer and blovvn dry vvith N2 before being loaded onto the SiC-coated graphite susceptor contained in a cold-vvall, vertical, pancake-style, MOVPE deposition system. The system vvas evacuated to <3xl0'5 Torr prior to initiating grovvth. The continuously rotating susceptor vvas RF inductively heated to the GaN (AlxGa,.xN) deposition temperature of 1050°C (1100°C) (optically measured on the susceptor) in 3 SLM of flovving H2 diluent. Hydrogen vvas also used as the carrier gas for the various metalorganic precursors. Deposition of AlxGai.xN vvas initiated by flovving various ratios of triethylaluminum (TEA) and triethylgallium (TEG) in combination vvith ammonia (NH3). Selective grovvths of GaN and Alo.2Gao.8N vvere achieved at 1000-1050°C vvith TEG flovv rates = 26.1-70.0 pm/min. on stripe (vvindovv vvidth = 3-80 pm) and circular (diameter = 5 pm) patterned GaN/AlN/6H-SiC(0001) multilayer substrates. To produce these patterned substrates, a Si02 mask layer (thickness = 1000A) vvas subsequently deposited on each GaN film via RF sputtering or lovv pressure chemical vapor deposition. Patterning of the mask layer vvas achieved using standard photolithography techniques and etching vvith a buffered HF solution. The edges of the stripe patterned samples vvere parallel to <1120>. Prior to selective grovvth, the patterned samples vvere dipped in a buffered HC1 solution to remove the surface oxide of the underlying GaN layer. Incorporation of the n-type Si dopant into the GaN pyramids during grovvth vvas achieved using SiH4 at a flovv rate of 5.5 nmol/min. Field emission measurements (FEM) vvere performed on the Si-doped GaN hexagonal pyramid arrays in a UHV-FEM system having a vvorking pressure of 2x10S Torr. Each array vvas placed beneath a five mm diameter movable Mo anode having a flat tip. The anode vvas controlled by a stepping motor such that one step yielded a translation of 0.44 pm. The current-voltage (I-V) measurements vvere taken from 2 to 40 pm for anode voltages in the range of 0 to 1100 V. The lateral overgrowth of GaN was achieved in a manner similar to that of the films12. The GaN grew ver-tically to the top of the mask and then both laterally and vertically over the mask until the lateral growth fronts from many different windows coalesced and formed a continuous layer. The samples were characterized by scanning electron microscopy (SEM-JEOL 6400 FE), atomic force microscopy (AFM-Digital Instrument NanoScope III) and transmission electron microscopy (TEM-TOPCON 002B, 200KV). 3 RESULTS AND DISCUSSION A. Billk GaN Growth Colorless vvurtzitic GaN crystals < 3 mm in size were achieved by sublimation of the pressed GaN pellets in a stream of ammonia. Figure 1 shows an optical mi-crograph of =1 mm long, well faceted, transparent GaN crystals with low aspect ratios which are in contrast to the commonly observed13 needle-shaped crystals grown via vapor phase reaction. The GaN crystals primarily grew by spontaneous nucleation on the BN seed holders. The use of temperatures above 1200°C resulted in the rapid conversion of the GaN source into Ga metal. Crys-tals were grown at source temperatures in the range of 1100-1200°C; however, the majority of experiments were conducted at 1200°C to achieve higher grovvth rates. The temperature of the BN surface where crystals nucleated was =1000°C. The grovvth time and pressure for the growth of the crystals shown in Figure 1 vvere 2.5 hrs and 760 Torr, respectively. The direction of fastest grovvth and thus the crystal shape vvere observed to change vvith the changing Ga/NH? flux ratio and the growth temperature. These ob-servations are in contrast to ali previous reports which Figure 1: GaN crystals grown by sublimation/recondensation on BN. Lines are spaced 1 mm Slika 1: GaN kristali zrastli s sublimacijo/rekombinacijo na BN. Črte so oddaljene 1 mm Figure 2: Secondary electron microscopy of a GaN crystal shovving well developed {1010} and {0001} crystallographic facets Slika 2: SEM posnetek GaN kristalov, ki kaže dobro razvite {1010} in {0001} kristalne ploskve indicate that grovvth of bulk GaN from the vapor phase results primarily in long needles. Figures 2 and 3 show SEM images of the same crys-tal. This crystal grew from a single isolated nucleation site and developed into a well faceted hexagonal shape terminated by flat {1010} and {0001} planeš. Figure 3 shows a higher magnification image in which the (0001) and (1010) facets are observed. A spectral mass scan via SIMS indicated that ali im-purities with the exception of oxygen vvere at back-ground levels. Quantitative analysis revealed an oxygen concentration of 3x1018 atoms/cm3 vvhich is similar to that present in high quality GaN thin films. A representative room temperature PL spectrum for bulk GaN taken at 300K is shovvn in Figure 4. Strong near band edge (bound exciton) emission vvith a peak po-sition at 365.0 nm (3.4 eV) and a FWHM of 9.0 nm (83 meV) was observed. The visible portion of the PL Figure 3: Higher magnification of the crystal in Figure 2 Slika 3: Kristal na sliki 2 pri večji povečavi C IT U <1 1 - (b) . (a) x 500 ___ J L : .... i .... i .. . . i . . . . i .... i .... i . i i ■ » - ■ ■ ■ - - • • 650 600 550 500 450 400 350 300 VVavelength [nm] Figure 4: Photoluminescence spectrum of GaN taken at 300 K Slika 4: Fotoluminiscentni spekter GaN pri 300 K spectrum is expanded 500 times in the inset in Figure 4. No yellow emission usually attributed to deep level tran-sitions vvas detected on this scale or to the naked eye. A peak position of 359.0 nm vvith a FWHM of 54 meV vvas detected for a PL spectrum obtained at 77 K. The allovved Raman modes of the vvurtzite structure are presented in Figure 5. The inset in this figure shovvs that the E2<2) mode is at 567 cm"1 and has a FWHM = 3.5 cm1. These values are indicative of a material of the highest quality reported to date14. The results of optical absorption studies are shovvn in Figure 6. The absorption band edge is distinct but is not as sharply deftned as observed in thin epitaxial films. This is due to the absorption tail belovv the band edge. The absorption edge is expected to shift to vvavelengths above the actual band gap (360 nm for GaN) as the material thickness increases. For example, in the absorption spectrum of a high quality 50 |im thick GaN film the absorption edge is observed at 369 nm, and 75% transmis-sion is observed at 379 nm 15. Since the GaN crystal Figure 5: Raman spectrum of GaN Slika 5: Raman spekter GaN VVavelength (nm) Figure 6: Optical absorption spectrum of GaN crystal Slika 6: Optični absorpcijski spekter GaN kristala from vvhich the above spectrum taken vvas = 300 |im thick, the absorption edge position of = 370 nm and 75% transmission indicate these crystals to be of high optical quality. B. AIN Bulk Growth Grovvth in the ?100-2250°C range Single crystal platelets of AIN having thicknesses to one millimeter and covering the vvhole seed crystal vvere obtained at a source temperature of 2150°C and a 4 mm source-to-seed separation. The grovvth rate vvas estimated to be 0.5 mm/hr. The results of XRD and Laue back re-flection studies confirmed the monocrystallinity. At higher grovvth temperatures betvveen 2150-2250°C several = 2x2 mm individual hexagonal crystals vvere obtained on the seeds, since at these temperatures, severe degradation of the SiC substrates resulted in isolated sta-ble nucleation sites. These crystals and the aforemen-tioned platelets ranged in color from green to blue. The coloration strongly indicated the incorporation of impu-rities vvhich vvas confirmed via SIMS analysis to be C and Si from the SiC substrates. Upon cooling, the AIN crystals frequently delami-nated and cracked. This vvas most probably due to the mismatch in the coefficients of thermal expansion betvveen the two materials; hovvever, intrinsic stress in the deposited material and/or the extension of pre-existing cracks at the edges of the SiC substrates may also have contributed to these phenomena. Unfortunately, the thermal expansion coefficients data for these materials are not available for the entire temperature range of the ex-periments. Since AIN boules vvill ultimately be grovvn on obtained AIN crystals, this cracking problem should not be a significant barrier to the attainment of much larger crystals. Grovvth in the 1950-2050°C range Grovvth of AIN in the temperature range of 1950 to 2050°C vvas conducted because complete structural and chemical stability of the SiC seeds and a significant re- Figure 7: Optical micrograph of a single crystal of A1N grovvn at 1950°C and a 4 mm source-to-seed separation (Scale: mm) Slika 7: Optični posnetek kristala A1N, ki je zrastel pri 1950°C in razdalji 4 mm med izvorom in kaljo (merilo: mm) duction in the deterioration of the SiC coated crucibles were attained. Crystals grown in this temperature range were always colorless regardless of the morphology or growth site and contained almost two orders of magni-tude less Si and C than the crystals deposited at >1950°C; whereas, the O levels were similar in ali crys-tals. Typical growth rates were reduced to 30-50 ftm/hr. Grovvth runs of 10-15 hrs yielded 0.3-0.5 mm thick crys-tals on 1 cm2 SiC substrates. A 0.4 mm thick transparent A1N platelet grown at 1975°C can be seen in Figure 7. Unfortunately cracking occurred in these crystals as well and presumably for the same reasons stated in the previ-ous subsection. Crystals grown in both temperature ranges had very smooth surfaces (~ RMS = 6A) as determined by atomic force microscopy (AFM). Ali crystals showed strong and well defined single crystalline XRD patterns. Only the (002) reflection posi-tioned at 36° was observed in symmetric E-2E scans for a crystal grown at 1950°C. This suggests that the resid-ual stress level in these crystals was low. Bright field, plan vievv TEM micrographs and associated selected area diffraction (SAD) patterns taken along the [0001] direc-tion shovved uniform contrast density throughout the specimen and spot patterns vvithout streaks or arcs, re-spectively, indicative of single-crystalline material vvithout high angle boundaries, stacking faults, misoriented grains or twinned regions. A Raman spectrum acquired using back scattering geometry from the (0001) face of an transparent A1N crystal grovvn at 1950°C is presented in Figure 8. The spectrum exhibits the allovved modes for this geometry, namely, Ai(LO) = 893 cm1, E2<» = 250 cm"1, E2(2) = 660 cm"1 with no detectable contribution from the forbidden modes. The results support the aforementioned crystal-lographic and microstructural results in that a vvell defined vvurtzite structure exists vvithout significant con-centrations of structural defects or internal stress vvhich Figure 8: Raman spectrum of transparent bulk A1N grown at 1950°C Slika 8: Raman spekter prosojnega A1N, kije bil zraščen pri 1950°C could relax the selection rules. The inset shovvs the high resolution spectrum of the E2(2) mode. The FWHM of this peak was 7.0±0.5 cm1; the same spectrum taken from a blue crystal grovvn at 2200°C had a FWHM value of 9.5+0.5 cm1. This marked difference complements the results of the SIMS analysis in vvhich the colored crys-tals contained tvvo orders of magnitude more Si. C. Metalorganic Vapor Phase Epitaxial Growth of GaN and AlxGai-xN films Previous research in our laboratories has shovvn that thin films of GaN deposited directly on 6H-SiC(0001) substrates at high and low temperatures had columnar-like grains, faceted surfaces and high net carrier concen-trations (nD-nA > 1 x 1019 cm 3)16. In contrast, in the pre-sent research monocrystalline thin films of both the HT-A1N buffer layers and the subsequently grovvn GaN films deposited on similar SiC substrates have been deposited vvith no misorientation or lovv-angle grain boundaries, as determined by selective are diffraction and microstructural analysis via transmission electron microscopy. Similar results have been achieved for AlxGai-xN vvithout the use of an A1N buffer layer. The stacking fault density vvas also very lovv. The dislocation density of the AlxGai_xN films at the SiC interface ap-peared similar to GaN films deposited on high temperature (HT) buffer layers8 9. The dislocation densities of the GaN and AUGa^N films decreased rapidly as a function of thickness; only threading dislocations vvhich result from misfit dislocations at the interface persisted through the film. The surfaces of the GaN and AlxGai.xN films exhib-ited a slightly mottled appearance as a result of the step and terrace features on the grovvth surface of the 6H-SiC(0001) substrates. Random pinholes, caused by in-compiete coalescence of the tvvo dimensional islands vvhich occurred as an intermediate grovvth stage betvveen the initial nucleation and the final layer-by-layer grovvth stage representative of the majority of the film, vvere also observed. An increasing number of pinholes appeared on the surface of AlxGai.xN compositions where x > 0.5. The pinhole density was decreased by increasing the growth temperature to enhanced surface mobility of the adatoms. The DCXRC measurements taken on GaN and AlxGa,.xN films revealed the FWHM of the (0002) re-flections to be as low as 58 and 186 arcsec, respectively. The low-temperature (8K) PL spectra of the undoped GaN films revealed an intense near band-edge emission at 3.466 eV, vvhich has been attributed to an exciton bound to a neutral donor'718. The FWHM value of this peak vvas 4 me V. Also, a less intense peak vvas observed at higher energies (3.472 eV) vvhich is attributed to free excitonic recombination. The lovv-temperature (4.2K) CL spectra of the undoped AlxGai.xN films for compositions in the range of 0.05 < x < 0.96 revealed an intense near band-edge emission vvhich has been attributed to an exciton bound to a neutral donor (I2-line emission)17 '8. Broadening of this emission is attributed to both exciton scattering in the alloys as vvell as small variations in al-loy composition in the film. The lovvest FWHM value observed in the AlxGai_xN alloys vvas 31 me V. Strong de-fect peaks, previously ascribed to donor-acceptor pair recombination19, vvere observed at midgap energies. The broad peak centered at 545 nm (2.2 eV) for GaN, com-monly associated20 vvith deep-levels (DL) in the bandgap, vvas also observed; hovvever, these emissions shifted sublinearly vvith changing composition. The na-ture of this behavior is under investigation. The compositions of the AlxGai.xN films vvere deter-mined using EDX, AES and RBS. Standards of A1N and GaN grovvn in the same reactor under similar conditions vvere used for the EDX and AES analyses. After care-fully consideration of the errors (±2 at.%) involved vvith each technique, compositions vvere assigned to each film. The data from EDX and AES measurements shovved excellent agreement. The RBS data did not agree as vvell vvith the other tvvo techniques due to small com-positional variations through the thickness of the film. Simulation of the composition determined by RBS vvas conducted only on the surface composition. These compositions vvere compared vvith their re-spective CL emission peaks and bandgap as determined by SE. Using a parabolic model, the functional relation-ships betvveen I2-line emission energy of the CL and the Al mole fraction for 0 < x < 0.96 is shovvn in Figure 9 and expressed analytically as E,2(x) = 3.47 + 0.64x + 1.78x2 (1) Clearly, this shovvs a negative deviation from a linear fit. This is in general agreement vvith earlier research over a smaller range of x by other investigators1617. D. Selective Growth and Lateral Growth The prismatic morphology of the GaN and Alo.2Gao.8N stripes deposited vvithin the various vvindovv vvidths of the Si02 masks vvas observed using scanning electron microscopy. Micrographs of these results are Figure 9: Low-temperature (4.2K) CL emissions of AlxGai_xN films as a function of aluminum mole fraction Slika 9: Nizko temperaturni (4.2K) CL emisije AlxGai_xN filmov v odvisnosti od molarnega deleža A1N shovvn in Figure 10. Both materials exhibited (1100) side facets and ridge lines (i.e., no truncation) vvhen deposited on the 3 |4m-wide Si02 vvindovvs. Truncated prismatic grovvth vvith (0001) top facets and (llOl) side facets vvas observed on stripe patterns vvith vvidths > 5 |im. Polycrystalline islands of AlxGai.xN nucleated on the Si02 mask because of the chemical interaction betvveen Al and Si02 2n. There vvas no significant difference in the final grovvth morphologies betvveen the GaN and the Alo.2Gao.8N patterns, except for a slight roughening of the (1101) facets of the latter. This roughening is believed due to the changes in the gas flovv dynamics caused by the formation of the polycrystalIine islands. No exces-sive grovvth vvas observed along the top edges of the truncated stripes, as shovvn in Figure 11; the (0001) top facets vvere very smooth and flat regardless of the vvidth of these stripes. This suggests that the lovv grovvth pres-sure reduced the lateral vapor phase diffusion of the re-active species over the mask to the vvindovv region rela-tive to that observed in related research conducted at one atmosphere21. The large ratio (=0.5) of the vvindovv-to-mask area may have also contributed to the perfection of the stripes, since lovver values of this ratio vvere observed22 to induce marked grovvth and rounding of the top edges at one atmosphere in GaAs, reportedly as a re-sult of inereased lateral vapor diffusion. An inerease in the flovv rate of TEG resulted in a de-crease in the area of the (0001) top facets and the deveiopment of (1101) side facets. This behavior supports the model23 that the resulting morphology of the selectively grovvn GaN depends on the balance betvveen the incom-ing vapor flux on the (0001) top facets and the rate of diffusion on the (0001) surface to the (1101) side facets. Inereased exposure of the former to the TEG via an inerease in the flovv rate causes the grovvth rate of these facets to become faster than the latter. The optimum conditions for the selective grovvth of the GaN pyramids on the circular patterns vvere based on the selective grovvth conditions on the stripe patterns. Each pyramid contained six (1101) side facets. The grovvth rate of these pyramids vvas strongly dependent Figure 10: Seeondary electron microscopy micrographs of GaN(left) and Alo.2Gao.8N(right) stripes selectively grown at 1050°C and having initial SiC>2 widths of (a and b) 3 pm and (c and d) 5 pm Slika 10: SEM posnetki GaN (levo) in Alo.2Gay.8N (desno) trakov selektivno zrastli pri 1050°C z začetno širino SiC>2 (a in b) 3 pm in (c in d) 5 pm Figure 11: Secondary electron microscopy micrographs of 10 pm wide GaN and Alo.2Gao.8N stripes selectively grown at 1050°C with 10 pm wide Si02 windows Slika 11: SEM posnetki 10 pm širokih GaN in Al0.2Ga0.sN lamel selektivno zraščeni pri 1050°C z 10 pm širokimi SiCh okni Figure 12: (a) SEM micrograph of a Si-doped GaN hexagonaI pyramid array grown at 1000°C. (b) High magnification SEM image of the apex of a hexagonal pyramid having a tip radius of 100 nm Slika 12: SEM posnetek heksagonalne združbe piramid GaN dopiranega s Si zrastlih pri 1000°C. (b) SEM posnetek vrha heksagonalne piramide z radijem konice 100 nm turn-on voltage corresponds to a turn-on field of 25 V/pm. Using the same system, a polycrystalline p-type diamond film (p = 2.5E17cm~3) grown on Si(100) exhib-ited a turn-on field intensity of 27 V/pm. The Fowler-Nordheim (F-N) plot obtained from the I-V data was lin-ear and, therefore, indicates that the emission occurred via electron tunneling through the GaN. The morphologies of the GaN layers selectively grown on the stripe openings were a strong function of the growth temperature, the flow rates of TEG and the stripe orientation. Continuous 2 pm thick GaN layers were obtained using 3 pm wide stripe openings spaced 7 pm apart and oriented along <1100> (Figure 14 (a)). The growth parameters were 1100°C and a TEG flow rate of 26 mmol/min. Plan view SEM of the coalesced GaN layer revealed a microscopically flat and pit-free surface, as shown in Figure 14 (b). Atomic force micros-copy showed the surfaces of the laterally grown GaN layers to possess a terrace structure having an average step height of 0.32 nm. The average RMS roughness val-ues of the regrown and overgrown layers were 0.23 nm and 0.29 nm, respectively. The cross-sectional TEM micrograph presented in Figure 15 shows a typical laterally overgrown GaN. Threading dislocations, originating from the GaN/AlN buffer layer interface, propagate to the top surface of the regrown GaN layer within the window regions of the mask. The dislocation density within these regions, cal-culated from plan view TEM micrographs is approxi-mately 109 cm 2. By contrast, there were no observable threading dislocations in the overgrown layer. Additional microstructural studies of the areas of lateral growth obtained using various growth conditions have shown that the overgrovvn GaN layers contain only a few dislocations. upon the ratio of the window-to-mask area in the pat-terned region as well as the selective growth conditions. The average diagonal width of the pyramids was 7.7 pm using a ratio of 0.1. Hovvever, increasing the ratio to 0.23 resulted in an average diagonal width of 5.7 pm for the same growth conditions. These results indicate that the lateral diffusion of the reactive species from the mask to the window area is also an important factor for the suc-cessful fabrication of the GaN pyramids. As shown in Figure 12(a), the grovvth of an uniform array of Si-doped GaN pyramids in a 0.5x0.5 mm2 area was achieved. The high magnification SEM image shown in Figure 12(b) reveals that the tip radius of the pyramids was less than 100 nm. The field emission current from the Si-doped GaN pyramid arrays was measured as a function of the anode voltage. The I-V curve in Figure 13 shovvs a turn-on voltage of =680V for a current of 10.8 nA at a distance of 27 pm betvveen the pyramid array and the anode. This 0.0E+00 400 500 600 700 800 900 1000 Figure 13: Emission current and anode voltage characteristics of Si-doped GaN hexagonal pyramid array shown in Figure 12 Slika 13: Karakteristike emisijskega toka in anodne napetosti heksagonalnih piramid s Si dopiranega GaN s slike 12 s.**« rt Figure 14: (a) Cross-section and (b) surface SEM micrographs of coalesced GaN layers grown on 3 ^im wide and 7 |im spaced stripe openings, respectively, oriented along Slika 14: Posnetki (a) prereza in (b) površina kolesciranih slojev GaN. ki so zrastli na 3 um širokih 7 |im med seboj oddaljenih lamelnih odprtinah orientiranih vzdolž 4 CONCLUSIONS Growth of bulk, vvurtistic GaN crystals to 3 mm length vvas achieved at a substrate temperature and pres- sure of 1100°C and 760 Torr, respectively, via sublima- tion of GaN pellets produced by uniaxial cold pressing of GaN povvder. The concentrations of H, C and Si vvere < 1016 atoms/cm3 and the concentration of O vvas = 3xl018 atoms/cm3. Strong, sharp near band edge (bound exciton) emission vvas observed in the PL spectra of these crystals. No yellow emission vvas observed. An op-tical absorption edge of = 370 nm and 75% transmission vvas determined. The Raman spectrum shovved narrovv and well positioned peaks. Seeded bulk grovvth of single crystalline A1N (001) platelets vvas achieved on 6H-SiC (0001) substrates in the temperature range of 1950-2250°C at 500 torr of N2. Color variations vvere observed above 2150°C and linked to the incorporation of Si and C from the substrate and the grovvth crucible. The results of TEM and XRD analy-ses revealed low densities of line and planar defects and Figure 15: Cross-section TEM micrograph of a section of a laterally overgrown GaN layer on an SiOj mask region Slika 15: TEM posnetek prereza lateralno zrastlega GaN sloja na področju Si02 maske the absence of residual stress in the grovvn crystals. No misoriented grains or tvvinned regions vvere observed. Very smooth surfaces (RMS=6 A) vvere observed via AFM. Monocrystalline GaN and AlxGa,.xN(0001) (0.05 < x < 0.96) thin films, void of oriented domain structures and associated lovv-angle grain boundaries, vvere ob-tained via MOVPE on a(6H)-SiC(0001) vvafers. A 1000A high temperature (HT) A1N buffer layer vvas em-ployed for the GaN deposition vvhile AlxGai_xN vvas deposited directly on 6H-SiC. Double-crystal XRC meas-urements shovved FWHM values as lovv as 58 and 186 are sec for the GaN(0002) and AlxGai_xN(0002) reflec-tions. Photoluminescence spectra of GaN shovved bound and free excitonic recombination. Spectra obtained via CL of AlxGai_xN shovved strong near band-edge emis-sions vvith FWHM values as lovv as 31 me V. The selective grovvth of GaN and Al0.2Ga0.sN has been achieved on striped and circular patterned GaN/AlN/6H-SiC(0001) multilayer substrates. Prismatic morphology vvith vvell-defined (1101) side facets vvas observed on 3 |im vvide stripes for both materials. Trun-cated prismatic grovvth vvith smooth, flat (0001) top facets and (1101) side facets vvere obtained on stripe pat-terns vvith vvidths > 5 pm. Uniform hexagonal pyramid arrays of Si-doped GaN vvere successfully grovvn on circular patterns having diameters of 5 |im. Field emission measurements of these arrays shovved a turn-on field of 25 V/pm and an associated emission current of 10.8 nA at an anode-to-pyramid array distance of 27 Lateral grovvth and coalescence over the Si02 masks have been achieved using stripes oriented along . A density of =109 cm 2 threading dislocations, originating from the underlying GaN/AlN interface, were contained in the GaN grown in the window regions. The overgrowth re-gions contained a very low density of dislocations. ACKNOWLEDGEMENTS The authors express their appreciation to Cree Research, Inc. for the SiC wafers. This work vvas supported by the Office of Naval Research under research contracts N00014-96-1-0765 and N00014-92-J-1477. R. Daviš vvas supported in part by the Kobe Steel, Ltd. Professor-ship. 5 REFERENCES 'M. T. Duffy, in Heteroepitaxia! Semiconductors for Electronic Devices, G. W. Cullen and C. C. Wang, Eds., Spinger Verlag, Berlin 1978 pp. 150-181 2R. F. Daviš, Proc. IEEE 79 (1991) 702 3 S. Strite and H. Morko?, J. Vac. Sci. Technol. B, 10, (1992) 1237 4J. H. Edgar, J. Mater. Res., 7 (1992) 235 5 J. L. Shaw, H. F. Gray, K. L. Jensen and J. M. Jung, J. Vac. Sci. & Technol, B14 (1996) 2072 6R. J. Nemanich, M. C. Benjamin, S. P. Bozeman, M. D. Bremser, S. W. King, B. L. Ward, R. F. Daviš, B. Chen, Z. Zhang and J. Bernholc, Proc. Mat. Res. Soc., 395 (1996), 777 7 M. C. Benjamin, C. Wang, R. F. Daviš and R. J. Nemanich: Appl. Phys. Lett., 64 (1994) 3288 * T. W. Weeks, Jr„ M. D. Bremser, K. S. Ailey, E. P. Carlson, W. G. Perry, R. F. Daviš, Appl. Phys. Lett., 67 (1995) 401 9T. W. Weeks, Jr., M. D. Bremser, K. S. Ailey, W. G. Perry, E. P. Carlson, E. L. Piner, N. A. El-Masry, R. F. Daviš, J. Mat. Res., 4 (1996) 1011 10C. M. Balkas and R. F. Daviš, J. Am. Ceram. Soc., 79 (1996) 2309 11 Cree Research, Inc., 2810 Meridian Parkway, Suite 176, Durham, NC 27713 12 O. H. Nam, M. D. Bremser, T. S. Zheleva and R. F. Daviš, to be pub-lished in Appl. Phys. Lett., 71 (1997), 2638 13 S. Sakai, S. Kurai, T. Abe and Y. Naoi, Jpn. J. Apl. Phys., 35 (1996) L77 14L. Bergman and R. J. Nemanich, Annu. Rev. Mater. Sci., 26 (1996) 551 15 J. F. Muth, Private communication, North Carolina State University (1997) 16T. W. Weeks, Jr., D. W. Kum, E. Carlson, W. G. Perry, K. S. Ailey and R. F, Daviš, Second International High Temperature Electronics Conference, Charlotte, NC, June 5-10 (1994) 17M. R. H. Khan, Y. Koide, H. Itoh, N. Sawaki, I. Akasaki, Solid State Commun., 60 (1986) 753 18B. V. Baranov, V. B Gutan, U. Zhumakulev, Sov. Phys.-Semicond., 16 (1982) 819 19 R. Dingle and M. Ilegems, Solid State Commun., 9 (1971) 175 20 W. Gotz, N. M. Johnson, R. A. Street, H. Amano and I. Akasaki, Appl. Phys. Lett., 66 (1995) 1340 21 Y. Kato, S. Kitamura, K. Hiramatsu and N. Sawaki, J. Cryst. Growth, 144 (1994) 133 22 K. Yamaguchi and K. Okamoto: Jpn. J. Appl. Phys„ 32 (1993) 1523 23 S. Kitamura, K. Hiramatsu and N. Savvaki, Jpn. J. Appl. Phys., 34 (1995) 1184 PIONEER YEARS OF ELECTRON PROBE MICROANALYSIS IN SLOVENIA PIONIRSKO OBDOBJE ELEKTRONSKE MIKROANALIZE V SLOVENIJI FRANC VODOPIVEC Institute of Metals and Technology Lepi pot 11, 1000 Ljubljana, Slovenia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Two periods are found in the pioneer years of electrons probe microanalysis (EPMA) in Slovenia: • a longer period up to 1969 when an electron probe microanalyser was put in operation in the Institute of Metallurgy in Ljubljana, and • a shorter period after this date until the spreading of EPMA backed by sufficent research achievents demonstrating it wide field of use and the sufficient mastering of methodology. The use of EPMA up to 1969 was of marginal extent but not of marginal scientific merit and centred to topics of selective oxydation of alloys of iron vvith arsenic, copper, tin and antimony. The interest for EPMA and the conviction that it vvill greatly improve the quality of the actual research as vvell as open nevv topics helped significantly vvere great. Prof. D, Kolar and his collaborators vvere among the best prepared and also among the must successfull. With the cooperation of some younger scientists he accomplished several projects vvhich found significant interest in the international research community and vvere realised thanks to the fast governing of EPMA methodology. Let us quote only some achievements published up to some years after the putting in operation of EPMA in 1969: • binary phase equilibria diagrams vvere established for niobium, titanium and circonium carbides vvith iron, nickel, chromium and cobalt; • binary phase equilibria diagrams vvere established for uranium sulphide and sulphides of calcium, barium and strontium; • several projects vvere accomplished vvith the aim to understand better the microstructure of ferrite ceramics, its sintering process and the effect of microstructure and sintering on magnetic and electrical properties. In binary phase equilibria diagrams solid solubilities and eutectic compositions vvere determined. Also because of the contribution of prof. D. Kolar the pioneer period od EPMA in Slovenia vvas short and successful and helped to strengthen it as one of the base scientific facility for research of solid materials on microstructure level. Key vvords: electron probe microanalysis, selective oxydation, binary phase diagrams Fe - NbC, TiC, ZrC, activated sintering of Ba titanate, binary phase diagrams US and CaS, SrS and BaS Pionirsko obdobje elektronske mikroanalize (EMA) delimo na dva dela: • daljše obdobje do postavitve elektronskega mikroanalizatorja na tedanjem Metalurškem inštitutu v Ljubljani leta 1969 in • krajše obdobje po zagonu naprave in začetku njene široke uporabnosti kot dokaz zadostnega obvladovanja metodologije dela. Uporaba elektronske mikroanalize je bila do začetka leta 1969 v Sloveniji po obsegu marginalna, vendar ne marginalna po vsebini. Raziskave so od leta 1962 posegale na področje selektivne oksidacije predvsem zlitin železa z elementi z majhno afiniteto do kisika, na pr. arzen, antimon, kositer in baker. Zanimanje za EMA in pričakovanje, da bo omogočila kvaliteten skok v raziskovalnih projektih je bilo veliko, okolje pa pripravljeno na intenzivno uporabo nove metodike. Prof. D. Kolar je bil s sodelavci pri tem gotovo nadpovprečno uspešen. Bil je snovalec in izvajalec vrste raziskav, ki so prinesle temeljne novosti na nekaj področjih raziskovanja. Omenjene bodo le tri, ker so bili izsledki objavljeni najkasneje nekaj let po postavitvi naprave tudi zaradi zelo hitrega osvajanja metodologije dela, še posebej kvantitativne analize: • določeni so bili binarni ravnotežni fazni sistemi niobijevega, titanovega in cirkonijevega karbida s prehodnimi kovinami železo, krom, nikelj in kobalt; • določeni so bili binarni ravnotežni fazni diagrami uranovega sulfida s kalcijevim, stroncijevim in barijevim sulfidom; • izvršena je bila vrsta raziskav s ciljem, da se bolje razpozna mikrostruktura feritne keramike, proces njenega sintranja in vpliv sestavin in procesa sintranja na magnetne in električne lastnosti, V binarnih faznih sistemih je bila določena topnost v trdnih fazah ter temperature in sestava evtektikov. Tudi zaradi velikega prispevka prof. D. Kolarja in sodelavcev je bilo pionirsko obdobje EMA kratko in uspešno ter je metodo utrdilo kot eno od temeljnih pri raziskovanju vseh vrst trdne snovi na nivoju mikrostrukture. Ključne besede: elektronska mikroanaliza, selektivna oksidacija železa, binarni fazni diagrami železa NbC, TiC in ZrC, aktivirano sintranje Ba titanata, fazni diagrami US in CaS, SrS in BaS 1 INTRODUCTION This paper vvas prepared in the frame of the celebra-tion of the 65th jubilee of prof. dr. Drago Kolar, eminent scientists at the Institute J. Štefan and teacher of ceramic materials at the University of Ljubljana. I had the oppor-tunity to meet prof. Kolar in major extent after april 1969, vvhen the second electron probe microanalyser (EPMA) in the former Jugoslavia vvas put in operation in the former Institute of Metallurgy in Ljubljana. The EPMA vvas purchased by combining funding from the Institute of vacuum technique and electronics, Institute of automation, Institute for research of materials and structures, Institute of metallurgy, Metallurgy dpt of the University of Ljubljana, Slovenian Steelvvorks, and the Slovenian governement. The project vvas coordinated by the Institute of metallurgy and the EPMA installed in his premises. 2 EPMA IN THE WORK A SLOVENIAN RESEARCHERS UP TO 1969 From disponible data it seems that EPMA vvas first used in the vvork of a slovenian scientist in 1962 in the investigation of the selective surface oxydation of the al-loy Fe - 0.075% As1-2. Arsenic free energy of oxydation is smaller than that of iron. Consequently, by surface oxydation only iron reacts vvith oxygen, vvhile arsenic is segregated in the metal layer in contact vvith the oxyde. By EPMA the distribution of arsenic in the segregated layer obtained by electrolytic dissolution of |4m layers of metal and microradiochemical analysis vvas verified. The distribution vvas different after surface oxydation above and belovv AC3 because of the limited solubility of arsenic in y phase (figure 1). The results obtained by both methods did agree very good. In the same reference EPMA vvas used also to determine the composition of the eutectic FeO - 3Fe0P205 obtained at surface oxyda-tion of an Fe - 0.092% P alloy. In the follovving čase EPMA vvas used also in the investigation of the selective oxydation of iron. In iron al-loys vvith copper, arsenic, tin, and antimony by EPMA point, line and scanning analyses the sequence of forma-tion of solid and liquid phases in binary, ternary and qua-ternary equilibria vvas established as consequence of selective oxydation, f.i.: Y Yi + Yi + «i + 'Pi y Yi + lp2 Yt + «i + IP2 Yi + ai + 'Pi + !Pa vvith a, y as solid and lpi, lp2 as liquid phases. Figure 2: Optical, back scattered electrons and X rays scanning pictures of different elements in the segregated layer after air surface oxydation of an iron alloy at I200°C. Ref.3 and 4 Slika 2: Optični, elektronski in specifični X posnetki za različne elemente v segregirani plasti na železovi zlitini po oksidaciji na zraku pri 1200°C. Ref. 3 in 4 For EPMA methodology it is of special importance the fact that the distribution of segregated elements vvas demonstrated also by scanning elemental pictures (figure 2). No use of EPMA vvas found in printed vvorks of Slovenian scientists up to the start of the facility put in operation in 1969. Figure 1: Distribution of arsenic in the segregated layer of an Fe-0.075% As alloy after surface oxydation at 800 and 1000°C determined by electron probe microanalysis (EMA). Ref, 1 and 2 Slika 1: Porazdelitev arzena v segregirani plasti zlitine Fe-0.075% As po oksidaciji pri 800 in 1000°C določena z elektronsko mikroanalizo (EMA). Po virih 1 in 2 3 SOME DATA ON THE OPERATION OF EPMA FROM 1969 TO 1974 EPMA vvas ready for qualitative and semiquantitative vvork in april 1969. In table 1 statistics on the vvork up to m : ...... m Ss# w . ŠK % 3........... m • O j % \ j j^C, o S f • ' V ; ■'>■: 'V' f>< y' •VV/r: A': fX "M .... M ZSBTf« Ai avMcfMo O S S: Figure 3: Optical, back scattered electrons and X rays scanning pictures of different elements. Spherical nonmetallic inclusion in steel. Ref. 9 Slika 3: Optični, elektronski in specifični X posnetki za različne elemente. Kroglasti nekovinski vključek v jeklu. Po viru 9 1974 are shown. Allready in the first year the work per-formed for users outside of the Institute of metallurgy reached a level vvhich did not change significantly up to 1974. This level shovvs that EPMA was really needed and also satisfactorily exploited. Methods for qualitative and quantitative investigations for basic, applied, and de-velopment research as vvell as routine analysis for different institutions and industrial companies from geology, mineralogy, metallurgy, ceramic, building materials, electronics, and even forensic cases vvere developed fastly. The reader can have an idea on the level of quality and accuracy from the scanning picture in figure 3 as vvell as the composition of carbides and nonmetallic in-clusions in table 2. netics to less than half of the so far prescribed length10. It vvas established also that after homogenisation a virtually ideally homogeneus distribution vvas obtained in some cases, vvhile in čase of mutual interactivity also after long tirne homogenisation the average segregation vvas approaching a level significantly far from homogeneity. 4 EPMA IN THE RESEARCH OF D. KOLAR D. Kolar and his research collaborators vvere frequent clients of the EPMA laboratory during the first year vvith different topics from ceramic magnets, hard metals and phase equilibria diagrams. Several papers based signifi- Table 1: Clients for EPMA work Year Academic institutions Companies Payed working hours Articles1 1969 10 14 1276 1970 12 17 1330 6 1971 12 10 1335 8 1972 12 11 1330 5 1973 10 11 1301 2 1974 11 17 1241 10 In the year 1969 to 1974 54 different institutions and companies com-mitted once or several times EPMA vvork, 29 ind. companies commit-ted the investigation from 1 to 18 different specimens yearly. ' - Authors from the EPMA laboratory Table 2: Composition of nonmetallic inclusions and carbides F. Vodopivec und B. Ralic: Radex Rundschau (1975) 1, 289-294 Inclusion1 MnO FeO CaO Vsota ut.% 1 28.0 8.3 - 63 - 99.3 2 16.4 2.3 37.8 7.5 36.0 100 3 55.5 6.3 31.1 5.9 - 99.8 4 50.3 6.3 32.4 9.7 - 98.6 5 21.4 4.6 30.4 2.4 41 99.8 Carbide2 W V Fe Cr Mo C M6C2 56.0 3.1 28.6 4.75 2.25 1.93 (Wi.6Fe3.3Vo.36Cro.56Ci) MC 14.2 57.2 3.3 7.65 1.6 16.95 (Vp.91 Wo.()6Feo.()5Cr(). 11 Mop.o i C i) Correction calculation after Bence-Albee 1 6 8 ' Correction calculation after Philibert and Reed vA /V \ j \/ v' /v V" \ i ir, V M f \ H / N ^ 650 °C. !h Ilhš5 Ca J In combination vvith optical microscopy it vvas possible to find reliable ansvvers also for significant techno-logical problems, f.i. inhomogenity and kinetics of homogenisation of steels as vvell as copper and aluminium alloys, composition of nonmetallic phases in steels and alloys. The allready mentioned figure 3 shovvs a non me-tallic inclusion enriched at the surface by calcium and sulphur9. This vvas one of the first proofs for the reaction betvveen calcium bounds to aluminate or alumosilicate inclusions vvith sulphur in the liquid steel. The homoge-nising times for aluminium and copper alloys vvere di-minished on the base of investigations of segregation ki- 650 =C Figure 4: Distribution of alloying elements in an Cu 8% Sn 0,38% P alloy as čast and after homogenisation. Ref. 10 Slika 4: Porazdelitev legirnih elementov v zlitini Cu 8% Sn 0.38% P po litju in po homogenizaciji. Po viru 10 cantly on EPMA vvork were printed in international jour-nals. The authors is avare of the possibiIity that some of the phase diagrams were later modified on the base of results of improved EPMA. Also if it happened, it could not change the type of phase diagrams which have there-fore a permanent value. The ambition of the author of the present survey is not to present ali the vvork of D. Kolar in the quoted years, but to shovv that D. Kolar vvas prepared for EPMA and prepared to exploit optimally the nevv research facil-ity in Slovenia due to the putting in operation of EPMA and vvas able in this way to improve considerably the scientific value of his investigations. Figure 4 is taken from ref. 11, vvhere Drofenik and Kolar reported on the effect of BijOi addition on sintering process and properties of strontium ferrite. The atten-tion of the reader is called on the quality of electron and scanning pictures in figure 4. vvhere details near the size of |im are discernible. The morphology of bismuth oxyde containing phase shovvs that it fills as liquid spaces betvveen polyhedric grains of ferrite vvith higher melting point. EPMA shovved in this phase 50% BiiOj, 31% Fe203 and 19% of SrO. It vvas concluded that the addition of bismuth oxyde lovvered the sintering temperature and inereased the volume density and energy product (BH)m. In the same year Komac, Golič, Kolar, and Brčič12 es-tablished the crystal strueture, phase composition and transformation temperatures in binary phase equilibria systems US-CaS, US-SrS and US-BaS. EPMA vvas used for the determination of solid solubilities and eutectic compositions shovvn in table 3, vvhile figure 5 presents the phase diagrams US-CaS and US-BaS. Jurca, Kolar and Trontelj investigated the effect of nickel on activated sintering of tungsten and established that nickel is not found in solid solution in tungsten in a deteetable con-tent and that also at grain boundaries nickel is not found in appreriable quantity13-14. 1.2 to 2.8% vvas found for the solid solubility of tungsten in silver, vvhich is lovver than the value found in published phase diagrams. H00 - *N 1 v 1 \ \ \ ) 1"0' N----- 1 1 X 1 1 j 1710' j' \ t 1 1 tn 1 1 l | t—> [Mol V.) Figure S: Back scattered electron and X rays scanning pieture for different eiements. Sintered strontium titanate with addition of Bi2Oi. Ref. 11 Slika 5: Elektronski in specifični X posnetki za različne elemente. Sintran stroncijev titanat z dodatkom Bi203. Po viru 11 10 50 I Mol 7. Figure 6: Phase diagrams US-CaS and US-BaS. Ref. 12 Slika 6: Fazna sistema US-CaS in US-BaS. Po viru 12 2100 2200 2000 ' 1800 : 1600 ' 1100 1730' v __ Figure 7: Phase diagrams NbC-Fe and NbC-Cr. Ref. 15 Slika 7: Fazna diagrama NbC-Fe in NbC-Cr. Po viru 15 Table 3: Phase composition in binary phase equilibria systems US-CaS, US-BaS in US-SrS M. Komac, L. Golič, D. Kolar and B. S. Brčič: J. Less-Common Metals, 24 (1971) 121-128 System Phase US-CaS US-SrS US-BaS Solid solution US',% 3.5 3.5 3.0 Solid solution MS',% 4.0 n.d. n.d. Intermediate phase,% 50 50 50 CaUS2 SrUS2 BaUS2 Eutectic 1,% 33.0 33.0 38.0 Eutectic 2,% 50.5 53.0 n.d. ' - Maximal solubility by eutectic temperature Guha and Kolar15 investigated the phase equilibria diagrams niobium carbide with transition metals iron, chromium, nickel, and cobalt. Solid solubilities and eutectic compositions are shown in table 4 and the phase systems NbC-Fe and NbC-Cr in figure 6. Eutectic points are deplaced near the metal side and the solid solubilities are in the range 1 to 4.3% Guha and Kolar16 investigated also the phase diagrams TiC-Cr and ZrC-Cr in figure 7. EPMA results in table 5 indicate small solid solubility and eutectic point deplaced on metal side. Weight percent Cr Weiqh( oercent Cr Figure 8: Phase diagrams TiC-Cr and ZrC-Cr. Ref. 16 Slika 8: Fazna diagrama TiC-Cr in ZrC-Cr. Po viru 16 Table 4: Phase composition in binary phase equilibria systems NbC-Fe, NbC-Cr, NbC-Ni, and NbC-Co J. P. Guha and D. Kolar: J. Less-Common Metals, 29 (1972) 33-40 System Eutectic_Solid solution',wght.% _wght.% metal metal in NbC NbC in metal NbC-Fe 91.2 1.8 0.98 NbC-Cr 76.0 2.8 0.85 NbC-Ni 89.0 1.8 3.5 NbC-Co 88.0 L2__4.3 1 - Maximal solubility by eutectic temperature Table 5: Phase composition in binary phase equilibria systems TiC-Cr and ZrC-Cr J. P. Guha in D. Kolar: J. Less-Common Metals, 31 (1973) 331-343 System Eutectic Solid solution ',wght.% Metal, wght.% Metal in Carbide in carbide metal TiC-Cr 89.0±0.5 3.5 3.5 ZrC-Cr 88.0±0.5 4.5 0.2 1 - Maximal solid solubility at eutectic temperature Finally Guha and Kolar17 established also the phase diagram BaTi03-BaGeC>3 on figure 8 and 9, determined Mol 7. 8aCe0j Figure 9: Phase diagram BaTi03-BaGe03. Ref. 17 Slika 9: Fazni diagram BaTi03 - BaGeOj. Po viru 17 the liquidus and solidus temperature, the eutectic composition as vvell as the solid solubilities 1 of mol % BaTi03 in BaGeO., and 2.2 mol % of BaGe03 in BaTiOj at eutectic temperature. 5 CONCLUSION The slovenian research community obtained relativen late the possibility to use EPMA at acceptable time and expense as standard research method for in situ quali and quantitative investigations of solid materials. Statistical data show that the community was well pre-pared for the use of the new facility. For that reason, the use expanded relatively fast in research academic and in-dustrial laboratories in metallurgy, geology, mineralogy, ceramic, building materials and electronics. On average, in the first years more EPMA work was performed for industrial companies than academic institutions. D. Ko- lar was between the researchers which did profit the must from EPMA. Based on optical microscopy and EPMA he and his collaborators reported in international journals on significant findings on topics of magnet ce-ramics and binary phase equilibria systems of metals and carbides as well as sulfide compounds. It is therefore justifield to conclude that D. Kolar helped greatly to strengthen EPMA as rutine investigation method for ba-sic, applied and development research of metallic and non metallic materials. 6 REFERENCES 1 F. Vodopivec: Dr. thesis, University of Pariš, 1962 2F. Vodopivec, A. Kohn, J. Philibert et J. Manenc: Revue de Metallur-gie, 60 (1963) 801-818 3 L. Kosec: Mag. thesis, University of Ljubljana, 1967 4 L. Kosec, F. Vodopivec et R. Tixier: Metaux-Corrosion-Industries, (1969) No.525, 1-25 5F. Vodopivec und B. Ralic: Radex-Rundschau, (1975) 1, 289-294 6J. Philibert: Metaux-Corrosion-Industries, 40 (1964) no. 465, 157-176, no. 466, 216-240, no. 469, 325-342 7 A. E. Bence and A. L. Albee: J. ofGeology, 76 (1968) 382-403 8S. J. B. Reed: Brit J. Applied Physics, 16 (1965) 913-926 9F. Vodopivec in B. Ralic': Železarski zbornik, 6 (1972) 215-229 l0L. Kosec, A. Podgornik in B. Ralic: Rudarsko Metalurški Zbornik, 4 (1972) 417-428 " D. Kolar and M. Drofenik: Proceedings of the British Ceramic Soci- ety, N 18 1970 125-138 12 M. Komac, L. Golič, D. Kolar and B. S. Brčič: Journal of Less-Com- mon Metals, 24 (1971) 121-128 13S. Jurca, D. Kolar and M. Trontelj: Activated sintering of Tungsten: Proceedings ofthe Inf. Conf. on Powder MetaUurgy, Zakopane, 1971, 247-258 14D. Kolar, S. Jurca and M. Trontelj: Rudarsko Metalurški zbornik, (1970) 1,35-41 15J. P. Guha and D. Kolar: Journal of Less-Common Metals, 29 (1972) 33-40 l6J. P. Guha and D. Kolar: Journal of Less-Common Metals, 31 (1973) 331-343 17 J. P. Guha and D. Kolar: J. Materials Science, 7 (1972) 1192-1196 LAUDATION IN HONOUR OF PROFESSOR DR. JOŽE GASPERIČ ON THE OCCASION OF HIS 65th BIRTHDAY MONIKA JENKO Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia Professor Dr. Jože Gasperič, scientific councillor, leading Slovenian vacuumologist is celebrating his 65lh birthday. This event is the occasion to look at the back-ground and the development of this well known scientist and at the influence which his research work has in the field of vacuum science, development, construction and produetion of vacuum diffusion, rotary and diaphragm pumps, valves, traps etc, measuring vacuum gauges like Pirani, Penning, ionization gauges, McLeods, vacustats, mercury manometers, vacuum metrology, etc. Jože Gasperič vvas born in Ljubljana on March 7, 1932. After finishing the grammar school education, he studied Electrical Engineering at the University of Ljubljana. In 1958 he passed the final examinations and second degree thesis. In 1957 he joined as Research As-sociate the Institute for Electronics and Vacuum Tech-niques in Ljubljana direeted by its founder Professor Dr. Dušan Lasič. He was also Assistant in Electronics at the University of Ljubljana from 1956 to 1958 and later from 1959 to 1964 the lecturer of vacuum technique at Electrical Technical High School, Ljubljana. He prepared his master thesis in the field of Electrooptics and Elec-trooptical devices at the University of Ljubljana and graduated in 1964. In 1972 he graduated at the Univer-sity of Ljubljana for doetor of Science in the field of Mi-croelectronics - thin films. In 1970 he was senior researcher and the manager of Vacuum Department from 1980 to 1985 at the Institute for Electronics and Vacuum Technique (IEVT). In 1986 he accepted the position of a visiting professor at the Department of Physics, Thin Film Laboratory, at Sri Venkateswara University, Tirupati, India and at Indian Institute of Science in Bangalore, India as visiting scientist. In 1988 he returned to Ljubljana and joined to Solid State Physics Department of Jožef Štefan Institute. Jože Gasperič, as a senior researcher and manager of Vacuum Department at IEVT Ljubljana, originated many new research programs, which received founding from institutes, industry, Slovenian and former Yugoslav research communities. His work has included characterization of evaporated and sputtered materials, metals com-pounds and alloys, especially cermets, decorative thin layers, etc. Developing high stabilized cermet resistor films. He developed and simplified theory for calculation of jet system for oil diffusion pumps for produetion in the range from 100 to 15000 l/s. iiiii: Dr. Jože Gasperič He developed many vacuum pumping systems and equipment on the base of his own technologies, for in-dustry and labs, for produetion of photo-sensitive and X-ray tubes, for degazation of insulating oils and other liq-uids for impregnation of electronic diserete circuits, condenser, power motor windings, vvood, tools made by powder technologies, etc. He developed also many types of medical inhalers and suetion devices for surgical purposes, for suetion of mother's milk for feeding prematurely born babies and he organized some centres in Slovenia for hiring such devices. He developed freeze-drying devices for pharma-ceutical and biological labs. He developed many special vacuum gauges as stan-dards for calibration of other electronic vacuum gauges, baffles and traps, cooled with Peltier couples, complete portable equipment for service work on cooling devices (refrigerators, deep freezers, air conditioning devices). At the IEVT he set up the universal calibration sys-tem for vacuum gauges, system for measuring ali charac-teristics for rotary, diaphragm and diffusion pumps, monopol mass spectrometer, leak deteetion, various rough, high and ultra high vacuum systems for investigations, thin film evaporation systems. He organized Leybold Heraeus and Jeol repre-sentative & service stations, both are novv private. Jože Gasperič is also an excellent organizer of con-ferences and congresses and he taught us how to organ-ize the meetings in Slovenian Vacuum Society as well as in Union of Vacuum Societies of former Yugoslavia. He vvas the president of the Union and organizer of 4 Yugo-slav vacuum congresses and Joined vacuum conference of Hungary-Austria-Yugoslavia and he vvas a member of organizing committee of the European Conference on Applications of Polar Dielectrics, FORUM BLED '97, and Solid State Protonic Conductors. He succeeded vvith his project Vacuum impregnation of fossil bones of mammoth for Natural museum of Slovenia to save the prehistoric mammoth for our de-scendants. He vvas editor of Nevvs of the Slovenian Society for Medical and Biological technique, co-editor of Slovenian journal Vakuumist - Vacuumologist and lector for Slovenian scientific journal Kovine zlitine tehnologije - Metals, Alloys, Technologies. Our colleague and friend Jože is full of development špirit and creative ideas. Jože Gasperič has published over 100 papers in international journals and conferences and 100 papers in Slovenian journals and conferences on the topics of sci-ence, technology, vacuum science and technique as vvell as vacuum metrology. Professor Gasperič has been supervisor to several Ph.D. and Master Degree students at the Universities of Ljubljana, Maribor and India. He is also very active in the international academic field. He is a member of executive council of Slovenian Vacuum Society, member of Slovenian Electronics and Micrelectronics Society, Slovenian Society of Biomedi-cine, member of Electronics Materials scientific division of International Union for Vacuum Science, Technique and Applications - IUVSTA. His colleagues and friends hope very much that he vvill take part in discussions, lectures and publications also in the future and vve vvould like to wish him and his family many years in good health. THE PROPER OPERATION OF THE HIGH VACUUM PUMPING SYSTEM PRAVILNO DELOVANJE VISOKOVAKUUMSKEGA ČRPALNEGA SISTEMA JOŽE GASPERIČ1 Jožef Štefan Institute, Jamova 39, 1001 Ljubljana, Slovenia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 The proper operation of high vacuum pumping systems with oil diffusion pumps and backing rotary putnps is very important, otherwise the contamination of vacuum chambers by backstreaming oil vapours is extremely high as well as the oxidation and the loss of diffusion pump oil. The forepressure svvitching point, vvhere the diffusion pump is put into the operation by opening the high vacuum and forepressure valves is discussed. There are three possible situations: the pumping throughput is just adapted, or it is to low, or to high. What is going on, when the pumping troughput is adapted, it is illustrated using the troughput-pressure diagrams. At the end some practical advices are done, how to recognize that the operation of the HV pumping system is correct. Key words: high vacuum pumping system, contamination, loss of diffusion pump oil, tolerable forepressure, switching point Pravilno upravljanje in delovanje visokovakuumskega črpalnega sistema z oljno difuzijsko črpalko in rotacijsko predčrpalko je zelo pomembno, kajti v nasprotnem primeru pride do močno povečanega povratnega toka oljnih par iz difuzijske črpalke v vakuumsko komoro in s tem do njene kontaminacije. Izguba olja v difuzijski črpalki in njegova pospešena oksidacija sta spremljajoča pojava. Pri ročnem ali avtomatiziranem upravljanju črpalnega sistema je zelo pomemben trenutek oz. točka preklopa, ko prenehamo črpati s predčrpalko po obtočnem vodu in odpremo visokovakuumski in predvakuumski ventil in začnemo črpati z difuzijsko črpalko. Možna so tri delovna stanja: delovanje obeh črpalk je usklajeno, predčrpalka ima premajhno ali preveliko črpalno hitrost. Usklajeno stanje smo ponazorili na diagramu. Podani so tudi praktični napotki, kako spoznamo, ali je črpalni sistem pravilno upravljan. Ključne besede: visokovakuumski črpalni sistem, kontaminacija, izguba olja difuzijske črpalke, mejni predtlak, preklopna točka 1 INTRODUCTION Most usual, the high vacuum pumping systems con-sist of diffusion pumps and corresponding rotary backing pumps. The basic sheme is shovvn on Figure 1. Nor-mally, ali producers of such high vacuum systems give the prescription how to vvork vvith them at the begining, vvhen the vacuum chamber is pumped from atmospheric pressure, down to 104 and 10 5 mbar, respectively, vvhen the technological process is started (e.g. evaporation). In practice this procedure is never exactly followed by us-ers. Only in the čase, when the high vacuum system is fully automatized, the users can avoid the mistakes in the pumping procedure. Usually it happens that not skilled persons change the programme by moving the pressure svvitching points of valves. The results of that action are: - by backstreaming oil vapours from the diffusion pump the vacuum chamber as vvell as ali material in it are contaminated - the oxidation, deterioration and loss of the diffusion pump oil are very intensive. The service and cleaning vvork of the system is re-quired. 2 EXPERIMENTAL The procedure of pumping from atmospheric pres- sure to the high vacuum is well known. The action of both pumps has to be adjusted to minimize the pumping time, which is very important in the industrial produc-tion. If shorter time is required ("The time is money!"), we have to know ali effects vvhich influence on it. One of them is the time svvitching programme of valves, vvhich Slika 1: Visokovakuumski črpalni sistem is also depended on the pumping characteristics of both pumps. The most evident way, how to explain the interrela-tion between diffusion and backing pumps, are their throughput-pressure characteristics. As an example let us use the throughput characteristics of DI 12000 diffusion pump (Leybold) and corresponding backing pump (a combination of Roots pump WA 250 and the one stage rotary pump S 60A). From the diagram (Figure 2) it is evident that both throughput characteristics have the cross-section point M at the throughput QM and pressure pt. The pumps are selected so that the end of the diffusion pump curve is just on the throughput curve of backing pump. The pressure p, is called the tolerable forepressure. Practically, this forepressure is a limit of the diffusion pump operation. The total air flow from the vacuum chamber is now depended only on the backing pump and conductivities of connected lines, valves etc. When the tolerable forepressure takes plače the oil va-pours which are generated in the diffusion pump boiler and ejected through the jet system do not reach the water cooled walls of the pump, vvhere the condensation of them is expected, but one part escapes in the direction of vacuum chamber, vvhere it condenses (contamination!), the other part of oil vapours is pumped by the backing pump (the loss of the oil from diffusion pump). The oxi-dation and deterioration of the oil in the boiler of the pump and on the surface of jet system (temp. approx. 200°C) is accelerated. Čase 1: When pumping of the chamber is started through the by-pass valve V2 from the atmospheric pressure (VI and V3 are closed) the air throughput Q and the pressure are slowly reducing (the direction from point A to M in diagram, Figure 2). When the point M on the Figure 2: Throughput Q vs. pressure p Slika 2: Pretok zraka Q v odvisnosti od tlaka p throughput curve is reached, the theoretical posstbility is done to pump with the diffusion pump. If in this moment the by-pass valve is closed, and VI and V3 are open, from the point M we are "driving" the pumping action of the chamber in the direction of DI 12000 (upper curve) to the next point C, where the pressure is Pc (M2) and forepressure pc (Ml) at the throughput point C'. The pressure pc is lower than tolerable one pt, and the diffusion pump can normally operate. After a longer time of pumping we "come" to the point D, where the throughput is Qd, pressure on high vacuum side Pd and forepressure pd (point D'). We can continue the pumping procedure as long as the operating (or ultimate) pressure is achieved. The diagram on Figure 2 is an example, how the diffusion and backing pumps are well adjusted. Čase 2: Supposing that the by-pass valve (V2) is closed and other valves (VI, V3) are open in the point A, vvhere the pressure pa is higher then the tolerable forepressure pt. The pump capacity of the diffusion pump is totally lost. The diffusion pump is novv like "a cooking pot" for oil. Bad results vvere described above, although the pumping action of backing pump is conttnued. The situation is normalized, vvhen the point M is achieved and after that, as described above. This means that on such a way vve can not shorten the total pumping time. Čase 3: If the by-pass valve (V2) is closed later, e.g. at the point E, and valves VI, V3 are open in next moment, the diffusion pump as vvell as backing pump throughput suddenly "jump" to the value at E' and the forepressure (Ml) increases from pe to pe". If in our pumping procedure is such a čase, vve had lost the time, vvhich is needed to pump the chamber from E" to E vvith backing pump. We have described three characteristical situations in the operating procedure, and novv vve can ask ourselves, how to recognize that the high vacuum pumping system is operating correct or not. Normally, vve have not the Figure 3: Pumping time characteristics of the adjusted high vacuum pumping system: a) inproper operation, b) proper and optimal operation, c), d) proper but not optimal operation Slika 3: Črpalna karakteristika usklajenega visokovakuumskega sistema: a) nepravilno delovanje, b) pravilno in optimalno delovanje, c), d) pravilno, vendar ne optimalno delovanje pumping diagram (like that shown on Figure 2) at the hand. The best way is monitoring of the both pressures readings Ml and M2. If the forepressure (Ml) increases to the values, vvhich are higher than the torelable forepressure, vvhen vve close V2 and open VI and V3, the operation of the diffusion pump is stopped (oil back-streaming and contamination of vacuum system, the oxi-dation and loss of the oil begin) (Figure 3a). The situ-ation is normalized, vvhen the pressure (Ml) is lovver then the tolerable forepressure. The optimal čase is, vvhen after svvitching of the valves, as desribed above, the forepressure (Ml) increases just to the value p, (tolerable forepressure), Figure 3b. Ali other cases, as vve can see on the pumping characteristics, Figure 3c, d, are also proper but not op- timal, vve are loosing time, vvhich is very important, especialy in the production in the industry. It is also very simply to practically identify the tolerable forepressure. For most types of oil diffusion pumps it is betvveen 0,1 and 0,5 mbar. Many other cases exist, vvhere the pump combinations are not adapted (e.g. the pumping speed of backing pump is to high or to lovv) vvhich vvill be described later in a separate paper. 3 CONCLUSION It is very simple to estimate that a high vacuum sys-tem is operating optimaly or not by observing the pressure changes in the vacuum chamber as vvell as the forepressure of diffusion pump during the svvitching period of values. Obveščamo vas, da je izšla knjiga Slovenska jekla - Jekla in železove litine. Njen namen je olajšati prehod na nove evropske in slovenske standarde in oznake z možnostjo primerjav s sedaj že bivšim označevanjem jekel tako pri nas, kot v državah EU. V knjigi je pregled slovenskih proizvajalcev jekel, jeklenih in železovih litin z njihovimi internimi oznakami. Poleg oznak, standardov ter primerjav so podane tudi kemijske sestave, razvrstitve po skupinah, opis, lastnosti ter uporaba. Jekla in litine so razvrščene po rastoči številki, indeks za iskanje pa je abecedni in pripelje uporabnika od oznake do številke jekla/litine. ZA LAŽJI PREHOD NA NOVE SLOVENSKE IN EVROPSKE STANDARDE IN OZNAKE • register evropskih jekel in žeiezovih fitin • primerjave oznak in standardov • sosrova. op*, laslnost. uporabo • proizvajale interne oznake SLOVENSKE ŽELEZARNE WLW SLOVENIAN STEELWQRK5 Izdajo knjige je sofinanciralo Ministrstvo za znanost in tehnologijo. Naročilnico lahko pošljete po pošti ali po faxu na številko: (0602) 23-013 ZA LAŽJI PREHOD NA NOVE SIOVENSKE iN EVSORKE SIAN0A&BE M OZNAKE • aw!Opskih j^tarf in . • j.^nr.■<;'!'." ■ ■ 10V ji ; siamSafdov • r.ph i..'.''vi ' y (. 'ii- ':.' ./i ■'.<• StOVfNSKt ?£l£«RNE SLOVENIAN STEftWORKS 1300 jekel 200 jeklenih litin 95 železovih litin 10000 primerjalnih oznak in pripadajoče številke standardov El\l, ISO, EU, UIC, SIST, DIN, SEW. JUS, BS. NF, SS, UNI, UNE, GOST, JIS. UNS, AISI, SAE, ASTM Proizvajalci: Slovenske železarne: Acroni, Metal Ravne, Jeklolivarna Ravne, Valji Štore, in pa Litostroj - Tovarna ulitkov, TAM, Titan, Livarna Vezir Štore, Feralit Žalec, IMP Livar, Unior Livarna, ETA Cerkno, Livarna Vuzenica, WP. Livarna Nova Gorica. ULTRA THIN DEPOSITED AND SEGREGATED FILMS ULTRA TANKE NANESENE IN SEGREGIRANE PLASTI MONIKA JENKO Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenja Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Dedicated to Prof. Jože Gasperič at the occasion of his 65th birthday Research, development and use of vacuum thin films started at the Institute for Electronics and Vacuum Techniques, IEVT, Ljubljana after its foundation around 1950. With the development of the miniature thin film potentiometers and thin films resistors of high stability at IEVT the first production of thin film electronic components in former Yugoslavia was established. The technology vvas successfully transferred to Slovenian foreign factory in Cormons Italy where Slovenian minority is living. At the same time the high tech research and development of the second and third generation image intensifier tubes was started. Prof. Dr. Jože Gasperič was one of the leading scientists investigating the sputtered cermet thin films in his BS and Ph.D. works. His findings are basic for understanding the mechanism of grovvth of thin sputtered cermet films. In the middle of eighties an experimental ultra high vacuum, UHV, system equipped vvith Auger spectrometer, vvas built at IEVT and the investigation of physical and chemical processes of ultra thin oxide film grovvth on the surface of liquid indium and indium alIoys in situ vvas achieved for the first time. The experimental method based on Auger Electron Spectroscopy for in situ investigation of the initial phase of the ultra thin oxide film grovvth on liquid indium, vvas developed at the institute. The modified experimental method vvas also used for the study of ultra thin segregated Sb, Sn or Se films on the surface of FeSiC alloy, microalloyed by Sb, Sn or Se. The investigation of ultra thin Sn. Sb or Se films on well defined Fe surfaces is the topic of our present research vvhich is close connected vvith the purchase of new AES/XPS instrument vvith the very high spatial resolution. The results of investigations of ultra thin oxide films on the liquid indium and InSn alloy as well as Sb and Sn ultra thin film grovvth on the surface of FeSiC alloy vvere presented. Key vvords: ultra thin films, deposited films, segregated films, surface segregation, oxidation, dissociation Prve raziskave, razvoj in uporaba vakuumskih tankih plasti so se začele na Inštitutu za elektroniko in vakuumsko tehniko v Ljubljani takoj po ustanovitvi, okrog leta 1950. Z razvojem miniaturnega tankoplastnega potenciometra MP in stabilnih tankoplastnih miniaturnih uporov se je pričela na IEVT tudi prva proizvodnja tankoplastnih elektronskih komponent v takratni Jugoslaviji. Tehnologija izdelave MP je bila uspešno prenesena v novo ustanovljeno slovensko zamejsko tovarno v Krminu v Italiji. Obenem pa so se vršile raziskave in razvoj specialnih fotoelektronk. Sb fotokatod druge in tretje generacije za slikovne ojačevalnike z bližinskim prenosom slike, ki je predstavljal "high-tech" v svetovnem merilu. Vakuumisti IEVT so s svojim znanjem sodelovali v svetovno znanih institucijah kot npr.: SAES Geters, Heimann, Leybold Heraeus. Skupne rezultate so že takrat objavili v tuji znanstveni periodiki. Z raziskavami vakuumskih tankih plasti se je na IEVT intenzivno ukvarjal tudi prof. dr. Jože Gasperič, ki je problematiko kermetnih napršenih plasti obdelal v svojem magistrskem in nato še v doktorskem delu. Njegova temeljna spoznanja so pomembeno prispevala k razumevanju mehanizma rasti tankih napršenih plasti. Z izgradnjo eksperimentalnega ultravisoko vakuumskega sistema, opremljenega s spektrometrom Augerjevih elektronov na IEVT v sredini osemdesetih let pa je bila dana možnost raziskav fizikalno kemijskih procesov pri nastanku ultra tankih oksidnih plasti na površini tekočih kovin in zlitin "in situ". Tovrstne raziskave so bile izvedene prvič. Načrtovana in osvojena je bila nova eksperimentalna metoda, ki je omogočila študij začetnih stopenj rasti oksidnih plasti na tekočem indiju, ki smo ga tudi naparili in situ v spektrometru Augerjevih elektronov. Metoda je bila uporabljena tudi za študij ultra tankih segregiranih plasti Sb, Sn in Se na površini zlitin Fe-Si-C, mikrolegiranih z Sb, Sn ali Se. Študij ultra tankih plasti Sb, Sn, Se na dobro definiranih površinah Fe in V pa je predmet naših sedanjih raziskav, ki so vezane na nabavo novega AES/XPS instrumenta z visoko lateralno ločljivostjo. Prikazani so rezultati raziskav ultra tankih oksidnih plasti na tekočem indiju in zlitini InSn ter ultra tankih segregiranih Sb in Sn plasti na zlitini FeSiC. Ključne besede: ultra tanke plasti, oksidacija, disociacija, In203, ln20, Sb, Sn, površinska segregacija, AES, XPS INTRODUCTION Advanced technologies are strongly dependent on products of electronic industries such as optoelectronics, sensors, high density integrated components, etc. Thin films of thicknesses from ten to several hundreds of nanometers are very important in the production of these products. Ultrathin films-UTF vvhose thickness is up to fevv monoatomic layers are very decesive in the segregation, corrosion, recrystallization and catalytic processes. UTF are influenced by their interaction vvith the substrate and open a completly nevv perspective in the development of nevv advanced materials vvith desired physical and chemical properties. Research, development and use of thin films started at the Institute for Electronics and Vacuum Techniques, IEVT, Ljubljana Slovenia after its foundation in early fif-ties. With the development of the miniature thin film potentiometers and thin films resistors of high stability at IEVT the first production of thin film electronic components in the country vvas established. The technology vvas successfully transferred to Slovenian factory in Cor-mons-Italy vvhere the Slovenian minority is living. Prof. Jože Gasperič vvas one of the leading scientists investigating the sputtered cermet thin films in his BS and Ph.D. vvorks. His findings are basic for understanding the mechanism of grovvth of thin sputtered cermet films. In the middle eighties the "high tech" research and development of the second and third generation image intensifier tubes vvas started at IEVT. An experimental ultra high vacuum, UHV, system equipped vvith Auger spectrometer, vvas built and the author vvas the first to investigate in situ the physical and chemical processes of ultra thin oxide film grovvth on the surface of liquid in-dium and indium alloys. The experimental method based on Auger Electron Spectroscopy for the in situ investigation of the initial phase of ultra thin oxide film grovvth on liquid indium, vvas developed at the IEVT institute. The simplified ex-perimental method vvas used for the investigation of seg-regated Sb, Sn or Se UTF on the surface of FeSiC alloy, microalloyed vvith Sb, Sn or Se at the Institute of Metals and Technology Ljubljana, vvhere the first studies of P segregation started already in 1962. The investigation of Sn, Sb or Se UTF on vvell de-fined Fe surfaces is being the topic of our present research vvork vvhich is close connected vvith the purchase of nevv AES/XPS device vvith the very high spatial reso-lution. The results of investigations of ultra thin oxide films on liquid In and InSn al!oy as vvell as Sb, Sn and Se ultra thin film grovvth on the surface of FeSiC alloy are presented. 1 AES INVESTIGATION OF INITIAL PHASE OF LIQUID In AND InSn ALLOY OXIDATION AND DISSOCIATION OF I112O3 1.1 Fluxless vacuum soldering In the production of the third generation image intensifier tubes the fluxless vacuum soldering is the most important process for hermetic encapsulation. Extremely clean surfaces are indispensable for obtaining good vvetting of liquid solder. In the first model experiments we found that the leakage of fluxless vacuum soldered seals may often be caused by thin oxide film, covering the liq-uid solder. The solder is lovv melting InBi or InSn alloy. For the basic investigation vve used pure indium as a solder and vve realized that only in situ surface characterization may give direct insight into these complex surface phenomena. For this purpose a very sensitive experimental method based on AES vvas developed at IEVT Ljubljana. The initial phase of surface oxidation on high purity in situ deposited indium and the mechanism of cleaning process of oxidised indium surface ln203 vvas the main goal of the investigation. 1.2 Experimental method for the investigation of surface phenomena at fluxless vacuum soldering The experiments were performed in an adapted Scanning Auger Electron Microprobe, additionally equipped vvith addapted sample holder, heater and thermocouple, evaporation source for in situ deposition of high purity indium, quartz microbalance for determination of In thin film thickness, quadrupole mass spectrometer-QMS for residual gas analysis and precise metal valve for oxygen introduction. Especially designed connections enabled the movement of the sample, figure 1. The sample high purity indium thin film vvas deposited in situ on a pure molybdenum substrate. The oxide ln203 film vvas obtained by exposure of the indium surface to pure oxygen at constant pressure 5x10"5 mbar vvith oxygen time exposure up to 100 minutes in temperature range from 25 to 250°C. The resistive heater for investigating In/In203 film vvas a Mo strip vvhich could be heated up to 1000°C. A thermocouple Fe-CuNi vvas vvelded on the rear side of the Mo strip. The indium source for in situ deposition vvas prepared from indium metal of 6N purity. 1.3 AES studies of the initial phase of liquid indium oxi-dation The surface oxidation of indium in bulk and thin film occurs as (1): 4 In (1) + 3 02 (g) ^ 2 ln203 (c) (1) vvhere (c), (1) and (g) mean crystalline, liquid and gas state, respectively. The solubility of oxygen in pure liq-uid indium is extremely lovv, lxl0~6 atomic percent at 550°C and it is negligible in the temperature range of our investigation from 25 to 250°C. The diffusivity of Figure 1: AES spectrometer adapted for liquid indium surface investigations: 1 - sample, 2 - Thermocouple, 3 - sample holder, 4 -flexible connections, 5 - rigid connections, 6 - In source for in situ evaporation, 8 - flange, 9 - CMA, 10 - ion gun, 11 - QMS, 12 - lead through, 13 - quartz microbalance, 14 - metal valve for oxygen introduction Slika 1: Spektrometer Augerjevih elektronov prirejen za raziskave procesov na tekočem indiju: 1 - vzorec, 2 - termočlen, 3 - nosilec vzorca, 4 - gibljivi priključki, 5 fiksni priključki, 6 - In izvir za "in situ" naparevanje, 8 - prirobnica, 9 - CMA, 10 - ionska puška, 11 - QMS, 12 - prevodnice, 13 - kremenova mikrotehtnica, 14 - vpustni ventil za kisik c .—> O cr 0. 0,6 0,4 0,2 _^250°C f / / / / -/ / i/ 150 °C 1 / f 25 °C 1 1 1 1 1 10 15 Time (min) 20 25 30 Figure 2: Surface oxidation rate of crystalline and liquid indium at temperatures 25, 150 in 250°C at a constant oxygen pressure of 5xl0"5 mbar Slika 2: površinska oksidacija trdnega in tekočega indija pri temperaturah 25, 150 in 250 °C in konstantnem tlaku kisika 5x10"5 mbar. oxygen in liquid indium is very low, 3.7xl0~7 cm2 s"1 at 550°C. It was concluded from these facts that the process of pure Iiquid indium oxidation occurs at the surface. The kinetics of thin oxide film growth on crystalline and liquid indium was investigated by AES, following the peak height ratio-PHR of amplitudes between O(KLL) and In (M5N45N45) Auger transition at kinetic electron energies of 512 eV and 402 eV (for In0) and 405 eV (for In3+) respectively. For a defined geometrical sample position in the AES spectrometer, the kinetics of the thin oxide film growth was followed up to the film thick-ness of 3.5 nm, vvhich corresponds to an effective electron depth escape for ln203. Surface indium oxidation vvas investigated at the temperatures of 25, 150, 250 in 550°C, figure 2. Thin oxide film thickness of 3.5 nm on pure indium vvere obtained at conditions listed in Table 1. Table 1: ln203 films, 3.5 nm thick obtained at different temperatures and different oxygen exposures Temperature (°C) Oxygen exposure (L) 25 6x104 250 3xl04 550 1.5x104 At higher temperatures T > 360°C, a volatile oxide was formed by the reaction: ln203 (c) + 4 In (1) <-» 3 ln20 (g) (2) The reaction betvveen the ln203 thin film and the un-derlying liquid indium, corresponding to equation (2) was studied at the temperature of 360, 400, 450 and 550°C in vacuum of lxl0"9 mbar. The results are shovvn in figure 3. OC ZC O. Figure 3: Isothermal dissociation of ln203 ultra thin solid film on liquid indium at the temperatures 360, 400, 450 in 550°C in a vacuum below lxl0"9 mbar Slika 3: Izotermna disociacija ultra tanke plasti ln203 na tekočem indiju pri temperaturah 360, 400, 450 in 550 °C in vakuumu pri tlaku < lxl0~9 mbar. 1.4 Investigation of huOj dissociation in uhv by AES At temperature T > 360°C the evaporation of volatile ln20 corresponding to equation (2) proceeded vvith per-ceivable velocity. At 550°C the process vvas so fast that AES studies of ln203 to In vvere not possible. The use of indium as a solder for vacuum fluxless soldering depends upon the fact that the thin ln203 film spontaneously disappeared - dissociated at T > 360°C by ln20 evaporation follovving the equation (2) ln203 (c) + 4 In (I) o 3 ln20 (g). 1.5 AES investigation of initial phases oxidation of InSn liquid solder In the second part of our investigation the knovvledge of the initial phase of surface oxidation on pure liquid In to InSn solder (20 at.% In, 80 at% Sn) vvas applied. The samples high purity InSn film, 2.5 jim thick vvere prepared in Balzers Sputron plasma beam apparatus, figure 4. On the oxidised InSn surface a difference betvveen AES spectra of pure metal In (402, 408 eV) and ln203 (399, 405 eV) vvas found. For tin (428, 435 eV) the char-acteristic chemical shift vvas not determined and only changes in the shape and intensity of Auger spectra vvere recognized. Figure 5 shovvs the AES spectra of the liquid InSn alloy exposed to pure oxygen 1.5x104 L, covered by thin oxide film, approximately 3.5 nm thick (figure 6), corresponding to an effective electron depth escape A^f for ln203. Figure 4: AES spectrum of InSn solder (20 at.% In and 80 at% Sn) after ion etching approximately 3 nm under surface Slika 4: AES spekter InSn spajke(20 at.% In and 80 at% Sn) po ionskem jedkanju približno 3nm pod površino The samples were oxidised in situ in Auger Spectrometer by exposure of a clean surface of Iiquid InSn alloy to pure oxygen (104 - 10" L) at 250°C. The results indicate that ali oxide films on the surface of liquid InSn solder vvere enriched in indium in varying amounts, depending on oxygen pressure, time exposure etc. In the first part of the investigation it was found that the surface oxidation of In, in bulk or in the form of a thin film can be formulated by equation (1): 4 In (1) + 3 02 (g) 2 ln203 (c) (1) Figure S: AES spectrum of 3.5 nm thick oxide UTF on the surface of liquid InSn alloy Slika 5: AES spekter 3.5 nm debele oksidne plasti na površini tekoče spajke InSn. where (c), (1) and (g) mean crystalline, liquid and gas state, respectively. The surface oxidation of Sn, in bulk or in thin film, occurs by the reactions: 2 Sn (1) + 02 (g) <-» 2 SnO (c) (3) Sn (1) + 02 (g) <-> SnO, (c) (4) AES chemical shifts of SnO and Sn02 are approxi-mately the same. On tin exposed to oxygen (104 - 106 L) both oxides SnO and Sn02 were found. As the same occurs for SnO and Sn02, chemical shift can not be used to identify the oxidized state of the tin film. It vvas pro-posed that a mixture of oxides SnO, Sn02 and ln203 vvas formed on InSn al!oy at the exposure to oxygen (104 -106 L). The mixture of oxides appeared to be thermody-namically unstable near the alloy-oxide interface; SnO and Sn02 oxides vvere reduced to Sn vvith the tendence to the formation of additional ln203 3SnO(oxidcc) + 2In(alloy]) <-> In203(oxidec) + 3Sn(a]loyl) (5) 3Sn02(oxide c) + 4In(alloyl) 2In203(oxide c) + 3Sn(alloyl) (6) Free energy AG" of reactions (5) and (6) are obtained by using the data for free energy of formation SnO, Sn02 and ln203 AG°(SnO) = = -69670 + 3.06 TlogT - 1.5xl0'3T2 - 0. + 18.39T (7) AG°(SnOj)= -143080 - 7.37 TlogT - - 0.7x10'3T2 + 2.38xl05T'+76.53T (8) AG°(In203)= -220970 + 24.22TlogT - 3xl0"3T2 - 0.3xl05T' + 41.36T (9) Figure 6: AES depth profile of oxide UTF on surface of liquid InSn solder. Oxide UTF was made in situ Slika 6: AES profilni diagram ultra tanke oksidne plasti na tekoči spajki InSn; oksidna plast je bila narejena in situ At the temperature 250°C AG° (5) = -525 kJmol1 and (6) = -285 kJmol"1 and the equilibrium constants: K(S) = (aSn3 x aIn203)/(asn03 * aIn2) = 2.2x1052 (10) K(6) = (as„3 x aIn2032)/(aSn03 x aIn4) = 2.8xl028 (11) where ai s are the activities of the reactants and products. The mixed oxide thin film formed during oxidation vvould be a mixture of pure I^Oi, S nO and Sn02. The driving force for reactions (5) and (6) is therefore AG(5) = AG" + RT ln[(l - NIn)3/N2,J (12) AG(6) = AG° + RT ln[( 1 - NIn)~VN4In] (13) Nin is the indium concentration in the Snln alIoy. At 250°C AG for Ni„ 10'6 (Ippm) is -108 kJmol'1 for reac-tion (5) and -351 kJmok1 for reaction (6). In other words, SnO and Sn02 are thermodynami-cally unstable are in the mixed oxide even when in contact vvith extremely dilute In in Sn. The only stable oxide formed at InSn alloy should be ln203 at 250°C. Since ali oxidation processes are of the nonequilibrium type, the amounts of SnO and Sn02 and the overall SnO, Sn02/In203 ratio depend on 02 pressure, temperature, diffusion coefficient, solubilities and other factors. Con-sequently the mixed oxides SnO and Sn02 in the oxide-alloy interface tend to be converted into Sn and ln203. 1.6 AES investigation of Itn03 dissociation on the surface ofliquid InSn solder in UHV The last part of fluxless vacuum soldering in UHV investigation dealt vvith the "cleaning process" by dissociation of thin ln203 film from the surface of the liquid Figure 1-. Changes in AES peaks of In, Sn and O betvveen heating of oxidized InSn solder at constant temperature of 450°C Slika 7: Spremembe AES vrhov značilnih za In, Sn in O med segrevanjem oksidirane spajke InSn pri konstantni temperaturi 450°C InSn solder. The reaction betvveen the thin ln203 film and the underlying liquid InSn solder correspond to equation 4 In (1) + 3 02 (g) 2 ln203 (c) (1) vvas investigated at 550°C and the results are shovvn in figure 7. It vvas found that at T>250°C in UHV the thin In203 film formed on the surface of liquid InSn alloy spontaneously disappeared by In203 dissociation according to equation (1). The oxides SnO and Sn02 or In203 are unstable in very thin oxide films on the surface of a liquid InSn solder at T>250°C. For fluxless vacuum vacuum soldering vvith liquid indium, previously cleaned at T > 360°C, recontamination is negligible in UHV in the temperature range: Tm < T < 360°C At fluxless vacuum soldering vvith liquid InSn solder, previously cleaned at T > 360°C, recontamination is negligible in UHV in the temperature range Tm < T < 360°C. 2 CHARACTERIZATION OF SEGREGATED Sb AND Sn UTF BY AES 2.1 Introduction Physical properties of metals and alloys depend on the composition and on the surface and interface structure of the material. These properties are affected by seg-regation processes of alloying elements and impurity elements during their manufacturing and use. Some of these elements vvhich segregates on free surfaces (surfaces, grain boundaries, interfaces) and ultra thin segregated films specifically affect adsorption, corrosion, adhesion, surface diffusion, recrystallization, catalytic activity, friction and vvear7 8. The atomic composition of grain boundaries is also very important because it affects physical properties as vvell as corrosion behaviour of metals and alloys. For materials applied at high temperatures, the composition of interfaces may be drastically changed by segregation, by enrichment of dissolved surface active atoms diffusing on the surface or grain boundaries and can cause metal embrittlement. The aim of the investigation vvas to examine the na-ture of segregation of antimony and tin and its effect on recrystallization process, grain grovvth and texture devel-opment of a cold rolled and annealed silicon non ori-ented electrical sheet to be used in generation of electrical energy. It has been experimentally confirmed that a small addition of antimony, tin and selenium into the melt of silicon iron by microalloying affect the magnetic properties of electrical sheets by enrichment on free surfaces, i.e. surfaces and grain boundaries91315"19. Such enrichment affects grain grovvth, producing an increase in the number of ferrite grains vvith soft magnetic lattice orientation vvhich grovv on the account of grains vvith other crystallographic orientations, and in this way improves the magnetic properties. Our investi-gations show a strong correlation between antimony and tin surface segregation and the orientation of surface grains17"19. The kinetics of surface segregation is determined by bulk diffusion of the segregate to the respective interface. Surface segregation kinetics was measured on non ori-ented silicon steel sheet in situ by Auger Electron Spec-troscopy-AES, by annealing and simultaneous analysis of the sputter cleaned sample at higher temperature in UHV. Non oriented silicon steel is a polycrystalline multi-component alloy of Fe, Si, Al, C, P and S. The addition of approximately 0.05 to 0.1% of single elements i.e. an-timony or tin starts a competition for free surface sites7'25. The grain boundary segregation of Sb and Sn was studied initially on polycrystalline non oriented silicon steel. The alloys were annealed in the temperature range betvveen 450 and 650°C to establish the equilibrium grain boundary segregation on samples quenched and mounted into UHV system, fractured in situ after cooling and analysed by AES. The main point of the research work was the determination of the physical nature of the surface segregation and its relationship to the internal grain boundary segregation grains at the sheet surface. The investigation also included the determination and evolution of the texture of grains at the sheet surface. Emphasis vvas placed on the understanding hovv texture affects the electrical en-ergy losses, as vvell as magnetic properties. 2.2 Surface segregation of antimony and tin Most elements dissolved in iron tend to enrich at ele-vated temperatures at surfaces, grain boundaries and in-terfaces and distribution equilibrium Ajissoivcd <-> A segregated are established at sufficiently high temperature7-25'26 34. 2.2.1 Antimonv Antimony surface segregation vvas studied using AES method on a 2.0% Si steel, alloyed vvith different mass contents of Sb (0.05 and 0.1%). The dependence of surface segregation on grain orientation and on the presence of other solute atoms of S, P, C, Al and Si vvas investigated in situ under UHV conditions by AES in the temperature range from 450 to 900°C. The antimony enrichment at the surface vvas esti-mated by follovving the peak height ratio - PHR of ara-plitudes betvveen the dominant SKMsN^N^s) and Fe(L Mi,3V) Auger transitions at kinetic energies of 454 and 651 eV, respectively. The mole fraction of Sb 0.05% and 0.1% in investigated steels, is clearly in the range of solubility in a-Fe at ali temperatures investigated but belovv the detection limit of AES method. The enrichment of Sb, caused by equilibrium segregation at the surface, can only be measured at or after annealing at elevated temperatures by AES method. AES measurements shovved a different quantity of segregated antimony on different grains (figure 8). Ali samples vvere metalographically polished, the orientation of single grains vvas determined by the etch pitting method. The temperature dependence of antimony surface segregation a) on grain vvith (001) and b) (111) orientation is shovvn on figure 9. The surface of investigated steel alloyed vvith 0.1% Sb vvas clean sputtered vvith Ar+ ions and in situ annealed in the analyzing chamber of the Auger spectrometer. The temperature vvas increased every 20 minutes for 50°C. The antimony segregation rate vvas perceived at temperature T > 650°C and it increased vvith the increasing temperature, vvhile at T > 850°C the antimony segregation rate declined. If the influence of a possible channelling effect is neglected, it is possible to estimate the Sb surface concentration by comparison vvith the results on Sb surface segregation on single crvstal surfaces of Fe - 4% Sb of defined orientation. For the same primary energy of exciting electrons, the saturation PHR vvere measured for single crystal surfaces of (100), (110) and (111) orientation. For the (100) oriented surface, the saturation coverage is half of a monolayer corresponding to LEED c(2x2) overlay pattern. For other surface orientations, no vvell defined ordered structure of surface coverage vvas observed. The PHR vvas of the same order; for (111) oriented grain 0.6, and for (100) oriented grain 0.4. In the investigated steels other solute elements such as C, S and P are present. Tvvo or more elements can simultaneously segregate to the surface. In such cases a competition for the sites available occurs24-32. The relative amount of seg-regating elements on the surface depends on their free energy of segregation and their concentration in the bulk29'32'347"37. Also the kinetics of antimony surface segregation vvas measured (figure 10). There are tvvo possible explanations for this effect, simultaneous antimony and sulphur segregation and competition for sites available on the surface, and/or desorp-tion from the segregated layer. Figure 8: SAM image of the surface of steel vvith 0.05% Sb. A different quantity of segregated antimony vvas measured on grains vvith different orientation in the plane of the sheet Slika 8: SAM posnetek površine jekla legiranega z 0.05%Sb. Površinska segregacija Sb je odvisna od kristalografske orientacije zrn. Slika 9: Temperaturna odvisnost površinske segregacije na jeklu z 0.1 %Sb a) na zrnu (100), b) na zrnu (111) Figure 10: Sb surface segregation on steel with 0.1% Sb on a) (100) and b) (111) oriented grain at 800 and 850°C Slika 10: Površinska segregacija Sb na jeklu z 0.1% Sb a) (100) zrno in b) (111) zrno pri 800 in 850 °C The competitive surface segregation of antimony and QSb _ sulphur is described by the follovving equations25: i_©s_esb - *Sb exP(-A 750°C. 2.2.2 Tin A scanning Auger image - SAM of non-oriented elec-trical steel annealed 10 minutes at 800°C was taken. The orientation of individual grains vvas determined by the etch pit method. Figure 11 shovvs SEM and SAM im-ages of the surface of the investigated steel. A different surface tin segregation rate on different grains vvas measured. Different grain orientation provided different sites for segregated tin atoms. Figure 12 shovvs the temperature dependence of surface segregation of alloying and tramp elements of non-oriented electrical steel alloyed vvith 0.05% Sn on grain orientations (001) and (111) respectively. Electrical steel is a multicomponent system vvith a very complicated temperature dependence behaviour of surface segregation on binary alloys. The relations of the surface segregation enthalpies and volume diffusivitiy are as follovvs: AH"Si < AH"C < AH"P and Dcv » DSiv > Dpv At lovver temperature, about 300°C, C segregated to the surface due to very high diffusion coefficient in com-parison to Si and P, although the bulk concentration vvas very lovv, only 15 ppm. At higher temperature, C atoms vvere displaced by Si atoms and P vvhile S atoms dis-placed silicon at higher temperatures. Their bulk diffusion coefficient is rather lovv, but their segregation en-thalpy is very high, therefore tin started segregating significantly above 600°C. Kinetics study confirmed the orientation dependence of tin surface segregation and of the thickness of the segregated layer. It vvas ascertained17 that on grains vvith (100) and (111) orientation in the sheet plane, the segregation of tin vvas beyond one monolayer, due to the strong decrease of surface energy. On a surface vvith a (111) orientation FeSn intermetallic compound of one unit celi thickness vvas found. Our measurements shovved that tin surface coverage dependence on tin bulk concentration and 0 value approached one for (100) and (111) orientations. 2.3 Grain boundary segregation 2.3.1 Antimonv Grain boundaries of FeSi steel alloyed vvith 0.05 and 0.1% Sb vvere also analyzed by AES after ageing for 200 and 500 hours at 550°C. The fracture facets vvere almost completely transgranular, only on some areas intergranu-lar decohesion vvas noticed. In the investigated alloys there vvas no indication of antimony grain boundary segregation (figure 13). Only a negligible grain boundary segregation of other solute elements such as carbon, silicon and aluminium vvas established. Figure 12: Temperature dependence of surface segregation on steel with 0.1% Sn on a) (100) and b) (111) oriented grains Slika 12: Temperaturna odvisnost površinske segregacije na jeklu z 0.1 %Sn a) (100) in b) (111) orientirana zrna. Figure 13: AES spectra taken on a) transgranular facets and SEM image of fractured sample and b) an intergranular facet of non oriented silicon steel with 0.1% Sb and SEM image of transgranular facet Slika 13: AES spekter posnet na a) transkristalni ploskvi in SEM posnetek prelomljenega vzorca in b) interkristalni prelom silicijevega jekla za neorientirano pločevino z 0.1 %Sb 111111 'I " 11!11'1!" 1 700 900 Kmetic / eV .................I'" S 00 700 900 Kinetic energy / eV b) SAMPLE B K)00'C 24N.A,r . 550*C.500h H,0 - 170 min a/lef (focluff SAMPLE B K)00"C . 24h .Air • 550»C. SOOh . H,0 -15 min olter fracture Figure 14: XPS spectra taken on intergranular facet and SEM image of fractured non oriented silicon steel vvith 0.1% Sn Slika 14: XPS spekter posnet na interkristalni ploskvi in SEM posnetek prelomljenega vzorca silicijevega jekla za neorientirano elektro pločevino Figure 15: Pole figure of (200) grains obtained by X-ray difractometry shows the share of grains with (001)(100) texture in the steel sheet vvith 0.05% Sb Slika 15: Polove figure zrn (200) narejene z rentgensko difraktometrijo prikazujejo delež zrn (001)(100) v teksturi elektro pločevine z 0.05% Sb. Figure 16: Texture fibres in the middle plane a) and b) on the surface of electrical steel vvith 0.05% Sn and vvithout Sn Slika 16: Tekstura vlaken v sredini vzorca a) in b) na površini elektro pločevine z 0.05% Sn in brez Sn. 2.3.2 Tin The equilibrium segregation of tin was attained after annealing the specimen alloyed vvith 0.1% Sn for 200 hours at 550°C, figure 14. Considering that tin is equally distributed on both fractured sides, a coverage of grain boundary surface of 0.05 ML vvas estimated. The scattering of results vvas rather large due to the strong dependence of tin segregation to grain boundary orientation. Steel alloyed vvith 0.05% Sn had much less intergranular facets. The evalu-ated equilibrium segregation vvas smaller than in steel al-loyed vvith 0.1% Sn. Detailed AES analyses of free sur-faces betvveen inclusion (A1N, A1203) and matrix clearly indicated that a considerable tin segregation occurs also at their interfaces. 2.4 Texture determination 2.4.1 Antimonv The results support the hypothesis that the texture formation results from orientation dependent effects of antimony and tin on the surface energy. The texture of sheets from antimony and antimony free steels vvas de-termined by X-ray difractometry. The pole figure ob- tained (figure 15), shovvs that only a small share of grains vvith (001)(100) texture vvas found in the investigated 0.05% Sb steel. 2.4.2 Tin The results support the hypothesis that the texture formation results from orientation dependent effects of tin on surface energy. The texture vvas measured on the surface and in internal plane after the half of the sheet thickness vvas removed. Taking into account that ap-proximately six crystal grains constitute the 0.5 mm thick cross-section steel sheet and the fact that penetra-tion depths of X-rays vvas less than 0.01 mm one might conclude that also some grains whose grovvth vvas not af-fected by the surface tin segregation vvere analysed. Nev-ertheless, there vvere not more than 10% of such grains. The orientation distribution functions (ODF) f (g) vvere calculated from the (200), (110) and (211) pole figures. The textures vvere presented as a, y and r| fibres. Figure 16 shovvs texture fibres in the internal plane (a) and on the surface (b) of electrical steels alloyed vvith and vvithout tin. The volume fraction of grains vvith the (100) planeš measured on the surface and in the middle plane increased by the order of tvvo vvhen compared the (nO> (ml (m} (00i> x 0 •/. Sn . o 0.05 V.Sn a- fibre 0* 30* 60* 90» y-(ibre steel vvithout tin and the steel vvith 0.05% tin. Softer magnetic orientations vvere found on the surface. Steel vvith 0.05% Sn, vvhich had previously been aged 25 hours at 550°C, shovved an inerease of (100) planeš par-allel to the roiling direetion by three times, compared to the steel vvithout tin.36 During annealing antimony and tin segregated at steel surface at temperatures T > 650°C. A strong correlation betvveen the antimony or tin surface segregation and the orientation of the grains at the sheet surface vvas estab-lished. The maximum equilibrium Sb surface segregation of 0.6 monolayer vvas measured after annealing at 750°C on grains vvith the (111) crystallographic orientation in the sheet plane. The maximum equilibrium Sn segregation on the surface vvas reached also at 750°C and ap-proached in the majority of orientations one monolayer. Grain boundary segregation of antimony and other solute elements, sueh as C, S, P, Al and Si vvere negligi-ble in non oriented silicon steel vvith 0.05 and 0.1% Sb. Tin surface segregation vvas much higher than grain boundary segregation. At equilibrium grain boundary segregation only 7 and 3% of tin atoms vvere found on a grain boundary for steel alloyed vvith 0.1 and 0.05% Sn, respectively. Antimony as vvell as tin surface segregation de-creased the surface energy of grains vvith (100) surface orientation in the sheet plane, and these grains grovv on account of grains vvith other surface crystallographic orientations, sueh as (110) and (111). Only a certain level of surface segregation promoted selective grain grovvth. By excessive surface coverage of segregated atoms, the surface energy of ali orientations is not affected selective^ and no preferential grain grovvth is obtained. Textures represented as sections through three-di-mensional orientation distribution space in fixed direc-tions shovved that the volume fraction of magnetically soft grains inereased for three times in tin steel sheets vvhen compared to steel vvithout tin. Better textures vvere obtained near the surface than in the middle plane of 0.5 mm thick steel sheet. The best results vvere obtained for steel alloyed vvith 0.05% Sn. It is concluded that only a certain level of segregation promoted the desired selective grain grovvth. The results of the present investigation support the hypothesis that the texture formation results from orientation dependent effects of antimony and tin on the surface energy. 3 REFERENCES 11, p. Csorba, Image Tubes, Hovvard W. Sams, Indianapolis 1985 M. Jenko, Surface phenomena at Fluxless vacuum soldering Ph.D ^ Thesis, University of Ljubljana, Ljubljana 1988 'M. Jenko, B. Erjavec, B. Praček, Vacuum, 40 (1990) 77 "M. Jenko, S. Jerič, B. Praček, B. Erjavec, Vuoto, Vol. XX. N2 (1990) 350 5D. Brigs. M. P. Seah Eds, PracticalSurface Analysis, Vol. 1 Auger and X-ray Photelectron Spectroscopy 2nd Edition, John Wiley&Sons Chichester 1994 6 R. C. VVeast, M. J. Astle, Eds, CRC Handbook of Chemistry and Phys-ics, 76th Edition, Chemical Rubber, Palm beach 1995/96 7O. Kubaschewski, C. B. Alcock, P. J. Spencer, Materials Thermo-chemistry, 6th Edition, Pergamon, Oxford 1993 8H. J. Grabke, Iron and Steels, /SIJInt., 35 (1995) 2, 95-113 9G. Lyudkovski, P. K. Rastogi, Metali. Trans, /t., 15A (1984) 257 10 H. Shimanaka, T. Irie, K. Matsumura and K. Nakamura, J. Magn. Magn. Mat., 19 (1980) 63 "P. Marko, A. Šolyom, V. Frič, J. Magn. Magn. Mat., 41 (1984) 12 S. Nakashima, K. Takashima, J. Harase and K. Kuroki, J. Japan Inst. 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Viefhaus and M. Rusenberg, Surface Science, 159 (1985) 1-23 24H. Viefhaus, Analytica Chimica Acta, 297 (1994) 43-53 25 H. J. Grabke, Kovine, zlitine, tehnologije, (1993) 1-2, 9 26C. Lea, M. P. Seah, Phil. Mag., 35 (1977) 1, 213 27 E. D. Hondros, M. P. Seah, Metal Trans., 8A (1977) 1363 28 C. L. Briant, M. Ritter, Acta metali, 32 (1984) 2031 29 P Gas, M. Guttman, J. Bernardini, Acta metali. 30 (1982) 1309 30 K. Iwayama, K. Kuroki, Y. Yoshitomi, K. Homma and T. Wada: J. Appl. Phys., 55 (1984) 2134 31 V. Rusenberg, H. Viefhaus, Surf. Sci., 172 (1986) 615 "Beguinot and P. Lesbats, Metalography, 10 (1977) 115-119 33 M. Godec, M. Jenko, F. Vodopivec, M. Ambrožič, D. Mandrino, L. Kosec, M. Lovrečič Saražin, Kovine, zlitine, tehnologije, 28 (1994) 1-2, 105-109 34 W. Jager, H. J. Grabke, R. Moller, 4th International Conference, Portorož, Jugoslavija, 1985 35 H. De. Rugy and H. Viefhaus, Surface Science, 173 (1986) 418-438 36 M. Godec, The influence of the segregated tin on the recrystalization behaviour of non oriented electrical steel sheet, PhD Thesis, Univer-sity of Ljubljana, Ljubljana 1997 37 D. Marton, J. Fine, Optical Socoiety of America, Technical Digest, 3 (1992) 146-148 38 M. H. Mintz, P. Shukeer, J. Fine, Surface Science Letters, 238 (1990) L473-L477 Acknovvledgement The investigation vvas supported by the Ministry of Science and Technology of Slovenia, Contract No J2-7228-96. IMT INŠTITUT ZA KOVINSKE MATERIALE IN TEHNOLOGIJE INSTITUTE OF METALS AND TECHNOLOGY 1001 LJUBLJANA, LEPI POT 11, SLOVENIJA, POB 431 Phone.: +38661/125 11 61, Fax: +38661/213780 VACUUM HEAT TREATMENT LABORATORY Vacuum Brazing Universally accepted as the most versatile method of joining metals. Vacuum Brazing is a precision metal joining technique suitable for many component configurations in a wide range of materials. ADVANTAGES • Flux free process yields clean, high integrity joints • Reproducible quality • Components of dissimilar geometry or material type may be joined • Uniform heating & cooling rates minimise distortion • Fluxless brazing alloys ensure strong defect free joints • Bright surface that dispense with expensive post cleaning operations • Cost effective Over five years of Vacuum Brazing expertise at IMT has created an unrivalled reputation for excellence and quality. Our experience in value engineering will often lead to the use of Vacuum Brazing as a cost effective solution to modern technical problems in joining. INDUSTRIES • Aerospace • Mechanical • Electronics • Hydraulics • Pneumatics • Marine • Nuclear • Automotive QUALITY ASSURANCE Quality is fundamental to the IMT philosophy. The choice of process, ali processing operations and process control are continuously monitored by IMT Quality Control Department. The high level of quality resulting from this tightly organised activity is recognised by government authorities, industry and International companies. THE NEW RESEARCH EQUIPMENT FOR SURFACE CHARACTERIZATION OF MATERIALS AT THE INSTITUTE OF METALS AND TECHNOLOGY, LJUBLJANA NOVA RAZISKOVALNA OPREMA ZA RAZISKAVE POVRŠIN TRDNIH SNOVI NA IMT, LJUBLJANA MONIKA JENKO Institute of Metals and Technology, Lepi pot 11, Ljubljana, Slovenia At the INSTITUTE OF METALS AND TECHNOL-OGY, LJUBLJANA is installed a field emission scanning Auger microprobe MICROLAB 310-F of VG Scientific from UK for research of solid surfaces, grain boundaries and phases, micro analysis of materials as well as research of physical phenomena on the free surfaces of metals and inorganic materials: adsorption, segregation of surface active elements, oxidation, corrosion, characterization of thin films, recrystallization, catalysis etc. The new instruments allows the follovving methods: • Auger Electron Spectroscopy - AES • Scanning Auger Electron Spectroscopy - SAM • Secondary Electron Microscopy - SEM • Reflected Electron Energy Loss Spectroscopy -REELS • X-Ray Photoelectron Spectroscopy - XPS One of the most important features of Microlab 310-F is its high spatial resolution in both SEM and SAM. It has field emission electron source with very high bright-ness, high performance electron column, very low drift stage simultaneous peak and background acquisition when mapping and image registration softvvare. Microlab 310-F has a spherical sector analyser which can be operated vvith high energy resolution. Adding a dual anode X-ray source therefore allovvs the instrument to perform high quality XPS analysis. The instrument is fitted vvith high quality ion gun, vvhich allovvs the ability to perform high quality, rapid depth profiles. The instrument is additionally equipped vvith fracture stage. This device allovvs the fracturing of specially Figure 2: A view through the monitoring window into the UHV analysis chamber on the sample, electron gun, ion gun and X-Ray source (see cover) shaped brittle samples in UHV; the stage allows that both halves of the fractured samples can be collected for analysis. The purchase of instrument was financially supported by industrial partners, research institutes and university: • Institute of Metals and Technology; Ljubljana • Institute Jožef Štefan, Ljubljana • National Institute of Chemistry, Ljubljana • Concern Slovenian Steelworks, Ljubljana • Nuclear Power Plant Krško • Kolektor, Idrija • Talum Kidričevo, • Impol, Slovenska Bistrica • Department for Materials and Metallurgy, University of Ljubljana • Centre for TriboIogy and Technical Diagnostic, Fac-ulty of Mechanical Engineering, University of Ljubljana The purchase was subsidized by Ministry of Science and Technology of Republic Slovenia. INFLUENCE OF HEAT TRANSFER DYNAMICS ON HARDNESS DISTRIBUTION AFTER QUENCHING VPLIV DINAMIKE PRENOSA TOPLOTE NA PORAZDELITEV TRDOTE PO KALJENJU BOŽIDAR LIŠČIC Faculty of Mechanical Engineering and Naval Architecture, Ivana Lučiča 5, Zagreb, Croatia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 The pattern of hardness distribution on round bars1 cross-section after quenching was studied in relation to the change of heat transfer on the workpiece surface. It was found that a 'delayed quenching', producing a discontinuous change of cooling rate, may result in higher hardness in the core, than at the surface. This phenomenon called 'inverse hardening' has been theoretically explained by Shimizu and Tamura. It depends on: hardenability of the steel, cross-section size of the workpiece and on quenching condition, and is related to the incubation period consumed before the cooling rate was changed. Own experiments using cylindrical specimens of 50 mm Dia, made of AISI-4140 steel, have shown that Controllable Delayed Quenching (CDQ) technology has a great potential to increase the depth of hardening, compared to conventional quenching practice. Bending fatigue tests vvith inverse hardened and tempered specimens have shown a significant increase of the fatigue life compared to specimens having normal hardness distribution after quenching. CDQ-technology and 'inverse hardening' can reproducibly be realized using adequate steel hardenability and cross-section size of the workpiece, by quenching in PAG polymer-solution of high concentration. or in high pressure-circulated gases. Key words: quenching, heat transfer Raziskane so bile značilnosti porazdelitve trdote na preseku kaljene okrogle palice v odvisnosti od spremembe prenosa toplote na površini palice. Kaljenje z zadržanjem, ki povzroča diskontinuirno spremembo hitrosti ohlajanja, lahko ustvari večjo trdoto v jedru kot na površini. Ta pojav imenovan "inverzna utrditev" sta teoretično razložila Shimizu in Tamura. Odvisen je od kaljivosti jekla, preseka kaljenca in od pogojev kaljenja ter je povezan z inkubacijsko dobo, ki je bila porabljena pred spremembo hitrosti ohlajanja. Naši poiskusi na valjastih vzorcih (J) 50 mm iz jekla AISI-4140 so pokazali, da ima "kontrolirano kaljenje z zadržanjem" velik potencial za povečanje globine kaljenja v primerjavi s klasičnim kaljenjem. Upogibni utrujenostni preizkusi na inverzno kaljenih in popuščenih vzorcih so pokazali pomembno povečanje življenjske dobe v primerjavi z vzorci z normalno porazdelitvijo trdote po kaljenju. CDQ - tehnologija in "kaljenje z zadržanjem" sta lahko reproduktibilna, če ima jeklo primemo kaljivost in je presek kaljenca ustrezen s kaljenjem v polimerni PAG raztopini velike koncentracije ali v visokotlačni krožeči atmosferi. Ključne besede: kaljenje, prenos toplote 1 INTRODUCTION The practice of quenching ferrous metals has a very long history, but development of quenching technology vvas first of ali concentrated on choosing the proper quenchant and quenching parameters, i.e. its temperature and possibly the agitation rate. Once this vvas fixed for a specific čase, the heat transfer from the vvorkpiece surface vvas governed solely by the selected quenchant and quenching parameters. Generally the idea prevailed that, for achieving a better through-hardening, a more severe quenching intensity should be applied right at the begin-ning of quenching. If vvorkpieces having bigger cross-section have to be hardened through, the heat extraction from the core is the main problem. Ali efforts vvere concentrated on shortening the quenching time i.e. cooling the core of the vvorkpiece, if possible, belovv Ms temperature before (according to the hardenability of the steel used) the transformation to ferrite and pearlite begins. As a result of applying a severe quenchant, high temperature gradients developed causing high thermal stresses and distortion. Using this approach tvvo factors on vvhich the through hardening depends, have not been taken into consideration: a) The cooling rate in every specific point of the cross-section from the austenitizing temperature to the transformation temperature (Ai) is not critical for the microstructure and hardness after quenching. Instead the cooling rate belovv Ai to the Ms point is critical, and different points of the cross-section pass through this temperature range (Ai to Ms) at different times. b) When severe quenching intensity is applied right from the beginning of the quenching process, the surface temperature of the vvorkpiece is rapidly decreased to lovv values vvhile the core stili retains high temperature. So, vvhen heat has to be extracted from the core, the temperature difference betvveen surface temperature of the vvorkpiece (T5) and the quenchant temperature (T0) is lovv and according to the Newton's lavv q = a (Ts-T0), the heat extracted is also lovv. This situation can only be im-proved if the heat transfer (characterized by the heat transfer coefficient a (W/m2K)) vvould be increased later during quenching, but this is not the čase in normal quenching practice. In 1977 the investigation published in USA by Loria1 has shovvn that 'delayed quenching' can in some in-stances increase the depth of hardening, compared to conventional quenching practice. 'Delayed quenching' means a relatively slow heat transfer from the vvorkpiece surface at the beginning of quenching, followed by a fast cooling with high quenching intensity. In the same tirne in Japan, Shimizu and Tamura2'3 have given theoretical explanation of this phenomenon stating that it is caused by discontinuous change in cooling rate and the incubation period (at relevant temperature) consumed, before the cooling rate vvas abruptly changed. Latter, experimental investigation by Liščič and Totten4 on one side, and numerical calculation by Chen and Zhou5 on the other side, have shown that at 'delayed quenching' the average cooling rate may be higher below the surface of the vvorkpiece, than at the surface itself. While in čase of normal quenching (vvithout discontinuous change of cooling rate) the cooling rates constantly decrease from the surface tovvards the core, in čase of 'delayed quenching' the cooling rate is lower at the surface (because of mild cooling at the beginning of the quenching process), becoming greater belovv the surface tovvards the core because of the latter abrupt change of heat transfer at the vvorkpiece surface. Through these vvorks it became evident that the heat extraction dynamics during quenching, and not the quenching time itself is responsible for the hardness distribution on the worpiece's cross-section after quenching. Studying the pattern of hardness distribution on round bars' cross-section after quenching Shimizu and Tamura3 have introduced the expression of 'inverse' hardening. Opposite to normal hardness distribution it shovvs lovver hardness at the surface and higher hardness in the core. The experiments have shovvn that the 'inverse' hardness distribution caused by the phenomenon of 'delayed quenching', depends on steel hardenability and on cross-section size of the vvorkpiece. They have also shovvn that (in čase of adequate hardenability and corresponding cross-section size) the 'delayed quenching' has a great potential to increase the depth of hardening, compared to conventional quenching practice. Chen and Zhou5 state also that 'delayed quenching' can reduce residual stresses and distortion. This state of the art gives, in some instances, the possibility to achieve the biggest possible depth of hardening, simultaneously vvith minimum residual stress and distortion, by a Con-trollable Delayed Quenching. When quenching in evaporable liquid quenchants, hovvever, the possibility to control a preprogrammed cooling cycle and cause intentionally a 'delayed quench-ing' is very limited, because the only parameter that can be changed during the quenching process is the agitation rate. Among ali liquid quenchants only the PAG polymer-solutions possess a mechanism that enables them to real-ize a preprogrammed Controllable Delayed Quenching by changing the polymer concentration. The advantage of PAG solution quenchants seams to be that it is possible to achieve the proper balance of the film thickness and film strength, depending of course on tvvo other parameters, namely the bath temperature and the agitation rate. As it is vvell known higher polymer concentration gives thicker film on the vvorkpiece surface, prolonging the vapor blanket stage i.e. causing a 'delayed quench-ing'. Recently, Liščič, Grubišič and Totten6 have shovvn that bending fatigue as vvell as impact strength of mechanical components can be increased by 'delayed quenching'. 2 HEAT EXTRACTION DYNAMICS It is interesting to analyse why 20 years have passed since the phenomenon of 'delayed quenching' vvas first published by Loria and by Shimizu and Tamura until a Controllable Delayed Quenching of real components has been investigated more in details. The ansvver may be found in tvvo follovving reasons: a) There vvas no an adequate method to test and re-cord the quenching intensity during quenching in real practice, that could describe the heat extraction dynam-ics. Neither the magnetic quenchometer method, nor the cooling curve analysis of small diameter (12.5 mm Dia x 60 mm length) inconel or silver specimens can describe the heat extraction dynamics vvhen quenching real components. b) Only just recent investigations7 have revealed that polymer solutions (PAG) of higher concentration can be used as a quenchant for preprogrammed Controllable Delayed Quenching. The newly developed Temperature Gradient Quench-ing Analysis System (TGQAS) using the LISCIC/NAN-MAC probe8 of 50 mm Dia x 200 mm length, made of AISI-304 steel, representing a real vvorkpiece, is capable of measuring, recording and evaluation of every quench-ing process in vvorkshop practice, describing the heat ex-traction dynamics by corresponding thermodynamic functions. The probe itself is instrumented vvith three thermocouples at the mid-length cross-section, measuring the temperature at the very surface, 1.5 mm belovv surface and in the center. Figure 1 shovvs cooling curves recorded in tvvo quenching tests: TEST-1 mineral oil of 20°C vvithout agitation and TEST-26 PAG polymer-solution (UCON-E) of 25% concentration, 40°C bath temperature and 0.8 m/s agitation rate. Figure 2 shovvs calculated heat flux density vs. time betvveen different thermocouple posi-tions. The characteristic feature in each of quenching tests vvith regard to heat extraction dynamics is the time period from the immersion up to the moment the maximum heat flux density occurs (tqmax). While for particular oil quenching (TEST-1) tqmax is 14 seconds it is for the described polymer-solution quenching (TEST-26) 72 seconds. The latter one is obvi-ously a 'delayed quenching'. TESTI.REC TEST2«.REC Figure 1: Two quenehing tests recorded by the LISCIC/NANMAC probe (50 mm Dia x 200 mm): TEST-1 - mineral oil, 20°C, without agitation; TEST-26 - PAG po!ymer-soIution (UCON-E), 25%, 40°C, 0.8 m/s agitation rate. Cooling curves for: surface (O), 1.5 mm below surface (□) and center (A) Slika 1: Dva preizkusa kaljenja registrirana z LISCIC/NANMAC preizkušancem (<|> 50 x 200 mm). Pr. 1 - mineralno olje, 20°C, brez mešanja: Pr. 26 - PAG raztopina (UCON-E), 25%, 40°C, hitrost mešanja 0.8 m/s. Ohlajevalne krivulje za površino (O), 1.5 mm pod površino (□) in sredino (A) quenching (TEST-26) 72 seconds. The latter one is obvi-ously a 'delayed quenching'. Because the heat flux density (W/m2) is the real physical measure of the heat extraction, it is interesting to analyse and compare the heat flux density (between 1.5 mm below surface and the surface itself) v.s. time curves for both mentioned tests, shown in Figure 2. For particular oil quenching (TEST-1) only 12.5 seconds, right in the beginning of the quenching process, vvere necessary for increasing the heat flux density from a lovv value of 200 kW/m2 to its maximum of 2600 kW/m2, and 35 seconds vvere necessary for the heat flux density to fall back to 200 kW/m2. For particular polymer-solution quenching (TEST-26), 67 seconds or 5.4 times more vvere necessary for increasing the heat flux density from 200 kW/m2 to its maximum of 2250 kW/m2, but only 23 seconds or 1.5 times less vvere necessary for the heat flux density to fall back to 200 kW/m2. This analysis clearly shovvs a distinct difference in heat extraction dynamics betvveen the described oil quenching characterized by a fast cooling from the beginning, and the described polymer-solution quenching characterized by a long period of relatively slovv cooling follovved by a sudden change in heat extraction, after burst of the polymer film, vvhich has caused a pro-nounced discontinuous change in the cooling rate, hav-'ng a speciftc influence on transformation behavior of the steel concerned. The discontinuous change in cooling rate, vvhen quenching in the used polymer solution (TEST-26) can he seen in Figure 1 as a distinct change in the slope of TESTI-REC TESTS* .REC Figure 2: Heat flux densities vs. time for TEST-1 and TEST-26 calculated from recorded cooling curves. Heat flux density betvveen 1.5 mm belovv surface and the surface itself (□); betvveen center and surface (O); betvveen center and 1.5 mm belovv surface (A) Slika 2: Gostota toplotnega toka v odvisnosti od časa za pr. 1 in 26 izračunana iz ohlajevalnih krivulj. Gostota toplotnega toka med globino 1.5 mm in površino (□), med sredino in površino (O) ter med sredino in globino 1.5 mm (A) the cooling curve for the thermocouple at 1.5 mm belovv surface, at 570°C. The best way to compare the heat transfer dynamics betvveen both described tests is to compare the amount of heat extracted at different time intervals after immersion of the probe. The curves marked vvith □ in Figure 3 rep-resent the values of the integral (/qdt) belovv the heat TESTI.REC TESTS«.REC Figure 3: Integral (Jqdt) belovv heat flux density curves vs. time for TEST-1, and TEST-26, representing the amount of heat extracted. Heat extracted betvveen 1.5 mm belovv surface and the surface itself (□); betvveen center and surface (O); betvveen center and 1.5 mm belovv surface (A) Slika 3: Integral (Jqdt) toplotnega toka v odvisnosti od časa za pr. 1 in 26, ki predstavlja ekstrahirano toploto. Toplota ekstrahirana med globino 1.5 mm in površino (□), med sredino in površino (O) ter med sredino in globino 1.5 mm (A) HEAT EXTRACTION DVNAMICS AT OUENCHING The Stainiess-steel Specimen of 50 mm Dia x 200 mm quenched tri: Mineral Oil of 20*C - vvithout agitation Cwetting kinetics not included) 88 s 120 s Color scale s ni inoanacjasm«« «S50 600 ?5P 7!» 650 «» 850 SOD 450 400 350 3K» 250 200 S5C >C Time after Temperature ffefds calculated by a 2-D heat transfer program based on heat transfer coeffiaents obtamed from the USCIC/NANMAC CafcuSatkm program by. B.Smoijan Graphtcat iftferpretatton program by: J.Galinec immersion: s Figure 4: 2-D simulation of temperature fields when quenching the stainless steel specimen of 50 mm Dia x 200 mm in standard mineral oil of 20°C, without agitation. The calculation is based on heat transfer coefficients obtained from the LISCIC/NANMAC probe Slika 4: 2-D simulacija temperaturnega polja med kaljenjem preizkušanca $ 50 \ 200 mm iz nerjavnega jekla v standardnem mineralnem olju in brez mešanja. Izračunano na osnovi koeficientov prenosa toplote pridobljenih z LISCIC/NANMAC sondo extracted (MJ/m2), vs. time. In oil quenching (TEST-1), the amount of heat extracted starts to rise immediately in third second after immersion, reaching already after 20 seconds a value of 35 MJ/m2. Durtng next 80 seconds it amounted to 55 MJ/m2. In the used polymer-solution quenching (TEST-26) only 5 MJ/m2 vvas extracted until 20 seconds, but in next 80 seconds it reached 87 MJ/m2. Using the heat transfer coefficient vs. time values calculated from the measured temperatures at the mid-length cross-section of the LISCIC/NANMAC probe, a 2-D heat transfer programme vvas developed for calculat-ing temperature fields during quenching. Figure 4 shovvs a graphical presentation of the cooling a stainless steel specimen of 50 mm Dia x 200 mm length at: 16, 42, 88 and 120 seconds by quenching it in mineral oil of 20°C vvithout agitation (TEST-1). Figure 5 shovvs the same vvhen quenching the specimen in PAG polymer-solution (UCON-E) of 25% concentration, 40°C bath temperature and 0.8 m/s agitation rate (TEST-26). Comparison of Figure 4 and Figure 5 clearly reveals the difference in heat extraction dynamics betvveen those tvvo tests. It should be emphasized that for transformation kinetics not the cooling rates from austenitizing temperature to Ai, but the cooling rates below Ai, are critical. For the steel grade AISI-4140 e.g. the Ai temperature is 730°C. Analysing the average radial temperature gradi-ents betvveen core and surface in half length cross-section from Figure 4 and Figure 5 respectively, one gets the values given in Table I. Table I Austenitizing temperature: 850°C; Radius of specimens: 25 mm Time after immersion (seconds) 16 42 88 120 Average temperature gradient betvveen core and TEST-1 10 12 6 4 surface in half length cross-section °C/mm TEST-26 2 4 10 6 From the calculated temperature fields in Figure 4 and Figure 5 respectively, and the values given in Table I we can derive the follovving: In TEST-1 (normal čase of quenching vvith continuous cooling rates), a cooling vvithin the critical tempera- HEAT EXTRACTION DYNAMICS AT QUENCHING The Stainless-steel Specimen of 50 mm Dia x 200 mm quenched in: PAG Polymer-solution of 25% concentration; 40°C temp.; 0.8 m/s agitation rate (vvetting kinetics not included) Figure 5: 2-D simulation of temperature fields by quenehing the stainless steel specimen of 50 mm Dia x 200 mm in PAG polymer-soIution (UCON-E) of 25% concentration; 40°C; 0.8 m/s agitation rate. The calculation is based on heat transfer coefficients obtained from the LISCIC/NANMAC probe Slika 5: 2-D simulacija temperaturnega polja pri kaljenju preizkušanca 50 x 200 mm iz nerjavnega jekla v PAG polimerni raztopini (UCON-E) s koncentracijo 25%. 40°C in hitrostjo mešanja 0.8 m/s. Izračunano z uporabo koeficientov prenosa toplote pridobljenih z LISCIC/NANMAC sondo 88 s 120 s Color scaie probe ■■^□□□□[□□□IM«™ 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150°C Time after immersion: 16s 42 s Temperature fields calculated by a 2-D heat transfer program based on heat transfer coefficients obtained from the LISCIC/NANMAC Calculation program by: B.Smoljan Graphical interpretation program by: J.Galinec ture range (700°C to 400°C) for the core, between 42 and 88 seconds is obtained with a decreasing temperature gradient, i.e. decreasing heat extraction flux from the core to the surface. Once the surface temperature has fallen to lovv values (about 200°C after 88 sec.), the heat transfer has decreased very much, because of the small temperature difference betvveen the vvorkpiece surface and the surrounding fluid. This heat extraction dynamics results in the normal hardness distribution i.e. substan-tially lovver core than surface hardness. In TEST-26 (a delayed quenching vvith discontinuous change of cooling rates), cooling of the core from 42 to 88 sec. (i.e. betvveen 750°C and 600°C) is obtained vvith increasing temperature gradient, i.e. tncreasing the heat extraction flux from the core to the surface, resulting in inereased core hardness. 3 TRANSFORMATION KINETICS WHEN DISCONTINUOUS CHANGE OF COOLING RATE OCCURS From the moment the austenitized vvorkpiece is im-mersed in the quenching fluid, two different processes start: the thermodynamic process of heat extraction and the metallurgical process of structure transformation. The latter one starts actually in different times for different points of the eross-seetion, vvhen the temperature in each point falls to A|. These times depend on the cross-seetion size and the cooling intensity of the quenching fluid. The resulting hardness in a particular point de-pends on constituents of the structure transformed, vvhich depend heavily on the hardenability of the steel concerned i.e. on ineubation times at every isotherm. Because ineubation times are counted only at temperatures belovv Ai, for each particular point of the eross-seetion the cooling rate in the critical temperature range A/ to Ms, is of paramount importance. Shimizu and Tamura2 have found that the pearlitic transformation behavior vvith cooling rates diseontinu- ously changed during cooling was different from that given by an usual CCT diagram, and that this transfor-mation is related to the incubation period consumed be-fore changing the cooling rate. In čase of delayed quenching some of the incubation period is consumed at the surface of the vvorkpiece, while it is not at the center. The incubation period at any given isotherm is the time until the transformation starts (Z), while (X) is the incubation period consumed before the discontinuous change of the cooling rate has taken plače. Figure 6 which is a schematic illustration of delayed quenching, shows that at time tj and temperature Ti (point P) a discontinuous change of cooling rate occurred. Up to this moment the surface of the vvorkpiece has consumed a share (X) of the total incubation time (Z), but the center has not, be-cause at the moment ti the center had a temperature above Ai. Further cooling belovv the point P has pro-ceeded vvith substantially increased cooling rate, changing the transformation start curve as shovvn in Figure 6. Because for the center no incubation time has been consumed, the cooling curve for center starts from temperature Ai at zero time! In this way the cooling curve for center, vvhich doesn't intersect any pearlitic region, results in higher hardness than the cooling curve for the surface vvhich has started from the point P and inter-sected a portion of pearlitic region. This is the theoretical explanation of 'inverse' hardness distribution. b) A,*—- \ /^Pearlitic transformation starts £ ft Yj (originated at Ai) ~ Yv V7— Pearlitic transformation starts 2 \\ N (originated at P) E X\l /V"Surface " f \rrA Center Time Figure 6: Schematic illustration how delayed quenching causes inverse hardening, according to2 Slika 6: Shematična predstavitev kako kaljenje z zadržanjem ustvari inverzno utrditev. Po viru 2 4 HARDNESS DISTRIBUTION AFTER QUENCHING AND AFTER TEMPERING Figure 7 shovvs the normal hardness distribution measured across the section of a 50 mm dia bar of AISI-4140 after quenching in ordinary mineral oil of 20°C bath temperature vvithout agitation (curve No 1), and the inverse hardness distribution measured after quenching the same bar in the PAG polymer solution (UCON-E) of 25% concentration, 40°C bath temperature, and 0.8 m/s agitation rate (curve No 2). This shovvs the high capacity of delayed quenching technique to influence the depth of hardening. Because low-alloyed structural steels (like the AISI-4140) are used in hardened and tempered condition, it is of interest to see hovv a normal and an inverse hardness distribution curve, respectively, look like after temper-ing. Figure 8 shovvs this for specimens used to plot the hardness distribution curves in Figure 7, after tempering at 480°C for 2 hours. Normal hardness distribution (curve No 1) has retained the same shape as after quenching, vvhile the inverse hardness distribution (curve No 2) gave a uniformly distributed hardness over the cross section. This is result of the knovvn fact that at tempering the higher hardness values decrease more than the lower hardness values. The hardness difference at the center of about 6 HRC indicates that inverse hardness distribution guaranties after tempering a structure of tempered martensite in the core, vvhile in čase of normal hardness distribution, besides tempered martensite other (softer) structure constituents are present in the core. With regard to mechanical properties, as it is vvell knovvn (especially for high strength levels), that tempered fine-grained martensite yields the highest toughness of ali mi-crostructures. 5 INFLUENCE OF HARDNESS DISTRIBUTION ON FATIGUE PROPERTIES For bending fatigue tests9 especially designed specimens of 300 mm length vvith the critical diameter of 50 mm vvere machined of the same heat of the American made steel AISI-4140. Ali specimens vvere austenitized in a protective atmosphere to 860°C for 80 minutes. The specimens having normal hardness distribution vvere quenched one by one, vertically, in used mineral oil of 20°C vvithout agitation. The specimens having inverse hardness distribution vvere quenched in PAG polymer-so-lution (UCON-E) of 25% concentration, 40°C bath temperature and 0.8 m/s agitation rate. After quenching ali specimens have been tempered in a vacuum furnace at 500°C for 2 hours. Figure 9 shovvs the used test rig for bending fatigue tests. Ali tests vvere performed in normal environmental conditions under a specific load programme. One round of the used load programme consisted of 7,000 cycles vvhich vvere subdivided into tvvo parts: - 5,000 load cycles vvith the regular load amplitude AISI-4140 Batch No 7345$ 3/4/? 1/2 R 1/4/? 0 1 UR MIR 3/4/? _ _50 mm Dia. Figure 9: Test rig for bending fatigue tests Slika 9: Priprava za preizkus upogibne utrujenosti Figure 7: Hardness distribution curves measured on the cross-section of a 50 mm Dia x 200 mm cylinder inade of AISI-4140, after quenching under the following conditions: 1) Mineral oil of 20°C, without agitation 2) PAG polymer-solution (UCON-E) of 25% concentration; 40°C bath temperature and 0.8 m/s agitation rate Slika 7: Porazdelitev trdote po preseku preizkušanca (J) 50 x 200 mm iz jekla AISI-4140 po kaljenju v naslednjih pogojih: 1) mineralno olje, 20°C, brez mešanja 2) PAG polimerna raztopina (UCON-E), 25%, 40°C in hitrost mešanja 0.8 m/s - 2,000 load marker cycles vvith 25% higher than the regular load amplitude. The 2,000 load marker cycles vvere used to obtain in-formation about the crack grovvth rate and a possible influence of the hardness distribution on it. The informa-tion about the crack grovvth rate is expressed in form of share of the crack grovvth phase in the total test Iife: o a: x vi rt 41 C T) i— O r Figure 8: Hardness distribution after tempering at 480°C for 2 hours: 1) Specimen of 50 mm Dia x 200 mm, quenched in mineral oil of 20°C, vvithout agitation 2) Specimen of 50 mm Dia x 200 mm, quenched in UCON-E: 25%; 40°C; 0.8 m/s Slika 8: Porazdelitev trdote po popuščanju 2 uri pri 480°C: 1) Preizkušanec 50 x 200 mm kaljen v mineralnem olju pri 20°C brez mešanja 2) Preizkušanec <|> 50 x 200 mm kaljen v UCON-E 25%, 40°C, 0.8 m/s NrNc Nf in %, vvhere Nf is the number of cycles of the total test life and Nc is the number of cycles to the initial crack. During the tests the cylinder displacement and the load amplitude vvere recorded to determine Nc and Nf values. The Nc value refers to the beginning of the stiffness loss of the specimen due to initiated crack. The fatigue tests vvere performed on different loading levels under pulsating sinusoidal Ioads vvith the fre-quency of f = 16 Hz and a stress ratio R = Fmin/Fmax = 0 vvhich led to the nominal stress amplitudes in the critical area of the specimens. The test results represented by fatigue life to the initial crack versus the nominal stress amplitude (S - N curves) are shovvn in Figure 10. Summarising these results it can be concluded, (al-though the number of tested specimens vvas lovv for a statistically confirmed data), that an increased fatigue life vvas achieved vvith specimens having inverse hardness distribution compared to specimens having normal Moltria! IZCrMflt (AISI-lllO) K, • t, 85 Stltlf - Rnlia R.^^.O 100-1-1--1 I I I I I- ---1111 ' ---- 1 1 1 ' ' Iti t«S Number §1 crclM |N) Figure 10: Bending fatigue test results of specimens vvith normal and vvith 'inverse' hardness distribution after quenching (both tempered to 500°C for 2 hours) Slika 10: Rezultati preizkusov upogibne utrujenosti preizkušancev z normalno in z inverzno porazdelitvijo trdote po kaljenju (oba sta bila popuščena 2 uri pri 500°C) 35-1_i_l_i_l i_i_i_i_i_i_i 0 2 4 6 8 10 12 14 16 18 20 22 24 26 Distance (rom the surface (50 mm Dia) /mm AISI-4140 Batch No 73456 hardness distribution. At the stress level of 270 MPa, at which most tests have been performed, this increase is expressed by a factor of about 7. The crack propagation phase, compared to the total fatigue life vvas more uniform for specimens vvith inverse hardness distribution and amounted to 13 to 20%, depending on the stress level. Additional fatigue tests are planned to increase the statistical validity of the achieved results. 6 CONCLUSION The above described investigation shovvs that the hardness distribution on the cross-section of the vvorkpiece after quenching can be influenced and greater depth of hardening and better mechanical properties can be achieved by a predetermined and controllable heat transfer dynamics. In future, therefore, the quenching technology vvill most probably adopt the control of heat transfer from the surface of the vvorkpiece instead of let-ting it occur by itself (depending only on the quenchant and quenching parameters selected), as in today's practice. If so, the question vvill arise: By vvhich means a controlled heat transfer at quenching is possible? For liquid, evaporable quenchants (as the hitherto in-vestigations shovv), this is possible by using polyal-kylene-glicol (PAG) polymer-solutions of sufficiently high concentration of adequate temperature and agitation rate. In gas quenching applications (especially in vacuum furnaces vvith pressurized high velocity gases), more time is available during quenching than in čase of liquid quenchants, to change the main cooling parameters i.e. the gas pressure and gas velocity. In order to find out vvhether in a particular čase the workpiece's cross-section size and hardenability of the steel grade in question are suitable for quenching with controlled heat extraction dynamics and to optimize the relevant quenching parameters the computer simulation vvill be necessary. The base for such a simulation are the tvvo follovving requirements: - The CCT-diagram of the steel-grade in question, vvhich characterizes its hardenability and allovvs to overiay the calculated cooling curves for different points on the cross-section, to evaluate the transformation kinetics. - Heat transfer coefficient values a = f(t) (W/m"K) betvveen the vvorkpiece surface and the quenching medium for the vvhole quenching process, character-izing the changes in quenching intensity, vvhich allovvs to calculate the relevant cooling curves in every cross-section point of different bar diameters. To get relevant heat transfer data, a vvorkshop de-signed method to measure and record the quenching in-tensity of different quenchants, as described in8, is re-quired. 7 REFERENCES 1 E. A. Loria: Transformation Behavior on Air Cooling Steel in A3-A1 Temperature Range, Metals Technology, (1977) october, 490-492 2 N. Shimizu and I. Tamura: Effect of Discontinuous Change in Cooling Rate During Continuous Cooling on Pearlite Transformation Behavior of Steel, Transactions /SIJ, 17 (1977) 469-476 3 N. Shimizu and I. Tamura: An Examination of the Relation Between Quench-hardening Behavior of Steel and Cooling Curve in Oil, Transactions ISIJ, 18 (1978) 445-450 "B. Liščic, G. E. Totten: Controllable Delayed Quenching, Proceedings of the International Heat Treating Conference Equipment and Processes, April 1994, Schaumburg, Illinois, USA, 253-262 5 M. Chen and H. Zhou: Numerical Heat Transfer Analysis on the Effect of Enhancing the Thickness of the Hardened Layer by Delayed Quenching, Jinshu Rechuli Xuebao (Transactions of Metal Heat Treatment), 14 (1993) 4, 1-6 (in Chinese) 6B. Liščic, V. Grubišic' and G. E. Totten: Inverse Hardness Distribution and its Influence on Mechanical Properties, Proceedings of the 2nd International Conference on Quenching and the Control of Distortion, 4-7 November 1996. Cleveland, Ohio, 47-54 1 B. Liščic: Investigation of the Correlation Betvveen Polymer-Solution (PAG) Concentration and Inverse Hardening Distribution Curves, Internat Report No 11/92 of Laboratory for Heat Treatment, Faculty of Mech. Engineering and Naval Architecture, Zagreb, March 1992 8B. Liščic, S. Švaič and T. Filetin: VVorkshop Designed System for Quenching Intensity Evaluation and Calculation of Heat Transfer Data, Proceedings of the Ist International Conference on Quenching and Control of Distortion, 22-25 Sept. 1992, Lincolnshire, Illinois, 17-26 9 Test Report Nr 7710, 24 Nov 1994 from the Fraunhofer Institut fur Betriebsfestigkeit, Darmstadt, Germany METHODS FOR THE VALIDATION OF ADVANCED THIN HARD PROTECTIVE COATINGS - AN EUROPEAN PROGRAM METODA ZA VALIDACIJO NAPREDNIH TANKIH ZAŠČITNIH PLASTI - EVROPSKI PROGRAM PETER MAYR, H. VETTERS, A. SCHULZ Stiftung Institut fur VVerkstofftechnik, Bremen, Badgasteinerstr. 3 D, 28359 Bremen Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Specific surface engineering technologies are widely used to improve decisively product characteristics vvhereas thin hard coatings are increasingly adopted in a broad range of industries. The quality assurance infrastructure for coated products is essential to determine their functional properties. For the reliable assessment of the intrinsic properties (coating thickness, hardness, chemical compositon, adhesion) as well as the tribological performance standardised test methods are required! International groups from research institutes and industries are working on this actual topic to develop comprehensive test methodologies including instrument calibration and reference samples. These will then be proposed to committees for standardisation for adoption as European standards. Key words: thin hard coatings, characterisation methods, properties, standards Specifične površinske inženirske tehnologije se široko uporabljajo za povečanje karakterističnih proizvodov in tanke trde prevleke se uporabljajo v širokem spektru te industrije v naraščajočem obsegu. Zagotovitev kakovsti infrastrukture za prekrite proizvode je bistvena za določitev njihovih funkcionalnih lastnosti. Za zanesljivo opredelitev specifičnih lastnosti (debelina, trdota, kemijska sestava in adhezija prekritja) in triboloških lastnosti so zahtevane standardne testne metode. Mednarodne skupine iz raziskovalnih institutov in iz industrije delajo na tej aktualni temi s ciljem, da razvijejo razumljive metodologije za testiranje vključno s kalibracijo instrumentov in referenčnimi etaloni. Te bodo kasneje predložene komitetom za sprejem kot evropski standardi. Ključne besede: tanke trde prevleke, metoda karakterizacije, lastnosti, standardi 1 SURFACE ENGINEERING GAINING ADVANCED THIN HARD PROTECTIVE COATINGS Specific surface engineering technologies are widely used to improve decisively product characteristics. Thin hard coatings are increasingly adopted in a broad range of industrial sectors as a means of achieving advanced products. The mechanical properties of these advanced coatings will determine the service life because elastic and plastic behaviour control fracture and adhesion of the coating. The use of wear resistant coatings can lead the retention of better tolerances through the lifetime of tools or machine parts. In ali these cases mechanical re-liability requires optimum matching of the different com-ponents to be "assembled", that can only be obtained by model calculations requiring precise knovvledge of the characteristics and functional properties1. It is estab-lished that surface coatings and treatments can lead to considerable improvements in the performance of a vvide range of components. Modern PVD and CVD hard coating techniques often allow for alternative, environmen-tally friendly solution to wear protection2 4. 2 QUALITY ASSURANCE - A KEY OBJECTIVE As reported5-6, a broad selection of materials is being offered for ceramic coatings. When selecting a coating for certain application, the substrate, the interface and possible interlayer and the environment influence strongly the on service condition of the coated part. A wide variety of coating procedures leads to a vvide range in functional properties, vvhich can be classified by methods of test7. In order to allovv industry to take fuli advantage of this rapidly developing area it is essential to establish a quality assurance infrastructure for coated products by standardised test methods. In vievv of foster-ing international collaboration betvveen research organi-sations, standard bodies and industry on pre-standar-disation research in advanced materials the "Versailles Project on Advanced Materials and Standards" (VAMAS) is fulfilling a unique role. Within several tech-nical vvorking areas (TWA) formal links vvith international standards organisations and increasing industrial involvement have been formed. In fact one activity on developing methods of test of thin hard coatings is novv established9. The European Committee for Standardisation (CEN) has also established a technical committee on ceramic materials vvith a vvorking group "Methods of test of ceramic coatings" (CEN TC 184AVG 5). 3 CHARACTERISATION OF PROPERTIES Many methods exist for the measurement of properties of coatings (table 1), but for thin hard coatings is a great paucity of standards. Improved test methods, there- fore need to be developed or the existing procedure should be formalised and draft standards prepared. The test routine should lead to a subsequent process control during the production routine which includes prelimi-nary quality control as well as quality control after the coating procedure. Their properties are defined as: hardness residual strain, composition, morphology, microstructure, thickness of coating, elasticity, electrical con-ductivity, magnetic susceptibility, thermal conductivity, etc and on service conditions are indicated by wear and corrosion resistance, fatigue and life time oriented behaviour, thermoshock stability, and other charactenstics " 10 Table 1: Characterisation of reference samples composition bulk materials_ spectroscopy, wet chemical analysis composition of coatings X-ray fluorescence, EPMA, AES, GDOS, SIMS, SNMS thickness of coat-ings roughness___ microstructure grain size and tex- ture__ coating internal stress__ cap grinding, cross-section ing, X-ray diffraction, step height measurement. NDT-test methods^ 3D profilometry optical microscopy, SEM, TEM, XRD phase-analysis XRD, quantitative metallography X-ray diffraction, flexural strain, Ravleigh wave analysis density hardness, hardness gradient vveighting and volumina evaluation indentation method ^iguioin------- adhesion of coatings scratch t™tin«>. indentation method ultrasonics, acoustic microscopy modulus of elastic- iH. 4 THE VALIDATION OF METHODS OF TEST In practice, many of the qualitative tests are used and recommended, because they are suitable for several coat- ing materials, simply to handle and commonly based on visual examination13. Because of limited applicability of the standard puli test a modified shear test is recom- mended for the test of adhesion of ceramic coatings12. In practice often accepted is the Rockvvell indentation test1- for the qualitative examination of thin hard coatings, where the remaining plastic deformation after indenta- tion causes a "spalling off" of the layer, so an area of failure remains. But in spite of reference samples pro- ducing calibration data under reproducible measurement conditions this method of test is not valuable until now to be adapted as a standard. 4.1 Reference specimens for calibration Calibration requires the production of an ensemble of vvell characterised specimens vvith hard coatings of per- fectly controlled chemical composition, microstructure, and thickness uniformity, likely to become certified ultimate^ as reference specimens. The follovving methods are used to assess these properties. 4.2 Measurement of the coating thickness For the measurement of the coating thickness the methods of stylus profilometry14 and cap grinding15 are employed. A further development of the cap grinding method allovvs the in-situ detection of the coating relief during abrasive extraction16. This method can also be modified for the determination of the coating resistance against abrasive vvear under defined friction control. 4.3 Measurement of the chemical composition Chemical analysis23 vvas carried out from various lay-ers of defined (N/Ti)-composition vvhich has been real-ised by reactive magnetron sputtering vvith nitrogen vvhere the N-concentration has been varied by trimming the gas flovv18. The spectrochemical analysis of the layer led to a constancy of the composition of ±1% atomic%, vvhich has been certified by reference labs18. 4.4 Measurement of the coating hardness It vvas found by round robin comparison that existing standards methods of hardness tests on hard coatings are rarely valuable for certification. Hardness measurement by load-indentation1819 on TiN coated test plates of tool steel shovved under certain conditions, regardtng the surface quality, chemical homogeneity, smooth interface morphology, hard substrate material, reproducible hardness values of 20 GPa by means of a test force betvveen 250 mN (HU 0.25) and 1 N (HU 1) vvithin an error vvidth of less than ±2,5% of the value as determined above. These platelets, described in18, could act as calibration samples for hardness measurement. The surface morphology, respectively the surface roughness, plays an important role on accuracy and re-producibility. Doubtless, the calibration of the Instruments, their stability and constancy during the test pen-ods give a guarantee for exact results. Several procedures, especially for the nanohardness scale, have been developed and controlled through various round robin tests19. 4.5 Adhesion of the coating In the same way the influences on scratch test sensi-tivity and reproducibility of results are carried out. Obeying the vvhole system, stylus geometry and adhesive debris, surface quality, the existence of lubricants, hu-midity and temperature the function of influencing parameters is studied22. Then, using various coating/sub-strate composites of defined combination, scratch test failure modes are analyzed and various features cata-logued. Improving the NDT techniques for in-situ control during process routines, ultrasonic test procedures are validated20. For thin hard films it vvill be realised by surface acoustic measurement techniques. The input ot one specified research vvork is to enhance and cahbrate the surface acoustic vvave velocity measurement tech-nique vis a vis reference coated substrate standards vvith the aim of developing a comprehensive test methodology for coating thickness. This measurement methodology will then be proposed to CEN for adoption as an Euro-pean standard. 5 assessment of tribological performance Engineering components often suffer from wear and friction resulting at best in energy inefficiencies and losses in performance, and in the worst cases cata-strophic failure. There has been considerable recent in-terest in improving the tribological performance of components by the application of wear resistant coatings to the surface of the components22. For reliable assessment of the tribological performance of potential coating systems, robust and effective testing procedures are required. Testing of the cavitation erosion by ultrasonic affects in water can be estimated as a valuable method for standardisation18. Current friction and wear testing procedures are not sufficiently well defined to allow data comparisons, and evaluation of the significance of reported data is difficult. The vvork to be carried out in one prenormative research22 involves the development of improved procedures for uniaxial sliding wear testing; reciprocating sliding wear testing and abrasive testing. 6 assessment of life time of coated parts Whatever the main technological function may be, in practice mechanical properties of the coating substrate compound vvill determine the Iife time vvith on service conditions because the interactive elastic and plastic behaviour of coating and substrate controls the fatigue en-durance, fracturing conditions and the adhesion of the coating. At first, the aims of the research vvork conducted in one current program22 are to develop and validate the methods of test to determine the elastic properties of the surface layer. In comparison to the tribological test procedures quantitative assessments based on scientific in-vestigations due to structure and composition of reference samples are provided. These items vvill involve the development of reference materials and the conduction of round-robin intercomparisons. 7 REFERENCES D- S. Rickerby & A. Matthews: Advanced surface coatings, A hand- ^book for surface engineering, Blackie, London, 1991 s. Buli & D. S. Rickerby: Compositional, microstructure and morpho- logical effects on the mechanical and tribological properties of chro- mium nitrogen films, Surface and Coatings Technology, 43/44 (1990) 732 -744 E. Lugscheider, P. Jokiel: Particle reinforced coatings - processing and mechanical properties, Surface Engineering (ed. P. Mayr, Proc. Of the International Conf. On Surf. Eng. 1993, Bremen, FRG, DGM Infor-mations GmbH Frankfurt/Oberursel ISBN 3-88355-189-9, 1993, 159-164 4 K. Keller: Economical and ecological aspects as design criteria for coating processing, Surface Engineering (ed. P. Mayr, Proc. Of the International Conf. On Surface Engineering 1993, Bremen, FRG, DGM Informations GmbH Frankfurt/Oberursel ISBN 3-88355-189-9, 1993, 3-12 5 D. S Rickerby et al.: The development of advanced erosion resistant coatings for gas turbine compressor applications, BRITE-EURAM Rep. BE-3339 Rep. (Brussels, 1994) 6 H. Holleck: Biniire und Ternare Carbid- und Nitridsysteme der Uber-gangsmetalle, Materialkundl, Techn. Reihe 6, Veri. Gebr. Borntraeger, Berlin, Stuttgart, 1984 7W. Gissler, H. Jehn: Advanced Techniques for Surface Engineering, Dordrecht, 1992 8 S. Ronkainen et al.: Mechanics of Coatings (Ed. D. Dawson, C. M. Taylor. M. Godet) Elsevier Sci. Publ., 1990, 453-462 ' S. R. J. Saunders: VAMAS (Versailles Project on Advanced Materials and Standards), Technical VVorking Area Project Initiation Form: Property Measurement of Thin Films and Coatings, Tokyo, Dec. 1992 10J. P. Celiš et al: Corrosion of Electrodeposited, PVD and CVD Coated Metallic Materials, Surface Engineering (ed. P. Mayr, Proc. Of the International Conf. On Surface Engineering 1993, Bremen, FRG, DGM Informations GmbH Frankfurt/Oberursel ISBN 3-88355-189-9, 1993, 43-53 11 European Envisaged Standard ENV 1071-5, Methods of Test of Ceramic Coatings: Determination of the Porosity, 1995 12 ISO standard 2819, Metallic Coatings on Metallic Substrates - Electrodeposited and Chemically Deposited Coatings - Review of Methods for Testing Adhesion "H. Jehn, G. Reiners: Charakterisierung diinner Schichten, DIN Fach-bericht 39, Beuth Verlag GmbH., Berlin, Wien, Ziirich, 1993, ISSN 0179-275X 14 European Envisaged Standard CEN ENV 1071-1, Determination of the Coating Thickness: Step height measurement by means of a contact profilometer, 1992 ''European Envisaged Standard CEN ENV 1071-2, Determination of the Coating Thickness; Cap grinding method, 1992 16H. Kltimper-VVestkamp: Prakt. Metallographie (German DGM, Spec. Vol. 26, 1994), Mikrotribometer zur Qualitatssicherung von Rand-schichten (Pat. DE-P 4434661.1) 433-442 17 European Envisaged Standard CEN ENV 1071- 3: Characterization of adhesion: Scratch adhesion test, 1992 18 A. Schulz, H.-R. Stock, H. Vetters and P. Mayr: Qualifizierung von Priifverfahren und Standards fur die Dunnschichttechnologie, Final Report Programme OSTEC 13N6242, (German Fed. Ministry of Edu-cation and Research BMBF, Feb. 1996) "S. R. J. Saunders et al.: Hardness (Mechanical Property) Testing of Surfaces, NPL Report DMA (D) 198, BCR MAT CT 92 - 0027, 1996 20BRITE EURAM BE 4398: Non Contacting Surface Characterization of Ceramics and Coatings vvith Micro Acoustic Waves (C-MAW), Final Report R/CJG/1093/95, 1996 21 K. Holmberg: Friction and Wear Mechanisms of Thin Surface Coatings on Metal Substrates, Surface Engineering (ed. P. Mayr, Proc. Of the International Conf. On Surf. Eng. 1993, Bremen, FRG, DGM Informations GmbH Frankfurt/Oberursel ISBN 3-88355-189-9, 1993, 13-22 22 Development and Validation of Test Methods for Thin Hard Coatings (FASTE) EU- MS&T MAT1-CT 940045, Workprogramme, 1994 -1997 23 European Envisaged Standard CEN ENV 1071-4; Determination of the chemical composition, 1995 kovine, zlitine, tehnologije 31 (1997) 6 531 slovenske železarne -fr # ZELEZABNA IESENIUL AcRONi ,0 IZDELUJE: □ nerjavna jekla □ jeklo za elektro pločevino □ nelegirana in legirana jekla - za poboljšanje - za cementacijo □ nelegirana, mikro in malolegirana konstrukcijska jekla toplo valjane pločevine, trakove in lamele hladno valjane pločevine, široke in vzdolžno razrezane trakove hladno oblikovane profile kovinske podboje za vrata izsekance varnostne ograje □ NUDIMO TUDI STORITVE: □ prevaljanje □ izsekovanje (štancanje) □ krojenje □ ravnanje □ toplotne obdelave pločevin SŽ ŽJ ACRONI d.o.o. Cesta železarjev 8, 4270 Jesenice, tel. centrala. +386 64 861-441 tel. direktor: 861-443, tel. komerciala: 861-474, fax: 861-379, telex: 37219 ZELJSN SI Sl<^eM|a AS-ROLLED MULTI-PHASE MICROALLOYED STEEL BARS WITH IMPROVED PROPERTIES VALJANE VEČFAZNE MIKROLEGIRANE JEKLENE PALICE Z IZBOLJŠANIMI LASTNOSTMI DJORDJE DROBNJAK1, A. KOPRIVICA2 'Faculty of Tech & Met University of Belgrade, Belgrade, YugosIavia 2Institute for Ferrous Metallurgy, Niksic Yugoslavia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 A series of experimental steels, based on a 0.3 C, 1.5 Mn, 0.1 V composition, with and vvithout 0.01% Ti addition, vvas made by laboratory and full-scale casting, and fabricated into 22 mm dia bars by full-scale hot-rolling. Multi-phase Polygonal Ferrite-Pearlite-Non Polygonal Ferrite (PF-P-NPF) structures, with varying amount of NPF, are obtained in as-rolled bars. Acicular Ferrite (AF) and classical Bainite Sheaves (BS) are found to be dominant NPF morphologies in steels vvith a lovv (<30%) and a high (>40%) fraction of NPF, respectively. In Ti-bearing PF-P-AF steels, the PF-grain and P-colony size control, obtained through fine TiN particles, vvhich also provide preferential sites for intragranular nucleation of AF, a tensile strength of 800/850 MPa and 900/950 MPa in 0.2 and 0.3 C steels vvas obtained, vvhile maintaining the room temperature CVN impact energy at a level of 65/75 J and 40/50 J, respectively. A high fraction of grain boundary nucleated BS is promoted by increasing the content of Cr. Mo or Mn above the base level. The main effect of introducing BS into structure is a drop in impact toughness. Even so, in some BS dominated steels (notably Cr treated) an impact energy of 30/35 J is maintained at a tensile strength level of 1050/1100 MPa. These results have provided a bases for the development of as-rolled medium carbon microalloyed engineering bars. that achieve satisfactory properties in the as-rolled conditions vvithout the need for subsequent heat treatment. Key vvords: microalloying, bar-rolling, polygonal ferrite, pearlite, non-polygonal ferrite, bainite, acicular ferrite, strength, toughness Vrsta eksperimentalnih jekel z osnovno sestavo 0.3 C, 1.5 Mn in 0.1 V z ali brez dodatka 0.01% Ti je bila izdelana z laboratorijskim in z industrijskim vlivanjem ter industrijsko izvaljana v 22 mm palice. Dosežene so več fazne poligonalni ferit-perlitne - poligonalni ferit (PF-P-NPF) mikrostrukture z različnim deležem NPF. Acikularni ferit (AF) in klasični bajnitni snopi (BS) so prevladujoče NPF morfologije v jeklih z majhnim (<30%) in velikim (>40%) deležem NPF. V PF-P-AF jeklih z dodatkom Ti, kjer je dosežena kontrola velikosti zrn PF in P kolonij z izločki TiN, ki so tudi prednostna mesta za intragranularno nukleacijo AF, je bila dosežena pri 0.2 in 0.3 C jeklih natezna trdnost 800/850 in 900/950 MPa. Pri tem je ostala CVN udarna energija pri temperaturi ambienta 65/75 oz. 40/50 J. Velik delež BS z nukleacijo na kristalnih mejah se doseže z dodatkom Cr, Mo ali Mn nad osnovno vsebnostjo. Glavna posledica prisotnosti BS v mikrostrukturi je zmanjšanje udarne žilavosti. Vendar je bila tudi v nekaterih jeklih s prevladujočo BS (predvsem z dodatkom Cr) ohranjena udarna energija 30/35 J pri trdnosti 1050/1100 MPa. Ti rezultati so bili osnova za razvoj srednje ogljičnih konstrukcijskih jekel, ki imajo v valjanem stanju dobre lastnosti brez dodatne toplotne obdelave. Ključne besede: mikrolegiranje, valjane palice, poligonalni ferit, perlit, ne poligonalni ferit, bainit, acikularni ferit, trdnost, žilavost 1 INTRODUCTION Medium-carbon microalloyed (MA) forging steels have been extensively studied over the past decade, and the results are reported at several international confer-ences (e.g.1"3). There are many examples to show that MA steels can replace Q&T steels in as-forged and air-cooled conditions, without subsequent heat treatment. Hovvever, in the ferrite-pearlite (FP) version, these steels suffer from inferiors notch toughness. In the last few years, bainite (B) and martensite (M) type grades, have received considerable attention as viable candidates to replace FP steels. Compared to M type (e.g.45) the air-hardened B-type grades need not quench, but the im-provement in toughness is not as-spectacular4613, and in some instances a deterioration in toughness is claimed14" 16. This as vvell as other disadvantage of B-grades, such as a lovv yield ratio13-17 and poor machinability7, may be among the reason why they are scarcely used17. The strength and toughness of as-hot rolled bars have been less extensively studied in comparison to forgings. Hovvever, vvhile considerable vvork has been done to improve the toughness of conventionally or controlled rolled bars in FP version (e.g.131819), little effort has been made to improve the toughness of bars by introducing B into structure. Improvements achieved in this vvork are mostly based on recent results vvhich shovv2021 that, vvhile some B-morphologies are beneficial, the other are detrimental to toughness. 2 EXPERIMENTAL DETAILS 2.1 Material A series of experimental heats, based on 0.3% C, 1.5% Mn, 0.1% V composition (small variations among different heats are included in Table 1) vvith and vvithout 0.01% Ti addition, is used in this vvork. A number of heats vvere modified by either reducing the content of some additions (e.g.: C to 0.2%; N to 15-60 PPM; V, Ni and Cu to traces) or increasing the content of other additions above the base level (e.g.: Mn to 1.55/1.65 or 1.72/1.78%; Cr to 0.37/0.38 or 0.57%; Mo to 0.21%; V to 0.16/19%; N to 160/240 ppm; S to 150/250 ppm). Table 1: Steel compositions (in wt.%) Tabela 1: Sestava jekel (v ut.%) C Si Mn P S Cr Mo Ni Al Cu N V 0.27 0.29 1.47 0.006 0.006 0.21 0.03 0.15 0.02 0.18 0.010 0.10 0.32 0.39 1.57 0.010 0.010 0.30 0.06 0.19 0.03 0.31 0.012 0.13 2.2 Casting and hot vvorking of steels Either laboratory vacuum or full-scale casting was used to produce 60 kg and 2630 kg ingots, labeled L and I-ingots, respectively. L-casting practice proved2" to be effective in producing the fine TiN particles in Ti-bearing steel, capable of imposing a pinning effect on austenite grain boundaries during subsequent reheating and rolling. The ingots were fabricated into 22 mm dia bars on production facilities. They were first fabricated into 120 mm (I-ingots) and 80 mm squares (L-ingots) by hot-roll-ing on a bloom mili or by press-forging, respectively. Then, the squares were hot-rolled to 22 mm bars, on either a continuous (120 mm squares) or a cross-country (80 mm squares) bar mili, using the conventional rolling practice, which involved soaking at 1150°C and finish-rolling above 950°C. 2.3 Testing Room temperature properties are evaluated from round tensile 0» = 40 mm; do = 8 mm) and standard Charpy V-notch (CVN) longitudinal specimens, which were taken mid-radius from the as-rolled bars. A few im-pact tests were run at -50°C. Conventional metal-lographic techniques were used for revealing the microstructure. 3 RESULTS 3.1 Structure A multi-phase Polygonal Ferrite-Pearlite-Non Po-lygonal Ferrite (PF-P-NPF) structure, with varying amount of NPF, is developed in the as-hot rolled bars. Acicular Ferrite (AF) and classical Bainite Sheaves (BS) are found to be dominant NPF morphology in steels with a lovv (<30%) and a high (>40%) fraction of NPF (to be referred to as PF-P-AF and PF-P-BS steels), respectively. Intragranularly nucleated, mostly needlelike plates, vvhich radiate in many directions, referred to as AF, are shovvn in Figure la, and as a part of PF-P-AF structure, in Figure lb. The former austenite grain boundaries are decorated by Grain Boundary Idiomorphs (GBI) in Figure la, but Grain Boundary Alotriomorphs (GBA) or Widmanstatten Sideplates (WSP) are also frequently observed20. Grain boundary nucleated parallel ferrite plates, referred to as BS, are shovvn in Figure 2a, and as a part of a PF-P-BS structure, in Figure 2b. AF is dominant NPF morphology in steels vvith composition vvithin the limits given in Table 1, vvhile a high fraction of BS is promoted by increasing Mn, Cr and Mo content above the base level. The tvvo morphologies (in-cluding some transient variants) generally coexist in various proportions. In PF-P-AF steels, the addition of Ti increases the AF/BS ratio (Ti addition also refines the PF-grain and P-colony size). In PF-P-BS steels the BS/AF ratio depends upon the alloying addition. Thus, in 0.57% Cr and 0.21% Mo steels, BS coexist vvith a de-tectable fraction of AF (Figure 3a), vvhile in 1.72/1.77% Mn steels BS are the only morphology present (Figure 3b). Ali three steels are L-cast and Ti-treated, but the tvvo latter are virtually free of PF and P. 3.2 Structure-Propert>• Relationship Strength and Impact Properties (YS = Yield Strength; TS = Tensile Strength; CVN20 = Charpy V-Notch impact energy at 20°C) are, in terms of NPF fraction, shovvn in Figures 4a and 4b, respectively. Each data point repre-sents an average of tvvo (strength) and three to five tests (toughness). The TS remains virtually unchanged vvith increasing fraction of NPF up to about 70% and then Figure 1: (a) Acicular Ferrite (AF), Grain Boundary Idiomorphs (GBI) and Pearlite(P); (b) Polygonal Ferrite-Pearlite-Acicular Ferrite (PF-P-AF) Slika 1: (a) Acikularni ferit (AF), idiomorfi (GBI) in perlit (P) po kristalnih mejah; (b) poligonalni ferit perlit - acikularni ferit (PF-A-AF) Figure 2: (a) Bainite Sheaves (BS); (b) Polygonal Ferrite-Pearlite-Bainite Sheaves (PF-P-BS) Slika 2: (a) Bainitni snopi (BS); (b) poligonalni ferit perlit - bainitni snopi (PF-B-BS) Figure 3: (a) Bainite Sheaves (BS) and Acicular Ferrite (AF); (b) Bainite Sheaves (BS) Slika 3: (a) Bainitni snopi (B) in acikularni ferit (AF); (b) bainitni snopi (BS) slightly increases, vvhile the YS first decreases and than, at 30-40% of NPF, attain a constant level. These changes are neither consistent with variations in fraction nor in morphology of NPF (AF = open symbols; BS = closed symbols, in Figure 4). A relatively broad scatter band in Figure 4a is presumably a reflection of small variations in composition. For instance, decreasing C from 0.3% to 0.2% produces a drop in YS and TS from 600/650 to 550/600 and from 900/950 to 800/850 MPa, respectively. Moreover Ti, Cr and Mn produce an effect vvhich can be discriminated vvithin the scatter-band itself. Thus, Ti-free PF-P-AF steels (Region la) exhibit a higher strength level then Ti-bearing steels (Region lb), vvhile 0.57% Cr PF-P-BS and 1.72/1.77% Mn B-steels (Region 2a) ex-hibit a higher TS level (1050/1100 and 1150/1200 MPa, respectively) than the other PF-P-BS grades (Region 2b). Data of Figure 4b shovv that an increase in impact energy vvith increasing fraction of NPF is interrupted by a pronounced drop on passing from AF dominated - Region 1 to BS dominated - Region 2. Within the PF-P-AF Region lc, the energy attains a level of 65/75 J at 20°C (33 J at -50°C), corresponding to YS = 550/600 MPa and TS = 800/850 MPa; and vvithin the Region lb, a level of 40/50 J at 20°C (32 J at -50°C), corresponding to YS = 600/650 MPa and TS = 900/950 MPa, in 0.2% C/10% AF and 0.3% C/30% AF steels, respectively. Both steels are L-cast and Ti-treated. In general, the L-cast/Ti-treated steels exhibit a higher impact energy level (+Ti band in Figure 4b) than the Ti-free steels (-Ti band). The I-cast/ Ti-treated steels take an intermediate position (open squares). Within the PF-P-BS Region 2, the en-ergy attains a level of 30/35 J at 20°C (25/30 J at -20°C), corresponding to YS = 600 MPa and TS = 1050/1100 MPa; and vvithin the Region 2c, a level of 15/25 J at 20°C, corresponding to YS = 550/600 MPa and TS = 1150/1200 MPa, in 0.57% Cr/70% BS and 1.75% Mn/98% BS steels, respectively. In 0.57% Cr steel, in addition to BS, the NPF morphology comprises a detect-able fraction of AF (Figure 3a), vvhile in 1.75% Mn steels, BS is the only NPF morphology present (Figure 3b). 4 DISCUSSION 4.1 Structure A slight difference in composition of the steels stud-ied in this vvork seems to be decisive in controlling not 535 PF-P-AF PF-P-BS MS #(L)MiS° 60 a > o 0 10 20 30 40 50 60 70 80 90 100 Non—Polygonal Ferrite (NPF), % Figure 4: (a) Yield Strength (YS) and Tensile Strength (TS) as a Function of Non-Polygonal Ferrite (NPF) Fraction; (b) Charpy V-Notch Impact Energy at 20 (CVNzo) as a Function of NPF Fraction (PF = Polygonal Ferrite; P = Pearlite; AF = Acicular Ferrite; BS -Bainite Sheaves; L = L-Cast Ingots; I = I Cast-Ingots; +Ti = Ti-Bearing Steels; -Ti = Ti-Free Steels) Slika 4: (a) Meja plastičnosti (YS) in natezna trdnost (TS) v odvisnosti od deleža ne poligonalnega ferita (NPF); (b) Charpy V udarna energija pri 20°C (CVN20) v odvisnosti od deleža NPF (PF - poligonalm fent, P - perlit, AF - acikularni ferit, BS - bainitni snopi, L-L - liti ingoti, I-I - liti ingoti, +Ti - jekla s Ti, -Ti - jekla brez Ti) only the fraction of NPF but, together vvith inclusions, its morphology also. Thus, the AF, vvhich is assumed to be either intra-granulary nucleated bainite22 or Widmanstatten ferrite23, together vvith various proportions of PF (e.g. Grain Boundary Idiomorphs, GBI) and pearlite, P (Figure 1), is produced in PF-P-AF grades, vvith a relatively low har-denability (<30% NPF). The Grain Boundary Ferrite (GBF) is assumed24 to render austenite grain boundaries inactive in respect to intergranular nucleation of BS, what in turn promotes the intragranular nucleation of AF on TiN or MnS inclusions20. The nucleation potential of inclusions varies vvith composition, crystal structure and dispersion, i.e. vvith their number, size and spacing22-25'29. For example, a low degree of misfit betvveen the ferrite matrix and the substrate crystal lattice is assumed25"31 to increase the nucleation potential of inclusions. There-fore, TiN vvith a misfit ratio of 3.827 should be much more effective than MnS vvith misfit ratio of 8.825. This could account for a higher fraction of AF observed in Ti- bearing (fine and coarse particles, vvhich are presumably developed in L and I-cast ingots respectively, seems to be equally potent nucleation sites) than in Ti-free (high S) steels. Hovvever, in steels vvith high V and N, VN particles can be precipitated on MnS, before austenite is transformed to ferrite3031. Since the misfit ratio of VN, estimated at 1.3 for (001) plane27, is lovver than that of TiN, the former particles, i.e. MnS coated by VN, should be more potent nucleation sites for AF. While the effect is not quite apparent in the present steel, the fact remains that the fraction of AF is higher in high-S than in lovv-S/Ti-free steels. The BS are produced in PF-P-BS grades vvith relativen high hardenability (>40% NPF). The nucleation of GBF is considerably suppressed, and an abrupt transition from AF dominated to BS dominated NPF morphology occurs not only in Ti-free but also in Ti-bearing steels. This supports the assumption that removal of GBF frees the boundaries to nucleate BS concurrently vvith intragranular AF. 4.2 Properties ViflH and Tensi|p .Strpnih (YS. TSV It is vvell knovvn (e.g.6 8) that the YS of Polygonal Ferrite-Pearlite (PF-P) steels increases vvith increasing fraction of P. Additional strengthening is obtained by precipitation of V (C,N) particles in ferrite. Precipitation strengthening effect de-creases vvith decreasing N-content. In Ti-bearing PF-P-AF steels tested in this vvork, Ti forms nitride particles vvhich reduce the N available for VN precipitation and hence, reduce (from Region la to lb in Figure 4a) the strengthening associated vvith this precipitation. Gradual replacement of PF-P structure vvith NPF structure re-duces the YS, as shovvn in Figure 4a, due to suppression of precipitation vvithin the NPF phase (e.g.811). Hovvever, the TS is maintained at the same level (Region 1), and even increases (Region 2a) in some steels. This latter observation can be associated vvith a high strain-harden-ing rate imposed by bainite32. rVN,„ Impact Tonphness (CVN.n), The present results, together vvith data presented in previous papers20'21, indicate that AF and BS are beneficial and detrimental to toughness, respectively. The brittle fracture of low-C bainites can be related to the cleavage facet size33, vvhich in the present steels can be related to either AF-plate or BS-packet size. AF-plates give rise to a finer facet size, and thus to a higher toughness, vvhile BS, in addition to being coarser itself (individual laths vvithin a sheaf have little effect, since the cleavage crack is deflected at the sheaf and not at the lath boundary33), contain coarse m-terlath carbides (a feature characteristic of upper bainite), vvhich are detrimental to toughness33. The Ti-bearing PF-P-AF steels (Region lb in Figure 4b) exhibit a considerably higher toughness in compari-son to Ti-free steels (Region la). This is because the PF-grain and P-colony size is finer and the AF fraction is presumably higher in Ti-bearing steels vvhich contain 90 80 70 - 60 150 Z > 40 O 30 i 20 10 "I 0 CVN +20°C □ PF-P (Ref. 13,18) ■ PF-P-AF (This vvork) ■ PF-P-BS (This work) CVN J" • PF-P-AF (This vvork) -50°C l @ PF-P-BS (This vvork) 600 700 800 900 1000 1100 Tensile Strength, MPa 1200 Figure S: Tensile Strength (TS) vs. Charpy V-Notch Impact Energy (CVN20 = 20°C; CVN.50 = -50°C) of Conventionally Hot Rolled 0.2-0.5% C Polygonal Ferrite-Pearlite (PF-P), and 0.2-0.3% C Polygonal Ferrite-Pearlite-Acicular Ferrite (PF-P-AF) and Polygonal Ferrite- Pearlite- Bainite Sheaves (PF-P-BS) Bar Steels Slika 5: Natezna trdnost (TS) v odvisnosti od Charpy V udarne energije (CVN20 = 20°C CVN50 = 50°C) pri konvencionalno vroče valjanih 0.2 - 0.5% C poligonalni ferit perlit (PF-P) in 0.2 - 0.3% C poiigonalni ferit perlit - acikularni ferit (PF-P-AF) in poligonalni ferit perlit - bainitni snopi (PF-P-BS) jeklenih palicah fine TiN particles. The role of particles is tvvofold, first they inhibit the austenite grain grovvth, and second, they provide the nucleation sites for intragranular nucleation of AF. Hovvever, Ti-bearing/I-cast steels exhibit a lovver toughness than Ti-bearing/L-cast steels, in spite of AF is a dominant NPF morphology in both. Coarser TiN particles in I-cast steels are not as effective in pinning austenite grain boundaries as fine particles in L-cast steels and lead to a coarser austenite grain, and conse-quently coarser PF-grain and P-colony size. 5 CONCLUDING REMARKS The conventionally hot-rolled and air-cooled multi- phase Polygonal Ferrite-Pearlite-Non Polygonal Ferrite (PF-P-NPF) microalloyed Ti-bearing steels, tested in this vvork (closed and shaded symbols in Figure 5), exhibit improved impact properties in comparison to conven- tional^ hot rolled PolygonaI Ferrite-Pearlite (PF-P) steels (open symbols), tested previously (e.g.18-19). The 0.2% C/10% AF and 0.3% C/30% AF PF-P-AF steels, based on a 1.5% Mn - 0.1% V - 0.01% Ti compo- sition, vvith an impact energy level of 65/75 J and 40/50 J at 20°C (33 and 32 J at -50°C), and tensile strength level of 800/850 MPa and 900/950 MPa respectively, can replace Q&T steels vvhich currently achieve these prop-erty levels. The use of a higher Cr or Mn contents give rise to PF-P-BS structure vvith 70-98% BS and increased tensile strength level up to 1050/1200 MPa at the expense of re-duced toughness. Acknovvledgment This vvork vvas supported by Steel Mili, Niksic, Yu-goslavia and permission to publish this paper is acknovv-ledged. 6 REFERENCES 1 Fundamentals of Microalloying Forging Steels, eds. G. Krauss and S. K. Banerji, The Metallurgical Society, VVarrendale, PA 1987 2 Microalloyed Bar and Forging Steels, ed. M. Finn, The Canadian Institute of Mining and Metallurgy, Montreal, QU 1990 3 Fundamentals and Applications of Microalloying Forging Steels, eds. C. J. Van Tyne, G. Krauss and D. K. Matlock, The Minerals, Metals and Materials Society, VVarrendale, PA 1996 4 W. A. Szilva et al., As Ref. 2, p. 227 5 M. Katsumata et al., Phys. Metali, of Direct-Quenched Steels, eds. R. A. Taylor et al., The Metallurgical Society, VVarrendale, PA 1993, p. 247 6 H. Hara and M. Kobayashi, Hot Forged MicroaIloyed Steels in Automobile Components, Vanadium Avvard, The Institute of Metals, 1987 7Vanadium As Forged Steels for Automobile Components, Vanitec Monograph No3, 1987 8 W, E. Heitmann and P. B. Babu, As Ref. 1, p. 55 9G. Tither, T. B. Cameron and D. E. Diesburg, As Ref. 1, p. 269 10P. H. VVright et al., As Ref. 1, p. 541 11 P. A. Khalid and D. V. Edmonds, As Ref. 2, p. 1 12 Y. Koyasu et al., As Ref. 2, p. 202 13 M. Cristinacce and P. F. Reynolds, As Ref. 3, p. 29 14 J. F. Held, Metal Progress, 128 (1985) 12, 17 15 V. Ollilainen, H. Hurmola and H. Pantinen, Journal of Materials En-ergy Systems, 5 (1984) 221 16B. Garbarz and R. Kuziak, Microalloying '95, The Iron and Steel So-ciety, VVarrendale, PA 1995, p. 409 17 H. Tokada and Y. Koyasu, As Ref.3, p. 143 18 P. E. ReynoIds and J. H. Reynolds, As Ref. 3, p. 79 19D. Tostenson, R. Bertolo and B. Glasgal, As Ref. 3, p. 327 20Dj. Drobnjak and A. Koprivica, As Ref. 3, p. 93 21 Dj. Drobnjak and A. Koprivica, Metal 97, Ostrava, Czech Republic 1997, p. 162 22H. K. D. H. Bhadeshia, Bainite in Steels, The Institute of Materials, London, 1992, p. 245 23 R. A. Ricks, P. R. Hovvell and G. S. Barritte, Journal of Materials Science, 17 (1982) 732 24 S. S. Babu and H. K. D. H. Bhadeshia, Materials Science and Tech-nology, 6 (1990) 1005 25 A. R. Mills, G. Thevvlis and J. A. VVhiteman, Ibid., 3 (1987) 12, 1051 26G. Thevvlis, Ibid., 10 (1994) 2, 110 27 Y. Tomita et al., ISIJ International, 34 (1994) 10, 829 28 J. L. Lee, Acta Metallurgica and Materialia, 42 (1994) 10, 3291 29 J. L. Lee and Y. T. Pan, ISIJ International, 35 (1995) 8, 1027 30F. Ishikavva and T. Takahashi, Ibid., 35 (1995) 9, 1128 31 F. Ishikavva, T. Takahashi and T. Ochi, Metallurgical and Materials Transactions /1, 25A (1994) 5, 929 32 K. Irvine and F. B. Pickering, ISI Spec. Rep. 93, London, 1965, 110 33 D. V. Edmonds and R. C. Cohrane, Metallurgical Transaction, 21A (1990) 6, 1527 impol industrija metalnih polizdelkov slovenska bistrica r A Wi v mm. jccflfflunoN JCffllKfflO sits EN 29001 /ISO 9001/BS 5750 APPROVED BY BVQI Izdelki iz aluminija: pločevine, trakovi, rondele, rondelice, prometni znaki, folije, palice, cevi, profili, žice, mreže, varilni materiali Telefon: 817-521, 817-421 Telefax: 811-219 Telex: 33-113 TWO-WAY SHAPE MEMORY EFFECT AND ITS DEGRADATION DURING THERMAL CYCLES IN Ni-Ti ALLOYS DVOSMERNI SPOMINSKI EFEKT V Ni-Ti ZLITINAH IN NJEGOVA DEGRADACIJA MED TOPLOTNIMI CIKLI HEINRICH SCHERNGELL, A. C. KNEISSL Institute of Physical Metallurgy and Materials Testing, University of Leoben, A-8700 Leoben, Austria Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 This work presents a study of the degradation of the Two-Way Shape Memory Effect (TWSME) due to working cycles. An intrinsic TWSME was induced in wire specimens of a near equiatomic Ni-Ti al!oy by thermomechanical training. The deveiopment of the two-way strain vvas analysed and discussed with respect to the different training parameters and the preliminary heat treatment of the samples. Subsequent to the training, the stability of the obtained TVVSME was examined by thermal cycling under stress-free conditions. Possible reasons and mechanisms for the degradation of the effect during thermal cycling are discussed. Key words: shape memory, two-way-effect, Ni-Ti alloy, stability, martensitic transformation, fatigue V delu se predstavlja raziskava degradacije dvosmernega spominskega efekta (TWSME) zaradi delovnih ciklov. Intrinsičen TWSME je bil induciran v žice iz equiatomske Ni-Ti zlitine s termomehanično obdelavo. Razvoj dvosmerne deformacije je bil raziskan in ocenjen glede na obremenilne in predhodno toplotno obdelavo vzorcev. Po obremenitvah je bila stabilnost dosežene TWSME preiskana s toplotnim cikliranjem brez napetosti. Razpravlja se o možnih vzrokih in mehanizmih degradacije efekta med termičnim cikliranjem. Ključne besede: oblikovni spomin, dvosmerni efekt, zlitina Ni-Ti, stabilnost, martenzitna premena, utrujenost 1 INTRODUCTION The term Shape Memory refers to the ability of certain alloys, to recover large strains perfectly either right after unloading (pseudoelasticity) or after heating (pseudoplasticity). Several alloys can show this phe-nomenon as a consequence of martensitic transformation1. In the čase of the intermetallic phase Ni-Ti, sueh a transformation occurs between the high temperature modification (austenite) vvith a CsCl-type B2 superlattice and the lovv temperature phase (martensite) vvith a mono-clinic BI9' strueture2. Furthermore, a TWSME may be obtained in these alloys after a suitable thermomechanical treatment, vvhich is often termed training. This spe-cial behaviour refers to the ability to produce spontane-ous shape changes on heating as vvell as on cooling, both vvithout the application of external forces. Consequently, trained elements can directly be used as temperature-sen-sitive actuators. The actuators are usually electrically ac-tuated and cooled by natural convection. One important eriterion for the aetual use of Shape Memory compo-nents in sueh multiple cycle applications is the stability of the funetional parameters throughout application. A reliable component should exhibit constant transforma-tion-temperatures and a two-way strain independent of number of cycles. In this vvork, the stability of an intrinsic TWSME during repeated thermal cycling has been investigated. 2 EXPERIMENTAL The investigations have been carried out on a binary Ni-Ti alloy vvith a nominal composition of Ni-50,3 at% Ti. The material vvas melted from pure metals in an arc-furnace, hot extruded and cold-dravvn vvith intermediate annealings. The as-received vvire material vvas cold vvorked by 13,5% vvith a diameter of 3 mm. Wire specimens of 20 cm in length vvere prepared and some of them annealed at 550°C / 20 min. The transformation temperatures vvere deduced from resistivity measurements and are listed in Table 1. Ali transformation temperatures are above room temperature, vvith Ms, Mf indi-cating the start and finish temperature for the forvvard transformation, and As, Af deseribing the reverse transformation. The mechanical properties of the alloy vvere investigated by tensile tests carried out at room temperature. The obtained stress-strain-curves of the martensitic phase are illustrated in Figure 1. The training procedure vvas simulated on a tensile testing machine. The specimens vvere fixed at room temperature, loaded vvith the constant training stress a,rain and repeatedly thermally cy-cled betvveen Mf and a temperature above the highest temperature, at vvhich martensite can be stress-induced (M 28 x 175 mm used in the present vvork are from steel W.No. 1.0116 vvith the chemical composition given in Table 1. Table 1: Chemical composition of steel W.No. 1.0116, (in wt-%) Tabela 1: Kemijska sestava jekla VV.No. 1.0116 (v ut.%) C Si Mn P S Cr Mo Ni Al Cu WNr 1.0116 0,15 0,013 0,53 0,011 0,008 0,023 0,006 0,019 0,049 0,031 The pulse plasma furnace used vvas a GP 1000/80 M nitriding unit manufactured by Metaplas-Ionon GmbH, Figure 3. The furnace is equipped vvith a convection heating system and vvith an internal gas/vvater heat-ex-changer for quick cooling. The gas shock absorber tubes in load configuration as shovvn in Figure 4 vvere pulse plasma nitrocarburised at 560 and 580°C at 5,2 hPa and 2,8 hPa pressure, using a total gas flovvrate of 100 and 67 1 h1. The gas shock ab- Figure 3: Pulse plasma nitriding furnace GP 1000/80 M Slika 3: Peč za nitriranje v pulzirajoči plazmi GP 1000/80 M sorber tube's temperature was measured with two chromel-Alumel termocouples embedded in a tubes on two different levels (top and bottom) in the first and the third circuit. Gas atmospheres vvith nitrogen contents 70,5 and 87%, carbon dioxide contents 2,5 and 2% and hydrogen contents 27 and 11% respectively, vvere employed. The pulse frequency used vvas 2 and 2,5 kHz, respectively. Convection and plasma heating to process temperature took appr. 4h and the isothermal treatment lentghs vvere 10 and 4 hr respectively, follovved by forced cooling in a flovv of nitrogen. 4 RESULTS AND DISCUSSION 4.1 Compound layer structures In pulse plasma nitrocarburising, the large number of freely definable treatment parameters make it possible to control precisely the structure, composition, and grovvth characteristics of the compound layer vvithout impairing the formation of the diffusion layer. The tubes nitricarburised for 10 and 4 hr in the pulsed plasma mode, considering the 0,480 ms glovv-on time, 0,020 ms glow-of time, the 0,200 ms glovv-on time, and 0,200 ms glovv-of time, respectively vvere transver-sally sectioned at the middle, metallographically prepared, and etched vvith 3% nital for the determination of the thickness of the compound layer on an optical micro-scope. The thickness of the compound layer vvas taken by averaging five measurements for each tube. Figure 5 shovvs the microstructure of the nitrocarbur-ised layer on the outer surface of the 5 tubes taken from the third circuit from 5 different levels of the charge no. 1 (560°C). The charge no.l contain 685 tubes in 5 circuits vvith 20 mm intercircuit distance, processed for 10 hr in pulsed plasma mode, considering the 0,480 ms glovv-on time and 0,020 ms glow-of time. The compound layers thickness appears to be 5 to 8 |im and the grovvth rate 0,5 Figure 4: Gas shock absorber tubes in load configuration Slika 4: Razporeditev cevi plinskega blažilca v sarži to 0,8 (im/hr. Metallographical analysis (Figure 5) indi-cates that the compound layer on tubes on the top and bottom (sample 1 and 5) obtained by the above pulse plasma nitrocarburising parameters mainly consisted of Y phase - Fe4(N,C)i-x. While the compound layers of the tubes betvveen two (samples 2 - 4) consisted beside of Y phase also of e phase- Fe2-3(N,C)i.x and carbide particles. In the compound layers grain boundaries are parallel to the diffusion direction and thus perpendicular to the surface. Under compound layers of these same tubes (samples 2 - 4) a 15 to 25 |am thick fringe of pearlite is found, vvhile this fringe is not found under the compound layer on top and bottom tubes (samples 1 and 5). •>: .-s?' t-s;-:.*,-*^, t,- • *<«;:<• • M. _' - J , ^ 0 J- , • ' V - > \ ; '"T - * ■ ' v,,,. v* V - ."t / ■ "V * A* * »- i? fr/t^T z***-1 J-\- "V , "i'/-- ^■ 'x "t- -V v * - -r^v: - ^ Figure 5: Microstructure of the nitrocarburised layer at the outer surface of tubes (200x) Slika 5: Mikrostruktura nitrokarburirane plasti ob zunanji površini cevi (200x) From the obtained microstructures it is possible to conclude that the temperature within the charge vvas not equalised or the distribution of gas mixture because of charge configuration was not fulfilled. The analysis of the process parameters actually shovvs that in spite of the relative high pressure (5,2 hPa) the temperature differ-ence between the two thermocouples was too large (~25°C), because of the hollovv cathode effect caused lo-cal overheating. This effect called the hollovv cathode can occur when the cathode drops to a dimension equal to the distance between tubes. Nitrocarburising depth on 5 tubes from top to bottom is shown in Table 2. Table 2: Metallographically determined nitrocarburising depth on tubes from charge no. I Tabela 2: Metalografsko določene globine nitrokarburirane plasti na ceveh iz sarže 1 No. of tube Nitrocarburising depth in mm 1 0,43 2 0,48 3 0,46 4 0,43 5 0,47 Microhardness profiles HV0,3 of the nitrocarburised layers for the same 5 tubes (top and middle of the tube) are shown in Figure 6. From the figures 5 and 6, it can be seen that the microstructure and hardness of diffusion layer on tubes from different levels are affected by the hollovv cathode efffect, vvhich causes also the irregular thickness and the type of compound layer vvhich is also too thin. As mentioned above the goal of the present vvork vvas to obtain at the surface of the gas shock absorber tubes a compound layer consisting predominantly of e phase vvith a thickness of > 10 |Ltm. In the čase of the gas shock absorber tubes the thickness of diffusion zone is not so very important. Such compound layer produced by pulse plasma nitrocarburisig process improves corrosion and HV 0.3 Figure 6: Microhardness profiles HV0,3 of the nitrocarburised layers Slika 6: Profil mikrotrdote HV0.3 nitrokaburirane plasti vvear resistance and after fine polishing one can obtain also satisfactory level of decorativeness. In order to avoid the hollovv cathode effect causing local overheating of tubes it vvas necessary to rearrange the load configuration in such a way that the distance betvveen tubes and each next circuit is appr. 1,3 time the distance betvveen tubes. With nevv load configuration charge no. 2 processed at 580°C contains 552 tubes in 6 levels. The thickness of the compound layer produced at 580°C vvith a 4 h treatment depends not only on the ni-trogen and carbon dioxide levels in the treatment atmos-phere, but also on the pulse frequency used. The results indicate that increasing the pulse frequency and the ni-trogen level in the atmosphere an increased compound layer thickness > 10 and a surface hardness in excess of 320 HV1 are obtained. The grovvth rate becomes greater than 2,5 pm/hr. This tendency is mostly due to the increased nitrogen "activity" in the plasma. Figure 7 shovvs the typical microstructure of the nitrocarburised layer on the outer surface of the shock absorber tubes vvhich consists predominantly of e phase -Fe2-3(N,C)i.x. The compound layer at the surface consists of 2 pm thick monophase range of e - Fe2-3(N,C)i.x, and it is follovved by a tvvo-phase field (e + y) up to 6 p.m thick. In the compound layer grain boundaries are paral-lel vvith the diffusion direction and thus perpendicular to the surface. The diffusion zone belovv the compound layer consisted of the eutectoid constituent braunit (a + Y) from the binary Fe-N1 system and some islands of pearlite and needles of y. The present experiments have confirmed that the use of high nitrogen atmospheres pro-duces no pores in the compound layers developed on steel W.No. 1.0116. 4.2 Reliability survey The reproducibility of the process is shovvn in figure 8, vvhich presents the results of the processing of 23 S ■8 +y' s phase - Fe2_3(N,C)1. f phase - Fe4(N,C)1.x B - braunit - (cc+y) P - perlit Figure 7: Microstructure of the nitrocarburised layer on the outer surface of the shock absorber tubes Slika 7: Mikrostruktura nitrokarburirane plasti na zunanji površini cevi plinskega blažilca fluctuations in the hardness of the core materials, i.e. 150-230 HV1 and used UIC (Ultrasonic Contact Imped-ance) hardness testing method4 can affected the nitrocar-burising results and are not taken into account in the sta-tistical control. Clearly, improved control over the variations experienced in core hardness vvould be ex-pected to reduce the amount of scatter observed in the nitriding results. Fortunately, the quality requirements are already satisfied to sueh an extent that these effects may be disregarded. 5 CONCLUSIONS Figure 8: Reproducibility of the pulse plasma nitrocarburising process on 23 charges Slika 8: Ponovljivost procesa nitrokarburiranja v pulzirajoči plazmi pri 23 saržah Mn,..: 3ZZ.00 I1ax..: 521.DO Range.: 199.00 Xq v : 4BB.B2 SO« t.: 28.95 VB ir;: 1174,79 |) ± lir: 67.5 Z j> ± Za95.1 X C ±31: 95.3 X P ±>3ir: 0.7 Z Cp....: 1.065 CpK: 1.046 p - Nean value - Toleranca -3c ~Zr -lff li »lr *Zc »3a _ — — 1 1 -- — -ff I -- BFl i 1 1 3Z2 346 379 334 41B 442 466 Surface hardness HV1 „ Figure 9: Statistical consideration of surface hardness HV1 data on 23 charges Slika 9: Statistična obdelava podatkov površinske trdote HV1 pri 23 saržah On the basis of the present experiments, it is con-firmed that the atmosphere consisting of 87% N2 + 2% CO2 + 11 % H2 and inereased pulse frequency are re-quired in the glow diseharge to produce a compound layer thickness > 10 |im without pores and vvith a pre-dominantly e phase strueture. From the results is evident that higher nitrogen con-tent in atmosphere, higher temperature and inereased pulse frequency strongly influenced the compound layer grovvth rate vvhich is by the second charge nearly three times higher than in by the charge no. 1 processed in a less suited atmosphere. With a nevv load configuration charge no. 2 and inereased pulse frequency the phenome-non called the hollovv cathode effect, vvhich causes local overheating among the tubes, vvas also avoided. Beside this, it is very important that pulse plasma ni-trocarburisig quickly overcomes its sometimes stili unfa-vourable image and that this modern and progressive technology is recognised as a reliable čase hardening process. What good are ali the remarkable technical, eco-nomical and environmentally clean properties of the process if it cannot be justified in practical use under in-dustrial conditions? The results presented in this vvork prove that sueh a demand can be fulfilled. charges. A typical charge may contain up to 552 tubes vvith a net vveight of around 94 kg. Statistically confirmed quality control data for surface hardness HV1 are shovvn in figure 9. These distributions satisfy customer's ± 3o (standard deviation) quality requirements, that mean 95% of ali pulse plasma nitrocarburised tubes have to meet this specification. Hovvever, it should be pointed out that 6 REFERENCES 'F. K. Naumann and G. Langenscheid: Arch. Eisenhiittenwes., 36 (1965) 677-682 2 J. Slycke, L. Sproge, and J. Agren: Scand. J. Metali., 17 (1988) 122-126 3 J. SIycke and L. Sproge: Surface Engineering, 5 (1989) 2, 125-140 4 Krautkramer: Technical Reference and Operating Manual, 1992, Ident. No. 28894 EUROMAT'98 ENVIRONMENT 22-24JULY LISBON. PORTUGAL, SCOPE »Materials in Oceanic Environment« is one of the conferences in the EUROMAT series vvhich is devoted to one main topic. The Conference vvill be held in Lisbon, from 22 to 24 july 1998, and its scope is related to the behaviour of systems, structures and materials in oceanic environment. Therefore this EUROMAT '98 vvill be an important event and its scope is closely related to the »International Year of Oceans«, both taking plače in 1998 The plače chosen - Lisbon has a very special meaning. An exhibition at this same city vvill be open to the public at this occas.on - EXPO 98 - vvhich theme is »The Oceans, a Heritage for the Future«. In the XV centurv the Portuguese ships - the caravells - left from Lisbon to open to the VVorld the maritime roads to the other Conti-nents and Seas. Understanding and prediction of the behaviour and performance of materials used in systems under marine environment are essential. The Conference vvill mainly discuss development related to ali aspects of safety and risk rel.abil.ty and l.fetime of equipments, pollution reduction and the sea as a source of resources. EUROMAT '98 MAIN THEME: Materials in Oceanic Environment Specific topics: I) Behaviour of systems and their structures. • ships • platforms offshore • pipelines • harbour systems and installations • airplanes • bridges and civil engineering structures Behaviour of materials and protection mechanisms: • corrosion • biodegradation • fatigue, fracture, stress-corrosion • lovv temperatures Materials characterization, testing and selection • metals (ferrous, non-ferrous) • concrete, reinforced concrete • wood, plywood • polymers, composites • rubber • ceramics and glass • adhesives • coatings, paints IV) Influence of manufacturing processes on materials behaviour: • metallurgical processes • povvder technology • vvelding, brasing • forming, machining • heat treatment • surface treatment • gluing V) The oceans as a source of material VI) Recycling and disposal of vvaste materials POSSIBILITIES AND PERSPECTIVES FOR DEVELOPMENT OF METALLURGY IN THE REPUBLIC OF MACEDONIA MOŽNOSTI IN PERSPEKTIVE ZA RAZVOJ METALURGIJE V REPUBLIKI MAKEDONIJI JOVAN K. MICKOVSKI1, N. NACEVSKI1, B. NIKOV2, S. MILOSEVSKI3 'Faculty of Technolo|>y and Metallurgy, University 'St. Cyril and Metodius', R. Boškovic b.b., 91000 Skopje, Macedonia -Department of Science 'Zletovo' - Metallurgical and Chemical Company, Veles 'Administration for International Scientific and Technical Cooperation, Ministry of Science Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 Installed metallurgical capacities in the Republic of Macedonia exceed the local market and a significant share of products is exported. These exports represent a very significant share of foreign currency inflovv. The production of steel is based on scrop import. Ferroalloys industry shows improving performances because of transformation of ownership and restructuring. The increasing of production capacities is expected and especially it is planned to build facilities for exploitation of ali lead in zine concentrates produced in Macedonia. Key words: Macedonia, metallurgical industry, production of steel, ferroalloys, lead, zine, cadmium, silver Instalirane metalurške kapacitete v Republiki Makedoniji presegajo absorbcijo domačega trga in precejšnja količina proizvodov se izvaža. Ta izvoz predstavlja pomemben deleže dotoka deviz. Proizvodnja jekla bazira na uvozu starega železa. Proizvodnja ferolegur kaže naraščujoče dosežke zaradi olastninjenja in restrukturiranja. Pričakuje se povečanje kapacitet, predvsem pa se načrtuje povečanje exploatacije koncentratov svinca in cinka. Ključne besede: Makedonija, metalurška industrija, proizvodnja jekla, ferozlitine, svinec, cinka, kadmij, srebro 1 INTRODUCTION The capacities of ferrous and non ferrous metallurgy are overextended considering the market requirements in the Republic of Macedonia. In accordance vvith the fifty years period of development of the Republic of Macedonia, vvithin the former Yugoslav Federation, and the natural resources, the strategic development of ferrous metallurgy of the Republic of Macedonia vvas projeeted in accordance vvith the capacities in Slovenia and the previously started construction of the Steel Complex in Zenica, Bosnia and Herzegovina (BH). The strategy of the Yugoslav industrial development vvas strongly ori-ented tovvards the West European market and the regions more closer to Europe vvere developed as final exporters for vvestern markets. Other regions should have sup-ported the technological and the industrial development of northern regions through ravv materials, and have pro-vided food and other less finalized products for local markets. The production of steel in Macedonia, the primary processing of steel sheets and the production of ferro-chrome and ferrosilicon, combined vvith Slovenian production should have supplied the Yugoslav market vvith beaded profiles. Profiled steel should have been provided by the Republic of BH vvhile the production of tubes vvas given to the Steel Complex in Sisak, Republic of Croatia. In the former SFRY, the planed roles did not change, not even after the year 1970 and in Macedonia, tvvo large extractive metallurgical capacities, one for ferroalloys (FeNi) and the second for lead and zine, have been built. Processing plants for these ravv materials have not been foreseen in Macedonia. Considering the industrial structure in Macedonia vvith the processing of steel and other metals vvas far be-lovv the installed capacities for steel constructions and seam tubes, as vvell as the disproportion betvveen extrac-tive and processing units in steel industry, the Mace-donian ferrous industry vvas forced tovvards foreign markets. The foreseen supply vvith semi finished products for the Steel Complex Skopje from the Steel Complex in Smederevo has never been accomplished since, and be-side the blast furnaces and the steel plant, rolling mills for profiles almost identical to the assortment of the Steel Complex in Skopje vvere built in Serbia. The steel processing capacities in Macedonia, vvere left vvithout ravv materials, and faced vvith the local market competi-tion. The solution vvas found in the import of semi-fin-ished products, mainly from the former USSR and other foreign markets. 2 FERROUS METALLURGY At present, in the Republic of Macedonia, the follovv-ing metallurgic capacities for production and processing of steel and ferroalloys are in operation: - Electric Steel Processing Plant and Rolling Mili in Skopje "Rudnici i Zelezarnica Skopje" - Chemical Electric-Metallurgical Complex "Jugo-hrom", in Jegunovce (in the vicinity of Tetovo) - Company with mixed ownership for production of ferronickel "Fenimak" in Kavadarci - Factory for welded tubes "11 Oktomvri" in Kuma-novo 2.1 Steel complex 'Skopje' The Steel Complex in Skopje was built in accordance to the silicate ores reserves on the territory of Mace-donia. Due to the lack of cocking coal, and considering the large reserves of lignite in Serbia, electrometallurgy procedure vvith lovv combustion electro reduction furnaces and prereduction in rotation furnaces vvith lignite, vvas selected. For the beneficiation of the charge up to 42% Fe, a peletisation unit for the magnetic iron ore from the Damjan Mine, in the vicinity of Radovis, vvas built vvith magnetic separation, and use of imported fer-rous concentrates. The 5 electroreduction lovv combustion furnaces vvith the installed povver of 195 MW and five 90 m long rotation furnaces, vvere projected to pro-duce about 600.000 t/years of pig iron. Hovvever, due to unsolved technological problems, the production of pig was obtained mainly by reduction of the cold charge in the electric furnaces, vvhich, besides the unfavorable chemical content - high concentration of silicium vvith-out manganese - significantly increased the priče of pig iron. Within a period of 25 years of production, the projected capacity vvas not achieved because of back of re-ducing agents and of electric power. Because of these limiting factors and technological problems in the pre-re-duction process, for vvhich numerous pilot and semi-in-dustrial researches have been carried out, the maximum production ever reached vvas 280.000 t/year'. The processing of pig iron vvith high content of silicon vvas achieved in tvvo LDAC converters, 130 t each. Because of the small individual capacity of the electric furnaces for homogenization of the chemical content and maintenance of temperature tvvo reservoirs for liquid iron vvere provided. Pig iron from the electric furnaces vvith more than 2% Si, vvas processed in the unit for desiliconition in pig iron ladle. The steel obtained from the converters vvas čast in slab ingots up to 1981, later a continuous caster for slabs vvas built. In order to provide the ovvn steel required by the roll-mg mili capacity, an electric are furnace of 100 t vvas build and additional 200.000 t of pig steel provided. In 1988, the capacity of the electric are furnace vvas increased to 350.000 t/year, vvhile in the second phase, by melting of serap iron steel production vvas planned to reach 500.000 t/year. Hovvever, due to technological problems in the computerized electric are furnace and difficulties in the supply of appropriate and sorted serap iron, the nevv furnace did reach only a yearly production of 250.000 t/year steel. The basic product are lovv carbon and carbon manganese structural as vvell as ship plates and boiler plates. 558 Later also the production of microalloyed steels vvith niobium, vanadium, titan and zirconium vvas developed. The converters vvere also suitable for the production of deep dravving steels. The Steel Complex 'Skopje' includes the follovving three rolling mills: - Hot rolling mili for 3.000 mm heavy plates vvith the capacity of 500.000 t/year, on a reversible four-high rolling stand, vvith a vertical duo-stand on line - Hot rolling mili for 1.600 mm rolled strips vvith the capacity of 850.000 t/year, vvith a four-high rolling pre-stand and a final six stands train vvith four-high rolling stands; and - Rolling mili for cold rolled strips vvith tvvo lines: (a) a five stands train vvith the capacity of 500.000 t/year and (b) a four-high reversible stand of 300.000 t/year. The cold rolling mili includes also a department zine coating vvith the capacity of 100.000 t/year as vvell as a line for plastification of plates vvith the capacity of 25.000 t/year. The rolling mili capacities vvere built for about 2.000.000 t/year of final products, vvhile the maximal production obtained by the Steel Complex 'Skopje' vvas 1.250.000 t/year because of the lack of steel of ovvn production. Considering the discrepancies in the primary metallurgical and processing production the Steel Com-plex vvas forced to import semi products or to undertake loan arrangements. The Macedonian market could absorb maximally 100.000 t/year cold roll and plates, vvhile the possibilities for absorption of hot mili strips are greater since the Fac-tory for vvelded tubes vvith the capacity of about 600.000 t/year is located at a distance of about 35 km from the Steel Complex. The Steel Complex disposed of the ma-jority of production on the markets of the former Yugo-slav republics and to export markets. After 1991 a significant decrease in production oc-curred due to the economic and political erisis in the former USSR, the main foreign partner and in the former SFRY. Consequently, in the follovving 4 years the production of the Steel Complex vvas significantly decreased and than even discontinued. The cost of production of pig iron in electroreduction lovv combustion furnaces and steel in converters vvas too high and in 1988 it vvas stopped. Also the costs analyses of steel production from local ores led to its stopping. Lately tvvo electric reduction furnaces vvere restruetured and the production of ferroman-ganese and siliconmanganese vvas started on the base on imported ravv materials. The actual production amounts to 36.000 t/year of ferromanganese and 44.000 t/year siliconmanganese. Other units vvere preserved and the converter unit vvas dismantled. 2.2 Production of 'Jugohrom' Jegunovce The enterprise 'Jugohrom' is the producer of mass ferroalloys as FeSi, FeCr, silicon metal and silicon-chrome primarily for the requirements of the ferrous metallurgy and casting industry of the former SFRY. The products are lately totally exported. The capacity of 'Jugohrom' vvas rebuilt for a modern production of ferroalloys, vvith melting aggregates vvith medium and large installed povver; permanently moder-nized in terms of technique and technology, providing: - Increased production compared to the originally pro-jected; - Alternative production and quick adjustment to the market conditions, necessary for a competitive mar-ket oriented production; - Improvement of operating conditions; - Environment protection etc. The production of ferroalloys in 'Jugohrom' in ac-cordance vvith its assortment can be performed in nine electric furnaces vvith the total installed capacity of 140.2 MVA, in accordance vvith the schedule presented in Table 1. The intensive development of processes of ladle processing for acquiring ferroalloys vvith improved physical-mechanical properties, as vvell as technological and exploitation characteristics required the application of a broad scale of complex alloys - modifficators for čast iron. Based on these trends of development in met-allurgy, in the current phase of modernization, 'Jugohrom' has developed the technology for production of complex alloys-modificators based on ferrosilicon used as inoculant and nodulators. The production of these alloys is based on FeSi, vvith addition of Mn, Ba, Ca, Al, Mg, Ce, MM, and C. By ap-plying the direct procedure, a further alloy-up of melted FeSi or its alloys into a melting pot vvith spilling, sinking and mixing homogenous complex alloys - modificators of a broad assortment like FeSi, FeSiAl, FeSiMn, FeSiBa, FeSiBaMn, FeSiMgCeMM and composite mix-tures FeSiC and FeSiBaC are obtained. The production capacity and assortment depend of the demand on local as vvell as on export markets. The metallurgical production in 'Jugohrom' vvas con-ditioned by the development of nevv technologies of steel production and casting of gray and nodular iron, primar-ily by the ladle processing by modification, alloying and microalloying, providing a high yield of metal and ferro alloys. From this point of vievv, the long-standing experi-ence of 'Jugohrom' vvill be directed in future tovvards: - quality improvement of the present assortment of ferroalloys and modificators; - production of special, fine ferroalloys, especially of fine FeSi, by application of nevv technologies; - extension of the production of complex alloys -modificators vvith nevv more efficient types and assortment of inoculators and nodulators; - introduction of quality FeSi vvith lovv content of Si: FeSi 15 (14-16 Si) for production of resolvable an-odes for cathodic protection, FeSi 15 povvder for separation of ore minerais in heavy liquids; - development of auxiliary devices for casting indus-try and metallurgy; Development of dust collecting and utilization of vvaste gases heat and its conversion into electric povver, ali contributing to the environment protection and improvement of the overall operation of the enterprise. 2.3 Production of ferronickel The Ferronickel producer 'Feninmak' in Kavadarci is organized as a share holding company and exploits local ravv materials of laterite type. The technological process includes are beneficiation and preparation for metallurgical processing based on differences in density and magnetic properties of minerais in the ore and the distribution of the nickel. The process is performed in the plant for ore pulverizing, pneu-matic, dry and vvet magnetic separation, as vvell as for Table 1: Characteristics of the melting units in 'Jugohrom' Furnace TVpe of the furnace Install. capacity MVA Type of electrodes Production of ferroalloys Basic Alternative Type Production technical capacities t/year I Electric-arc reduction 6.5 A Si-metal 3.400 FeSi45/75/90 11 " 10.0 A " 4.000 " III " 6.5 A 3.00 FeSi45/75/90 SiCr IV " 16.0 A " 5.200 FeSi45/75/90 Cr V Electric-arc rafin. 3.5 G LC FeCr 4.500 " VI Electric-arc slake 4.4 So FeSi 75 13.300 FeSi 45/CaC2 VII Electric-arc reduction 21.3 So FeSi 75 13.300 FeSi 45/CaC2 VIII „ 48.0 So 34.000 FeSi 45 IX " 24.0 So " 14.000 FeSi 45HCFeCr Total 9 140.2 77.300 pelletisation of nickel concentrate. It has been foreseen that the magnetic fraction in the ore should be about 30%, representing the ferrous concentrate, vvith a Iower content of nickel and the difference with higher nickel content. Besides preparation and pelletisation, the technologi-cal process includes roasting of the pellets, their pre-re-duction in rotation furnaces by addition of lignite and melting of the pre-reduced material into 16% FeNi, vvhich is further refined up to 45% FeNi into oxidind converters. Two pyrometallurgical lines with separate ro-tating and rectangular electric furnaces with six Sode-berg electrodes set in line are in operation. The projected total capacity of the plant vvas 21.000 t/year nickel in FeNi by average ore content of 1.03% Ni. So far only one technological line vvas used:. Changes in mining technology and unprecise previ-ous geological investigations lead to a very small magnetic fraction vvith higher percentage of nickel during ex-ploitation and affected the production costs. Consequently, magnetic concentration is being avoided and the overall ore supply is ground and pelletized. Nickel is a stock exchange product vvhich priče in the last 10 years changed significantly. In 1984 and 1985 it vvas very lovv and the production of FeNi vvas interrupted only one and a half year follovving the start of production. As a result of changes in nickel prices on vvorld market and after investments of several companies the production of one technological line re-started at the end of 1991. During recent years the production increased permanently, hovvever the projected values, vvill not be obtained due to the decrease average content of nickel in the ore. Table 2 indicates the trend of production in the restart period. Table 2: Production of Ni as FeNi in 'Fenimak' Year 1992 1993 1994 1995 Produced in t 4.220 4.493 3.981 4.960 Due to the second decrease of the nickel priče in the period of 1993 to 1995, the society in the period of 1993/94 operated vvith loss and profit vvas obtained later because of the light increase of nickel priče. If the present trend of increase of nickel priče vvill continue, the production could increase to 5.500 t/year vvith only one technological line and be profitable. Follovving the re-start, rigorous economic measures have been undertaken related vvith the restructuring of the production, to the decrease of the number of employees, to the improvement of the technology vvithin given conditions related to the supply of ravv materials and direct marketing. Fenimak' is forced to import lignite from SR Yugoslavia. The enterprise undertakes serious and de-tailed investigations of the mineralogy of the mine de-posit, as well as for possible alternatives for economic beneficiation of the nickel ore. The production could increase only if the nickel content in the charge of furnaces is increased. This can be obtained through the supply of rich ravv materials and requires additional vvorking capi-tal. Domestic investments are almost impossible because of the present economic situation, since Macedonia is exhausted by the political and economic changes im-posed by the disintegration process and the vvar on the territory of the former SFRY as vvell as the economic and transport blockades of some neighbours of the Republic of Macedonia. Nevv investments in the present production of Fenimak' and its increase vvith the re-start of the second technological line vvill be vvelcome and of benefit for the investors since the enterprise employs qualified managerial staff and disposes of modern technological devices vvith capacity non exploited. Ferro-nickel is sold on foreign markets and only a very small quantity vvas sold on the local market, because of the crisis in steel metallurgy during the last years. 3 CAPACITIES OF NONFERROUS METALLURGY IN MACEDONIA Moderate quantities of nonferrous metals are pro-duced in the MHK 'Zletovo'. Smelter 'Zletovo' is using Imperial smelting process for exstraction of zine, lead, cadmium and silver. 3.1 Lead and zine Lead and zine ores have been exploited for centuries in the Kratovo-Zletovo ore deposit. Traces such as tools, slag, pots etc. indicate that lead has been smelted in the region during the Roman period. 'Zletovo' Metallurgical and Chemical Company in Titov Veles is the only producer of lead and zine in the Republic of Macedonia. It is based mainly on the ore de-posits and capacities of the three surrounding lead and zine mineš: Zletovo, Saša and Toranica. The Imperial Smelting process route vvas the most convenient for treating lead and zine concentrates simul-taneously. Moreover, it offered an opportunity to pro-duce bulk concentrates, thus increasing the overall metal recovery. Therefore, an agreement vvas signed, the site preparation began, and the first quantities of slab zine and lead bullion vvere produced in November 1972. 'Zletovo' Smelter vvas designed for a maximum production of 65,000 tpa of slab zine and 35,000 tpa of lead bullion. Figure 1 shovvs the annual production rates m the period from 1973 to 1995. Numerous prerequisites are required to reach the designed capacity of the ISF. The break of the continuous grovvth of metal production from 1986 to 1991 vvas due to series of problems arising from the disintegration of former Yugoslavia, in-ternational sanetions against the Federal Republic of Yu-goslavia, and Greek embargo against the Republic of Macedonia. These events created enormous difficulties in transporting both ravv materials and products and led to higher production costs. Production rate[1000 tpa] 60 50 40 30 20 10 1973 1978 1983 Vear 1988 1993 Figure 1: Annual production of slab zine, lead bullion and secondary lead from plant start-up to 1995 Slika 1: Letna proizvodnja slabov cinka, primarnega in sekundarnega cinka od zagona podjetja do 1995. Most of the refined lead produced at 'Zletovo' smelter is consumed within the country, mainly in the lead bat-teries plant having a capacity of 24000 tpa. Hovvever, due to the same reasons as above, especially the disinte-gration of SFR Yugoslavia, the market the battery plant was designed for, the production rate has been reduced dovvn to 30%. Lead and zine production rates are inereased since the Dayton and New York agreements vvere signed last year, but a period of several years is necessary for a fuli recovery. 3.2 Cadmium Most of the cadmium fed onto the sinter machine is eliminated during the sintering process. The degree of elimination depends mainly on sulfur and cadmium con-tents of the ravv mix, but the usual level is as high as 65 to 80%. With the construction of the cadmium plant based on the Ion Exchange Process the recovery of cad- New cadmium input 300 Cd plant residue 361 JL Sinter plant Dross and blue powder 71 HGP dust 571 Sinter 143 IS - Furnace Cadmium plant 228 Slab zine 72 Caustic Cadmium 210 Zn Refinery mium is accomplished vvith high efficiency (over 92% as shovvn in figure 2). Cadmium is leached from the hot gas dust precipita-tor by means of vveak sulfuric acid. Depending on the chemical compounds in vvhich cadmium is present in the dust, leaching efficiencies from 30 to 60% are obtained. The resulting leach liquor is countercurrently vvashed in a system of three decanters, filtered through a pair of sand ftlters and subjeeted to ion exchange on IR 120 cat-ion exchange resin. Stripping is performed by means of 10% brine solution. Cadmium sponge produced by ce-mentation on zine rods in suitable trammel tanks is melted in a caustic furnace and combined vvith the zine refinery to a cadmium alloy for further refining. Despite the high stage efficiencies, the magnitude of losses is high and disturbing. As shovvn in figure 2, cadmium recirculating load is very high relative to the nevv input and this feature must contribute considerably to the losses. Cadmium production rate in a zine and lead smelter depends primarily on the quantities of nevv cadmium fed vvith the ravv materials. Since significant quantities of zine concentrates have been purchased from various pro-ducers around the vvorld, it is obvious that the Zn/Cd ra-tio is rather a varying parameter. Hovvever, there are tvvo objeetives that a zine smelter must achieve: - High cadmium elimination to provide good zine quality - High cadmium recovery to avoid environmental problems The annual production of cadmium from the 'Zletovo' Smelter from its start up to 1994 is shovvn in figure 3. 3.3 Silver Unlike cadmium, most of the silver fed vvith concentrates reports in the lead bullion. Desilvering of the later is performed by adding metallic zine and removing the resulting solid intermetallic compounds (mainly Ag2Zns) together vvith a substantial amount of mechanically en-trained lead as a silver erust. Further treatment of the erust includes evaporating of zine, oxidizing of lead and electrolytic refining of silver. Production rate [tpa] Figure 2: Overall cadmium balance Slika 2: Celovita bilanca kadmija. Figure 3: Annual cadmium production from plant start-up to 1995 Slika 3: Letna proizvodnja kadmijev od zagona podjetja do leta 1995. Production rate [tpaj Year Figure 4: Annual silver production from plant start-up to 1995 Slika 4: Letna proizvodnja srebra od zagona podjetja do 1995. The electrolytic silver refinery vvas introduced in 1982. Its total capacity amounts 30 tpa electrolytic silver, but the highest production achieved so far vvas 24.35 t in 1986. 4 CONCLUSIONS - The installed metallurgical capacities of iron, its al-loys and nonferrous metals in the Republic of Mace-donia encompasses the requirements of the local market and is directed tovvards the foreign market; - The participation of steel, ferro alloys and nonferrous metals alloys in the nationai foreign currency inflovv is very significant; - due to the discrepancies betvveen the primary steel production and the installed melting capacities, as vvell as the limited possibilities for supply of ravv materials, the metallurgy in Macedonia is forced to import steel in a slabs and serap; - considering the 30 years of experience in the steel industry and in the production of ferro alloys, follovving the carried out transformation of ovvnership and completion of the restrueturing processes, more profitable operating and its further development may be expected; - increasing the production capacities regarding various metals could also be expected, but it is intended to provide facilities for treating ali the lead and zine concentrates produced in the Republic of Macedonia. With respect to this, installing a nevv lead smelter plant has been considered. 5 REFERENCES ' Program of the restrueturing for Iron and steel work 'Skopje' during the period 1991-1995, vvith vision to 2000, Iron and steel work 'Skopje', Department for development, Skopje, 1990 2 Analysis of production posibilities, markets condition and financial effects of project FEN1- Kavadarci. RTB Bor, Institut za bakar. Bor, 1983 INVESTIGATION OF KINETICS LEACHING AND EXTRACTION OF VANADIUMPENTOXYDE AS A FUNCTION OF TEMPERATURE RAZISKAVE KINETIKE LUŽENJA IN EKSTRAKCIJE VANADIJEVEGA PENTOKSIDA V ODVISNOSTI OD TEMPERATURE NIKOLA NACEVSKI1, B. NIKOV2 'Faculty of TechnoIogy and metallurgy, Skopje, Macedonia 2Smelter Zletovo, Veles, Macedonia Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 In several thermal povver plants in operation in the Republic of Macedonia a substantial quantity of ash is produced by oil burning. Ashes are considered as highly hazardous for the environment due to their fine particle size. On the other hand, analyses carried out so far, indicate appreciable contents of vanadium, gallium, beryllium etc. in the ashes. Key words: oil ashes. V2O5, leaching, effect of temperature and solution composition, activation energy of leaching V Makedoniji obratuje več termoelektrarn, kjer pri zgorevanju olj nastaja pepel, ki je nevaren za okolje zaradi drobnozrnatosti. Po drugi strani pepel vsebuje pomembne količine vanadija, galija, berilija itd. Ključne besede: oljni pepel, V2O5, luženje, vpliv temperature in sestave raztopin, aktivacijska energija luženja 1 INTRODUCTION Investigations presented in this paper are aimed to ex-amine the possibility of hydrometallurgical treatment of ashes, produced with burning of fuel in povver and met-allurgical plants. The topics of the present investigations are the recovery of vanadiumpentoxyde as value compo-nent and the utilization of dust vvhich is an ecological problem. The investigations of the hydrometallurgical treatment of ashes vvere aimed to determine the vvorking conditions and process lavvs of leaching of vanadiumpen-toxyde in solution. The purification of V2O5 solution and its concentration of V205 is obtained vvith liquid-liquid extraction with D2EHPA (DI - 2 etil heksil phosphoric acid). The effects of temperature (298 - 373 K), phase ratio (S/L : 1/50 - 1/5), concentration of H2SO4 in solution (0,5 ; 1 ; 1,5) mol/dm3, vvere investigated by constant particle size (-0,074 mm 100 %), velocity of mixing 8000 rev./min and leaching time 3 hours. Experimental results shovving the influence of temperature, concentration of H2SO4 and phase ratio on V205 leaching are shovved on figures 2, 3, 4. 2 RESULTS AND DISCUSSION The kinetics shovvs that by the maximal investigated temperature of T = 373 K and the follovving conditions S/L 1/50, H2SO4 1 mol/dm3 in the first 30 min of leaching 67,4% V205 is dissolved. Prolonging the leaching time is vvithout significant influence on volume of V2O5 in solution. Changes of concentration of H2SO4 (0,5 - 1,5 mol/dm3), of phase ratio (1/50 - 1/5) affect by constant temperature (343 K) also in the first period the V205 leaching efficiency. A leaching activation energy Ea = 24,8 kJ/mole vvas determined through Arhenius analysis of the kinetics curves in figure 2. Figure 1: Apparatus for leaching Slika 1: Naprava za izluževanje Figure 2: Kinetics of V2O5 leaching for different temperatures Slika 2: Kinetika izluževanja V2O5 za različne temperature • 373 K • 3(3 K x30K • 3?i K O 313 k »2MK Figure 3: Kinetics of V2Os leaching for different concentrations of H2S04 Slika 3: Kinetika izluževanja V205 za različne koncentracije H2S04 Figure 7: Effect of concentration D2EHPA on coefficient of distribution D(V205) (Cjniliai = 0,4 mol/dm3) Slika 7: Vpliv koncentracije D2EHPA na razdelitveni koeficient D(V205) (Cza&lna = 0.4 mol/dm3) 0,1 M D2EHPA -O-0.2M 02EHPA —*— 0.4M 02 E HPA —0.6M 02EHPA X -1«5 A -1:10 O O -1:30 log cD2 EHPA Figure 8: Log-log dependence of D(V205) and (D2EHPA) for different concentrations of HC1 (Cjniuai = 0,2 mol/dm3) Slika 8: Log-log odvisnost med D(V205) and (D2EHPA) za različne koncentracije HC1 (Czačetna = 0.2 mol/dm3) log CD2 EHPA Figure 4: Kinetics of V2Os leaching for different phase ratios Slika 4: Kinetika izluževanja V1O5 za različna razmerja faz -s ----— vo }00 VO V0 V0 A/T » 103 Figure 5: Graph of variables in Arhenius presentation Slika S: Odvisnosti v Arhenius predstavitvi Figure 6: Effect of concentration D2EHPA on coefficient of distribution D(V205) (Cinitiai = 0,2 mol/dm3) Slika 6: Vpliv koncentracije D2EHPA na razdelitveni koeficient D(V205) (Czagetna = 0.2 mol/dm3) Figure 9: Log-log dependence of D(V205) and (D2EHPA) for different concentrations of HCl (Cj„jtjai = 0,4 mol/dm3) Slika 9: Log-log odvisnost med D(V2Os) in (D2EHPA) za različne koncentracije HCl (C2ačema = 0.4 mol/dm3) The experimental investigation of liquid-liquid ex-traction using D2EHPA was carried out vvith initial con-centrations of V2O5 of 0,2 mol/dm3 and of 0,4 mol/dm3. In the tests sulfate solutions vvere used and the liquid-Iiq-uid extraction investigated as function of the follovving parameters: a) pH of solution: 1 ; 2 ; 4 ; 6 ; 8 ; 10 mol/dm3 b) Concentration of D2EHPA: 0,1 ; 0,2 ; 0,4 ; 0,6 mol/dm3 3 RESULTS AND DISCUSSION The experimental results shovving the coefficient of distribution DCV2O5) and the level of extraction ECV2O5) as a function of parameters a) and b) are given in table 1 and 2 and figure 6 and 7. The analyses of the experimental data shovv by determined changes of the coefficient of distribution and level of extraction V2O5 as a function of pH an intial period of decreasing grade of extraction vvhile by increasing of pH, the extraction efficiency of V205 is increased. In logarithmic presentation the functions are straight lines vvhich slopes represent the solvent coefficients. In figure 8 and figure 9 the line slope have a tangents value of 2. It is concluded that vanadium vvill be recov-ered vvith a phase ratio CD2EHPA/LPhase = 2. With increasing the pH solutions until 10 mol HC1 the slope is tangent decreased to 1, 2 and in this čase extraction vvill be real-ized vvith a ratio phase D2EHPA/LphaSe =1:1. 4 REFERENCES 'A. N. Zelikman, T. M. Voldman, A. B. Beloevsija: Teorija gidrometalurgicheskih procesov Moskva, Metalurgija, 1983 2 Processing of petroleum coke for recovery vanadium, Hazen Research Inc. 4601 Indiana str. Golden C.O. 80403, USA, 1986 3O. B. Michesen: Recovery of vanadium from dust in the aluminum industry, Institute for energy technology P.O. 40 Norway, 1987 "N. Nacevski, F. Popovska, B. Nikov: Extraction of indium from sul-phate solutions vvith D2EHPA solutions; Journal de Physique III, 5, (1995) nov. THE DIFFERENCE BETWEEN THE MAGNETO-CRYSTALLINE ANISOTROPY OF THE INTERMETALLIC ALLOY Pr2(Coo.5Feo.5)l7 AND INTERSTITIALLY MODIFIED Pr2(Coo.5Feo.5)l7N3-5 RAZLIKA MED MAGNETNO KRISTALNO ANIZOTROPIJO Pr2(Coo.5Feo.5)l7 IN Pr2(Coo.5Feo.5)l7N3-5 MATEJ KOMELJ, S. KOBE Institut Jožef Štefan Jamova 39, 1000 Ljubljana, Slovenija Prejem rokopisa - received: 1997-10-0!; sprejem za objavo - accepted for publication: 1997-10-21 The al!oy vvith the composition PrjfCoo.sFeo.-On has an easy-axis magneto-crystaIline anisotropy. The anisotropy is changed to the easy-plane by introducing nitrogen on interstitial sites. We proved the difference betvveen the anisotropy of the basic alloy and the nitrided composition directly by the magnetic measurements and by observing the domain structure by means of optical and magnetic force microscopy. The transition from one to another type of anisotropy can be explained by a simple model based on crystal structure and shape of the electronic cloud of the Pr ion. Key vvords: permanent magnet materials, magneto crstalline anisotropy, nitriding Intermetalna zlitina Pr2(Coo.5Feo.5)i7 ima osno magneto-kristalno anizotropijo. Z uvajanjem dušika na intersticijska mesta anizotropija preide v ravninsko. Razliko med tipoma anizotropij med obema spojinama dokažemo neposredno z magnetnimi meritvami in opazovanjem domenske strukture z mikroskopom na magnetno silo (MFM). Prehod iz ene anizotropije v drugo kot posledico spremenjene sestave lahko razložimo s preprostim modelom, ki temelji na kristalni strukturi in obliki elektronskega oblaka iona Pr. Ključne besede: trajno-magnetni materiali, magneto-kristalna anizotropija, nitriranje 1 INTRODUCTION It is vvell knovvn that R2Tn, vvhere R stands for a rare earth and T for a transition metal, intermetallics exhibit interesting magnetic properties and represent important permanent magnet material1. To obtain high coercivity of the magnet it is necessary that the material has an easy-axis magneto-crysta!line anisotropy and that the value of the coefficient Ki, vvhich is a measure for the energy of the magneto-crystalline anisotropy, is as high as possible2. The magneto-crystalline anisotropy of the basic compound can be influenced by introducing nitrogen on interstitial sites in the crystal lattice3. The Pr2(Coo.5Feo.5)n compound crystallizes in the rhombohe-dral Tf^Znn type structure and it has easy-axis magneto-crystalline anisotropy4-5. But the anisotropy is too vveak and the magnet based on this material does not exhibit desired properties. In our vvork vve studied the influence of nitrogen in the Pr2(Coa5Feo.5)i7 alloy. In Sm2Fei7 inter-metallic alloy the magnetic properties vvere successfully improved by introducing nitrogen to the interstitial sites of the crystal lattice6. 2 EXPERIMENTAL The samples vvere prepared from 99.9% pure ele- ments by are melting. Excess of Pr vvas added to a nomi- nal composition to offset Pr evaporation losses during melting. After the fourth melting the samples vvere vvrapped in a Ta foil and encapsulated after evacuation in quartz tubes and then annealed at 1000°C for 24 hours. Before and after the heat treatment their phase purity vvas determined by JEOL JXA 840 SEM/EPMA electron probe microanalysis. Nitriding, as a gas-solid reaction, vvas performed at 450°C for 10 hours in a high purity N2 1 bar gas atmosphere. The nitriding temperature vvas pre-viously determined by using DTA/TGA facilities (Netzch). The parent alloy and the nitrided povvder vvere characterized by XRD. The magnetization measurements on the povvdered and aligned samples vvere provided by the magnetometer-susceptometer (Manics) based on the Faraday principle. Magnetic domains vvere examined by magnetic force microscopy (MFM) using a Dimension 3000 scanning probe microscope (Digital Instruments, Inc.), vvhich allovvs separate atomic force and magnetic force images to be collected in the course of one scan. Surface topography vvas obtained using Tapping Mode7 AFM. High resolution MFM image vvas obtained by using Lift Mode softvvare7 and the ultra-soft Fe-Si02 tip. Images of the domain patterns vvere previously taken by Kerr microscopy using a Nikkon Optiphot XP-2 polariz-ing light microscope vvith a 150W Xe lamp. 3 RESULTS OF THE MEASUREMENTS The magnetization versus applied field curves of the Pr2(Coo.5Feo.5)i7 bonded povvder measured parallel and perpendicular to the direction of the alignment are shovvn in Figure 1. From these curves it is evident that the an-isotropy field is greater then 30 kA/cm vvhich implies the existence of vveak easy-axis magneto-crystalline anisot-ropy. The domain pattern of this alloy, observed by optical microscope in a polarized light using the magneto-optic Kerr effect is shovvn in Figure 2. A star shaped or "labyrinth" pattern in the grains cut perpendicular to the c-axis and a banded or "strip" structure vvithin the grains cut parallel to the c-axis are present. Such domain structure applies for materials vvith easy-axis type of mag-neto-crystalline anisotropy vvhere the crystallographic c-axis deftnes the easy direction8. Figure 3 shovvs the same area observed by the magnetic force microscope (MFM) vvhich appears to be in a good agreement vvith Kerr mi-croscopy. Both magnetization curves of the nitrided povvder, measured parallel and perpendicular to the direction of the alignment are essentially the same (Figure 4) that means that the nitrided material does not have an easy-axis magneto-crystalline anisotropy. This fact vvas confirmed also by observation of the domain structure. Figure 5 shovvs the Kerr image of a large (-100 pm) particle. Because of the slovv nitrogen bulk diffusion9 just a layer of vvidth -5 pm vvas nitrogenated. The core area represents the basic P^CoosFeos)]? material. The shell resolution is lovv, and no magnetic structure vvas observed in the nitrided layer. Only strip domains vvere found in the core region. On Figure 6 is shovvn a MFM detail image of the core-shell border area of the same particle vvith a sharp demarcation betvveen the strip domain pattern in the core area and the labyrinth domain structure in the nitrided shell vvith the star domain vvidth of -1-1.2 pm vvhich is significant for easy-plane mag-neto-crystalline anisotropy10. Figure 2: The domain pattern of the alloy Pr2(Coo.5Feo.s)i7 observed by optical microscope in a polarized light using magneto-optic Kerr effect. Star shaped or "labyrinth" pattern in grains cut perpendicular to the c-axis and a banded or "strip" structure vvithin grains cut parallel to the c-axis are present Slika 2: Domenska struktura zlitine Pr2(Coo.5Feo.5)i7, opazovana z optičnim mikroskopom v polarizirani svetlobi s pomočjo Kerrovega efekta. V zrnih, odrezanih pravokotno glede na os c, vidimo labirintno strukturo domen zvezdaste oblike. V zrnih, ki so odrezana vzporedno z osjo c pa so črtaste domene v obliki pasov 4 THEORETICAL Undesired transition from the easy-axis to the plane magneto-crystalline anisotropy due to the introduced nitrogen in the čase of Pr2(Co0.5Fe0.5)i7 contrary to the čase of SmiFei?6 can be explained in the frame of the simplified crystal field theory". We assume that the energy of the magneto-crystalline anisotropy is given by the elec-trostatic interaction betvveen the 4f charge distribution of the rare earth atom and the non-4f charges present in the Figure 3: MFM image of the same area as in Figure 2 Slika 3: MFM posnetek istega območja kot na sliki 2 Figure 1: Magnetization versus applied field of the P^tCoo.sFeo.s)^ bonded povvder measured parallel (upper curve) and perpendicular (lovver curve) to the direction of the aligment. The anisotropy field is greater then 30 kA/cm Slika 1: Magnetizacija prašnega vzorca P^CoasFeosJn v odvisnosti od zunanjega magnetnega polja merjena vzporedno (zgornja krivulja), in pravokotno (spodnja krivulja), glede na smer predhodne namagnetenosti prahu 25um Figure 4: Magnelization curves of nitrided powder measured parallel, and perpendicular, to the direction of the alignment are the same Slika 4: Krivulja magnetizacije nitriranega prahu, merjena pravokotno in vzporedno glede na smer predhodne namagnetenosti prahu Iattice. The change of the coefficient Ki upon the inter-stitial modification in the first approximation depends: • on the angle 6 between the directions of the nitrogen atom and the magnetization relative to the position of the rare earth atom: Figure 7 • and to the quadrapole contribution n2 to the 4f charge density. One can schematically conclude that rare earth atoms with n2<0 (Pr, Nd, Dy etc.) have the oblate shape of the 4f electron cloud while in the čase of Sm with n2>0 it can be described as a prolate. To estimate vvhether the Ki is increased or decreased after the nitriding there is a simple rule": sgn(AK,) = sgn(n2) sgn(9) Figure 5: Kerr image of a large (-100 pm) particle. Just a layer of width -5 pm vvas nitrogenated. The core area represents the basic Pr2(Co().5Feo.5)i7 alloy Slika 5: Posnetek velikega (-100 pm) delca s pomočjo Kerrovega efekta. Nitrirana je samo zunanja plast debeline -5 pm. Jedro predstavlja osnovna zlitina Pr2(Coo.5Feo.s)i7 Figure 6: MFM detail image of the core-shell border of the same particle as in Figure 5. A sharp demarcation betvveen the strip domain pattern in the corearea and the labyrinth domain structure in the nitrided shell is shovvn Slika 6: MFM detajlni posnetek meje med nitriranim in nenitriranim območjem delca iz slike 5. Ostro se vidi razlika med črtastimi domenami v nenitriranem območju ter zvezdastimi domenami iz nitrirane plasti where sgn(0 = 0°) = -1 and sgn(6 = 90°) = 1. It im-plies that in the čase of Pr (n2<0) we have to look for interstitial sites with the axial coordination (0 = 0°) vvhich is not the čase for the site 9e in Th2Zn17 type of crystal structure. It has in-plane interstitial coordination (6 = 90°) vvhich is favorable for the Sm (n2>0) based materials. earth Figure 7: Angle 6 betvveen the directions of the nitrogen atom and the magnetization relative to the position of rare earth atom Slika 7: Kot 6 med zveznico atoma dušika ter atoma redke zemlje in smerjo magnetizacije 5 CONCLUSION It was shown that besides the magneto-optic Kerr effect MFM can be used as an important technique for rapid and simple characterization of the magnetic structure of nevv magnetic materials. When the magnetic structure is too fine for optical microscopy, MFM can serve as a very convenient method in observing and char-acterizing the magnetic structure of different and un-knovvn magnetic materials. After the successful intersti-tial modification of the Sm2Fen 36 and some other intermetallics3 it was hoped that the same procedure could be applied also to the Pr2(Coo.5Feo.5)n alloy. In-stead of the increasing of magneto-crystalline anisotropy even a transition from the easy-axis to the undesired easy-plane type was observed. Therefore the nitrided al-loy Pr2(Co0.5Fe0.5)i7 can not be used as a permanent magnet material. Nevertheless it has very interesting properties from which we can learn much on domain structure and the effects of nitriding. Finally the experimental re- sults obtained on the investigated alloy agree with the predictions of a model based on a crystal field theory". 6 REFERENCES 'K. H. J. Buschow: Ferromagnetic Materials, Vol. 2, ed. E. P. Wohlfarth (North-Holland Publishing Co„ Amsterdam, 1980) p. 297 2 A. H. Morrish: The Physical Principles of Magnetism, (John Wiley & Sons, Inc., Nevv York, 1965) 3 K. H. J. Buschovv, G. J. Long and F. Grandjean: Interstital Intermetal-lic Alloys (Kluvver Academic Publishers, Dordrecht, 1995) 4 M. Jurczyk, Phys. Stat. Sol., (a) 80 (1989) 657-662 5 H. Y. Chen, B. M. Ma, S. G. Sankar and W. E. Wallace, Journal de Physique, Colloque C8, Suppl. no 12, 49 (1988) C8, 507-508 6 B. Saje, B. Reinsch, S. Kobe. D. Kolar, I. R. Harris: Nitrogenation of Ta Modified Sm2Fei7 AlIoy, Metals, Alloys, Technologies, 30 (1966) 307-309 7 Trademark of Digital Instruments, Santa Barbara, CA SU. Schafer, G. Schneider, G. Petzovv, Pract. Met., 26 (1989) 59-67 'T. Mukai, T. Fujimoto, JMMM, 103 (1992) 165-173 10 B. Grieb, H. H. Stadelmaier and E.-Th. Henig, Materials letters, 8 (1989) 396-399 11 R. V. Skomski, Interstitial Nitrogen, Carbon and Hydrogen: Modification of Magnetic Properties, Interstitial Intermetallic Alloys, Kluvver Academic Publishers. Dordrecht. 1995 MODEL POLYMERS WITH DIMETHYLAMINE AND SULFOZWITTERIONIC END-GROUPS. SYNTHESIS AND SELF ASSEMBLY IN SOLUTION AND IN BULK MODELNI POLIMERI Z DIMETILAMINSKIMI IN SULFOZWITTERIONSKIMI KONČNIMI SKUPINAMI NIKOS HADJICHRISTIDIS, S. PISPAS, M. PITSIKALIS University of Athens, Department of Chemistry, Panepistimiopolis Zografou, 15771 Athens, Greece Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-10-21 The dilute solution and bulk properties of a variety of vvell-defined polymers of different architectures (linear homopolymers, diblock and triblock copolymers and star homopolymers) having dimethylamine and sulfobetaine end groups mainly synthesized in our laboratory are reviewed. The end functionalized polymers were synthesized by means of anionie polymerization high vacuum techniques, using 3-dimethylaminopropyl-lithium as initiator for the introduction of the dimethylamine group at the chain end. This group was converted to sulfozwitterionic by reaction with cyclopropanesultone. Extensive molecular characterization proved the high homogeneity of these model materials. Their aggregation properties in dilute solutions, of solvents of different polarity and selectivity tovvards different parts of the molecules, vvere studied by viscometry, static and dynamic light scattering. The co-functionalized polystyrenes and the block copolymers of styrene have a much lovver degree of association, than the homopolydienes, probably due to the polarizability of the phenyl group. The bulk properties of end-functionalized homopolymers and diblocks vvere studied by SAXS, reology and dielectric spectroscopy revealing nevv features of self organization at this lovv ionic content and extraodinary phase behavior at high temperatures. The adsorption behavior of stars vvith different number of functionalized arms in dilute solutions vvas also investigated by ellipsometry shovving different behavior compared to linear polymers. Key vvords: end-functionalized polymers, anionie po!ymerization, macromolecular arehiteeture, association, phase separation, adsorption V delu je podan pregled lastnosti vrste dobro definiranih polimerov z različnimi arhitekturami (linearni homopolimeri, diblok in triblok kopolimeri, zvezdasti homopolimeri) z dimetilaminskimi in sulfobetainskimi končnimi skupinami, v razredčenih raztopinah in v masi. Polimere s funkcionalnimi končnimi skupinami smo sintetizirali z anionsko polimerizacijo z visoko-vakuumsko tehniko. Z iniciatorjem 3-dimetilaminopropiIitijem smo na konec verige uvedli dimetilaminsko skupino, ki smo jo z reakcijo s ciklopropansultonom prevedli v sulfozvvitterionsko. Temeljita molekularna karakterizacija je potrdila, da so sintetizirani modelni materiali zelo homogeni. Z viskozimetrijo ter statičnim in dinamičnim sipanjem svetlobe smo raziskali njihove agregacijske lastnosti v razredčenih raztopinah, v topilih različne polarnosti in selektivnosti do določenih delov molekul, co-funkcionalizirani polistireni in blok kopolimeri stirena imajo, verjetno zaradi polarizabilnosti fenilne skupine, mnogo nižjo stopnjo asociacije kot homopolidieni. S SAXS reologijo in z dielektrično spektroskopijo smo študirali lastnosti co-ftinkcionaliziranih homopolimerov in diblokov v masi ter ugotovili nove oblike samoorganiziranosti pri tej nizki koncentraciji ionov ter nenavadno obnašanje faz pri visoki temperaturi. Z elipsometrijo smo raziskali tudi adsorpcijske lastnosti zvezdastih polimerov z različnim številom funkcionaliziranih vej v razredčenih raztopinah in ugotovili, da se razlikujejo od lastnosti linearnih polimerov. Ključne besede: polimeri s funkcionalnimi končnimi skupinami (to-funkcionalizirani polimeri), anionska polimerizacija, makromolekularna arhitektura, asociacija, fazna separacija, adsorpcija 1 INTRODUCTION The presence of even a few highly polar groups dis-tributed along or fixed at the ends of nonpolar chains changes dramatically the properties of polymers'-7. These changes are caused by association of polar groups in the nonpolar environment of the hydrocarbon chains in the bulk or of the aliphatic solvents in solution. The least complicated examples of polymeric associ-ating species are chains vvith one polar group89. These simple materials offer an essential starting point for testing theories and establishing the basic strueture-proper-ties relationships, vvhich vvill help to design associating polymers for practical applications. Although many routes exist for the synthesis of end functionalized polymersUH2, living anionie polymeriza-tion has been proven to be the most efficient method for synthesizing vvell defined macromolecules1314, since it gives the possibility to control many struetural variables including placement of the ionic groups. This revievv vvill be focused on the dilute solution and bulk properties of dimethylamine and sulfozvvitterionic end-functionalized polymers having different architectures (linear homopolymers, diblock and triblock copoIy-mers and star polymers vvith a different number of functional groups), synthesized mainly in our laboratory. 2 SYNTHESIS AND CHARACTERIZATION Homopolymers 3-Dimethylaminopropyl-lithium (DMAPLi) vvas used as initiator for the introduction of the dimethylamine group at the end of the polymer chain in ali cases. DMAPLi vvas prepared by reaction of the corresponding chloride (DMAPCl) and Li dispersion according to Ste-vvart et al.15. Styrene (St), Isoprene (Is) and butadiene (Bd) were polymerized with DMAPLi. The molecular vveight distributions are low in the čase of polydienes. Stoichiometric molecular weights are in very good agreement vvith the number average molecular vveights, measured by osmometry. These results indicate that DMAPLi is an efficient initiator for the polymerization of isoprene and butadiene. The microstructure of the polydienes vvas investigated using 'H-NMR spectroscopy. The results clearly show an increase of the vinyl content with decreasing chain length, due to the presence of the polar dimethy-lamine group in the initiator. The slow initiation rate vvas readily observed during the polymerization of St by the gradual appearance of the orange color16, vvhich is characteristic of the living polystyIyllithium chains. This fact in combination vvith the very fast propagation rate for the polymerization of St resulted in very broad molecular vveight distributions (1=1.23-1.27). In addition, the M„(SEC) of samples vvith stoichiometric molecular vveights Ms<9300 vvere much higher than the stoichiometric ones, vvith the difference being higher by decreasing Ms. This behaviour can be explained by partial consumption of the initiator. This vvas verified by the subsequent addition of Is, vvhich pro-duced polymers having bimodal distribution (figure 1). The lovver molecular vveight peak, not seen by the UV detector, corresponds to NPI homopolymer, produced by the DMAPLi, vvhich remained unreacted during the po-lymerization of St. The higher molecular vveight peak is attributed to the NPSt-b-PI block copolymer vvith the amine group at the PSt chain end, produced by the cross-over reaction of NPStLi vvith Is. Addition of THF to the mixture of St and DMAPLi ([THF]/[Li] > 3) gave poly-mers vvith close agreement betvveen Ms and Mn and lovver polydispersities. 3 DIBLOCK AND TRIBLOCK COPOLYMERS Block copolymers of styrene and isoprene having di-methylamine end-groups at the one or the other chain end vvere prepared using DMAPLi and sequential addition of monomers17. When Is is polymerized first, a small amount of THF is added after the polymerization of the diene is completed to accelerate the crossover reaction vvith St. The reaction scheme is the follovving: (CH3)2NCH2CH2CH2Li + n CH2CHC(CHj)CH2 —benzene > ch3 ch3 I I (CH3)2NCH2CH2CH2-eCH2—CH-C—CH2-^,CH2-CH=C- CH2LI mCH2 CH O ™3 -► (CH3)2NCH2CH2CH2-(CH2—CH=C—CH2->-tCH2—CH-VLi THF n i CH,OH ---► NIŠ Triblock copolymers, having dimethylamine groups at both chain ends vvere prepared by coupling diblock chains vvith dimethyldichlorosilane, (CH3)2SiCl2. The products are characterized by compositional and chemical homogeneity and lovv molecular vveight distributions. The samples are designated vvith the letter N corresponding to the end-amine group, follovved by the sequence of blocks starting vvith the block at vvhich the functional group is attached. 4 co-FUNCTIONALIZED STAR POLYISOPRENES AND Mono-, Di- AND Tri-co-FUNCTIONALIZED THREE ARM STAR POLYBUTADIENES Three and tvvelve arm PI stars18 and three arm star PBd vvith ali ends functionalized vvith dimethylamine groups19 vvere synthesized by the reaction of end-func-tionalized living polymers with suitable chlorosilanes. As an example the 3-arm polybutadienes have been prepared according to the follovving scheme: Elutlon volumt (mL) Figure 1: SEC chromatograms of (a) NS-3B (purifted DMAPLi; polymerization in pure benzene) and (b) NS-3B after the addition of isoprene (first peak, diblock formed; second peak, homopolyisoprene formed by reaction of isoprene vvith unreacted DMAPLi). The UV detector sees only the PS part Slika 1: SEC kromatogrami (a) NS-3B (očiščen DMAPLi; polimerizacija v čistem benzenu) in (b) NS-3B po dodatku izoprena (prvi vrh ustreza diblok kopolimeru; drugi vrh ustreza homopoliizoprenu, ki nastane v reakciji med izoprenom in nezreagiranim DMAPLi). UV detektor zazna samo polistirenski del blok kopolimera Bd +DMAPLi 3NPBdLi + CH3SiCl3 (-) (+) • (CH3)2NaaaaaaA ; Lf ' NBdLi Q (nm-1) OJ 0^5 Q (nm"1) Figure 7: SAXS profiles for tvvo (o-functionalized IS diblock copolymers at T=303 K. Data vvere corrected for density fluctuations and the intensities are given in absolute units Slika 7: SAXS krivulje dveh co-funkcionaliziranih izopren-stirenskih (IS) diblok kopolimerov pri T=303 K. Pri podatkih so upoštevane fluktuacije gostote, intenzitete so podane v absolutnih enotah a) a background originating from density and concentration fluctuations b) an excess intensity at lovv Q related to heterogeneities vvith long correlation lengths in the čase of ionom- ers31 c) the microdomain peak32 characteristic of the micro-phase separation process betvveen PI and PS phases and d) the peak related to the polar groups, vvhich emerged in the čase of the zvvitterionic sample. The last three characteristics are temperature depend-ent vvith the aggregate peak intensity being much less sensitive to changes of temperature for the specific ex-periment temperature range. The microdomain peak in-tensity has a similar temperature dependence for both the amine and the zvvitterion-capped copolymers. A completely different behavior is observed vvhen the functional group is attached to the PS chain-end, as shovvn in figure 8. The microdomain peak dominates the scattering pattern in this čase. The peak increases in in-tensity, sharpens, and moves to slightly higher Q values vvith increasing temperature. The absence of any dissolu-tion process clearly indicates that the microdomain structure is stabilized by the ionic aggregates. In the čase of ZvvSI samples the ionic groups are trapped vvithin the PS phase vvithout being able to aggregate. The increase of temperature increases the mobility of the polar groups leading to the formation of aggregates vvithin the "hard" phase. This is schematically shovvn in figure 9 for both systems, ZvvIS and ZvvSI. As a consequence the incom-patibility of PI and PS is enhanced and a completely different phase behavior is observed. So only by changing the position of the polar group, from the PI to the PS chain-end it is possible to change the phase diagram. 10a CO | lO4-D aj 103 • ° • ° ' \ \\ \\ • : NHS*5 • :ZwHS#5 • \ Q (nm-1) 1 Figure 8: Comparison of the SAXS profiles for the dimethyIamino-and zvvitterion-substituted to-functionalized copolymers at tvvo temperatures Slika 8: Primerjava SAXS krivulj dimetilamino- in zvvitterionsko substituiranih co-funkcionaliziranih kopolimerov pri dveh temperaturah Zw-IS Zw-SI (g) Low T (b) Hgh T (O) tT„m rrinL|__jJlll Figure 9: Schematic illustration of the microstructures in to-functionalized SI block copolymers, showing the Zw-IS (left) and Zw-SI (right) cases at low (upper) and high (lower) temperatures. The corresponding electron density distributions are also shown Slika 9: Shematska predstavitev mikrostrukture co-funkcionaliziranih SI blokkopolimerov pri nižji (zgoraj) in višji temperaturi (spodaj) za Zw-IS (levo) in Zw-SI (desno). Prikazana je tudi ustrezna porazdelitev elektronske gostote The conclusions derived by SAXS studies vvere confirmed by rheology. In the čase of the zvvitterionic co-polymers an extension of the rubbery plateau is observed. This behaviour is explained considering that the aggregates act as physical crosslinks vvithin the PI phase. Furthermore, vvithin the temperature range investigated no sign of an order-disorder transition vvas observed in agreement vvith SAXS results, meaning that the cubic microdomain structure is stable up to high temperatures. Dielectric spectroscopy also offers the means to ver-ify the conclusions dravvn so far through the selective probing of the Pl chains. In the čase of ZvvIS copolymers in addition to the fast segmental and the slovv normal mode an intermediate process, vvith activation parameters which are reminiscent of the segmental process, is observed. This intermediate process arises from regions of the reduced mobility created around the aggregates impending the motion of the PI chains in their immediate environment. Hovvever differential scanning calorimetry, DSC is not so sensitive and the size of these regions very small in order to detect an intermediate Tg value, al-though an increase on the Tg of the polyisoprene block has been observed at lovv molecular vveights33. The combination of the association process caused by the presence of polar groups in a nonpolar solvent vvith the micellization procedure, promoted in selective solvents leads to interesting solution behavior. The dilute solution properties of ©-functionalized diblock copoly-mers having dimethylamine or zvvitterion groups at the PS chain-end vvere studied in n-decane a nonpolar selective solvent for the PI blocks34. The presence of the polar groups introduces another factor capable to enhance the aggregation numbers for the zvvitterionic samples in n-decane. Much lovver Nw I ■ 1 1 1 ' 1 i - NSMF D 0 o„ 0 Oo _ o o ° o o _ _ o o 1 1 t 1 - (Ml MM cftj/mL) 12.00 ZMSMF o ooooo Oo O H - Oo, m, £ t Oq0 MM* Oj) - Tonparetui* fC) Figure 10: Kc/ARe vs concentration plots given for (a) sample NSI-4F and (b) sample ZwSI-4F in n-decane at 25°C. (c) Intensity vs temperature plot for the same samples at c=2.800 x 10"3 g/mL for NSI-4F and c=1.629 x 10"3 g/mL for ZwSI-4F Slika 10: Kc/ARe v odvisnosti od koncentracije za vzorca (a) NSI-4F in (b) ZwSI-4F v n-dekanu pri 25°C; (c) odvisnost intenzitete od temperature za NSI-4F pri c=2,8 x 10'3 g/mL in za ZwSI-4F pri c= 1,629 x 10"3 g/mL values were observed for the amine-capped copolymers, meaning that the amine groups are not polar enough to enhance the association process. TVpical LALLS plots are given in figure 10. From DLS measurements negative kD values vvere obtained for the amine-capped polymers as expected having in mind the negative A2 values. For the zvvitte-rionic samples the kD values vvere positive meaning that the equilibrium is shifted in favor of the micelles. Viscometry measurements vvere also performed. The Huggins coefficients increase vvith increasing molecular vveight for the amine-capped polymers. This behavior is consistent vvith a star-like structure. For the zvvitterionic samples constant kH values, around 1.1 vvere obtained, meaning that rather compact structures exist in solution. The Rv and RH values are identical vvithin experimen-tal error for the amine polymers but for the zvvitterionic polymers RH is much higher than Rv. The former result is consistent vvith star-like structures, vvhereas the latter can be explained considering the high sensitivity of DLS to large structures and/or to the development of shear forces in the capillary tube able to disrupt the larger ag-gregates. The fact that the polar core probably has an elongated structure vvith antiparallel placement of the zvvitterionic groups is able to support the above assump-tion, since a break of the association at one point can cause a large reduction of the micelle's size. Intensity vs temperature measurements at concentra-tions vvhere micelles are the dominant species revealed that the micelles formed by the zvvitterionic copolymers are stable at much higher temperatures than the ones made of amine-capped precursors. It seems that in the former čase the high temperature resistive ionic cores stabilise the micelles (figure 10(c)). 8 STAR SHAPED POLYBUTADIENES VVITH END-FUNCTIONAL GROUPS The amine-capped star polymers provide no evidence of association in cyclohexane, vvhereas strong association is observed in the čase of zvvitterionic samples. It is evident that (a) among the different series of polymers the aggregation number decreases vvith increasing num-ber of functional groups and (b) among the samples vvith the same number of polar groups the degree of association decreases vvith increasing molecular vveight of the precursor polymer, due to excluded volume repulsions. These results are given schematically in figure 11. Multifunctional samples, especially the trifunctional stars form gels even at lovv concentrations. This result connected vvith the lovv aggregation numbers for these samples leads to the conclusion that in very dilute solution intramolecular association dominates and by increasing concentration there is a rather sharp transition from intramolecular to intermolecular association able to produce stable gels. 20 15 I 10 S o 0 SOOOO 100000 190000 200000 (Mw)N Figure 11: VVeight-average aggregation number, Nw vs base molecular vveight (MJN of the star polymers: Zw-lN-3PBd (o), Zw-2N-3PBd (■). and Zw-3N-3PBd (A) Slika 11: Utežno povprečje števila agregacije Nw v odvisnosti od molske mase (MW)N zvezdastih polimerov: Zw-lN-3PBd (o), Zw-2N-3PBd (■) in Zw-3N-3PBd (A) The degrees of association of monofunctional stars are lovver than those measured for the linear co-function-alized PBd, meaning that the star structure prevents the association due to the steric hindrance caused by the un-functionalized arms. The hydrodynamic behavior of the functionalized stars vvas studied by DLS and viscometry35. The increased values of p2/T2 (>0.2) indicate that the aggre-gates produced by the zvvitterionic samples are polydis-perse in agreement vvith the MO and LALLS results. Lovv kD values vvere observed in most cases as a con-cequence of the decreased second virial coefficients. The strongly negative kD values for the trifunctional stars indicate the existence of strong hydrodynamic in-teractions betvveen macromolecular chains eventhough these samples have lovv aggregation numbers and shovv only small increases in RH compared to their precursors. This behavior can be seen as evidence of intramolecular association in very dilute solutions. For the čase of di-functional stars the above analysis is not straightforvvard. It is clear that intermolecular association cannot be ruled out. For monofunctional samples there is no possibility of intramolecular association. The star model can be used for these samples considering that the aggregates corre-spond to star polymers and their precursors to the arms of these stars. Consequently, it is possible to calculate the aggregation numbers from DLS measurements, Ndls-The results shovv that the aggregates formed from the monofunctional samples behave hydrodynamically as star polymers vvith functionality equal to 2NW. It seems that the tvvo unfunctionalized arms anchored at the pe-riphery of the aggregates are responsible for the overall size of micelles. The conclusions drawn by DLS are verified by vis-cometry for the amine-capped polymers. Zwitterionic tri-functional samples have lovver intrinsic viscosities than their precursors but the kH values are extremely high, in-dicating the presence of strong hydrodynamic interactions. This behavior implies that in very dilute solutions compact structures are formed through intramolecular association. This result is in agreement vvith LALLS and DLS data. Comparative examination of Rv and RH values shovvs that R„Mo>W/dioxane>W/benzene. Poly(7) is stable in solutions exposed to air vvhereas poly(5) and poly(6) are not. Photoconductivity of soluble polymers prepared by WOCI4 based catalyst is reported23"25. HteCHjo)-W02 8 1 j. vohlidal et al.: recent advances in synthesis of First polymerization of 8 and its copolymerization with PA by WOCl4/Me4Sn in dioxane/benzene and [Rh(nbd)(PPh3)2(-C=CPh)]. WOCl4 by itself does not transform 8 to any oligomer or polymer. Homopolymers of 8 are insoluble. Photoconductivity measurements on the copolymer of 8 with PA are reported. Nitro group was found to act as a trap for photogenerated charge car-riers25-26. HteC-^) 1 HteC-/OV-Me 9 Polymerizations in vvater, THF, Et3N and toluene in-duced by various Rh'(nbd) and Rh'(cod) complexes: other ligands: tosyl, H20, Cl, piperidine, o-phenyle-nediamine, N-methylimidazole, bis(4-tBu)-2-pyridyl-methanethiolate, tBuNH2, NH3. [Rh(cod)(tosyl)(H20)] complex yields all-cis polymers. Acetylenes of aliphatic type (l-octyne, l-butyne-4-ol, 5-hexyne carboxylic acid and 2-butyne dicarboxylic acid) do not polymerize on this Rh catalyst27. OCONH-X HfeCHg^ where X = : (R,)-CH(CH )-Ph m- 10 3 1 « p- 11 00-CH(CH )-a-naphtyl 3 p- 12 -0-SiMe -tBu m- 13 2 p- 14 -0-SiPh -tBu p- 15 z PA 1 4-ethynylbiphenyl 16 a-ethynylnaphtalene 17 Homopolymerization of phenylacetylenes with bulky, optically active groups linked to phenyl ring and their copolymerization with non-chiral monomers. [Rh(nbd)Cl]2 in THF solvent vvas found to be efficient initiator yielding high cis-transoidal polymers vvhereas WCyPh4Sn and MoCl5/Ph4Sn systems have provided oligomers and/or low-MW polymers only. Upfield shifts of olefinic protons' NMR signal up to 0.25 ppm are cor-related to increasing co-monomer bulkiness resulting in tvvisting up of the main chain. Polymers of 10,11 and 12 as vvell as their copolymers vvith achiral acetylenes 1 and 13 to 17 shovv circular dichroism, CD, in 300 to 500 nm range. Stereoregularity of main chains vvas found to be essential for CD activity (non stereoregular polymers of chiral monomers do not shovv significant CD bands). Computational study of the polymers' helical structure is presented28. HfeC-^O)-000-(ch2 }n" -o-©-©-« 18 n = 6, 12 Successful transformation of both monomers 18 into cis-transoid stereoregular PPAs vvith pendant polar mesogenic groups by using [Rh(nbd)Cl]2 catalyst. WCls/Ph4Sn yields either cyclotrimers (in THF) or their mixture vvith lovv MW polymer (in toluene). MoCl5/Ph4Sn catalyst has not shown activity in any solvent. DSC records as vvell as slovv polymer dissolving prove to a formation of mesogenic structures29. HC=C-^^y-C=C-SiIPr3 19 where X = CsC-SiJPr 20 3 Selective polymerization of 19 and 20 by Mo, W and Rh based initiators taking plače on terminal ethynyl group is reported. Polymer formed by WOCl4/Ph4Sn catalyst in benzene involves a small amount of soluble high-MW fraction. Dioxane cosolvent suppresses this fraction formation and increases content of cis units in poly(19) and poly(20). Content of cis units increases in order: W/benzene-C=C—Fc 22 (Fc is ferrocenyl). TaCl5 quantitatively cyclotrimer-izes 21 to 1,2,4- and l,3,5-triferrocenylbenzenes (mole ratio 3:2). Solid state structure of 1,3,5-isomer vvas es-tablished: up-up-down arrangement of Fc groups. 21 vvas copolymerized vvith 1 to a soluble statistical copolymer. 22 vvas selectively polymerized on terminal ethynyl group by using W and Rh based catalysts to partly soluble polymers3233. HC=C-^ HCsC-/ 23 P NO NO x = cooch ch ooc—(o NO The first reported polymerization of acetylene bear-ing nitro group. Cyclopolymerization of dipropargylic monomer induced by MoCyPh4Sn and PdCl2 catalysts. The former yields only partly soluble (solubility depends on the solvent used in polymerization), whereas the latter eompletely soluble poly(23). W-based catalysts were found as inactive. Polymer shows UV/vis absorption up to ca 650 nm34. V hc=c-\ O hc=c-^ r = h r = Me r'= h r2= pentyl 26 rj = Me r2= ph 27 R1= R2= cyclohexyl 28 hc=c-ch hc=c-ch hc=c-ch N 30 31 [0 32 MoOCIVMejSn and MoCl5/EtAlCl2 polymerize 30 to insoluble polymer, 31 to insoluble polymer and metha-nol-soluble fraction, and 32 to soluble, high-MW polmer (W value up to 480 000) and methanol soluble fraction. Methanol soluble fractions formed on M0OCI4 consist of oligomers only (MW below 1000), whereas in those formed on MoCl5 involve polymers of „ value up to 35000. The former catalyst is more active than the latter one. WOCl4/Me4Sn system in dioxane/benzene (highly active in polymerization of nitroPA, 8) shovvs lovv activity at room temperature (only methanol soluble polymer is reported) but no activity at 60°C 37. b c h2" 9 2 11 hc=c-ch -s co 2 \ 3+ 33 b c h2" 9 2 U Cyclopolymerization of series of dipropargyl ethers. MoC15 based catalysts (EtAlCl2 and Bu4Sn cocatalysts) vvere found to be most active providing high yields of medium-MW polymers. WC16 based catalysts are almost inefficient and PdCl2 gives only 25% yield of poly(27). Poly(24) is insoluble. Solubility of poly(25) and poly(26) depends on the monomer concentration in po-lymerization mixture (above [M] = 0.5 mol/L, the formed polymers are insoluble). On the contrary, poly(27) and poly(28) are vvell soluble. Bulky a-substi-tuents are suggested to support intramolecular cycliza-tion and suppress intermolecular crosslinking, thus en-suring good polymer solubility. UV/vis absorption up to 600 nm and dark conductivity in both native and iodine doped state are reported35. O. OEt V HC=C-CH CH7 XOEt 2 ^COOEt 29 By itself M0CI5 and WC16 do not induce polymeriza-tion of 29 but together vvith EtAlCl2 or Ph4Sn cocatalysts provide good yields of low-to-medium-MW yellow polymers (W belovv 10000). PdCl2 gives only lovver yield of brovvn poly(29). UV/vis absorption up to 500 nm is reported36. First preparation of polyacetylene vvith deltahedral sandvvich carborane pendant groups is reported. WOCl4/Ph4Sn catalyst induces polymerization of 33 to a polymer partly soluble in DMSO. Strong intermolecular interactions of zvvitterionic carborane groups (dipole moment 17.7x10"30 Cm) are perhaps responsible for lovv solubility. The same catalyst copolymerizes 33 vvith 1 to a soluble statistical copolymer38. HC^O) h c7 + 37 18 34 , Br Quaternization of 2-vinylpyridine vvith 1-bromooc-tadecane is accompanied by a spontaneous polymeriza-tion of formed 34. Poly(34) vvas also prepared by quaternization of thermally prepared poly(2-vinylpyrid-ine). Multilayers thin films of poly(34) vvere prepared by LB technique and their properties vvere investigated. Electrical conductivity of native and iodine doped polmer and oxygen and nitrogen permeation of membranes deposited on Nafion as substrate are reported. The multi-layer membranes have shovvn excellent long term stabil- ity39,40 N-/ ,Br 34 h t/ + 37 18 HC=C—>,+ R HC=C-^ ^Bu iK SO 3 SO R = Et 35 R = Bu 36 R = hexyl 37 R = octyl 38 Synthesis of amorphous, conjugated polybetaines by cyclopolymerization of 35 to 38 induced by M0CI5, WC16 and PdCl2 catalysts. Negative effect of cocatalysts (EtAlCl2 and Bu4Sn) has been observed for the first two catalysts (viz. also polymerization of iodophenylacety-lene 5). Solubility of polymers in various solvents, UV/vis absorption up to 600 nm, dark conductivity in native and iodine doped state are reported41. 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Kalisz, J. Sedlaček, V. Blechta, P. Matijka, Polymer, in print 38J. Vohlfdal, J. Plešek, J. Sedlaček, I. Cfsarova, P. Matejka, S. Hermanek, Collect. Czech. Chem. Commun., 61 (1996) 877 39P. Zhou, A. Blumstein, Polymer, 37 (1996) 1477 40P. Zhou, L. Samuelson, K. S. Alva, C.-C. Chen, R. B. Blumstein, A. Blumstein, Macromolecules, 30 (1997) 1577 41 D.-C. Choi, S.-H. Kim, J.-H. Lee, H.-N. Cho, S.-K. Choi, Macromolecules, 30 (1997) 176 INTERFACIAL PHENOMENA IN THIN POLYMER FILMS STUDIED BY DIRECT PROFILING TECHNIQUES ŠTUDIJ POJAVOV NA MEJNIH PLOSKVAH TANKIH POLIMERNIH PLASTI Z DIREKTNIMI TEHNIKAMI PROFILIRANJA ANDRZEJ BUDKOWSKI Institute of Physics Jagellonian University Reymonta 4, 30-059 Krakow, Poland Prejem rokopisa - received: 1997-10-01; sprejem za objavo - accepted for publication: 1997-12-11 Various interfacial phenomena, such as: phase coexistence, surface segregation and wetting, as well as surface directed phase separation, determine many properties of po!ymer mixtures. These phenomena are studied in blends conftned in a thin film geometry. Direct composition vs. depth profiling techniques are used, which have been developed in the last decade. Present paper describes briefly direct profiling methods and interfacial phenomena observed with their help. Discussion is illustrated by experimental results obtained for homopolymer mixtures with nuclear reaction analysis and secondary ion mass spectroscopy. Key words: polymer blends, liquid thin films, ion beam analysis, composition vs. depth profiling techniques, miscibility conditions, surface segregation, wetting, phase separation Razni pojavi na mejnih ploskvah kot so npr. soobstoj faz, površinska segregacija in omakanje na površini pa tudi s površino usmerjena ločitev faz, določajo mnoge lastnosti polimernih mešanic. Te pojave smo študirali na polimernih mešanicah (blendih) z geometrijo tankih plasti. Uporabljene so bile direktne tehnike profiliranja koncentracije z globino plasti, ki so bile razvite v zadnjem desetletju. Članek na kratko opisuje direktne metode profiliranja in pojave na mejnih ploskvah, ki smo jih opazovali s pomočjo omenjenih metod. V diskusiji so predstavljeni eksperimentalni rezultati homopolimernih mešanic z jedrsko reakcijsko analizo in sekundarno ionsko masno spektroskopijo. Ključne besede: polimerne mešanice, tekoče tanke plasti, analiza z ionskimi snopi, tehnike profiliranja koncentracije z globino, pogoji mešljivosti, površinska segregacija, omakanje, ločitev faz 1 INTRODUCTION Alloying poIymers provides an inexpensive method to produce new materials vvith desired properties, often supertor to either blend component alone1. The spatial blend structure is rarely homogeneous. Compositional inhomogeneities are related vvith internal interfaces, separating coexisting phases inside the blend, and exter-nal interfaces exposed by the blend (Figure 1). The most complex situation occurs in blends conftned in a thin film geometry. Various phase domain morphologies are encountered in thin films, and exemplified in Figure 1. Their characterization precedes an enforcement of the proper performance of many lovv- and high- tech applications. The local concentration of the surface segregation 'cuticle' of one- phase layer (Figure la) is different from the composition in the bulk, modifying e.g. the surface vvettabil-ity by paints. Complex 3- dimensional tvvo- phase structure (Figure lb), expected for the separation of polystyrene (PS)/ polybutadiene blends, results in very tough 'high impact PS'. The separation process can be directed by external surfaces leading to self- stratified films (Figure lc), vvhere individual domains have often different properties (e.g. gas permeation and mechanical characteristics in gas separation membranes). Apart from these technology oriented aspects2,3, the interfacial phenomena pose a fundamental scientific challenge to soft matter physics4. They can be catego- rized according to complexity. The internal interface specifies miscibility conditions (Section 3a). These conditions, augmented by the knovvledge of the specific segment interactions at given external interface, explain surface segregation (Section 3b). Finally, vvhen ali interfaces are treated explicit, the self- stratified films, created in the due course of surface directed phase separation (Section 3c), can be described. Nowadays the spatial structure of blend films (phase morphology and local composition) can be determined vvith a nanometer precision, comparable vvith the polmer chain dimensions. Even the 3-dimensional complex morphology of tvvo- phase systems can be resolved, e.g. vvith transmission electron microtomography5. The concentration vs. depth profiles <(>(z) are examined by modem techniques6 yielding the volume fraction of the blend component(s) as the function of depth z vvithin the thin film (Figure 1). Indirect profiling techniques, such as X-ray and neutron reflectivity, yield model dependent profiles (z) (although vvith excellent resolution 8 = 1 nm). To contrary, the straightforvvard profiles (j)(z) are obtained vvith the commonly used direct methods6. 2 DIRECT PROFILING TECHNIQUES The direct methods analyze the film composition vvith ion beams of medium (3-7 keV in dynamic Secon-dary Ion Mass Spectroscopy (SIMS)) or higher (0.7 - 7 a) vacuum/ air OC C) II z N R A ■ E ■ <' lil! ■h II 2V3He+ ~5keV ^r+\beam Figure 1: Thin polymer films eomposed of one phase (j) (a), or two coexisting phases (f> i and (b, c) are not homogeneous. External interfaces I and II cause segregation (a), internal interface i separates coexisting phases (b and c) Slika 1: Tanke polimerne plasti, sestavljene iz ene faze (j> (a) ali iz dveh soobstoječih faz in <)>2 (b. c), niso homogene. Zunanji mejni plasti I in II povzročita segregacijo (a), notranja mejna plast i ločuje soobstoječi fazi (b, c) Me V) energy (Rutherford Back Scattering (RBS), For-ward Recoil Spectrometry (FRES), Nuclear Reaction Analysis (NRA)). Bulk of polymers are made up of elements which rarely provide an effective contrast for high energy tech-niques. RBS can in principle yield composition profiles of heavy elements present in polymers, but it is excep-tionally used to trace polymers themselves6. This is because the labeling a polymer with a heavy element se-verely alters the extent of its mixing with other polymers. Therefore a deuterium labeling is commonly used instead, which allows for the profiling of 'stained' polymers in such methods as FRES and NRA. The deuterium 'staining' of one of the chemically distinct blend components introduces much smaller thermodynamic perturbation, visible only for longer chains, and easily evaluated7. Non-resonant NRA8 is the high energy method of choice providing profiling deuterium in polymer films with the highest range (even of few microns) and best resolution (5 ' 7 nm at the free surface deteriorating to 5 ' 30 nm at depth z = 600 nm). As a standard procedure thin polymer films are mounted on Si vvafers (spin čast from solution either directly on Si, or čast on mica, floated on vvater, and picked up by Si backing bearing a precast film to form a multilayer if necessary), annealed at temperatures above polymer glass transition, and measured at room (or lovver) temperature. The monoen-ergetic 3He+ beam (vvith mm diameter) impinges on and penetrates into the thin film sample, as illustrated in Fig- mam. E or H filter secondary ion detector mass spectrometer Au + sacrificial layer sample Figure 2: Schematic illustration of setups used to yield the composition (J) vs. depth z profiles (z) in thin film samples with nuclear reaction analysis (NRA) (a) and dynamic secondary ion mass spectroscopy (SIMS) (b) Slika 2: Shematska predstavitev priprav za merjenje koncentracije (|> z globino z profila ij>(z) v vzorcih tankih plasti z jedrsko reakcijsko analizo (NRA) (a) in dinamično sekundarno ionsko masno spektroskopijo (SIMS) (b) ure 2a. At different depths z the reaction: 3He + 2H ® 4He + 'H + 18.4 MeV takes plače and the magnetic or electric filter allovvs only 4He+ particles to reach the detector. The measured 4He energy is related vvith the depth z, vvhich can be calculated based on reaction kinematics and knovvn energy losses of 3He and 4He in the sample. Finally, the correction of 4He count rate vvith respect to the reaction cross section provides a relative profile (j>(z) of the polymer 'stained' by deuterium. The absolute values of the volume fractions (\>{z) are determined from the knovvn (from preparation) overall amount of the deuter-ated material in the sample9, or by profiling the studied sample covered vvith an additional reference layer built of pure deuterated material10. Typical NRA profiles are shovvn in Figures 3a and 4a. An alternative profiling method of dynamic SIMS1112 is accomplished by monitoring individual atomic and molecular secondary ions emitted vvhen the polymer sample is exposed to the primary ion (Ar+ or another) beam vvith a medium energy (Figure 2b). The primary beam is scanned over an area of mm diameter, thereby eroding the sample and forming a flat crater vvith a grovving depth. The secondary ions ejected from the central region of the crater are analyzed vvith mass spectrometer (vvith respect to their mass- to- charge ratio) and moni-tored as a function of the sputtering time. Prior to SIMS measurements, the polymer samples are covered by a polymer sacrificial layer and evaporated vvith Au. This is 0 200 600 depth z [nm] 0.2 0.4 0.6 0.8 dPS vol. fr. 0.2 0.6 dPS vol. fr. * Figure 3: ReIaxation of an initially sharp interface between pure polystyrene (PS) (N = 27.8 k) and pure deuterated polystyrene (dPS) (N = 9.2 k) leads (here after a month long annealing at varied T) to coexisting profiles ((»(z) (a). NRA profiles, tracing local dPS concentration, determine coexisting compositions, 0! and 2, used to plot experimental phase diagram (b). This is well fltted by theory (see solid line in b) to yield the specific form of segmental parameter Xsans((z> (a). NRA profili, ki spremljajo lokalno dPS koncentracijo, določajo soobstoječe sestave, $1 in 2, so bili uporabljeni za eksperimentalni fazni diagram (b). Ta se dobro ujema s teorijo (neprekinjena črta v b), tako da dobimo specifično obliko segmentnega parametra xsans(), ki je prikazan (pri T = 160°C) v (c) kot neprekinjena črta. Vrednosti Xsans(), izmerjene s SANS za polimerne mešanice v masi, so pri (c) označene z odprtimi simboli za PS (N = 15,4 k)/dPS (N = 11,5 k) in s polnimi simboli za PS (N = 8,7 k)/dPS (N = 11,5 k) ' < *_1_I—1—i—1—I—1—1— 0 100 200 depth z [nm] 0 200 400 600 depth z [nm] 0 200 400 depth z [nm] Figure 4: (a) NRA profiles (f>(z) of the surface exposed by the mixture of random olefinic copolymers [(C4H8)i.x(C2H3(C2H5))x]N : a hydrogenous h52 (x=52%, N= 1510) and a partly deuterated d66 (x=66%, N=2030), after a few hours of annealing at T= 99°C. The open and solid symboIs correspond to the surface enriched in d66 and completely wetted by the d66- rich phase 2, respectively. (b and c) SIMS profiles (z> illustrating surface directed phase separation. Its initial stages vvere recorded (see b) for the blend of dPS (N= 6.4k)/ brominated polystyrene PBrxS (N=1.7k, x=0.08) annealed for 1 day at T=180°C. Its late stages (see c) vvere observed in the blend of dPS (N=17.4k) / PS (N=27.8k) annealed for 20 days at T=190°C. (Br', 'HC7 C' and 2HC7 C" profiles are marked by crosses, open and solid symbols, respectively) Slika 4: (a) NRA profili <|>(z) za površine, ki so bile izpostavljene zmesi naključnih olefinskih kopolimerov [(C4Hg)i.x(C2H3(C2H5))x]N: vodikov h52 (x=52%, N=1510) in delno devterirani d66 (x=66%, N=2030) po nekaj urah kondicioniranja pri T=99°C. Odprti simboli ustrezajo površini, ki je obogatena z d66 in polni simboki površini, ki je popolnoma omočena z d66 - bogato fazo $2. (b in c) SIMS profili (z) predstavljajo s površino usmerjeno ločitev faz. Začetne stopnje so posnete (glej b) za polimerno mešanico dPS (N=6,4 k) / bromirani polistiren PBrxS (N=l,7 k, x=0,08), ki je bila kondicionirana en dan pri T=180°C. Kasnejše stopnje (glej c) so prikazane za polimerno mešanico dPS (N=17,4 k) / PS (N=27,8 k), ki je bila kondicionirana 20 dni pri T=190°C. (Br" je označen s križci, 'HC /C" z odprtimi simboli in 2HC"/C" s polnimi simboli) to obtain a steady sputtering state before the real sample is reached by primary ions, and to avoid charging effects, respectively. Sputtering rates are determined by NRA (FRES or ellipsometric) measurements of selected control samples. This allovvs us to evaluate the absolute depth scale for each sample. The very good depth resolu- tion of 5 = 5 nm, vvhich deteriorates only slightly vvith depth z, is the one of two main SIMS advantages. The simultaneous profiling of various species sueh as 'H, 2H, C, O, Br, Si, N, etc., labeling polymers or present in the sample, is the second virtue. Most of these species are detected hovvever only in semi- quantitative fashion. It has been concluded that the absolute local concentrations j and (j):) are expected to coexist in thermodynamic equilibrium at temperatures belovv critical point (TTC. Until recently the phase coexistence of high polymer mixtures have been evaluated vvith a dynamic method determining cloud-point loci or vvith Small Angle Neu-tron Scattering (SANS). While the first technique is problematic due to extremely lovv molecular mobility, the second one measures the segmental interaction xSans away from coexistence curve. A nevv direct approach has been developed1314 in vvhich the profiles (z) are measured (for different T) across the internal interface betvveen tvvo coexisting phases forming a bilayer morphol-ogy as in Figure lc. Such samples are obtained from bilayers composed of pure blend components as a result of an annealing process, involving the relaxation of the initial sharp internal interface and a material transport across the interface. Figure 3a presents the exemplary coexistence profiles obtained vvith this novel method for the isotopic PS blend14. The corresponding coexistence curve presented in Figure 3b shovvs Tc = 197°C, vvhich is much elevated as compared to Tc = 0.9°K characterizing the isotopic mixture of simple liquids 3He and 4He. While unfavorable segment-segment interaction is comparable in both cases, the mixing entropy is reduced only for the isotopic PS blend. The question of accordance betvveen the coex-istence conditions determined by the novel approach1314 involving thin submicron films, and evaluated by SANS for bulk samples (vvith a size of c.a. 1 mm) is addressed by Figure 3c. The composition dependence of the segmental interaction parameter %sans for the isotopic PS mixtures determined by SANS" (and marked by points) is in very good agreement vvith that (dcnoted by a solid line) based on the thin films data corresponding to Figures 3a and b. This suggests that the coexistence conditions yielded by the interface relaxation method should be valid also for polymer blends in the bulk. 3.b Surface segregation and wetting The local concentration at the external surface differs usually from the constant concentration <(>„, of one-phase in the bulk of the sample16. This is demonstrated in Figure 4a for the free surface of an olefinic blend17. The reason for this surface segregation (or enrichment) is the specific surface interaction of polymer segments, lovv-ered vvhen the surface blend concentration is changed. The amount of the segregation is a result of a trade-off betvveen this specific surface energy fs and the bulk term, expressing the free energy of mixing (three factors men-tioned in Section 3a) and opposing the segregation. For knovvn bulk concentration ())„ the segregation profile (j)(z) is generated by the bulk energy term, specified by coex-istence conditions. ,. The thickness L of the surface segregation layer can be then microscopically thin or macroscopically thick (as in Figure 4a). This corresponds to a partial and complete wetting, respectively. While a complete vvetting for polmer blends has been first observed a fevv years ago18, a partial- to complete vvetting transition has just been reported19. According to a conventional vievv point the surface of the polymer mixture is enriched in the component vvith lovver cohesive energy, regardless of the value of the composition ()>„ in the bulk of the sample. This is not necessary true. First, entropy- related forces driving the segregation have been concluded20 besides those related to cohesive energy difference. Second, an enrichment-depletion duality has been advocated by theory21 and computer simulations22, and just observed in real polmer blends23. The surface is enriched in one blend component vvhen the bulk composition is belovv a certain value ()>„ < Q, and it is depleted in this component for larger bulk concentration <)>„ > Q. 3. c Surface directed phase separation A binary mixture is thermodynamically unstable vvhen its average composition corresponds to the tvvo- phase region bounded by a spinodal curve. In such conditions spontaneous bulk- and surface- driven phase separations occur. The bulk separation, driven by thermal fluctuations, results in composition waves vvith random directions and phases. Different scenario is expected vvhen a surface segregation is observed. Then a concentration gradient, created at the surface, induces composition vvaves propagating vvith a fixed phase in a direction normal to the surface. The concentration oscillation <|>(z), characteristic for this surface directed phase separation, extends from the surface and decays inside the sample, vvhere the bulk mode of the phase separation domi-nates24. This is presented in Figure 4b for the mixture composed of deuterated and brominated PS12. Finally, at the late stages of this process, a stratified plate morphol-ogy can be obtained25 as presented in Figure 4c for the isotopic PS mixture. This layered structure can be controlled in a tunable fashion by a surface active copolymer admixed to the polymer blend25. 4 CONCLUSIONS Binary polymer blends are usually incompatible or only partly compatible. Already very vveak interactions betvveen unlike segments, as in isotopic mixtures, vvould lead to phase separation. Even miscible polymer 'alloys' are inhomogeneous due to the effects related vvith an ex-ternal blend interface. Ordered segregation and separation processes can be initiated at the external interfaces of thin films. To describe them proper!y coexistence conditions needed first to be evaluated. Nowadays thin films are studied vvith direct composition vs. depth profiling techniques, vvhich are best represented by SIMS and NRA. The advent of real 3- dimensional profiling is ex-pected, vvhich vvould enable to study directly complex tvvo- phase morphologies. ACKNOWLEDGMENTS The author thanks Dr. A. Bernasik and J. Rysz for their help in performing SIMS experiments. 5 REFERENCES 'F. S. Bates, Science, 251 (1991) 898 2 a special issue of Physics World, March (1995) 'a special issue of MRS Bulletin, January (1996) 4K. Binder, Acta Polymer„ 46 (1995) 204 5J. H. Lauer, J. C. Fung, F. S. Bates, et al., Langumir, 13 (1997) 2177 6E. J. Kramer, Physica B, 174 (1991) 189; MRS Bulletin, January (1996) 37 7 A. Budkowski, J. Klein, U. Steiner, et al., Macromolecules, 26 (1993) 3858 8U. K. Chaturvedi, U. Steiner, J. Klein, et al., Appl. Phys. Lett., 56 (1989)1228 9 A. Budkowski, J. Klein, U. Steiner, et al., Macromolecules, 26 (1993) 2470 10 A. Budkowski, U. Steiner, J. Klein, J. Chem. Phys„ 97 (1992) 5229 "S. A. Schwarz, M. H. Rafailovich, et al., Molecular Phys„ 76 (1992) 937 12 A. Bernasik, J. Rysz, A. Budkowski, K. Kovvalski, J. Camra, J. Jedlin-ski, ECASIA 97, ed. by I. Olefjord, L. Nyborg and D. Briggs (J. Wiley & Sons, Chichester 1997) pp. 775-778 "F. Bruder, R. Brenn, Macromolecules, 24 (1991) 5552 14 A. Budkovvski, U. Steiner, J Klein, G. Schatz, Europhys. Lett., 18 (1992) 705 ,5J. D. Londono, F. S. Bates, et al., Macromolecules, 27 (1994) 2864 16Q. S. Bhatia, D. H. Pan and J. T. Koberstein, Macromolecules, 21 (1988) 2166 17 A. Budkowski, F. Scheffold, J. Klein, et al., J. Chem. Phys„ 106 (1997)719 18U. Steiner, J. Klein, E. Eiser, A. Budkowski, et al., Science, 258 (1992) 1126 19J. Genzer, E. J. Kramer, Phys. Rev. Lett., 78 (1997) 4946, in press 20M. Sikka, A. Karim, F. S. Bates, et al., Phys, Rev. Lett., 70 (1993) 307 21 R. A. Jerry and A. Dutta, J. Colloid Int. Sci., 167 (1994) 287 22 S. K. Kumar, H. Tang and I. Szleifer, Molecular Physics, 81 (1994) 867 23 A. Budkovvski, J. Rysz, F. Scheffold, J. Klein, L. J. Fetters, 17tli Disc. Conf. 'Surface and Int. Phenomena in Macromol. Systems', Inst. Macromol. Chem. Ac. Sci. Czech Rep., Vol. K67, 1997 24R. A. L. Jones, L. J. Norton, et al., Phys. Rev. Lett., 66 (1991) 1326 25J. Rysz, A. Bernasik, H. Ermer, A. Budkovvski, R. Brenn, T. Hashi-moto, J. Jedlinski, Europhys. Lett. 40 (1997) 503 MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF DUPLEX STEEL MIKROSTRUKTURA IN MEHANSKE LASTNOSTI DUPLEKS JEKEL MIRKO GOJIČ1, L. KOSEC2, L. VEHOVAR3 'Željezara Sisak, Sektor za razvoj, B. Adžije 2, 44000 Sisak, Croatia 2OMM, Naravoslovnotehniška fakulteta, Ljubljana 3Inštitut za kovinske materiale in tehnologijo, Ljubljana Prejem rokopisa - received: 1997-05-26; sprejem za objavo - accepted for publication: 1997-10-21 In this work mechanical properties and microstructure of duplex steel after heat treatment are shown. Heat treatment of the steel consisted of water quenching from 1050°C. A ferrite-austenite microstructure was obtained and the brittle a-phase was avoided. The results show that the impact energy depends on the direction of rolling. In rolling direction the share of ferrite and austenite was approximately equal. Key words: duplex steel, mechanical properties, ferrite-austenite microstructure, impact energy V članku so opisani rezultati raziskav mikrostrukture in mehanskih lastnosti dupleks jekel po gašenju v vodi s 1050°C. Na ta način je jeklo dobilo mikrostrukturo iz ferita in austenita in brez krhke 0-faze. Rezultati kažejo, da je udarna energija odvisna od smeri valjanja. Na vzdolžnem prerezu cevi sta deleža ferita in austenita približno enaka. Ključne besede: dupleks jeklo, mehanske lastnosti, feritno-austenitna mikrostruktura, udarna energija 1 INTRODUCTION Because of excellent strength and toughness as well as high resistance to corrosion the high alloy stainless steels are used in car, electronic and petrochemical in-dustnes. Investigations of the development of high alloy steels vvhich have simultaneously a high strength and other physical-chemical characteristics are important1. Depending on chemical composition, especially the content of chromium, nickel, and carbon as vvell as heat treatment high alloy steels can have a ferrite, austenite, martensite or duplex microstructure. Betvveen the high alloy steels duplex stainless steel (DSS) vvith austenite-ferrite microstructure has an important role26. It is a relative^ nevv class of engineering material for different applications because of the excellent combination of mechanical and corrosion characteristics. DSS offer benefits over austenite stainless steels and carbon steels because of their higher strength, good toughness and ductility in combination vvith equivalent resistance to general corrosion, as vvell as better resistance to local-ized corrosion and stress corrosion cracking. Today DSS have lovv carbon content (<0.002 wt.%) and contain opti-mal contents of chromium, nickel, molibdenum, copper and nitrogen for obtaining the required properties. In process industries materials vvith a favorable microstructure are used because it determines their mechanical and corrosion behavior. DSS vvith a austenite-ferrite microstructure are desirable, if free of brittle a-phase7. In the present vvork the investigation of mechanical and microstructural properties of DSS after heat treatment are presented vvith the accent on impact energy and the share of phases. 2 EXPERIMENTAL 2.1 Material A section of commercially produced duplex stainless tubing vvas used for this investigation. The thermal treatment consisted of solution annealing at 1050°C and vvater quenching. The chemical composition the steel is given in Table 1. Table 1: Chemical composition of duplex stainless steel, wt. % C Si Mn P S Cr Mo Al Ni N 0.02 0.45 0.88 0.024 0.018 24.97 3.19 0.04 8.20 0.12 2.2 Mechanical and microstructural testing The mechanical properties vvere assessed on an In-stron 1196 tensile testing machine in accordance vvith standard ASTM procedures8. The average hardness vvas determined by the Brinell method (HB), vvhile the micro-hardness of austenite and ferrite grains vvas determined using the indentor on a Leitz-Wetzlar optical microscope 8196. Impact testing vvas performed at room temperature in both directions of rolling. Microstructural tests vvere carried out vvith optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), image analysis system and X-rays diffraction (XRD). Specimens for metallographic analysis vvere mechanically polished and M. GOJIČ ET AL.: MECHANICAL AND MICROSTRUCTURAL PROPERTIES ... Table 2: Results of mechanical properties of duplex steel Re MPa Rm MPa A %_Z%_Hardness HB Microhardness HV»,io_Impact energv J_ 645 774 33 53 225 a=140y= 292 dir.of rolling: 41 ________transverse to dir, of rolling: 33 Figure 1: Microfractography of fracture surface of duplex steel after tensile testing (a) and impact testing in longitudinal (b) and transverse direction (c) Slika 1: Mikrofraktografije prelomnih površin dupleks jekla po raztržnem preiskusu (a) in preiskusu udarne žilavosti v vzdolžni (b) in v prečni smeri valjanja (c) Figure 2: Scanning electron microscopy image of duplex steel in longitudinal direction (a) and the scanning picture for nickel (b) Slika 2: Raster elektronski posnetek dupleks jekla v vzdolžni smeri valjanja (a) in x slika niklja (b) Figure 3: Scanning electron microscopy image of duplex steel in transverse direction (a) and the scanning picture for nickel (b) Slika 3: Raster elektronski posnetek dupleks jekla prečno na smer valjanja (a) in x slika niklja (b) Figure 4: Optical (a) and transmission electron bright-field micrographs (b) of duplex steel. D - twins Slika 4: Optični (a) in transmisijski elektronski posnetek (b) dupleks jekla. D - dvojčki • * WPLEX STEEL 011671 280.8 1671 288.8KV 188ci Figure S: Transmission electron microscopy bright-field micrograph of ferrite phase (a) with indexed area diffraction pattern (b) Slika 5: Transmisijski elektronski posnetek feritne faze (a) z indeksirano difrakcijo za ferit (b) etched in the Kallings reagent, an acid chloride solution (1.5 g of CuCl2, 33 ml of HC1, 33 ml alcohol and 33 ml of distilled vvater)9. The microstructure was examined in optical and SE microscopes, which was equipped for wave dispersive X-ray (WDX) analysis. The quantitative shares of ferrite and austenite were determined using an image analysis system. Thin foil samples for transmission electron microscope were prepared electrochemi-cally and examined TEM operated at 200 kV and equipped for diffraction analysis. The phase identifica-tion was obtained by X-rays diffraction using CuKa ra-diation. 3 RESULTS Mechanical properties (Re -yield strength, Rm - tensile strength, A - elongation and Z - reduction of area), impact energy, hardness and microhardness of DSS vvere measured at room temperature on three specimens. The average values of the properties are given in Table 2. When compared to usual stainless steels DSS have a sig-nificantly higher yield strength (tvvice that of austenite steels) and a good impact energy. Hovvever, the steel shovved also a significant anisotropy in impact energy. The fracture process and valuable evidence concerning the cause of failure can be obtained through microfrac- $ «s M £ <9 -C co Phases Figure 6: Quantitative shares of the ferrite-austenite microstructure in roiling direction Slika 6: Kvantitativni delež ferita in austenita v mikrostrukturi v vzdolžni smeri valjanja 60 70 Angle 20 / degree Figure 7: X-ray diffraction spectrum of duplex stainless steel Slika 7: X-ray difrakcijski spekter dupleks jekel tography10. Figure 1 shovvs the fracture surfaces of DSS after tensile and impact testing. The difference in fracture surfaces is only in size of dimples. At tensile testing DSS fracture in the ductile mode by microvoid coales-cence mechanism (Figure la). The fracture surfaces after impact testing are also ductile but vvith elongated dimples (Figures lb and lc). Figures 2 and 3 show the microstructure of DSS in both rolling directions. In both directions the microstructure is similar and consists of austenite grains embeded p ff £ a a. E |2 1400 1200 1000 800 . L L+5+y L+y —^^^ LTO / S / 8+y / r 1 10 15 Ni _L 30 25 20 15 Cr Content of chromium and nickel, wt. % Figure 8: Quasi binary diagram of FeCrNi alloy with located duplex steel Slika 8: Kvazi binarni diagram Fe-Cr-Ni zlitin z lokacijo dupleks jekel in ferrite. In rolling direction austenite grains are more elongated. Austenite grains contain more and ferrite grains less nickel (Figures 2b and 3b). No o-phase vvas found also by TEM observation, vvhile frequent tvvins vvere observed in ferrite grains (arrovv D, Figure 4a), vvhich vvas identified by selected area diffraction (SAD) pattern (Figure 5). Figure 6 shovvs the results of the quantitative phase analysis in rolling direction. An aver-age of the ten continuous fields vvas used for estimation of the phase share. In the longitudinal direction the shares of ferrite and austenite vvere approximately equal. Figure 7 shovvs the X-ray spectrum the steel. The phases vvere identified using of JCPDS data". Only the presence of ferrite and austenite vvas confirmed by X rays diffrac-tometry. 4 DISCUSSION The microstructure and the depending mechanical and corrosion properties are explained the best through the solidification process according to the quasi binary FeCrNi phase diagram, vvhich is shovvn shematically in Figure 812 vvith dashed lines locating the DSS. By equi-librium solidification, 8-ferrite is the primary solidification phase. 8-ferrite then undergoes solid-state transformation in a tvvo-phase region consisting of austenite (y) and ferrite (5) as the temperature is lovvered. The nuclea-tion of austenite occurs at grain boundaries enriched in carbon and nitrogen because of their limited solubility in ferrite. Given sufficient time, soluble carbon and nitrogen in solid solution diffuse uniformly throughout the austenite phase. It is knovvn that a slovv cooling under 815°C or aging at about 850°C can result in the formation of o-phase13, vvhich is prevented by a final solution annealing at 1050°C and vvater quenching, as shovvn al-ready. In this čase a microstructure consisting of ap-proximately equal shares of austenite and ferrite in the rolling direction is obtained. Taking into account the chromium and nickel equivalents14 the properties of both phases (5 and y) and their respective compositions can be approximately calculated for a given alloy and annealing temperature. The DSS tested here vvas represented in Figure 8 by the dashed lines. It can be seen that at 1050°C for the composition given in Table 1, the steel is located in the tvvo phases 5+y region having an approxi-mate 5/y fraction of 55:45 in accordance to the share of phases shovvn in Figure 6 for the rolling direction. The high tensile strength (Table 2) is the result of several simultaneous mechanisms15: interstitial solid solution hardening (carbon and nitrogen); substitutional solid solution hardening (chromium, molibdenum and nickel) and strengthening by grain refinement (the presence of tvvo phases prevents their mutual grovvth during heat treatment). The values of impact energy are higher in the longitudinal than in the transverse direction of rolling. Thus, the properties of DSS depend on the shape and arrangement of both phases as vvell as on the direc- tion of rolling. The difference in micromorphology frac-ture is explained through the fracture stresses and shape of both phases. The effect of deformation mode is usu-ally explained in terms of localized shear deformation16. Probably, also the interface betvveen the austenite and ferrite in DSS plays a considerable role in the fracture process. Crack propagation may take plače through austenite and ferrite grains. The propagation is associated with the interface it depends greatly on the orienta-tion of ferrite and austenite stringers17. There is a ten-dency of the propagation cracks to deflect along the interface to produce delamination when stringers lie par-allel to the applied stress. Taking into consideration the microstructural texture (Figure 2a), as well as their microhardness lovver impact energy in transverse to the direction vvas expected. A higher ductility of DSS in the longitudinal direction of rolling could indicate to the crack propagation along the 5/y boundaries because of axial stress, in contrast to the transverse direction of rolling vvhere the fracture is produced by orthogonal stresses. This is in agreement vvith the results by Odelstam18 shovving that elongation is by DSS lovver in the transverse than in longitudinal direction. 5 CONCLUSION In this vvork the results of investigation of mechanical and microstructural properties of the duplex stainless steel (DSS) are shovvn the heat treating consisted of an-nealing at 1050°C and vvater quenching, vvhich produced a ferrite-austenite microstructure free of brittle c-phase. Compared vvith usual stainless steels the DSS has a sig-nificantly higher mechanical strength (tvvice higher yield strength than that of austenite steels) vvith a good impact energy. It vvas found that the impact energy depends on the direction of rolling. In the longitudinal direction of rolling the fractions of the ferrite and austenite were ap-proximately equal. A higher ductility of steel in rolling direction could indicate to the crack propagation along the boundaries because of axial stress, in contrast to the transverse direction of rolling vvhere the fracture produced by orthogonal stress. 6 REFERENCES 1 Y. Murata, S. Ohashi, Y. Uematsu, ISIJ International 33 (1993) 7, 711 2F. H. Hayes, M. G. Hathering, R. D. Longbotton, Materials Science and Technology 6 (1990) 6, 263 3S. M. VVilhelm, R. D. Kane, Corrosion 40 (1984) 8, 431 4N. Sridhar, J. Kolts, Corrosion 43 (1987) 11, 646 5J. M. A. Quik, M. Geudeke, Chemical Engineering Progress 11 (1994) 11, 49 6K. Ravindranath, S. N. Malhotra, Corrosion Science 37 (1995) 2, 121 7J. O. Nilsson, A. VVilson, Materials Science and Technology 9 (1993) 7, 545 8ASTM standard E 370 9Metals Handbook vol.8, Metals Park, OH: ASM, 1973, p. 99 10 Y. 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Pulp and Paper Industry Corrosion, Stock-holm Vol. 4, 1983, p. 140 LETNO KAZALO - INDEX KOVINE ZLITINE TEHNOLOGIJE, 31, 1997, 1-6 Kronološko kazalo Vodopivec Franc: Industrijska in tehnološka politika..... ............................................KZT31 (1997) 1-2, 011-013 Mihelčič Miran: O ugodnosti ekonomskih kategorij odločajo tudi inženirji ....... KZT 31 (1997) 1-2, 015-023 Maček Jadran, A. Degen: Priprava nikljevih prahov v različnih reakcijskih medijih ............................................ ............................................KZT 31 (1997) 1-2, 025-028 Rudolf Rebeka, A. Križman: Vpliv procesnih parametrov pri postopku thixocasting na mikrostrukturo zlitine AlSi7 ............................................KZT 31 (1997) 1-2, 029-033 Jotanovič M., E. Pivič, D. Pihura: Določevanje temperaturnega polja kontinuirano odlitih blumov ...................... ............................................KZT 31 (1997) 1-2, 035-037 Šuštar Tomaž, B. Ule, M. Lovrečič-Saražin, T. Rodič: Projekcija a - nov koncept obravnave lezenja ................ ............................................KZT 31 (1997) 1-2, 039-040 Anžel Ivan, A. Križman: Visokotemperaturna stabilnost mikrostrukture hitro strjene zlitine Cu - Zr..................... ............................................KZT 31 (1997) 1-2, 041-045 Rawn Claudia J., D. Makovec, Z. Samardžija, D. Kolar: Structural Investigation of Ba6-xLn8+2/3xTiig054 Isostruc-tural Ce Compound...........KZT 31 (1997) 1-2, 047-050 Podlipnik Mojca, M. Valant, D. Suvorov: Raziskave vgrajevanja Pb2+ v keramiko na osnovi trdnih raztopin Ba6-xNd8+2/3xTii8054 ...........KZT 31 (1997) 1-2, 051-054 Zupan Klementina: Priprava materialov na osnovi LaCr03 z zgorevalno sintezo citratno-nitratnega gela .... ............................................KZT 31 (1997) 1-2, 055-057 Marinšek Marjan, J. Maček: Priprava Ni-YSZ kompozitnih materialov za visokotemperaturne gorivne celice...... ............................................KZT 31 (1997) 1-2, 059-062 Samardžija Zoran, M. Čeh: Electron Probe Microana- lysis in Materials Characterization .................................. ............................................KZT 31 (1997) 1-2, 063-067 Huskič Miroslav: Psevdoživa radikalska polimerizacija ............................................KZT 31 (1997) 1-2, 069-071 Stropnik Črtomir, L. Hausvald, V. Nežmah: Mehanizem nastajanja polimerne asimetrične porozne membrane z mokrim postopkom fazne inverzije.................................. ............................................KZT 31 (1997) 1-2, 073-076 Mirčeva Aneta, N. Oman, M. Brecl, T. Malavašič: Stransko verižni tekočekristalinični poliuretani ............... ............................................KZT 31 (1997) 1-2, 077-080 Poljanšek Ida, T. Kozamernik, A. Šebenik: Radikalska polimerizacija stirena in metilmetakrilata z bifosfinom . ............................................KZT 31 (1997) 1-2, 081-084 Brecl Marko, T. Malavašič: Opredelitev mezofaz 4-[co-[bis(2-hidroksietil)amino]-alkoksi]-4'-nitroazobenzenov in ustreznih poliuretanov ..KZT 31 (1997) 1-2, 085-090 Žagar Ema, M. Žigon, T. Malavašič: Viskoznost raztopin poliuretanov (PU) in PU-ionomerov ................................ .............................................KZT 31 (1997) 1-2, 091-095 Radonjič Gregor, V. Musil, M. Makarovič: Vpliv koncentracije kompatibilizatorja na mehanske lastnosti PP/PS mešanic ..............................KZT 31 (1997) 1-2, 097-100 Gubane Marko, P. Munih, Z. Šušterič, A. Šebenik: Vpliv mehčanja in premreženja naravnega kavčuka na dušenje vulkanizatov ......................KZT 31 (1997) 1-2, 101-106 Musil Jindrich: Sputtering of Thin Films......................... .............................................KZT 31 (1997) 1-2, 107-111 Irmančnik Belič Lidija, M. Remškar, K. Požun: Študij tankih plasti Ni-Cr z elektronsko mikroskopijo .............. .............................................KZT 31 (1997) 1-2, 113-116 Koller Lidija, K. Požun, M. Bizjak, J. Leskovšek, D. Railič: Primerjava vakuumsko razplinjenih in plazemsko čiščenih kontaktnih materialov za elektronske sestavne dele.....................................KZT 31 (1997) 1-2, 117-119 Požun Karol, L. Koller, L. Irmančnik Belič: Uporaba polietersulfona za kapacitivni tankoplastni senzor relativne vlažnosti zraka..............KZT 31 (1997) 1-2, 121-123 Sešelj Andreja, J. 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Šarler: Sistem za zajemanje, arhiviranje, spremljanje in analizo procesnih parametrov polkontinuirnega ulivanja v IMPOL-u, Slovenska Bistrica ....................................KZT 31 (1997) 3-4, 255-259 Tušek Janez: Kaj morajo načrtovalci novih proizvodov vedeti o tehniki spajanja? . KZT 31 (1997) 3-4, 261-265 Rokavec Duška, B. Mirtič: Uporabna vrednost različnih vrst glin iz Globokega, Slovenija ..................................... .............................................KZT 31 (1997) 3-4, 267-269 Musil Vojko: Razvoj novih poliolefinskih materialov na podlagi metalocenskih katalizatorjev ............................... .............................................KZT 31 (1997) 3-4, 271-274 Bernard Franc, I. Borovničar: Računalniško orodje v okenskem okolju za izbiro in določitev tesnil na osnovi dveh različnih računskih metod........................................ .............................................KZT 31 (1997) 3-4, 275-279 Berič Boris, M. Drab, A. Pregelj, S. 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Bavdek: Op-timiranje priprave prahov za sintrane magnete Alnico ... ................................................KZT 31 (1997) 5, 377-385 Manojlovič Gojko: Izboljšanje kakovosti gredic kvadrat 180 mm z omejitvijo ohlajanja ........................................ ................................................KZT 31 (1997) 5, 387-389 Filipič Bogdan, B. Šarler: Optimizacija procesnih parametrov pri kontinuiranem ulivanju jekla v železarni ACRONI Jesenice .................KZT 31 (1997) 5, 391-395 Nardin Vladimir, M. Terčelj, R. Turk, T. Rodič: Nova ekspertna metoda za določevanje obrabe orodij v laboratoriju ..........................................KZT 31 (1997) 5, 397-402 Rihar Gabriel: Konstrukcijski materiali in tehnike spajanja .......................................KZT 31 (1997) 5,403-407 Kejžar Rajko, B. 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M. Balkas, M. D. Bremser, O. H. Nam, W. G. Perry, B. L. Ward, L. Bergman, R. J. Nemanich, Z. Sitar, T. Zheleva, I. K. Shmagin, J. F. Muth, R. M. Kolbas: Grovvth of III-Nitrides Via Sublimation and Metalorganic Vapor Phase Epitaxy............................ .................................................KZT 31 (1997) 6, 485-494 Vodopivec Franc: Pionieer Years of Electron Probe Mi-croanalysis in Slovenia .........KZT 31 (1997) 6, 495-500 Jenko Monika: Laudation in Honour of Professor Dr. Jože Gasperič on the Occasion of his 65th Birthday........ .................................................KZT 31 (1997) 6, 501-502 Gasperič Jože: The Proper Operation of the High Vacuum Pumping System ...........KZT 31 (1997) 6, 503-505 Jenko Monika: Ultra Thin Deposited and Segregated Films ......................................KZT 31 (1997) 6, 507-517 Liščič Božidar: Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching ........................... .................................................KZT 31 (1997) 6, 521-528 Mayr Peter, H. Vetters, A. Schulz: Methods for the Vali-dation of Advanced Thin Hard Protective Coatings - an European Program.................KZT 31 (1997) 6, 529-531 Drobnjak Djordje, A. Koprivica: As-Rolled Multi-Phase Microalloyed Steel Bars vvith Improved Properties ........ .................................................KZT 31 (1997) 6, 533-537 Scherngell Heinrich, A. C. Kneissl: Two-Way Shape Memory Effect and its Degradation During Thermal Cy-cles in Ni-Ti Alloys...............KZT 31 (1997) 6, 539-543 Etienne F., E. Ziarovski: Introduction of Unshaped Refractories in the Wear Lining of Steel Ladles.................. .................................................KZT 31 (1997) 6, 545-549 Leskovšek Vojteh, M. Doberšek, A. Rodič: Pulse Plasma Nitrocarburising of Gas Shock Absorber Tubes from Steel W.No. 1.0116 ...............KZT 31 (1997) 6, 551-555 Mickovski Jovan K., N. Nacevski, B. Nikov, S. Milo-sevski: Possibilities and Perspectives for Development of Metallurgy in the Republic of Macedonia....................... .................................................KZT 31 (1997) 6, 557-562 Nacevski Nikola, B. Nikov: Investigation of Kinetics Leaching and Extraction of Vanadiumpentoxyde as a Function of Temperature .......KZT 31 (1997) 6, 563-565 Komelj Matej, S. Kobe: The Difference Betvveen the Magneto- Crystalline Anisotropy of Intermetallic Alloy Pr2(Coo.sFeo.5)i7 and Interstitially Modified Pr2(Coo.5Feo.5)i7N3-5 ..............KZT 31 (1997) 6, 567-570 Hadjichristidis Nikos: Model Polymers vvith Dimethy-lamine and Sulfozvvitterionic End-Groups. Synthesis and Self Assembly in Solution and in Bulk ........................... .................................................KZT 31 (1997) 6, 571-580 Vohlidal J., J. Sedlaček, M. Žigon: Recent Advances in Synthesis of Monosubstituted Acetylene Polymers......... ................................................KZT 31 (1997) 6, 581-585 Budkovvski Andrzej: Interfacial Phenomena in Thin Polymer Films Studied by Direct Profiling Techniques . ................................................KZT 31 (1997) 6, 587-591 Gojic' Mirko, L. Kosec, L. Vehovar: Mechanical and Microstructural Properties of Duplex Steel ......................... ................................................KZT 31 (1997) 6, 593-598 Avtorsko kazalo Anžel Ivan, A. Križman: Visokotemperaturna stabilnost mikrostrukture hitro strjene zlitine Cu - Zr..................... ............................................KZT31 (1997) 1-2, 041-045 Anžel Ivan, L. Kosec: Kinetika notranje oksidacije v hitro strjenih zlitinah Cu-Zr ............................................. ............................................KZT 31 (1997) 3-4, 201-204 Anžlovar Alojz, I. Anžur, T. Malavašič: Študij morfologije prepletenih polimernih mrež z vrstično elektronsko mikroskopijo .....................KZT 31 (1997) 3-4, 237-241 Berič Boris, M. Drab, A. Pregelj, S. Sulčič: Avtomatizacija postopka naprševanja na laboratorijskem visoko-vakuumskem sistemu ........KZT 31 (1997) 3-4, 281-283 Bernard Franc, I. Borovničar: Računalniško orodje v okenskem okolju za izbiro in določitev tesnil na osnovi dveh različnih računskih metod ....................................... ............................................KZT 31 (1997) 3-4, 275-279 Bizjak Milan, L. Kosec, G. Dražič, P. Panjan, A. Cvelbar: Določitev kinetike sprememb v hitro strjenih zlitinah aluminij-železo na osnovi meritev električne upornosti . ................................................KZT 31 (1997) 5, 337-340 Bizjak Milan, A. Pregelj, B. Praček: Razplinjevanje prahov pred zgoščevanjem ........KZT 31 (1997) 5, 341-344 Brecl Marko, T. Malavašič: Opredelitev mezofaz 4-[co-[bis(2-hidroksietil)amino]-alkoksi]-4'-nitroazobenzenov in ustreznih poliuretanov .. KZT 31 (1997) 1-2, 085-090 Budkovvski Andrzej: Interfacial Phenomena in Thin Polymer Films Studied by Direct Profiling Techniques . ................................................KZT 31 (1997) 6, 587-591 Cvelbar Robert, I. Emri, A. Nikonov: Prehodni pojav pri merjenju strižnega lezenja ................................................ ............................................KZT 31 (1997) 3-4, 233-235 Cop Rudi: Dimenzioniranje posebnih vrst betona z določeno prostorninsko maso........................................... ................................................KZT 31 (1997) 5, 357-360 Čop Rudi: Zagotavljanje kvalitete betonskih polizdelkov ................................................KZT 31 (1997) 5, 437-440 Črnilogar Vesna, I. Anžur, S. Orešnik, A. Gantar: Akrilni sintani - nova generacija usnjarskih mastilnih sredstev .. ............................................KZT 31 (1997) 1-2, 167-172 Daviš Robert F., C. M. Balkas, M. D. Bremser, O. H. Nam, W. G. Perry, B. L. Ward, L. Bergman, R. J. Ne-manich, Z. Sitar, T. Zheleva, I. K. Shmagin, J. F. Muth, R. M. Kolbas: Grovvth of III-Nitrides Via Sublimation and Metalorganic Vapor Phase Epitaxy............................. .................................................KZT 31 (1997) 6, 485-494 Drobnič Katarina, I. Prebil: Vpliv toplotne obdelave na statično nosilnost kotalnega stika..................................... ............................................. KZT 31 (1997) 1-2, 135-138 Drobnjak Djordje, A. Koprivica: As-Rolled Multi-Phase MicroalIoyed Steel Bars vvith Improved Properties ........ .................................................KZT 31 (1997) 6, 533-537 Etienne F., E. Ziarovski: Introduction of Unshaped Re- fractories in the Wear Lining of Steel Ladles.................. .................................................KZT 31 (1997) 6, 545-549 Fajfar Peter, R. Turk, V. Nardin, R. Robič: Računalniško podprta simulacija plana valjanja trakov na valjalnem stroju Steckel .....................KZT 31 (1997) 3-4, 193-196 Filipič Bogdan, B. Šarler: Optimizacija procesnih parametrov pri kontinuiranem ulivanju jekla v železarni ACRONI Jesenice .................KZT 31 (1997) 5, 391-395 Gasperič Jože: The Proper Operation of the High Vacuum Pumping System ...........KZT 31 (1997) 6, 503-505 Gliha Vladimir, I. Rak, N. Gubeljak: Vpliv mehkega korena na vedenje zvarnega spoja pri lomu .................... .............................................KZT 31 (1997) 3-4, 205-207 Godec Boštjan, A. Černe, M. Vončina, Č. Remec: Možnosti ugotavljanja velikosti napake in njene lege v materialu z ultrazvočno difrakcijo.................................... .............................................KZT 31 (1997) 1-2, 129-133 Gojič Mirko, L. Kosec, L. Vehovar: Mechanical and Microstructural Properties of Duplex Steel .......................... .................................................KZT 31 (1997) 6, 593-598 Grum Janez: Vpliv mikrostrukture aluminijevih zlitin s silicijem na hrapavost površine po finem struženju......... .................................................KZT 31 (1997) 5, 319-326 Grum Janez, P Žerovnik, D. Ferlan: Vpliv toplotne obdelave in brušenja na zaostale notranje napetosti............. .................................................KZT 31 (1997) 5, 327-335 Gubane Marko, P. Munih, Z. Šušterič, A. Šebenik: Vpliv mehčanja in premreženja naravnega kavčuka na dušenje vulkanizatov ......................KZT 31 (1997) 1-2, 101-106 Hadjichristidis Nikos: Model Polymers vvith Dimethy-lamine and Sulfozvvitterionic End-Groups. Synthesis and Self Assembly in Solution and in Bulk ........................... .................................................KZT 31 (1997) 6, 571-580 Huskic Miroslav: Psevdoživa radikalska polimerizacija . .............................................KZT 31 (1997) 1-2, 069-071 Irmančnik Belič Lidija, M. Remškar, K. Požun: Študij tankih plasti Ni-Cr z elektronsko mikroskopijo............... .............................................KZT 31 (1997) 1-2, 113-116 Jaklič Anton, B. Breskvar, B. Ule: Računalniško podprt merilni sistem pri preizkusih lezenja............................... ............................................KZT 31 (1997) 1-2, 143-145 Jenko Monika: Laudation in Honour of Professor Dr. Jože Gasperič on the Occasion of his 65th Birthday........ ................................................KZT31 (1997) 6, 501-502 Jenko Monika: Ultra Thin Deposited and Segregated Films ......................................KZT 31 (1997) 6, 507-517 Jotanovic' M., E. Pivic, D. Pihura: Določevanje temperaturnega polja kontinuirano odlitih blumov ...................... ............................................KZT 31 (1997) 1-2, 035-037 Kejžar Rajko, B. Kejžar: Legirani praški za navarjanje z večžično elektrodo ................KZT 31 (1997) 5, 409-411 Kejžar Rajko: Prednosti navarjanja s strženskimi žicami ................................................KZT 31 (1997) 5,413-417 Kevorkijan Varužan M.: Razvoj postopkov pridobivanja kompozitov na osnovi zlitin Al, diskontinuirano ojačanih s kemijsko aktiviranimi pepeli ......................................... ............................................KZT 31 (1997) 1-2, 177-186 Kevorkijan Varužan M.: Some General Considerations about a "Ideal" Ceramic Reinforcement for Structural Discontinuously Reinforced A1MC Composites Prepared by Liquid Metal Routes .... KZT 31 (1997) 3-4, 213-218 Koc Pino, B. Štok: Računalniško podprta karakterizacija termo-reoloških lastnosti snovi ........................................ ............................................KZT 31 (1997) 3-4, 197-200 Kok Iztok, T. Marinovič, J. Bohinc: Vulkanizacija zmesi na osnovi kavčuka EPDM za pripravo hidroizolacijskih membran ............................KZT 31 (1997) 3-4, 243-245 Kolar Drago: Chemistry Controlled Sintering and Microstructure Development in Ceramics................................. ................................................KZT 31 (1997) 6, 477-484 Koller Lidija, K. Požun, M. Bizjak, J. Leskovšek, D. Railič: Primerjava vakuumsko razplinjenih in plazemsko čiščenih kontaktnih materialov za elektronske sestavne dele ....................................KZT 31 (1997) 1-2, 117-119 Komelj Matej, S. Kobe: The Difference Betvveen the Magneto- Crystalline Anisotropy of Intermetallic AIloy Pr?(Coo 5Feo5)n and Interstitially Modified Pr2(Coa5Fea5)i7N3-5..............KZT 31 (1997) 6, 567-570 Kos Ivan: Vpliv stopnje hladne deformacije na potek re-kristalizacije pri jeklu 18/8 ...KZT 31 (1997) 5, 459-462 Kos Ivan: Hladna deformacija jekla 18/8 ........................ ................................................KZT 31 (1997) 5, 463-464 Kundak Mijo, J. Črnko: Analysis of State and Possibili- ties for a Profitable Production of Steel in Croatia ........ ............................................KZT 31 (1997) 3-4, 285-290 Legat Franc: Primerjava rezultatov cementacije zaščitnih verig v soli in plinu ..............KZT 31 (1997) 5, 445-448 Legat Franc: Upogibanje verižnih členov ....................... ................................................KZT 31 (1997) 5, 449-454 Legat Franc: Čiščenje valjanega jekla s peskanjem ........ ...............................................KZT 31 (1997) 5, 455- 458 Leskovšek Vojteh, M. Doberšek, A. Rodič: Pulse Plasma Nitrocarburising of Gas Shock Absorber Tubes from Steel W.No. 1.0116 ...............KZT 31 (1997) 6, 551-555 Lisjak Darja, M. Drofenik: Vpliv mikrostrukture na električne lastnosti keramike Zn-Ni-0 ................................... .................................................KZT 31 (1997) 5, 345-349 Liščič Božidar: Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching ........................... .................................................KZT 31 (1997) 6, 521-528 Lukan Alessandro: Sušenje peska pri proizvodnji asfaltov ..........................................KZT 31 (1997) 5,431-435 Maček Jadran, A. Degen: Priprava nikljevih prahov v različnih reakcijskih medijih ............................................ .............................................KZT 31 (1997) 1-2, 025-028 Manojlovič Gojko: Izboljšanje kakovosti gredic kvadrat 180 mm z omejitvijo ohlajanja......................................... .................................................KZT 31 (1997) 5, 387-389 Marinšek Marjan, J. Maček: Priprava Ni-YSZ kompozit- nih materialov za visokotemperaturne gorivne celice..... .............................................KZT 31 (1997) 1-2, 059-062 Matijaševič M., M. Mekuč: Priprava bromobutilne gume za farmacevtske namene ...KZT 31 (1997) 1-2, 163-166 Mayr Peter, H. Vetters, A. Schulz: Methods for the Vali-dation of Advanced Thin Hard Protective Coatings - an European Program.................KZT 31 (1997) 6, 529-531 Mickovski Jovan K., N. Nacevski, B. Nikov, S. Milo-sevski: Possibilities and Perspectives for Development of Metallurgy in the Republic of Macedonia....................... ...............................................KZT 31 (1997) 6, 557-562 Mihelčič Miran: O ugodnosti ekonomskih kategorij odločajo tudi inženirji .......KZT 31 (1997) 1-2, 015-023 Mirčeva Aneta, N. Oman, M. Brecl, T. Malavašič: Stransko verižni tekočekristalinični poliuretani................ .............................................KZT 31 (1997) 1-2, 077-080 Mladenovič Ana, N. Vižintin: Alkalno-silikatna reakcija v betonu .............................KZT 31 (1997) 1-2, 173-175 Musil Jindrich: Sputtering of Thin Films ........................ .............................................KZT 31 (1997) 1-2, 107-111 Musil Vojko: Razvoj novih poliolefinskih materialov na podlagi metalocenskih katalizatorjev ............................... .............................................KZT 31 (1997) 3-4, 271-274 Nacevski Nikola, B. Nikov: Investigation of Kinetics Leaching and Extraction of Vanadiumpentoxyde as a Function of Temperature.......KZT 31 (1997) 6, 563-565 Nardin Vladimir, M. Terčelj, R. Turk, T. Rodič: Nova ekspertna metoda za določevanje obrabe orodij v laboratoriju ..........................................KZT 31 (1997) 5, 397-402 Nemanič Vincenc: Procesiranje vakuumskih izolacijskih panelov................................KZT 31 (1997) 3-4, 251-254 Ogrinc Nives, P. Vidmar, I. Kobal, M. Senegačnik: Inves-tigations of Surface Reactions by Kinetic Isotope Effects ............................................KZT 31 (1997) 3-4,219-222 Pangeršič Dare, U. Primožič: Poliestrski polioli za poli-uretane....................................KZT 31 (1997) 5, 441-443 Petzow G.: Contemporary Ceramic Research - a Čase Study ......................................KZT 31 (1997) 6, 473-476 Pihura Derviš, M. Jotanovic: Segregiranje posameznih elementov v konti odlitkih visokoogljičnega jekla.......... ............................................KZT 31 (1997) 1-2, 147-149 Podlipnik Mojca, M. Valant, D. Suvorov: Raziskave vgrajevanja Pb2+ v keramiko na osnovi trdnih raztopin Ba6-xNd8+2/3xTii8054 ...........KZT 31 (1997) 1-2, 051-054 Poljanšek Ida, T. Kozamernik, A. Šebenik: Radikalska polimerizacija stirena in metilmetakrilata z bifosfinom . ............................................KZT 31 (1997) 1-2, 081-084 Požun Karol, L. Koller, L. Irmančnik Belič: Uporaba polietersulfona za kapacitivni tankoplastni senzor relativne vlažnosti zraka .............KZT 31 (1997) 1-2, 121-123 Radonjič Gregor, V. Musil, M. Makarovič: Vpliv koncentracije kompatibilizatorja na mehanske lastnosti PP/PS mešanic ..............................KZT 31 (1997) 1-2, 097-100 Rawn Claudia J., D. Makovec, Z. Samardžija, D. Kolar: Structural Investigation of Ba6-xLn8+2/3xTii8C>54 Isostruc-tural Ce Compound...........KZT 31 (1997) 1-2, 047-050 Remškar Maja, Z. Škraba, F. Cleton, R. Sanjines, F. Levy: Mikrocevke M0S2 .. KZT 31 (1997) 3-4, 247-249 Rihar Gabriel: Konstrukcijski materiali in tehnike spajanja .......................................KZT 31 (1997) 5,403-407 Rokavec Duška, B. Mirtič: Uporabna vrednost različnih vrst glin iz Globokega, Slovenija..................................... ............................................KZT 31 (1997) 3-4, 267-269 Rudolf Rebeka, A. Križman: Vpliv procesnih parametrov pri postopku thixocasting na mikrostrukturo zlitine AlSi7 ............................................KZT 31 (1997) 1-2, 029-033 Sabolič-Mijovič Mojca, B. Šarler: Sistem za zajemanje, arhiviranje, spremljanje in analizo procesnih parametrov polkontinuirnega ulivanja v IMPOL-u, Slovenska Bistrica ....................................KZT 31 (1997) 3-4, 255-259 Samardžija Zoran, M. Čeh: Electron Probe Microana- lysis in Materials Characterization .................................. ............................................KZT 31 (1997) 1-2, 063-067 Scherngell Heinrich, A. C. Kneissl: Two-Way Shape Memory Effect and its Degradation During Thermal Cy-cles in Ni-Ti Alloys ..............KZT 31 (1997) 6, 539-543 Sešelj Andreja, J. Stražišar: Čiščenje onesnaženih Zemljin in voda s kolonsko flotacijo ...................................... ............................................KZT 31 (1997) 1-2, 125-127 Smolej Anton, P. Panzalovič, M. Jelen: Vpliv dodatka Al- Ti-B na mikrostrukturo zlitine AlMgSi0,5 ...................... ................................................KZT 31 (1997) 5, 313-317 Steiner Petrovič Darja, M. Jenko, F. Vodopivec, H. J. Grabke: Vpliv antimona na razogljičenje zlitine Fe-Si-AI .............................................KZT 31 (1997) 3-4, 209-211 Stropnik Črtomir, L. Hausvald, V. Nežmah: Mehanizem nastajanja polimerne asimetrične porozne membrane z mokrim postopkom fazne inverzije .................................. .............................................KZT 31 (1997) 1-2, 073-076 Šelih Jana: Visokovredni betoni na osnovi domačih materialov ...............................KZT 31 (1997) 1-2, 159-161 Šuštar Tomaž, B. Ule, M. Lovrečič-Saražin, T. Rodič: Projekcija a - nov koncept obravnave lezenja ................ .............................................KZT 31 (1997) 1-2, 039-040 Šuštaršič Borivoj, V. Uršič, Z. Lengar, U. Bavdek: Op-timiranje priprave prahov za sintrane magnete Alnico ... .................................................KZT 31 (1997) 5, 377-385 Tušek Janez: Ročno obločno varjenje s hlajenjem oplaščene elektrode ...........KZT 31 (1997) 1-2, 139-142 Tušek Janez, M. Suban, J. Tome: Sinergija v varilstvu .. .............................................KZT 31 (1997) 1-2, 155-157 Tušek Janez: Kaj morajo načrtovalci novih proizvodov vedeti o tehniki spajanja? .KZT 31 (1997) 1-2, 261-265 Umek Urban, B. Mirtič: Karakterizacija surovin za žganje cementnega klinkerja............................................. .............................................KZT 31 (1997) 3-4, 223-225 Urek Sandra, M. Drofenik: Sinteza in lastnosti prahov Bai-xLaxTi03, pripravljenih s hidrotermalno sintezo ...... .................................................KZT 31 (1997) 5, 351-355 Vasevska Trajanka: Lastnosti aluminija A199,7, ki je namenjen za izdelavo znotraj zaščitenih stisljivih tub z udarnim brizganjem ..........KZT 31 (1997) 1-2, 151-154 Vehovar Leopold, S. Ažman: Določanje vezalne energije pasti za vodik z visokotemperaturno vakuumsko ekstrak-cijo .........................................KZT 31 (1997) 5, 299-304 Vehovar Leopold, S. Ažman: Vpliv prehodnih elementov in njihovih karbidov na aktivacijsko in vezalno energijo pasti v mikrolegiranih jeklih ............................................ .................................................KZT 31 (1997) 5, 305-311 Vodopivec Franc: Industrijska in tehnološka politika ..... .............................................KZT 31 (1997) 1-2, 011-013 Vodopivec Franc, B. Ule, J. Zvokelj: O deformacijski odpornosti jekel po uporabi v visokotlačnem parnem kotlu .......................................KZT 31 (1997) 5, 361-368 Vodopivec Franc: Pionieer Years of Electron Probe Mi-croanaIysis in Slovenia .........KZT 31 (1997) 6, 495-500 Vohlfdal J., J. Sedlaček, M. Žigon: Recent Advances in Synthesis of Monosubstituted Acetylene Polymers......... .................................................KZT 31 (1997) 6, 581-585 Vojvodič Gvardjančič Jelena, D. Korošec: Neporušne preiskave reaktorske tlačne posode v jedrski elektrarni Krško......................................KZT 31 (1997) 5, 369-375 Zore Borut, L. Kosec: Mehanske lastnosti spajkanih spojev ...........................................KZT 31 (1997) 5,419-424 Zore Borut, L. Kosec: Armirani spajkani spoji povečane žilavosti .................................KZT 31 (1997) 5, 425-430 Zupan Klementina: Priprava materialov na osnovi LaCrCb z zgorevalno sintezo citratno-nitratnega gela .... ............................................KZT 31 (1997) 1-2, 055-057 Žagar Ema, M. Žigon, T. Malavašič: Viskoznost raztopin poliuretanov (PU) in PU-ionomerov................................ ............................................KZT 31 (1997) 1-2, 091-095 Žigon Majda, T. Malavašič: Polifosfonati kot surovina za sintezo epoksidnih smol ... KZT 31 (1997) 3-4, 227-231 Stvarno kazalo - Subject Index Poslovno tehnični del - Managing Technical Part Vodopivec Franc: Industrijska in tehnološka politika..... ............................................KZT 31 (1997) 1-2, 011-013 Mihelčič Miran: O ugodnosti ekonomskih kategorij odločajo tudi inženirji .......KZT 31 (1997) 1-2, 015-023 Petzow G.: Contemporary Ceramic Research - a Čase Study ......................................KZT 31 (1997) 6, 473-476 Jenko Monika: Laudation in Honour of Professor Dr. Jože Gasperič on the Occasion of his 65th Birthday........ ................................................KZT 31 (1997) 6, 501-502 Kovine - Metals Maček Jadran, A. Degen: Priprava nikljevih prahov v različnih reakcijskih medijih ........................................... ............................................KZT 31 (1997) 1-2, 025-028 Rudolf Rebeka, A. Križman: Vpliv procesnih parametrov pri postopku thixocasting na mikrostrukturo zlitine AlSi7 ......................KZT 31 (1997) 1-2, 029-033 Jotanovič M., E. Pivič, D. Pihura: Določevanje temperaturnega polja kontinuirano odlitih blumov ...................... ............................................KZT 31 (1997) 1-2, 035-037 Šuštar Tomaž, B. Ule, M. Lovrečič-Saražin, T. Rodič: Projekcija a - nov koncept obravnave lezenja................ ............................................KZT 31 (1997) 1-2, 039-040 Anžel Ivan, A. Križman: Visokotemperaturna stabilnost mikrostrukture hitro strjene zlitine Cu - Zr..................... ............................................KZT 31 (1997) 1-2, 041-045 Godec Boštjan, A. Čeme, M. Vončina, Č. Remec: Možnosti ugotavljanja velikosti napake in njene lege v materialu z ultrazvočno difrakcijo ................................... ............................................KZT 31 (1997) 1-2, 129-133 Drobnič Katarina, I. Prebil: Vpliv toplotne obdelave na statično nosilnost kotalnega stika .................................... ............................................KZT 31 (1997) 1-2, 135-138 Tušek Janez: Ročno obločno varjenje s hlajenjem oplaščene elektrode...........KZT 31 (1997) 1-2, 139-142 Jaklič Anton, B. Breskvar, B. Ule: Računalniško podprt merilni sistem pri preizkusih lezenja ............................... .............................................KZT 31 (1997) 1-2, 143-145 Pihura Derviš, M. Jotanovič: Segregiranje posameznih elementov v konti odlitkih visokoogljičnega jekla........... .............................................KZT 31 (1997) 1-2, 147-149 Vasevska Trajanka: Lastnosti aluminija A199,7, ki je namenjen za izdelavo znotraj zaščitenih stisljivih tub z udarnim brizganjem ..........KZT 31 (1997) 1-2, 151-154 Tušek Janez, M. Suban, J. Tome: Sinergija v varilstvu .. .............................................KZT 31 (1997) 1-2, 155-157 Kevorkijan Varužan M.: Some General Considerations about a "Ideal" Ceramic Reinforcement for Structural Discontinuously Reinforced A1MC Composites Prepared by Liquid Metal Routes ....KZT 31 (1997) 1-2, 177-186 Fajfar Peter, R. Turk, V. Nardin, R. Robič: Računalniško podprta simulacija plana valjanja trakov na valjalnem stroju Steckel .....................KZT 31 (1997) 3-4, 193-196 Koc Pino, B. Štok: Računalniško podprta karakterizacija termo-reoloških lastnosti snovi ............................. .............................................KZT 31 (1997) 3-4, 197-200 Anžel Ivan, L. Kosec: Kinetika notranje oksidacije v hitro strjenih zlitinah Cu-Zr............................................. .............................................KZT 31 (1997) 3-4, 201-204 Gliha Vladimir, I. Rak, N. Gubeljak: Vpliv mehkega korena na vedenje zvarnega spoja pri lomu ................... .............................................KZT 31 (1997) 3-4, 205-207 Steiner Petrovič Darja, M. Jenko, F. Vodopivec, H. J. Grabke: Vpliv antimona na razogljičenje zlitine Fe-Si-AI .............................................KZT 31 (1997) 3-4, 209-211 Kevorkijan Varužan M.: Razvoj postopkov pridobivanja kompozitov na osnovi zlitin Al, diskontinuirano ojačanih s kemijsko aktiviranimi pepeli ......................................... .............................................KZT 31 (1997) 3-4, 213-218 Sabolič-Mijovič Mojca, B. Šarler: Sistem za zajemanje, arhiviranje, spremljanje in analizo procesnih parametrov polkontinuirnega ulivanja v IMPOL-u, Slovenska Bistrica ....................................KZT 31 (1997) 3-4, 255-259 Tušek Janez: Kaj morajo načrtovalci novih proizvodov vedeti o tehniki spajanja? ................................................. .............................................KZT 31 (1997) 3-4, 261-265 Kundak Mijo, J. Črnko: Analysis of State and Possibili- ties for a Profitable Production of Steel in Croatia......... .............................................KZT 31 (1997) 3-4, 285-290 Vehovar Leopold, S. Ažman: Določanje vezalne energije pasti za vodik z visoko temperaturno vakuumsko ekstrak-cijo .........................................KZT 31 (1997) 5,299-304 Vehovar Leopold, S. Ažman: Vpliv prehodnih elementov in njihovih karbidov na aktivacijsko in vezalno energijo pasti v mikrolegiranih jeklih ............................................ .................................................KZT 31 (1997) 5, 305-311 Smolej Anton, P. Panzalovič, M. Jelen: Vpliv dodatka Al- Ti-B na mikrostrukturo zlitine AlMgSiO,5 ...................... ................................................KZT 31 (1997) 5, 313-317 Grum Janez: Vpliv mikrostrukture aluminijevih zlitin s silicijem na hrapavost površine po finem struženju......... ................................................KZT 31 (1997) 5, 319-326 Grum Janez, P. Žerovnik, D. Ferlan: Vpliv toplotne obdelave in brušenja na zaostale notranje napetosti............ ................................................KZT 31 (1997) 5, 327-335 Bizjak Milan, L. Kosec, G. Dražič, P. Panjan, A. Cvelbar: Določitev kinetike sprememb v hitro strjenih zlitinah aluminij-železo na osnovi meritev električne upornosti . ................................................KZT 31 (1997) 5, 337-340 Bizjak Milan, A. Pregelj, B. Praček: Razplinjevanje prahov pred zgoščevanjem .................................................... .................T..............................KZT 31 (1997) 5, 341-344 Vodopivec Franc, B. Ule, J. Žvokelj: O deformacijski odpornosti jekel po uporabi v visokotlačnem parnem kotlu ................................................KZT 31 (1997) 5, 361-368 Vojvodič Gvardjančič Jelena, D. Korošec: Neporušne preiskave reaktorske tlačne posode v jedrski elektrarni Krško .....................................KZT 31 (1997) 5, 369-375 Šuštaršič Borivoj, V. Uršič, Z. Lengar, U. Bavdek: Op-timiranje priprave prahov za sintrane magnete Alnico ... ................................................KZT 31 (1997) 5, 377-385 Manojlovič Gojko: Izboljšanje kakovosti gredic kvadrat 180 mm z omejitvijo ohlajanja ........................................ ................................................KZT 31 (1997) 5, 387-389 Filipič Bogdan, B. Sarler: Optimizacija procesnih parametrov pri kontinuiranem ulivanju jekla v železarni ACRONI Jesenice ............................................................. ................................................KZT 31 (1997) 5, 391-395 Nardin Vladimir, M. Terčelj, R. Turk, T. Rodič: Nova ekspertna metoda za določevanje obrabe orodij v laboratoriju ..........................................KZT 31 (1997) 5, 397-402 Rihar Gabriel: Konstrukcijski materiali in tehnike spajanja .......................................KZT 31 (1997) 5, 403-407 Kejžar Rajko, B. Kejžar: Legirani praški za navarjanje z večžično elektrodo ................KZT 31 (1997) 5, 409-411 Kejžar Rajko: Prednosti navarjanja s strženskimi žicami ................................................KZT 31 (1997) 5, 413-417 Zore Borut, L. Kosec: Mehanske lastnosti spajkanih spojev ..........................................KZT 31 (1997) 5, 419-424 Zore Borut, L. Kosec: Armirani spajkani spoji povečane žilavosti .................................KZT 31 (1997) 5, 425-430 Liščic Božidar: Influence of Heat Transfer Dynamics on Hardness Distribution after Quenching ........................... ................................................KZT 31 (1997) 6, 521-528 Mayr Peter, H. Vetters, A. Schulz: Methods for the Vali-dation of Advanced Thin Hard Protective Coatings - an European Program ................KZT 31 (1997) 6, 529-531 Drobnjak Djordje, A. Koprivica: As-Rolled Multi-Phase Microalloyed Steel Bars with Improved Properties ........ .................................................KZT 31 (1997) 6, 533-537 Scherngell Heinrich, A. C. Kneissl: Two-Way Shape Memory Effect and its Degradation During Thermal Cy-cles in Ni-Ti Alloys ...............KZT 31 (1997) 6, 539-543 Etienne F., E. Ziarovski: Introduction of Unshaped Re- fractories in the Wear Lining of Steel Ladies.................. .................................................KZT 31 (1997) 6, 545-549 Leskovšek Vojteh, M. Doberšek, A. Rodič: Pulse Plasma Nitrocarburising of Gas Shock Absorber Tubes from Steel W.No. 1.0116 ...............KZT 31 (1997) 6,551-555 Mickovski Jovan K., N. Nacevski, B. Nikov, S. Milo-sevski: Possibilities and Perspectives for Development of Metallurgy in the Republic of Macedonia ....................... .................................................KZT 31 (1997) 6, 557-562 Nacevski Nikola, B. Nikov: Investigation of Kinetics Leaching and Extraction of Vanadiumpentoxyde as a Function of Temperature.......KZT 31 (1997) 6, 563-565 Gojič Mirko, L. Kosec, L. Vehovar: Mechanical and Mi- crostructural Properties of Duplex Steel .......................... .................................................KZT 31 (1997) 6, 593-598 Anorganski materiali - Inorganic Materials Rawn Claudia J., D. Makovec, Z. Samardžija, D. Kolar: Structural Investigation of Ba6-xLn8+2/3xTii8054 Isostruc-tural Ce Compound ...........KZT 31 (1997) 1-2, 047-050 Podlipnik Mojca, M. Valant, D. Suvorov: Raziskave vgrajevanja Pb2+ v keramiko na osnovi trdnih raztopin Ba6-xNd8+2/3xTii8054 ..........KZT 31 (1997) 1-2, 051-054 Zupan Klementina: Priprava materialov na osnovi LaCrOj z zgorevalno sintezo citratno-nitratnega gela .... .............................................KZT 31 (1997) 1-2, 055-057 Marinšek Marjan, J. Maček: Priprava Ni-YSZ kompozitnih materialov za visokotemperaturne gorivne celice...... .............................................KZT 31 (1997) 1-2, 059-062 Samardžija Zoran, M. Čeh: Electron Probe Microana- lysis in Materials Characterization................................... .............................................KZT 31 (1997) 1-2, 063-067 Selih Jana: Visokovredni betoni na osnovi domačih materialov ...............................KZT 31 (1997) 1-2, 159-161 Ogrinc Nives, P. Vidmar, I. Kobal, M. Senegačnik: Investigations of Surface Reactions by Kinetic Isotope Effects .............................................KZT 31 (1997) 3-4, 219-222 Umek Urban, B. Mirtič: Karakterizacija surovin za žganje cementnega klinkerja............................................. .............................................KZT 31 (1997) 3-4, 223-225 Rokavec Duška, B. Mirtič: Uporabna vrednost različnih vrst glin iz Globokega, Slovenija ..................................... .............................................KZT 31 (1997) 3-4, 267-269 Lisjak Darja, M. Drofenik: Vpliv mikrostrukture na električne lastnosti keramike Zn-Ni-0 ................................... .................................................KZT 31 (1997) 5, 345-349 Urek Sandra, M. Drofenik: Sinteza in lastnosti prahov Bai-xLaxTi03, pripravljenih s hidrotermalno sintezo ...... ................................................KZT 31 (1997) 5, 351-355 Čop Rudi: Dimenzioniranje posebnih vrst betona z določeno prostorninsko maso........................................... ................................................KZT 31 (1997) 5, 357-360 Lukan Alessandro: Sušenje peska pri proizvodnji asfaltov ..........................................KZT 31 (1997) 5, 431-435 Čop Rudi: Zagotavljanje kvalitete betonskih polizdelkov ..............................................KZT 31 (1997) 5, 437-440 Kolar Drago: Chemistry Controlled Sintering and Microstructure Development in Ceramics ................................. ................................................KZT 31 (1997) 6, 477-484 Daviš Robert F., C. M. Balkas, M. D. Bremser, O. H. Nam, W. G. Perry, B. L. Ward, L. Bergman, R. J. Ne-manich, Z. Sitar, T. Zheleva, I. K. Shmagin, J. F. Muth, R. M. Kolbas: Grovvth of III-Nitrides Via Sublimation and Metalorganic Vapor Phase Epitaxy............................ .................................................KZT 31 (1997) 6,485-494 Vodopivec Franc: Pionieer Years of Electron Probe Mi-croanalysis in Slovenia ..........KZT 31 (1997) 6,495-500 Komelj Matej, S. Kobe: The Difference Between the Magneto- Crystalline Anisotropy of Intermetallic Alloy Pr2(Coo5Feo