VSEBINA – CONTENTS PREGLEDNI ^LANKI – REVIEW ARTICLES Operation mikrostructure and lifetime of gas turbine engine (GTE) components Delovna mikrostruktura in trajnostna doba sestavnih delov plinskih turbin (GTE) L. B. Getsov, G. P. Okatova, A. I. Rybnikov, D. G. Fedorchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 IZVIRNI ZNANSTVENI ^LANKI – ORIGINAL SCIENTIFIC ARTICLES Modeling of the piezoelectric effect using the finite-element method (FEM) Modeliranje piezoelektri~nih pojavov z metodo kon~nih elementov S. Avdiaj, J. [etina, N. Syla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Variable thermal loading analysis of (110) single crystal tungsten Analiza spremenljive termi~ne obremenitve volframovega (100) monokristala R. Murugavel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Superplasticity of the 5083 aluminium alloy with the addition of scandium Superplasti~nost aluminijeve zlitine 5083 z dodatkom skandija A. Smolej, B. Skaza, E. Sla~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Wear resistance of chromium pre-alloyed sintered steels Obrabna obstojnost kromovih sintranih jekel R. Bidulský, M. Actis Grande, J. Bidulská, T. Kva~kaj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Preparation and testing of prototype Mg2Si-Mg-TiC and Mg2Si-TiC/TiB2 composites Priprava in preizku{anje prototipnih kompozitov Mg2Si-Mg-TiC/TiB2 in Mg2Si-TiC/TiB2 V. Kevorkijan, S. D. [kapin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 The effect of water cooling on the leaching behaviour of EAF slag from stainless steel production Vpliv vodnega hlajenja na izlu`evalne karakteristike bele EOP-`lindre M. Loncnar, M. Zupan~i~, P. Bukovec, A. Jakli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Modifikacija polimera polietilen naftalat z obdelavo v kisikovi plazmi Modification of a polyethylene naphthalate polymer using an oxygen plasma treatment A. Vesel, K. Eler{i~, I. Junkar, B. Mali~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 STROKOVNI ^LANKI – PROFESSIONAL ARTICLES The properties of a sintered product based on electrofilter ash Lastnosti sintranega produkta iz elektrofiltrskega pepela M. Krgovi}, M. Kne`evi}, M. Ivanovi}, I. Bo{kovi}, M. Vuk~evi}, R. Zejak, B. Zlati~anin, S. Ðurkovi} . . . . . . . . . . . . . . . . . . . . . . . . 327 LETNO KAZALO – INDEX Letnik 43 (2009), 1–6 – Volume 43 (2009), 1–6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 ISSN 1580-2949 UDK 669+666+678+53 MTAEC9, 43(6)275–342(2009) MATER. TEHNOL. LETNIK VOLUME 43 [TEV. NO. 6 STR. P. 275–342 LJUBLJANA SLOVENIJA NOV.–DEC. 2009 L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... OPERATION MIKROSTRUCTURE AND LIFETIME OF GAS TURBINE ENGINE (GTE) COMPONENTS DELOVNA MIKROSTRUKTURA IN TRAJNOSTNA DOBA SESTAVNIH DELOV PLINSKIH TURBIN (GTE) Leonid B. Getsov1, G. P. Okatova2, A. I. Rybnikov3, D. G. Fedorchenko4 1State Polytechnic University, SPb; Zakevskii pr. 43 appt. 89, 195213 Russia, St. Petersburg 2Byelorussian Scientific & Research Institute of Powder Metallurgy 3NPO CKTI 4Energomash Corporation guetsov@yahoo.com Prejem rokopisa – received: 2008-11-15; sprejem za objavo – accepted for publication: 2009-06-04 Changes of microstructure and mechanical properties of stels and alloys and protection coatings decreasing the serviceability of components after long time use in gas turbine engines are described. Different examples of damage on turbine blades are shown. Methods for the evaluation of residual life of components are suggested. For a large series of metals and alloys, the high temperature properties after annealing up to 40 000 in temperature range 550 °C to 900 °C and are given, also. Key words: gas turbine components, steels and alloys, changes of microstructure and properties, method of evaluation of serviceability Opisane so spremembe mikrostrukture in mehanskih lastnosti jekel in zlitin ter varovalnih prevlek, ki zmanj{ajo trajnostno dobo sestavnih delov plinskih turbin. Prikazani so razli~ni primeri po{kodb lopatic teh turbin. Predlagane so metode za oceno preostale trajnostne dobe sestavnih delov. Za precej{nje {tevilo jekel in zlitin so navedene mehanske lastnosti pri visokih temperaturah do 40 000 h `arjenja v razponu temperatur med 550 °C in 900 °C. Klju~ne besede: sestavni deli plinskih turbin, jekla in zlitine, sprememba mikrostrukture in lastnosti, metode za oceno preostale trajnostne dobe 1 INTRODUCTION For the manufacture of components for gas turbines a great variety of special steels and alloys are used because of the continuously increasing operating temperature. This led to the situation of components and materials in use in various GT units with serviceability not suited sufficiently for the operating temperature and time. Therefore, the acquisition of data on the microstructural state of GTE components from such materials may indicate to operationl damages and highlight the poten- tial of the prolongation of their lifetime. 2 MATERIAL MICROSTRUCTURE AND CONTINUOUS OPERATION BEHAVIOR The serviceability features related to the operating times at elevated temperatures include 1: 1. Needle-like topological close-packed phases ( and ) appearing in the Ni-based high-temperature alloys microstructures may degrade the ductility and long-term strength causing possibly, also, non expected changes of high-temperature strength and low-cycle fatigue resi- stance. 2. A des-alloyed layer formed at the surface of high- temperature alloys may lower the long-term strength, low-cycle fatigue and thermal fatigue resistance, while the change of composition and thickness of the coating layer due to the diffusion redistribution of elements with the parent metals may degrade significantly the protec- tive capability of the coating. 3. The decrease of grain size in austenitic steels and Ni-alloys indicates to the progressing of recrystalliza- tion, while, grain size coarsening indicates to a signi- ficant increase of temperature. 4. Creep pores along the grain boundaries testify for a considerable material degradation, particularly the lowering of ductility. 5. The decrease of the share of –phase and it coarsening at continuous operation is sign of softening of Ni-based high-temperature alloys caused by high tempe- ratures. The increase of the share of finely dispersed -phase indidates either to a long-time exposure of the alloy to low temperatures that may cause embrittlement, or to a considerable overheating with -phase dissolu- tion and precipitation at cooling as fine dispersion (Figure 1). 6. With increased presence of a second-phase at grain boundaries, the alloy ductility is diminished. 7. The recrystallization at the surface of single- crystal blades, irrespective of its reason (manufacture, operation, coating application), degrades the long-term strength and thermal fatigue resistance of blades. A careful metallographic examination may discover microcracks of different origin appeared in the manu- Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 277 UDK 669.1:621.438:620.18 ISSN 1580-2949 Pregledni ~lanek/Review article MTAEC9, 43(6)277(2009) facturing of the alloy, the manufacturing of components, GTE testing and GTE operation. Micro-cracks impair the alloy properties, affect its serviceability and can, in certain conditions, grow in size at static and at low-cycle stressing creep and at vibratory stressing. 3 EFFECT OF CONTINUOUS OPERATION ON MATERIAL PROPERTIES Long-term exposure of a material to elevated temperatures can significantly affect its serviceability. Relationships have been proposed that connect the mechanical properties with the operating conditions5. Extending the concept of the creep equation with Rabotnov’s structural parameters si. p= F(s1(,T), s2(,T), s3(,T), ..... T,) (1) to other material properties the relationships have been proposed: B = F(s1(,T), s2(,T), s3(,T), ....T,v) (2) 0,2 = F(s1(,T), s2(,T), s3(,T), ....T, v) (3) lts.= F(s1(,T), s2(,T), s3(,T), ... T,t) (4)  = F(s1(,T), s2(,T), s3(,T), ... T,v) (5)  = F(s1(,T), s2(,T), s3(,T), ... Tmax, Tmin, N, c) (6) S0,4 = F(s1(,T), s2(,T), s3(,T), ... T,v) (7) dl/d = F(s1(,T), s2(,T), s3(,T), ... T,K1) (8) With: v – deformation rate, c, Tmax, Tmin, N – respec- tively, cycle period, maximal and minimal cycle tem- perature, number of cycles to the initiation of thermal fatigue cracks for thermal cyclic loading, 1 – stress intensity factor. Note that, unlike1 this article is aimed to define the criteria characterizing the microstructural state, thus, to impart a physical meaning to the micro- structural parameters s1(,T), s2(,T), s3(, T), ... To estimate the stress-strain state and safety margins for the components of a definite alloy allowing for changes of microstructure, it is necessary to know the kinetics of change of yield strength 0,2, elongation , creep rate p, creep cracks growth rate dl/d , cyclic de- formation strength S0,4, thermal fatigue  and long-term strength lts. after long time high temperature exposure of the component. Tables 1–5 show the mechanical properties and long-term strength tested on a number of steels and alloys applied in GT units in continuous operation5. It is possible to derive digitally a discrete form for the equations (2) to (8) applying the data given in the tables. 4 CONCEPT OF LIFETIME PROLONGATION FOR GTE COMPONENTS To estimate the quality of the microstructure of components after long time operation, which is the basis of a reliable prediction fof lifetime prolongation, diffe- rent methods may be applied2,3,4, metallographic exami- nation with the replication method, X-ray inspection 278 Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... Figure1: Microstructure of a blade overheated in operation Slika 1: Mikrostruktura lopatice, ki je bila pregreta pri uporabi Table 1: Effect of long time exposure on mechanical properties of steels and alloys Tabela 1: Vpliv dolgotrajnega zadr`anja na mehanske lastnosti jekel in zlitin Material Anneling Conditions Test Conditions Time to Fracture, tf/h Elongation T/oC Time, t/h Tt/oC /MPa /% EI481 (37Õ12Í7Ã8ÌÔÁ) 650 0 650 270 1000 4.14 40000 72 30 EP126 (ÕÍ28ÂÌÀÁ) 800 0 900 50 242 18 5000 65 45 EI787 (ÕÍ35ÂÒÞ) 650 0 650 380* 1350 - 10000 148 - 0 650 350 8000 1,6 50000 442 15 EP99 (ÕÍ50ÌÂÊÒÞÐ) 800 0 800 200 374 24 5000 193 20.4 EP126 (ÕÍ28ÂÌÀÁ) 800 0 800 100 684 28.8 5000 151 10 800 0 900 50 242 18 5000 65 45 L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 279 Table 2: Effect of long time exposure on mechanical properties of Ni-based steels and alloys Tabela 2: Vpliv dolgotrajnega zadr`anja na mehanske lastnosti nikljevih jekel in zlitin Alloy Aging Temperature, Ta/°C Aging Time, ta/h Test Temperature, Tt/°C 0,2/ Mpa b/MPa /% /% EP99 Initial 20 815 1170 50.2 – 750 5000 610 900 57 – 800 2000 982 1040 0.5 – 5000 848 1230 5.0 – 900 2000 858 990 1.0 – 10000 502 765 4.7 – GS6U Initial – 760–850 770–900 5.9–27.8 12–28 800 2000 880 1030 1.2 – 5000 853 862 12.7 – 850 2000 710–900 880–910 1.5 7.0 5000 820 1040 5.9 5.9 900 2000 678 832 11.1 12.6 EP220 Initial – 800 771 1008 6.5 10.8 800 16000 816 892 1?9 6,5 EI929 (ÕÍ55ÂÌÒÊÞ) 550 10000 20 777 1170 18 18 600 10000 780 1160 15 17 650 10000 810 1130 11.5 11.5 700 10000 750 1200 17 16 750 10000 690 1220 23 22 800 10000 630 1030 15 15 EI893Ë Initial – 513 734 23.5 22 700 5000 578 817 13.1 18,2 750 5000 470 757 16.2 22.7 800 5000 442 706 16.1 19.1 EP126 Initial – 468 890 41 – 750 10000 479 819 3.9 – 800 10000 446 872 14.2 – 900 10000 364 814 24.4 – EI703 (ÕÍ38Ò) Initial – 460 808 40.3 – 750 10000 338 713 19.8 – 800 10000 313 709 30.2 – 900 5000 165 550 44 CNK–7 RS 700 3000 20 864–975 880–1007 0.8–3.9 0.7–7.5 700 847 1082 7 14.4 750 3000 20 838 888 1.7 7.9 750 793–826 931–1021 3.2–5.0 6.2–10 800 3000 20 718–753 791–867 1.9–4.5 6.2–12.9 800 690–753 796–862 6.1–10.8 9.7–24.9 850 3000 20 672–772 779–833 2.3–5.1 2.2–12 850 584–650 690–760 3.1–13.1 8.4–24.9 ZMI–3 650 5000 20 845–877 909–944 1.8–1.5 8.1 650 817 976 3.7 700 3000 20 842–917 934–972 1.8–4.1 3.6–4.0 700 891–905 1050 4.0–6.4 4.0–8.2 750 3000 20 807 874 2.0 4.9 750 745 947 12.4 18.7 800 3000 20 701–848 764–948 1.4–5.0 2.7–7.0 800 649–848 745–948 4.0–12.0 6.2–19.7 850 3000 20 617–772 724–859 2.9–4.0 4.6–5.0 850 460–690 626–820 3.7–13.6 5.2–22.0 GS6K 600 10000 20 1000–1100 1070 2.1 4.6–5.6 600 1000 1080 2.2 5.6 650 10000 20 1040 1080 2.9 4.3–5.3 650 990 1060 1.6 3.0 700 10000 20 1000 1020 1.5–1.7 1.4–1.6 700 1000 1060 0.8 0.9 800 10000 20 830 950 1.6 2.0 800 820 950 2.2 4.3 850 10000 20 730–780 920–890 2.5–3.5 5.0–5.6 850 710 810 1.7 2,1 900 10000 20 680 840–890 3.0–4,3 5.5–6.5 900 620 670 2.2 2,0 950 10000 20 630 800–870 3.0–3.5 4.5–8.2 950 500 560 5.4 7.5 1000 1000 20 740 860–900 2.3–2.5 2.8–4.8 EI481 Initial – 20 733–806 1054–1068 17.8–23.7 24.5–43.2 650 497–506 599–614 14.3–14.7 45.0 550 10000 20 772–792 103–106 18.4–22.2 28.4–40.7 650 557–595 620–658 9–10 35.2–35.5 600 10000 20 613–622 964–955 20.6–24.2 28.9–29.9 650 422–437 540 15.0–15.5 41–43.2 650 10000 20 415 813 24.8 29.2 650 328 453 18.5 39.5 with phase analysis, X-ray spectral micro-analysis, etc. and appying interrelation of microstructure and proper- ties. The quality criteria for microstructure and it distri- bution all over the component body should be established up for each material considering the stressing and stress distribution of the GTE component consi- dered. Based on the all-inclusive study of the interrelation between residual endurance and some microstructural features emerging in the metal as result of its damage, the blades of engines run at different operating and climatic conditions1,6,7.8,9 can be examined and the effect of operating rate on damage rate increase estimated. The base for decision is the comparison with the initial microstructure. For the indirect evaluation of the quality of the surface layer, it is advisable to measure its hardness and micro-hardness. With turbine blades as example, in the scheme of the methodology for predicting the residual capacity of GTE high-temperature components after long time operation is shown in Figure 2. 280 Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... Table 3: Effect of long time exposure on plasto-elastic deformation strength for pearlitic and martensitic steels (0.2 aged/0,2init) at 20 °C Tabela 3: Vpliv dolgotrajnega zadr`anja na plasto-elasti~no deformacijsko trdnost perlitnih in martenzitnih jekel (0.2 aged/0,2init) pri 20 °C Aging Temperature, Ta/°C Aging Time, ta/h 15ÕÌÔ EI802 (15Õ12ÂÍÌÔ) EP752 EP291 15Õ11MÔ 20Õ13 500 40000 0.88 550 5000 0.92 550 10000 0.86 600 5000 0.89 0.92 600 10000 0.78 0.75 600 30000 0.78 620 2500 0.84 650 2500 0.78 650 5000 0.86 650 10000 0.82 Table 4: Effect of long time exposure on plastoe-elastic deformation strength for austenitic steels (0.2 aged/0,2init) at 20 °C Tabela 4: Vpliv dolgotrajnega zadr`anja na plasto-elasti~no deformacijsko trdnost avstenitnih jekel (0.2 aged/0,2init) pri 20 °C Aging Temperature, Ta/°C Aging Time, ta/h 20Õ23Í18 EI572 EI481 EI787 EI703 600 5000 1 1 1,2 650 10000 1.13 - 0.83 0.94 20000 1 0.87 30000 0.91 700 5000 0.79 0.7 10000 1.1 750 5000 1 0.75 0.8 Table 5: Effect of long time exposure on plasto-elastic deformation strength for Ni-based alloys (0.2 aged/0,2init) at 20 °C. Tabela 5: Vpliv dolgotrajnega zadr`anja na plasto-elasti~no deformacijsko trdnost nikljevih zlitin (0.2 aged/0,2init) pri 20 °C Aging Temp., Ta/°C Aging Time, ta/h EI868 EP99 EP220 EI607 VG85 EI867 EI437B 700 10000 0.69 0.89 750 500 1 - - - - - 1.36 1000 1 - - - 1.03 - - 5000 0.9 - - - 1.07 - - 10000 0.83 - - - - - - 800 2000 0.9 1.2 0.9 - 1.03 - - 5000 0.87 1.04 0.83 - 0.95 - - 16000 0.77 - 0.9 - - - — 900 1000 0.75 - - - 1 0.82 - 2000 0.78 1.05 0.93 0.82 5000 0.78 - 0.85 - 0.59 - - 10000 0.68 0.62 - - - - - 5 COATING QUALITY CRITERIA The reliability of the prediction of the residual service life of coated parts depends largely on the state of the coating1,10. After long time the coating quality use depends on its type: diffusion, condensation, metallic, metallic with an outer ceramic layer. As a rule, the quality of the coating after use is evaluated in comparison with its initial quality. In this case, the quality criteria for diffusion and metal condensation coatings after long use are: layer thickness uniformity, absence of chipping and coating layer peeling, absence of cracks, especially thermal fatigue cracks (Figure 3), of significant surface oxidation (Figure 4) and pit-type corrosion damage, absence of significant redistribution of the basic alloying elements of the coating (Al, Cr) and significant changes in phase composition of the coating. The impoverishment of a diffusion coating with aluminum and chrome reduces sharply it protective properties and, as with pits formation, leads to the decrease of service life. The methods of calculated prediction of the diffusion redistribution of coating elements were examined in1. As criterion of service- ability of diffusion coatings the decrease of surface concentration of the element determining the protection against corrosion by up to one third of the difference between the initial concentration in the coating and in L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 281 Figure2: Methodology for predicting the residual capacity of turbine blades (Kmin is the minimal safety margin value all over the blade) Slika 2: Metodologija za napovedovanje rezidualne uporabnosti turbinskih lopatic (Kmin je vrednost minimalnega varnostnega razpona na celi lopatici) Figure 4: Turbine blades without (a) and with a thermal-barrier ceramic coating (b, c) after comparison tests in an impeller of an aircraft gas-turbine engine: b – view of the blade before carbon deposit removal, c – view of the blade after carbon deposit removal Slika 4: Turbinske lopatice brez (a) kerami~ne pokrivne plasti in z njo (b, c) po primerjalnih preizkusih v impellerju letalske plinske turbine; b- videz lopatice pred odstranitvijo depozita ogljika, c – vodez lopatice po odstranitvi depozita ogljika Figure3: Appearance of burning-out thermal fatigue cracks in the basic material of the edge of a turbine blade of @S6 alloy with NiCrAlY coating Slika 3: Videz od`ganih termi~nih razpok v materialu roba lopatice iz zlitine @S6 s pokrivno plastjo NiCrAlY Figure 5: Peeling of the ceramic layer of the thermal protection coating of a turbine blade after the expiration of its operating time in the engine Slika 5: Lu{~enje varovalne kerami~ne prevleke po preteku dobe uporabnosti v motorju the basic metal can be used. Coating corrosion damage with depth up to 2/3 of the layer thickness can be used as second criterion. For ceramic coating layers, the criteria of quality are: porosity (density), uniformity of layer thickness, thick- ness of the interlayer Al2O3 on the side of the metallic layer and, most importantly, the presence of chipping, cracking and peeling (Figures 5 and 6). On the contrary, the fragmentation of the thermal protection coating layer (Figure 7) increases the resistance to cracking and peeling and is not a defect. 6 CONCLUSION The investigations of changes of microstructure and mechanical characteristics of materials and coatings after long use enable to solve, on scientifical base, questions connected with the possibility of increasing the service life of parts. Knowing the dependence of properties and microstructure of materials, it is possible to evaluate the change of initial properties with examination of the microstructure and predict the residual service life. The data for a number of materials cited in this report can serve as the basis for such predictions. 7 REFERENCES 1 Getsov L. B. Materials and strength of gas turbine parts. M: Nedra, 1996, 590 p 2 Artamonov V. V., Artamonov V. P. Improvement of metal prediction methods for heat-power engineering equipment. Energetika (2000) 7, 34–39 3 Express control method for metal microstructure of power equipment (method of replicas). Report of the Scientific and Production Association attached to the Central Boiler-and-Turbine Research Institute (NPO TsKTI), 1987 4 V. P. Goltsev, T. T. Dedekaev, A. M. Dergay, A. I. Rybnikov, A. I. Rytvinski. X-ray spectral and electron-microscopic methods of examining the structure and properties of materials/ Minsk. Nauka I Tekhnika. 1980, 190 p 5 Getsov L. B., Rybnikov A. I., Pigrova G. D. Changes in the structure and properties of steels and alloys during long operation at high tem- perature. /EUROMECH-MECAMAT 98, 3rd European Mechanics of Materials Conference on mechanics and multi-physics processes in solids: experiment, modeling, applications, Oxford-U. K., 23–25 November, 1998, Ed. E.Busso, G.Cailletaud, Pr.9-105-115 6 Zakharova T. P., Pimenova G. P. Calculated experimental deter- mination of the residual durability of turbine blades. Intercollegiate Collection of Articles "Vibration Strength and Reliability of Engines and Aircraft Systems", Issue 8, Kuibyshev, 1981, 47–57 7 Gordeyeva T. A., Gerchikova N. S., Kozlova M. N., Samoilov A. I. et al. Methods of investigating the state of the materials of gas-turbine rocket engine parts and its change during operation. Instruction ¹ 1050-75. M., All-Russian Research Institute for Aircraft Materials (VIAM), 1975, 39 p 8 Pimenova G. P. Investigation of blades made of ZhS6KP alloy and ways of extending their service life. Thesis for a Scientific Degree (Candidate of Engineering Science) Kazan, 1973 9 Pimenova G. P. Metallurgical criteria of serviceability and sub- stantiation of the service life of turbine blades of engines in NK series. Theses of the Scientific and Technical Conference "High- Temperature Deformable Alloys for Gas-Turbine Engines". M., VIAM, 1977 10 Pimenova G. P. Investigation of the calorized layer and damage- ability of the turbine blades of NK engines. Theses of Reports at the 5th All-Union Conference "Structural Strength of Engines", Kuibyshev, 1978 L. B. GETSOV ET AL.: OPERATION MIKROSTRUCTURE & LIFETIME OF GAS TURBINE ENGINE ... 282 Materiali in tehnologije / Materials and technology 43 (2009) 6, 277–282 Figure 6: Cracks in and below the ceramic layer. Cracking and peeling of the ceramic layer of the blade in the process of operation Slika 6: Razpoke v in kerami~ni prevleki in pod njo. Razpokanje in lu{~enje kerami~ne prevleke med uporabo Figure 7: Fragmentation of the thermal protection ceramic coating Slika 7: Fragmentacija kerami~ne varovalne plasti S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... MODELING OF THE PIEZOELECTRIC EFFECT USING THE FINITE-ELEMENT METHOD (FEM) MODELIRANJE PIEZOELEKTRI^NIH POJAVOV Z METODO KON^NIH ELEMENTOV Sefer Avdiaj1, Janez [etina2, Naim Syla3 1Lotri}, d.o.o. Selca 163, 4227 Selca, Slovenia 2Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia 3University of Prishtina, Faculty of Natural Science and Mathematics, Mother Teresa av. 3, 10000, Prishtina, Kosovo sefer.avdiaj@imt.si Prejem rokopisa – received: 2009-06-08; sprejem za objavo – accepted for publication: 2009-07-16 Some solid, crystalline materials exhibit the piezoelectric effect, which is very interesting for a variety of technological applications. Piezoelectric materials are widely used in electromechanical sensors and actuators, such as robotics’ sensors, actuators, ultrasonic transducers for medical imaging and non-destructive testing. The paper presents the modeling of the piezoelectric effect in quartz, which is the most widely used material. The basic ideas of the finite-element method (FEM) for solving the problem of piezoelectric media are presented. All the results are based on linear piezoelectricity, in which the elastic, piezoelectric, and dielectric coefficients are treated as constants, independent of the magnitude and frequency of the applied mechanical stresses and electric fields. Starting with the tri-dimensional finite-element method, we have developed a numerical computational method for a determination of the electrical voltage (the direct piezoelectric effect) and the eigenmodes of vibration (the inverse piezoelectric effect). The finite-element method is normally used for solving problems related to macrostructures. The aim of this work is to show that the finite-element method (FEM) is also a useful and convenient method for solving problems in relation to microstructures. Here we present the solution to the problem of the piezoelectric effect using the FEM, approaching the problem from the microstructural point of view. Key-words: Finite-Element Method, Piezoelectricity, Modeling, Ansys, Quartz, Voltage, Eigenfrequencies Nekatere kristalini~ne trdne snovi izkazujejo piezoelektri~ni pojav, kar je zelo zanimivo za {tevilne tehnolo{ke aplikacije. Piezoelektri~ni materiali se ve~inoma rabijo za elektromehanske senzorje in aktuatorje, na primer v robotiki, za ultrazvo~ne pretvornike pri raznih slikanjih v medicini in neporu{nih presku{anjih. V prispevku obravnavamo modeliranje piezoelektri~nega pojava v kremenu, ki se najpogosteje uporablja v piezoelektri~nih napravah. Predstavljene so osnove metode kon~nih elementov (MKE) za numeri~no re{evanje problemov piezoelektri~nih struktur. Vsi prikazani rezultati so bili dobljeni za primer linearnega piezoelektri~nega pojava, kjer smo obravnavali elasti~ne, piezoelektri~ne in dielektri~ne koeficiente kot konstante, neodvisne od velikosti in frekvence mehanskih napetosti in elektri~nih polj. Za obravnavo prakti~nih primerov smo MKE aplicirali v treh dimenzijah in razvili numeri~ne ra~unske postopke za dolo~itev elektri~ne napetosti v odvisnosti od mehanskih napetosti (neposredni piezoelektri~ni pojav) ter dolo~itev lastnih nihajnih na~inov in frekvenc v primeru inverznega piezoelektri~nega pojava. Klju~ne besede: metoda kon~nih elementov, piezoelektri~ni pojav, modeliranje, Ansys, kremen, lastne frekvence 1 INTRODUCTION The Curie brothers, Jacques and Pierre, were two of the first people to experiment with common crystals such as quartz, topaz and sugar cane in the field of piezoelec- tricity in 1880 to 1882. The next 25 years (1882–1917) brought a substantial amount of information to be supported by mathematical calculations. Woldermar Voigt published a book that dealt with the physics of crystals, and research work was done in support of the book in reference to the effects of piezoelectricity such as, the changing of electrical into mechanical energy and vice versa. These French workers, along with P. Langevin, put together a submarine detector made of steel sheets and quartz. In this paper we treat the piezoelectric effect in quartz in a theoretical way; in Section 2 we treat a mathematical formalization that describes the piezoelec- tric effect; and in Section 3 we present the modeling of the piezoelectric effect with the FEM. The equations of piezoelectricity are sufficiently complex to preclude a closed form solution for all but the simplest cases. This is unfortunate since the piezoelectric effect plays an important role in the field of crystal physics and transducer technology (sensors and actuators). Previously, in the past 70 years, variational principles have been derived that serve as the basis of approximate solution techniques, such as the powerful Rayleight-Ritz method. Noteworthy contributions along these lines were made in the papers of Henno Allik and Thomas J. R. Hughes.1,2,4,8,16 Although these important developments have opened the way to wider class problems, they are not sufficiently general in themselves to be considered a universal method of piezoelectric analysis. For instance, a significant deficiency of the Rayleigh-Ritz technique is the necessity to select a trial function, which often becomes intractable for complex geometries. This paper concerns the development of a general method of electrostatic analysis by incorporating the Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 283 UDK 622.362:519.2 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)283(2009) piezoelectric effect in a finite-element method (FEM). The theory presented is, essentially, an expansion of the variational principle, which was used before by Holland and EerNisse1, presented here in a matrix fashion. The dynamical matrix derived for linear piezoelectricity is found to be reducible, in form, to the ordinary matrix equation encountered in structural dynamics. The electrostatic matrices for a simplex šdisplace- ment-potential’ for three-dimensional analysis are presented, thereby illustrating the method.1,2,3,8,16. The FEM is normally used for solving problems related to macrostructures. The aim of this work is to show that the FEM is also a useful and convenient method for solving problems in relation to micro- structures. Here we present the solution of the problem of the piezoelectric effect using the FEM, approaching the problem from the microstructural point of view. 2 FINITE ELEMENT APPROACH The study of physical systems frequently results in partial differential equations, which either cannot be solved analytically or lack an exact analytic solution due to the complexity of the boundary condition or domain. For a realistic and detailed study, a numerical method must be used to solve the problem. The finite-element method is often found to be the most appropriate. The FEM has successfully penetrated many areas, such as heat transfer, fluid mechanics, electromagnetism, acoustics and fracture mechanics. Basically, the finite element method consists of a piecewise application of classical variational methods to smaller and simpler sub-domains called finite elements connected to each other at a finite number of points called nodes.6,15 The fundamental principles of the finite-element method are: • The continuum is divided into a finite number of elements of a geometrically simple shape. • These elements are connected in a finite number of nodes. • The unknowns are the displacements of these nodes. • Polynomial interpolation functions are chosen to prescribe the unknown displacement field at each point of the element related to the corresponding field values at the nodes. • The forces applied to the structure are replaced by an equivalent system of forces applied to the nodes.2 A finite-element formulation accounting for the coupling between the equations of electrostatics and elastodynamics becomes necessary when the piezo- electric material represents a non-negligible fraction of the entire structure. Piezoelectric Finite Elements The constitutive equations of a linear piezoelectric material3 are: { } [ ]{ } [ ] { }T c S e EE T= − (1) { } [ ]{ } [ ]{ }D e S ES= − (2) where { } { }T T T T T T T= 11 22 33 23 13 12 is the vector of the mechanical stress, { } { }S S S S S S S= 11 22 33 23 13 122 is the vector of mechanical strains, { } { }E E E E= 1 2 3 is the vector of electric field, { } { }D D D D= 1 2 3 is the vector of dielectric displacement, [c]E is the mechanical stiffness matrix for a constant electric field E, [ ]S is the dielec- tric constant matrix for constant mechanical strain S, [e] is the piezoelectric coupling coefficients matrix, [e]T is transposed. The dynamic equations of a piezoelectric continuum can be derived from the Hamilton principle, in which the Lagrangian and the virtual work are properly adapted to include the electrical contribution as well as the mecha- nical ones. The potential energy density of a piezoelec- tric material includes a contribution from the strain energy and from the electrostatic energy2. The electric field E is related to electrical potential by E = –grad (3) and the mechanical strain S to the mechanical displace- ment u in the Cartesian coordinates by S / x / y / z / y / x / z / z / y / x = ⎡ ⎣ ⎢ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ 0 0 0 0 0 0 0 0 0 { } [ ]{ } ⎢ ⎤ ⎦ ⎥ ⎥ = T u B u (4) The elastic behavior of piezoelectric media is governed by Newton’s law: { } { } div T u t = ∂ ∂ 2 2 (5) where is the density of the piezoelectric medium, whereas the electrical behavior is described by Maxwell’s equation, taking into account the fact that the piezoelectric media are insulating (no free volume charge): { }div D = 0 (6) Equations (1) to (6) constitute a complete set of differential equations, which can be solved with the appropriate mechanical (displacement and forces) and electrical (potential and charge) boundary conditions. An equivalent description of above boundary-wave problem is Hamilton’s variational principle as extended to piezoelectric media,  ( )L W t t t + =∫ d 1 2 0 (7) where the operator  denotes the first-order variation, t1 and t2 define the time interval (all variations must vanish at t = t1 and t = t2) and the Lagrangian term L is determined by the energies available in the piezoelectric S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... 284 Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 medium and W is the virtual work of the external mechanical and electrical forces1,2,4. In the finite-element method the body to be computed is subdivided into small, discrete elements, the so-called finite elements. The mechanical displacement u and the forces f as well as the electrical potential and the charge q are determined at the nodes of these elements. The values of these mechanical and electrical quantities at an arbitrary position on the element are given by a linear combination of the polynomial interpolation function N(x,y,z) and the nodal point values of these quantities as a coefficient. For an element with n nodes (nodal coordinates: (xi, yi, zi), (i=1,2,….,n) the continuous displacement function u(x, y, z) (vector of order three), for example, can be evaluated from its discrete nodal point vectors as follows (the quantities with "0" are the nodal point values of one element): { } [ ]{ }u x y z N x y z u x y zu i i i( , , ) ( , , ) ( , , )= 0 (8) [ ]{ } = N x y z u x y zi i i( , , ) ( , , )0 (9) where{}u0 is the vector of the nodal point displacement and [Nu] is the interpolation function for the displace- ment. Therefore, the strain field { }S and the electric field { }E are related to the nodal displacement and potential by the shape-function derivatives [Bu] and [B ] defined by,12 { } [ ]{ }S B uu i= 0 (10) { } [ ]{ }E B i= − 0 (11) The substitution of the polynomial interpolation function into (8) yields a set of linear differential equations that describe a single piezoelectric finite element. { }{} [ ]{ } [ ]{ } { }M ü K u K fuu i u i i0 0 0 0+ + = (12) [ ]{ } [ ]{ } { }K u K qu i i i 0 0 0+ = (13) Each element k of the mesh is connected to its neighboring elements at the global nodes and the displacement is continuous from one element to the next. The element degrees of freedom (dof) { }{ }u i i0 0, ⎛⎝⎜ ⎞⎠⎟ are related to the global dof { } { }( )u , F by the mean of the localization matrices L u 0⎡ ⎣ ⎤ ⎦ and L 0 ⎡ ⎣ ⎤ ⎦: Hamilton’s principle (7) must be verified for the whole structure, which results in (by summation of the contribution from each finite element).1,2,3,4,8 { }{ } [ ]{ } [ ]{ } { }M U K U K FUU U + + =F F (14) [ ]{ } [ ]{ } { }K U K QUF FF F+ = (15) where the assembled matrices are given by: [ ] [ ] [ ][ ]M L M Luii T i ui= ∑ ( ) – kinematically consistent mass matrix [ ] [ ] [ ][ ]K L K Luu uii T uu i ui= ∑ ( ) – stiffness matrix [ ] [ ] [ ][ ]K L K LU uii T u i iF f f= ∑ ( ) – piezoelectric "stiffness" matrix [ ] [ ] [ ][ ]K L K LU ii T u i uiF f f= ∑ ( ) – transponse piezoelectric "stiffness" matrix [ ] [ ] [ ][ ]K L K Lii T i iFF f ff f= ∑ ( ) – dielectric "stiffness" matrix { } [ ] [ ]F L fuii T i= ∑ – external forces applied to the structure { } [ ] [ ]Q L qii T i= ∑ f – electrical charges brought to the electrodes Equations (14) and (15) couple the mechanical va- riables { }U and the electrical potentials { }F . Based on this formulation, a piezoelectric finite element of the type multilayered Mindlin shell and volume has been derived.2,3 For shell elements, it is assumed that the electric field and the displacement are uniform across the thickness and aligned on the normal to the mid-plane. The elec- trical degrees of freedom are the voltages k across the piezoelectric layers; it is assumed that the voltage is constant over each element (this implies that the finite element mesh follows the shape of the electrodes). One electrical degree of freedom of the type voltage per piezoelectric layer is defined. The assembly takes into account the equipotentiality condition of the electrodes; this reduces the number of electric variables to the number of electrodes. For volume elements, one additional degree of freedom of the type electric potential is introduced in each node of the piezoelectric volume element. 3 MODELING AND RESULTS As for selecting the element types, the decision is based on the characteristics of the element type to the best model that applies to the problem, geometrically and physically. The material properties are required for most element types. Depending on the element types, the material properties may be linear or non linear; isotropic or anisotropic; and constant temperature-independent or temperature-dependent. The starting points of the modeling of the effect of quartz are the differential equations (14) and (15). These equations are solved according to the FEM, supported by the ANSYS software, whereas the program was ADPL (ANSYS PARAMETRIC DESIGN LANGUAGE). In this paper, ANSYS was used as a computational tool for modeling the piezoelectric effect 6,7. For this purpose, a quartz sample is taken, with a density of 2695 kg/m3 and these dimensions: 90 mm × 120 mm × 27 mm 5, (Figure 2). We know that the crystal quartz is S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 285 in the form of a hexagonal cylinder surmounted by a hexagonal pyramid; the faces of the crystal, which may vary in length and breadth, lie at definite angles with each other (Figure 1) 9,13. Also, we know that pressure applied to the crystal parallel to electric axes produces a piezoelectric polarization in the same direction. Then, according to the FEM, the meshing is carried out (the division of the domain of integration into the finite integrating elements) into 1000 elements with 1331 nodes, Figure 3, and Table 1. As a finite element, from the library of ANSYS, the element SOLID 5 is taken, (Figure 4)6,7. The nodes of this element have degrees of freedom (dof): displace- ments along the axes x, y, z, the intensity of the electric potential, the intensity of the magnetic field and tempe- rature, so this is a multi-field element. Since we are discussing the linear piezoelectricity, the displacements (mechanical quantities) and electric potential (electrical quantities) are of interest to us. Coupled-fields in the ANSYS software can be treated on two ways to create a finite-element model: automatic meshing (also called the direct modeling in ANSYS terminology) and manual meshing (also called the direct generation in ANSY terminology). In automatic meshing the users are required to have a solid model available prior to the creation of a finite-element model. When such a solid model becomes available, the users can then S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... 286 Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 Figure 2: The quartz sample in the ANSYS window7 Slika 2: Kremenov vzorec v prikaznem oknu programa ANSYS Figure1: A section of a quartz crystal showing the direction of the optical axes (AB) and the electrical axes (CD, EF, GH)9 Slika 1: Prerez kremenovega kristala in prikaz smeri opti~nih osi (AB) in elektri~nih osi (CD, EF, GH) Table 1: Element and nodes of the sample7 Tabela 1: Matemati~ni opis kon~nih elementov in vozli{~ vzorca Elements Nodes LIST ALL SELECTED ELEMENTS. (LIST NODES) ELEM MAT TYP REL ESY SEC NODES 1 1 1 1 0 1 2 32 41 11 251 333 603 449 2 1 1 1 0 1 32 33 42 41 333 334 684 603 3 1 1 1 0 1 33 34 43 42 334 335 765 684 4 1 1 1 0 1 34 35 44 43 335 336 846 765 5 1 1 1 0 1 35 36 45 44 336 337 927 846 6 1 1 1 0 1 36 37 46 45 337 338 1008 927 995 1 1 1 0 1 926 1007 396 387 197 206 148 149 996 1 1 1 0 1 1007 1088 405 396 206 215 147 148 997 1 1 1 0 1 1088 1169 414 405 215 224 146 147 998 1 1 1 0 1 1169 1250 423 414 224 233 145 146 999 1 1 1 0 1 1250 1331 432 423 233 242 144 145 1000 1 1 1 0 1 1331 530 350 432 242 142 133 144 LIST ALL SELECTED NODES. DSYS = 0 SORT TABLE ON NODE NODE NODE NODE X Y Z 1 0.00000000000 0.120000000000 0.00000000000 2 0.00000000000 0.00000000000 0.00000000000 3 0.00000000000 0.108000000000 0.00000000000 4 0.00000000000 0.960000000000E-01 0.00000000000 5 0.00000000000 0.840000000000E-01 0.00000000000 6 0.00000000000 0.720000000000E-01 0.00000000000 1326 0.810000000000E-01 0.108000000000 0.108000000000E-01 1327 0.810000000000E-01 0.108000000000 0.135000000000E-01 1328 0.810000000000E-01 0.108000000000 0.162000000000E-01 1329 0.810000000000E-01 0.108000000000 0.189000000000E-01 1330 0.810000000000E-01 0.108000000000 0.216000000000E-01 1331 0.810000000000E-01 0.108000000000 0.243000000000E-01 Figure 3: Meshing of the integral zone for the quartz sample7 Slika 3: Razdelitev integracijskega obmo~ja kremenovega vzorca v kon~ne elemente instruct ANSYS to automatically develop a finite- element model (nodes and elements). The purpose of using automatic meshing is to relieve the user of the time-consuming task of building a complicated finite- element model. In manual meshing, the users need to define the nodes and elements directly (the development of a solid model is not required). The manual meshing method offers complete control over the geometry and connectivity of every node and every element, as well as the ease of keeping track of the identities of the nodes and elements. However, this method may not be as convenient as the automatic meshing method when dealing with a complicated finite-element model. It is, however, possible to combine both methods. In this paper we used the automatic meshing method. This is provided by the element SOLID 5, because it has a degree of freedom of different physical fields. SOLID 5 is a type of element that occupies three-dimensional space. In addition, it has eight nodes. Each of these nodes has three displacements along the x, y and z axes, respectively. The SOLID 5 element is capable of modeling seven different types of disciplines. When this particular type of discipline is chosen, ANSYS will only compute the behaviors of SOLID 5 in the UX, UY, UZ and VOLT degrees of freedom. It should be noted that UX, UY and UZ are to indicate the displacements in the X, Y and Z directions (the X, Y and Z axes are based on the global coordinate system), while VOLT is to indicate the difference in the potential energy of the electrical particles between two locations 6. More precisely, when we have the action of the mechanical field, we can automatically obtain the output quantities of the electric field from the element SOLID 5, and vice versa (the case of the inverse piezoelectric effect). Besides the geometry of the sample, the density of the quartz and the meshing, and introducing the element SOLID 5, we also have to take into account the other physical characteristics of quartz, in order to establish the initial condition for solving the differential equation. The physical characteristics that determine the solution of the differential equation are: the stiffness matrix cE, the dielectric constant matrix S, and the piezoelectric constant matrix e. The values for the above matrices at a temperature of 25 °C are: 8 [ ]c E = −86 74 6 99 11 91 17 91 0 0 6 99 86 74 11 91 17 91 0 0 11 9 . . . . . . . . . 1 11 91 107 2 0 0 0 17 91 17 91 0 57 94 0 0 0 0 0 0 57 94 17 91 0 0 . . . . . . . − − 0 0 17 91 39 88 109 2 − ⎛ ⎝ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⋅ . . N m (16) [ ]          S = ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⋅ ⋅ −10 12 C V m (17) [ ]e = − − − ⎛ ⎝ ⎜ ⎜ ⎞0171 0171 0 0 0406 0 0 0 0 0 0 0 0406 0171 0 0 0 0 0 0 . . . . . ⎠ ⎟ ⎟ C m 2 (18) Depending on the geometry of the sample, the physical characteristics of quartz, we have built a program to calculate the potential differences as a function of mechanical force, as well as the intensity of the deformation of the sample as a function of the electric voltage. In both cases, the calculations are carried out along the x axis (the electrical axis of the quartz). Below, we present the result of modeling for all cases: when the external mechanical forces compress the sample, when this force stretches the sample, and when an electric voltage is applied on the lateral faces of the sample (the inverse piezoelectric effect). 3.1.1 The direct piezoelectric effect (longitudinal) The external mechanical forces compress sample Assume that a mechanical force with intensity F is acting in the direction of the x-axis, i.e., in the direction of the normals of the lateral faces of the sample, in the positions x = 0 and x = 90 mm (in the opposite directions with the normal’s vector)9. Then, as a result of the action of this force, the sample will be stressed. The intensity of this stress is the force on the unit of the surface yz, Figure 5. As a result of the action of a mechanical force, we will have the accumulation of a positive and negative S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 287 Figure 4: Geometry of the SOLID 5 6,7 Slika 4: Geometrija elementa SOLID 5 v programu ANSYS Figure 5: The force acting in the direction of the x axis Slika 5: Mehanska sila pri stiskanju vzorca v smeri osi x electrical charge on the opposite lateral faces of the sample along the x-axis. In other words, we will have the transformation of mechanical energy into electric energy. This phenomenon is called the direct piezoelectric effect. Calculations are carried out for the cases when the force has the following intensities: 0.1 N, 0.08 N, 0.06 N, 0.04 N and 0.02 N. For these values of the intensities, we have calculated the potential difference as a function of depth. But, for practical reasons, we have not taken into account the fact that the opposite sides of the electrical poles in the interior of the sample are neutralized, and as a result the electric charges appear only on the surface. We made this approximation in order to prove the dependence of the intensity of the electrical potential on the depth. In Figure 6 we have presented the modeling result for two cases. The main results are the potential difference as a function of depth and the mechanical force, Figure 7. According to Figures 6 and 7 we can conclude the following: • The intensity of the electrical potential depends on the external mechanical force. For equal depths the intensity of the potential increases with the increase of the force. This dependence is shown in Table 2. Table 2: Potential difference [mV] as a function of depth [cm] and mechanical force F(N) – compression case Tabela 2: Razlika elektri~nega potenciala pri razli~nih silah stiskanja na robovih in v sredini vzorca Force F/N Depth, d/cm / Potential difference,  /mV 0 4.5 9 0.1 -80.17 0 80.17 0.08 -64.13 0 64.13 0.06 -48.10 0 48.10 0.04 -32.06 0 32.06 0.02 -16.03 0 16.03 • From Table 2 and Figures 6 and 7 we see that during the compression of the sample, in the interval from x=0m to x=0.045m, the electrical potential is negative, whereas on the other side, i.e., from x=0.045m to x=0.09m the potential is positive. It is known that the electrical potential is proportional to the intensity of the electric charge; therefore, we can conclude that on the upper part of the sample we have the accumulation of the negative charge and then, from the half-depth on, there is an accumulation of the positive charge. • The accumulated electrical charge depends on the intensity of the external force and the depth. For a given force, the electrical charge decreases with an increase of the depth decrease of the thickness of the sample along the x axis, whereas for a certain depth, it increases with the increase of the force. External mechanical forces stretches the sample In Figures 8 and 9 are the results of modeling for the case of stretching. From these figures we can draw the same conclusions as in the case of the stress of the sample. The only difference is that by changing the direction of the mechanical force, the sign of the electrical potential changes. More precisely, by changing the direction of the force, the side of the accumulation of the electric charges will switch. In the case of stretching, on the upper part of the sample the positive charge will be accumulated. In the other part of the sample (depth S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... 288 Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 Figure 7: Potential difference [mV] as a function of depth [cm] and mechanical force F/N – compression case Slika 7: Razlika elektri~nega potenciala v odvisnosti od razdalje pri razli~nih silah stiskanja Figure 6: Potential difference as a function of depth and mechanical force – compression case: (a) F = 0.1 N, (b) F = 0.08 N Slika 6: Prikaz izra~una razlike elektri~nega potenciala v odvisnosti od razdalje s programom ANSYS – primer tla~ne sile: (a) F = 0.1 N, (b) F = 0.08 N from x=0.045m to x=0.090m) the negative charge will be accumulated. In both cases at a depth of x=0.045m the electrical potential is zero, which means in the mid-depth of the sample the centers of positive electrical charges will coincide with the centers of the negative electrical charges and the net charge is zero. As a consequence, the electrical potential will also be zero. 3.1.2 The direct piezoelectric effect (transversal) The same phenomena occur in the case when compression (stress) or stretch is applied along the Y-axis perpendicular to X. The only difference is that in the case of stress (compression) along the Y-axis, negative electrical charges are accumulated on the opposite side compared to the first case (when the sample was compressed or stretched in the direction of the X-axis. In Figure 10, the case for the force 0.1 N is shown, for the case when the sample is stressed or stretched along the Y-axis (the so-called transversal piezoelectric effect). The results presented in Figure 10 show that the net accumulated electrical charge is not the same (for the same force in the case of transversal piezoelectricity, the net accumulated electric charge is greater). This occurs because in the case of longitudinal piezoelectricity, the net accumulated electrical charge depends only on the intensity of the applied force and the thickness of the sample, whereas in the case of the transversal piezoelectric effect, this net charge depends on the ratio between the surface area where the electrical charge is accumulated and the surface area upon which the force is exerted, y z x z ⋅ ⋅ . 3.2 Converse piezoelectric effect In this section we present the results of the inverse piezoelectric effect. The question is, what happens if an S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 289 Figure 10: Transversal piezoelectric effect: (a) Case of specimen compression, (b) Case of specimen stretch Slika 10: Transverzalni piezoelektri~ni pojav: (a) primer stiskanja in (b) primer raztezanja Figure 9: Potential difference [V] as a function of depth and mechanical force [F] – stretch case Slika 9: Razlika elektri~nega potenciala v odvisnosti od razdalje pri razli~nih razteznih silah Figure 8: Potential difference as a function of depth and mechanical force – stretch case: (a) F = 0.1 N, (b) F = 0.08N Slika 8: Prikaz izra~una razlike elektri~nega potenciala v odvisnosti od razdalje za primer raztezne sile: (a) F = 0.1 N, (b) F = 0.08N external AC voltage is applied to the sample? From practice we know that piezoelectric materials (in our case the crystal is quartz) can change their physical dimensions with the application of an electric field. Again, we have taken a sample with the same geometry. The element for meshing is the same, whereas as the initial condition we take the voltage applied on the ends of the x-axis. We have analyzed what happens to a sample when an electrical voltage applied on it. This analysis belongs to the so-called modal analysis. With this analysis we can determine the process of oscillations of a system10. More precisely, if the system performs oscillations under the action of an external factor, then with this analysis we find the proper frequencies of these oscillations and the shape of the oscillations (deforma- tions of the system related to the initial undeformed shape). This part of the analysis is supported by the ANSYS software, with the condition that during the solution of the equation, it must be indicated that we are dealing with the modal type. The degrees of freedom of the element SOLID 5 provide the transfer from the quantities of one physical field to another. In our case, the applied voltage is given as U = 220 V. Then the element SOLID 5 provides the transfer from this electrical quantity to the mechanical quantity – the displacement of the nodes or the deformation of the sample. The software (ANSYS) automatically calculates the frequency of the deformation – the oscillations of the nodes as well as its shape. With this program we can also find the frequencies of all modes of oscillations and their shapes for any applied voltage. In Figure 11, the 10 first modes of oscillations and their shapes are shown. According to11, the frequencies of the oscillations along the electric axis x for the quartz take values from 50 Hz to 200 kHz. From the last presentation we see that the frequency of oscillations for the 10 first modes take the values 51 815 Hz to 59 518 Hz. We have proved that the other modes, for example, the 40th mode, has a frequency of 93 000 Hz, whereas the 100th mode has the frequency 120 819 Hz. The results also prove that under the voltage applied, the geometry of the sample is deformed and that this deformation is caused by oscillations with different frequencies. It appears that an improvement in the computational accuracy of highly ordered modes depends, above all, on the number of finite elements used, and is not limited by the use of the finite-element method. 4 CONCLUSIONS From the results obtained, presented in Figures 5, 6, 7, 8, 9, 10 we can conclude as follows: • In principle, the differential equation of the coupled- field (mechanical and electrical) is solvable with the finite-element method (FEM) • The commodity of the solution provides the applica- tion ANSYS. • Both types of piezoelectric effect can be modeled with the aid of the FEM package, whereas simula- tions in ANSYS prove the corrections of the theore- tical model. • For the direct piezoelectric effect, we proved that depending on the intensity of the force and its direc- tion (stress or stretch), we have the accumulation of the electrical charges along the electric axis x, which can be seen in Figures 7 and 9. • Modal analyses provide an elegant presentation of the different shapes of oscillations of the sample when an S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... 290 Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 Figure 11: The first 10 modes of vibration and their shapes Slika 11: Prvih 10 lastnih nihajnih na~inov kremenovega vzorca electric voltage is applied to it. With this analysis we have proved the inverse piezoelectric effect. • With the same procedure the piezoelectric effect can be modeled for other materials, when only the three characteristic matrices of the material are known. 5 REFERENCES 1 H. Allik, T. J. R. Hughes, Finite element method for piezoelectric vibration, International Journal for Numerical Methods in Engi- neering, 2 (1970), 151–157 2 V. Piefort, Finite Element Modeling of Piezoelectric Active Struc- tures (doctoral thesis), University of Brussels, 2001, 51–69 3 IEEE standard of piezoelectricity, Standards Committee of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society, USA, 1988, 176 4 G. L. C. M. de Abreu, J. F. Ribeiro, V. Steffen, Finite element mode- lin gof a plate with localized piezoelectric sensors and actauators, J. Of the Braz. Soc. Of Mech. Sci. & Eng, 26 (2004)2, 117–128 5 www.korth.de/ 6 R. C. Tjiptoprojo, On a finite element approach to modeling of piezoelectric element driven compliant mechanisms (doctoral thesis), Saskatchevan, Canada, April 2005, 22–45 7 ANSYS 2004 8 Jiashi Yang, An introduction to the theory of piezoelectricity, Springer, Lincoln, 2005 9 L. H. Dawson, Piezoelectricity of crystal quartz, Physical Review, April 1927, 532–541 10 G. Mueller, C. Groth, FEM fuer Praktiker- Band I, Expert Verlag, 2002 Renningen, Germany 11 www.axtal.de 12 D. Boucher, M. Lagier, C. Maerfeld, Computation of the vibration modes for piezoelectric array transducers using a Mixed Finite Element-perturbation method, IEEE Transactions on Sonds and Ultrasonic, SU 28 (1981) 5, 318–330 13 C. Z. Rosen, V. Basvaraj, V. Hiremath, R. Newnham, Piezoelec- tricity, Key Papers in Physics, (1992) 5, 227–248 14 V. Kochin, J. Davaausambuu, U. Pietch, K. Schwarz, P. Blaha, The atomistic origin of the piezoelectric effect in  quartz, Journal of Physics and Chemistry of Solids, 65, (2004), 1967–1972 15 J. N. Reddy, The finite element method, Department of Mechanical Engineering, Texas University, New York, 2005 16 A. Benjeddou, Advances in piezoelectric finite element modeling of adaptive structural elements: a survey, Elsevier, Computers and Structures, 76 (2000), 347-363 17 S. Avdiaj. Modelling of the piezoelectric effect (Master thesis), Tirana, Albania, July 2008 S. AVDIAJ ET AL.: MODELING OF THE PIEZOELECTRIC EFFECT ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 283–291 291 R. MURUGAVEL: VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN ANALIZA SPREMENLJIVE TERMI^NE OBREMENITVE VOLFRAMOVEGA (100) MONOKRISTALA Rathinam Murugavel Paavai Institutions, Paavai Nagar, NH-7, Namakkal-637018, Tamilnadu, India mrgvel@yahoo.com Prejem rokopisa – received: 2009-05-21; sprejem za objavo – accepted for publication: 2009-07-13 The temperature response of properties of single crystal tungsten (110) is still not well understood. Tungsten was chosen to illustrate the temperature dependence behaviour because of its isotropic elastic behaviour at low loads. All the mechanical properties are temperature dependent. The experiments were performed with tailor made Berkovich tip of radius 100 nm at 265 K, 373 K, 473 K and 623 K to study the behavior of tungsten single crystal at various temperatures. The phenomenon of material under the indenter, bouncing back at the end of unloading due to the accumulation of energy was observed. It was noted that the elastic recovery was lower at higher temperature. The experiments showed the onset of the first strain burst, the onset of plastic deformation in connection with periodic bursts, and the softening effects. Pile up, significant drop in hardness, change of elastic modulus and increase in displacement with increasing temperature were observed. Because of softening, the indentation depth is increased for the same loading conditions. Clear bursts were seen showing the nucleation of dislocations. At higher peak loads, the indentation contact in tungsten was not just elastic. This work attempted to explore the complete behaviour of metals at various temperatures, including the initial burst, the complete elastic recovery, the softening effect, the modulus and hardness. Keywords: Nanoindentation, Mechanical Properties, Tungsten, Effect of Temperature Vpliv temperature na lastnosti monokristala volframa (100) {e ni popolnoma razjasnjen. Volfram je bil izbran za prikaz temperaturne odvisnosti zaradi elasti~nega izotropnega vedenja pri majhnih obremenitvah. Vse mehanske lastnosti so odvisne od temperature. Preizkusi so bili opravljeni s prirejeno Berkovichovo konico s polmerom 100 nm pri temperaturah 265 K, 373 K, 473 K in 623 K, da bi ugotovili vedenje monokristala volframa pri razli~nih temperaturah. Opa`en je bil pojav v materialu, da se vtis po razbremenitvi s konico sprosti zaradi velike nakopi~ene energije. Elasti~na poprava je bila manj{a pri visokih temperaturah. Poskusi prikazujejo za~etek vtisa in plasti~no deformacijo, ki je povezana s periodi~nimi vtisi in u~inke meh~anja. Kopi~enje materiala, zmanj{anje trdote in elasti~nega modula ter pove~anje razmika pri povi{anju temperature je bilo tudi opa`eno. Zaradi meh~anja se pove~uje globina vtisa pri enaki obremenitvi. Deformacije je spremljal nastanek dislokacij. Pri velikih obremenitvah kontakt pri vtisu ni bil popolnoma elasti~en. Klju~ne besede: nanovtis, mehanske lastnosti, volfram, vpliv temperature 1 INTRODUCTION The ability to perform nanotest measurements at elevated temperatures opens up significant new possibilities. The behavior of the material is different when subjected to temperatures deviating from the room temperature and the temperature response of tungsten is still not clearly understood. Thorough study of the behaviour of the materials in different temperatures is very important for the design and applications of materials for different operating conditions. Experiments were already performed on (100) tungsten 1. It was found that the yielding under contacts can produce a 250 nm displacement extrusion. Nano- indentation experiments on tungsten revealed that the load displacement was not linear and an analytic technique was proposed for determining the contact area at peak load 2. Experiments were performed on single crystal ionic materials with ultra sharp tips with R < 10 nm and special attention was given to the elastic response before the onset of plastic yield 3. The load displacement curves exhibit periodic bursts in indenter penetration depth that was interpreted chiefly as consequence of the nucleation of dislocations. Plastic deformation in polycrystalline copper films clearly revealed the existence of a significantly higher density of dislocations around the nanoindentation. The characterisation of mechanical properties of thin films using spherical tipped indenters were investigated, also 4 and it was shown that the use of very small spherical tipped indenters provided a better solution of the contact problem. The role of substrate and interface adhesion on the force-displacement behavior of thin films indented with spherical tipped indenters was discussed, also 4. The analytical formulation of the elastic limit predicting the location and slip character of a homogeneously nucleated defect in crystalline metals extends this formulation to the atomic scale in form of an energy-based local elastic stability criterion was investigated 5. A fundamental framework for describing incipient plasticity that combines results of atomistic and finite-element modeling, theoretical concepts of structural stability at finite strain and experimental Materiali in tehnologije / Materials and technology 43 (2009) 6, 293–297 293 UDK 546.78:620.17:539.377 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)293(2009) analysis were discussed, also 5. Detailed interpretation of the experimentally observed sequence of displacement bursts was proposed to elucidate the role of secondary defect sources operating locally at stress levels considerably lower than the ideal strength required for homogeneous nucleation 6. The advancements in making low dimensional structures from inorganic and organic compounds, determining the resulting, and necessarily local properties and assembling complex structures were explained7. The homogenous nucleation of dislocations was found in dislocation-free single crystals to be related to a sudden jump in the force-displacement curve. Experi- mental results of dislocation loop nucleation show good agreement with the continuum theory of dislocations8. It is found that the dislocations with a screw component are shown to glide across {111} planes and by a cross-slip mechanism giving rise to revolving terraces in the neighborhood of the nanoindentation trace with their edges parallel to compact n directions 9. Molecular dynamics simulation showed that the burst and arrest of stacking faults were the key factors for the plastic deformation of nanocrystalline copper under nano- indentation 10. High temperature nanotesting with micro materials measuring technology introduced the technique of high temperature nanoindentation 11. The experiments were carried out on gold, soda-lime glass, fused silica and a polyimide. Results from fused silica show that its mechanical properties exhibit completely different temperature dependence from those of soda-lime glass, as expected since fused silica is an anomalous glass 12. The small scale hardness and elastic modulus measure- ments on glass, gold, and single crystal silicon at room temperature and 473 K, show that the hardness and elastic modulus of soda lime glass and gold are lower at 473 K than at room temperature. In contrast, indentation testing of Si (100) at 473 K produced a similar hardness value to that obtained at room temperature, although the modulus was again reduced, from 140.3 GPa to 66.0 GPa. The 'pop out' event observed during unloading of a silicon indentation at room temperature, disappeared at 473 K 13. The temperature response of properties of tungsten at high temperature is still not well understood, as relatively little research was focused on its high temperature behaviour 14 and the effect of temperature on dislocation nucleation process is not well understood. The behaviour of the material during loading and unloading was analyzed to understand the temperature effects on the reconstruction of the material during the removal of load. Emphases were placed on defects generation mechanisms during the elastic plastic contact of crystals and special attention was given to the elastic response before the onset of plastic yield. This work attempted to explore the complete behavior of tungsten at increased temperatures, including the initial burst, the complete elastic recovery, the softening effect, the modulus and the hardness. 2 EXPERIMENTAL METHODOLOGY In the present investigation, the effects of temperature on properties of single crystal tungsten (110) were stud- ied. The experiments were performed with tailor made Berkovich tip of radius 100 nm at temperatures of 265 K, 373 K, 473 K and 623 K. To perform the experiment at high temperature, insulating material was used to protect the piezoelectric setup of the indenter. A small heater ca- pable of maintaining a constant temperature was added to the stage. The hot stage itself consisted of a thermally insulating ceramic block attached to the nanotest sample holder. The sample surface was brought to a constant temperature before the indentation for each experiment. A new attachment was made to circulate dry nitrogen gas to avoid ice formation during the low temperature exper- iments. The loading rate was kept constant for different temperatures experiments. The size of the sample was 2 mm thick and 9 mm in diameter. It took about 15 min. to reach the required temperature. The force on the sample during the imaging was of 2 mN. The topography and gradient images were captured to show the surface mor- phology after the indentation. In-situ imaging provides the capability to observe and quantify material damage while minimizing the time for material recovery. In the case of thin hard films on soft substrates, for instance, the indentation depth should generally not exceed 10 % of the film thickness in order to preclude any influence of the substrate. The sample was prepared with an ad- vanced technique using the ultra precision machining technique producing a very fine surface. This method does not affect the orientation. But in case of other pol- ishing methods, there is possibility of changing the ori- entation of the sample. Compared to other methods, this method also avoids the surface oxide formation. R. MURUGAVEL: VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN 294 Materiali in tehnologije / Materials and technology 43 (2009) 6, 293–297 Figure 1: Image of the sample after indentation (6 µm) Slika 1: Posnetek preizku{anca po vtisu (6 µm) 3 RESULTS AND DISCUSSION Figure 1 shows the AFM image of the sample after the indentation. The tip imprint is very clear. The dis- placement of the material on the surface indicates the dislocation pile-ups of the material during the indenta- tion. Figure 2 shows the loading and recovery process during loading and unloading at different temperatures and at the maximum load of 10 000 µN and loading rate of 2000 µN/s. These curves were obtained for the pur- pose of comparison during the loading and unloading process and to observe the maximal penetration depth and elastic rebound. The end of unloading curve in fig- ure 2 shows the sudden bump in the unloading curve for a short distance. Also, we observed a small increase in the penetration depth indicating the softening effects at higher temperatures. The softening effects were due to increase in temperature and plasticity. At high tempera- tures, the material was subjected to great plastic global deformation, instead of periodic local burst of disloca- tions at low temperature. The pile up was clearly visible an explained with the rotation of the axis of the atoms to conserve the volume during the penetration of the in- denter. We could also note the elastic rebound at the end of loading. Figure 3 shows the loading and recovery process during loading and unloading at higher temperature. The R. MURUGAVEL: VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN Materiali in tehnologije / Materials and technology 43 (2009) 6, 293–297 295 Figure 4: Loading and unloading pattern at 265 K for 1,000 µN and loading rate of 200 µN/s. Multiple curves indicate the experiments at different locations on the sample. The curves starting from the origin till the maximum point indicate the loading. Slika 4: Zna~ilnosti obremenitve in razbremenitve pri 265 K pri 1 000 µN in hitrosti obremenitve 200 µN/s. Krivulje pomenijo odtise na razli~nih mestih na preizku{ancu. Krivulji z za~etkom v koordinatnem sredi{~u pomenita obremenitev. Figure 2: Loading and unloading pattern at 373 K (a) and 473 K (b) for 10,000 µN and loading rate of 2000 µN/s. Multiple curves indicate the experiments at different locations on the sample. The curves start- ing from the origin till the maximum point indicate the loading. Slika 2: Zna~ilnosti obremenitve in razbremenitve pri 373 K (a) in 473 K(b) pri 10 000 µN in hitrosti obremenitve 2000 µN/s. Krivulje pomenijo vtise na razli~nih mestih na preizku{ancu. Krivulji z za~etkom v koordinatnem sredi{~u pomenita obremenitev. Figure 3: Loading and unloading pattern at 623 K for 10,000 µN and loading rate of 2000 µN/s. Multiple curves indicate the experiments at different locations on the sample. The curves starting from the origin till the maximum point indicate the loading. Slika 3: Zna~ilnosti obremenitve in razbremenitve pri 623 K pri 10 000 µN in hitrosti obremenitve 2 000 µN/s. Krivulje pomenijo vtise na razli~nih mestih na preizku{ancu. Krivulji z za~etkom v koordinatnem sredi{~u pomenita obremenitev. displacement of the material under the indenter was large compared to the displacement at 373 K and 473 K, indi- cating the softening of the metal at higher temperature. Also, Figure 3 exhibits a similar kind of unloading curve. The exact data on the amount of softening will en- able the proper selection of materials for different ther- mal loading conditions. The softening effects observed at higher temperatures below the recrystallization tempera- ture are useful for the proper selection of materials for variable thermal loading conditions as the softening ef- fects increase the plasticity. As global, the deformation is understood, which involves the entire body, in contrast to poking and squeezing, which involve relatively small re- gions of the deformable object. It was also noted that the elastic recovery was smaller at higher temperatures. Figure 4 was obtained to study the initial burst and the periodic bursts clearly visible at low loading rate and load when the initial burst was clearly observed, while, it was not visible at greater load. During loading and un- loading at low temperature, the curves exhibit large vi- bration. The unloading curve was not linear and was sim- ilar to that for copper. The material recovery rate was less and rebounding sharp at the end of the recovery pro- cess by low temperatures and loading conditions. The curve shoved, also, that the elastic recovery was minimal as the displacement smaller. Also the curves at 265 K showed a brittle behavior, because the material withstanded higher load before first yield. As evident from the curves, the initial burst occurred very early, while, the metal accommodated in itself without signifi- cant pile up. Displacement bursts were due to nucleation of dislocations. At low temperarute, the material exhib- ited brittle behavior and at 265 K, the recovery rate was less and, at the end of the recovery process, the rebound- ing was sharp. In Tables 1 and 2, it can be noted that the difference between hplastic and hmax varied with the tests temperature showing that the plasticity range increased with the tem- perature and the displacement. Also, the recovery range increased comparatively and it was proportional to the displacement. The overall plastic region increased as the displacement was large at higher temperatures. In other words, the elastic recovery was lower at higher tempera- ture, while the displacement was greater. As shown in Tables 1 and 2, the loading rate and load also affected the hardness value as seen in Tables 1 and 2. The elastic modulus (E) was high by great difference hplastic and hmax and heff was high, also. The elastic modulus decreases with the temperature, while, the penetration depth in- creases. The difference hplastic and hmax was less at smaller loading rate and indicated that the loading rate affects the range of plasticity. Also, it was noted that the elastic modulus (E) was high when the difference between plas- tic displacement (hplastic) and maximum displacement (hmax) was large. The hardness (H) value does not depend on the difference hplastic and hmax. The maximum displace- ments (hmax) in Tables 1 and 2 shows the softening ef- fects at different temperature and can be used for the proper materials selection for different thermal loading conditions. 4 CONCLUSIONS The tests on tungsten showed that different events oc- cur in the metal during the penetration of the indenter and the unloading at different temperature. Clear bursts showed the nucleation of dislocations and pile up was observed. It was found that the load displacement was not linear during unloading and that at higher peak load the indentation contact in tungsten was not purely elas- tic. At high temperature, the material showed higher dis- location mobility and a greater plastic deformation. It was concluded that the stored dislocations and the ther- mal recovery were responsible for maintaining a high mobile dislocation density that was temperature-depend- ent and sustained a large uniform elongation. At higher temperature the deformation was global, unlike the multi-bursts (brittleness) due to local dislocation motion at low temperatures. Changes of force and rate indicate to strain bursts due to the breakout of dislocations. The maximual displacements (hmax) at higher temperatures in- dicate that significant softening may occur at sufficiently high stress. Tungsten (111) planes showed lower hard- ness values than (110) planes as also evident from the re- sults from investigations on aluminum. The noise in the loading and unloading curves at low temperature can be improved by cooling to a lower level and then heating to the required temperature. The small R. MURUGAVEL: VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN 296 Materiali in tehnologije / Materials and technology 43 (2009) 6, 293–297 Table 1: Data for a load of 1000 µN and loading rate of 200 µN/s Tabela 1: Podatki za obremenitev 1 000 µN in hitrost obremenitve 200 µN/s Temp/ Data hmax/nm hplastic /nm H/GPa E/GPa 265 K 76.16 72.31 4.02 576.64 81.24 77.83 3.55 6297.58 52.48 49.38 7.53 9190.52 Table 2: Data for a load of 10,000 µN and loading rate of 2,000 µN/s. Tabela 2: Podatki za obremenitev 10 000 µN in hitrost obremenitve 2 000 µN/s Temp/ Data hmax / nm hplastic / nm H/GPa E/GPa 373 K 190.62 154.24 12.22 202.16 196.79 163.75 10.9 209.17 473 K 201.9 163.98 10.91 182.65 201.29 149.86 12.69 144.8 623 K 249.02 191.92 8.28 105.82 231.93 172.25 10.01 111.22 211.49 141.71 14.09 112.84 212.03 148.37 13.01 118.86 231.93 172.25 10.01 111.22 variations in the penetration depths in the p-h curves for same testing conditions must be avoided in case of single crystal. Our experiments clearly showed the onset of the first strain burst, the onset of plastic deformation in con- nection with the periodic bursts, and the strain harden- ing/softening/ recovery effects. The elastic modulus was lower at higher temperaturesand the softening increased with the increase of indentation depth for the same load- ing conditions. The elastic recovery was smaller at higher temperatures. The pop-ins shown on p-h curves correspond to the formation of dislocations. The contact pressure (nanohardness) increased with decreasing in- dentation depth. We attribute the temperature effect to the increased dislocation mobility and the reduced dislo- cation density. Dislocation pile up around the indentation was clearly visible. The onset of plastic deformation was identified from the periodic bursts. The difference in pile up was ob- served for different temperature and the new phenome- non of material under the indenter bouncing back at the end of unloading was established, also. Because of dy- namic softening the penetration depth and plastic defor- mation were greater at higher temperature. The indenta- tion rate affected the modulus and the hardness. 5 REFERENCES 1 William W. Gerberich, Natalia I. Tymiak, Donald E. Kramer, Funda- mental aspects of friction and wear contacts in <100> surfaces, Ma- ter. Res. Soc. Proc., 649 (2000) 2 W.C. Oliver, G. M. Pharr, An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J. Mater. Res., 7 (1992), 1569 3 J. Fraxedas, S. Garcia Manyes, P. Gorostiza, F. Sanz, Nanoinden- tation: Toward the sensing of atomic interactions, PNAS, 99 (2002), 5228–5232 4 M. V. Swain, J. Mencik, Mechanical property characterization of thin films using spherical tipped indenters, Thin Solid Films, 253 (1994), 1–2, 204–211 5 Krystyn J. Van Vliet, Ju Li, Ting Zhu, Sidney Yip, Subra Suresh, Quantifying the early stages of plasticity through nanoscale experi- ments and simulation, Phys. Rev. B, 67 (2003), 104–105 6 Ju Li, Krystyn J. Van Vliet, Ting Zhu, Sidney Yip, Subra Suresh, Atomistic mechanisms governing elastic limit and incipient plasticity in crystals, Nature, 418 (2002), 307–310 7 Dawn A. Bonnell, Materials in Nanotechnology: New structures, new properties, new complexity, J. Vac. Sci. Technol. A, 21 (2003), S194–S206 8 D. Lorenz, A. Zeckzer, U. Hilpert, P. Grau, H. Johansen, H. S. Leipner, Pop-in effect as homogeneous nucleation of dislocations during nanoindentation, Physical Review B, 67 (2003), 172101 9 E. Carrasco, O. Rodriguez de la Fuente, M. A. Gonzalez, J. M. Rojo, Dislocation cross slip and formation of terraces around nanoinden- tations in Au(001), Phys. Rev. B, 68 (2003), 180102 10 Xin-Ling Ma, Wei Yang, Molecular dynamics simulation on burst and arrest of stacking faults in nanocrystalline Cu under nanoinden- tation, Nanotechnology, 14 (2003), 1208–1215 11 High temperature NanoTesting, MICRO MATERIALS measuring nanotechnology-http://freespace.virgin.net/micro.materials/ 12 Ben, D. Beake, James, F. Smith, High-temperature nanoindentation testing of fused silica and other materials, Philosophical Magazine A, 82 (2002), 2179–2186 13 J. F. Smith, S. Zhang, High temperature nanoscale mechanical prop- erty measurements, Surface Engineering, 16 (2000), 143–146 14 J. A. Zimmerman, C. L. Kelchner, P. A. Klein, J. C. Hamilton, S. M. Foiles, Surface step effects on nanoindentation, Phys. Rev. Lett., 87 (2001), 165507-1 R. MURUGAVEL: VARIABLE THERMAL LOADING ANALYSIS OF (110) SINGLE CRYSTAL TUNGSTEN Materiali in tehnologije / Materials and technology 43 (2009) 6, 293–297 297 A. SMOLEJ ET AL.: SUPERPLASTICITY OF THE 5083 ALUMINIUM ALLOY ... SUPERPLASTICITY OF THE 5083 ALUMINIUM ALLOY WITH THE ADDITION OF SCANDIUM SUPERPLASTI^NOST ALUMINIJEVE ZLITINE 5083 Z DODATKOM SKANDIJA Anton Smolej1, Brane Skaza1, Edvard Sla~ek2 1University of Ljubljana, Faculty of Natural Science and Engineering, A{ker~eva 12, 1000 Ljubljana, Slovenia 2Impol, Aluminium Industry, 2310 Slovenska Bistrica, Slovenia anton.smolej@ntf.uni-lj.si Prejem rokopisa – received: 2009-07-14; sprejem za objavo – accepted for publication: 2009-08-24 This paper deals with the superplastic properties of an Al-4Mg-0.6Mn alloy (AA5083) with the mass fraction of scandium 0.3 %. The investigated alloy was produced by ingot casting and thermomechanically treated with hot and cold rolling into sheet with a thickness of 1.4 mm. The superplastic properties of the alloy were investigated with tensile tests at strain rates in the range 3 × 10–4 s–1 to 1 × 10–2 s–1 and at temperatures from 470 °C to 570 °C. The true-stress, true-strain characteristics, the elongation to failure, the strain-rate sensitivity index and the microstructure of the alloy were determined. The elongation to failure increased with the test temperature and was over 1400 % at an initial strain rate of 7.5 × 10–4 s–1 and a temperature of 550 °C. Key words: 5083 aluminium alloy, scandium, superplasticity ^lanek obravnava superplasti~ne lastnosti zlitine Al-4Mg-0.6Mn (AA5083) z dodatkom masnega dele`a skandija 0,3 %. Zlitina je bila izdelana pri laboratorijskih pogojih z ulivanjem v jekleno kokilo in termomehansko obdelana z vro~im in hladnim valjanjem v plo~evino z debelino 1,4 mm. Superplasti~ne lastnosti zlitine so bile preiskane z nateznim preizkusom pri preoblikovalnih hitrostih 3 × 10–4 s–1 do 1 × 10–2 s–1 in temperaturah od 470 °C do 570 °C. Dolo~ene so bile odvisnosti dejanska napetost-dejanska deformacija, razteznosti, indeksi ob~utljivosti za preoblikovalno hitrost in mikrostruktura preizkusne zlitine. Najve~ja razteznost ve~ kot 1400 % je bila dose`ena pri za~etni preoblikovalni hitrosti 7,5 × 10–4 s–1 in temperaturi 550 °C. Klju~ne besede: aluminijeva zlitina 5083, skandij, superplasti~nost 1 INTRODUCTION Superplasticity is the ability of polycrystalline mate- rials to exhibit high tensile elongations prior to failure under special forming conditions. These elongations are up to 1000 % and sometimes higher. Superplastic sheet metals enable the fabrication of complex-shaped products with a single working operation using relatively inexpensive tools. From among the numerous materials with superplastic properties, aluminium alloys like AA2004 (Al-Cu-Zr), AA7075, AA7475 (Al-Zn-Mg-Cu) and AA5083 (Al-Mg-Mn) are of commercial interest.1–3 The requirements for the superplastic behaviour of alloys are well known.4,5 In general, the following conditions need to be satisfied to achieve superplasticity: (1) a very small grain size (<10 µm); (2) a deformation temperature above 0.5Tm; (3) a strain-rate interval in the tensile test within the range 1 × 10–5 s–1 to 1 × 10–1 s–1; and (5) a low flow stress (<10 N mm–2) during the superplastic forming (SPF). The strain rates at which superplasticity normally occurs in aluminium alloys (<1 × 10–3 s–1) are often too slow for industrial applications. In recent years, there have been numerous attempts to produce aluminium- based materials that would exhibit a high-strain-rate (>1 × 10–2 s–1) superplasticity combined with a low-tem- perature (<400 °C) superplasticity.6–8 This can generally be achieved by further refining the grain size using a complex thermomechanical treatment that involves large reductions during cold rolling, by new processes such as equal-angular channel pressing7, 9 or by adding small amounts of Cu, Cr, Zr or Sc to the base alloy.10–12 AA5083 is one of the principal aluminium alloys used for SPF and its superplastic characteristics have been extensively investigated.3,6,13–15 Generally, with this alloy, maximum elongations to failure of about 400 % and, rarely, up to 600 %3 were achieved at slow or inter- mediate strain rates of 1 × 10–4 s–1 to 5 × 10–3 s–1. It is now well established that small quantities of scandium added to the Al-Mg-16,17 and Al-Mg-Mn-18,19 type alloys lead to an increase in the superplasticity. Elongations without failure of 1020 % and 1130 % were reported for Al-4Mg-0.5Sc16 and for Al-6Mg-0.3Sc17, whereas an elongation of 680 % has been achieved for a con- ventionally manufactured Al-Mg-Mn alloy with mass fractions 0.25 % Sc and 0.12 % Zr at 1.67 × 10–3 s–1 and at 490 °C.19 The present paper describes the effect of a 0.33 % addition of scandium on the superplastic behaviour of a standard 5083 alloy. The examined alloy sheet was prepared by a simple thermomechanical treatment simi- lar to conventional industrial processing. The aim of the investigation was to determine the superplastic properties of the sheet, which are characterised by the flow stresses, Materiali in tehnologije / Materials and technology 43 (2009) 6, 299–302 299 UDK 669.715:669.793:539.3 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)299(2009) the elongations to failure, the strain-rate sensitivity indexes and the microstructure. 2 EXPERIMENTAL The Al-4Mg-0.6Mn-0.3Sc alloy was prepared by induction melting using Al99.9, Mg99.8, the master alloys Al-2.1Sc, Al-80Mn and Al-5Ti-1B. The melt was cast into a steel mould with dimensions of (175 × 80 × 27) mm. The chemical composition of the alloy is shown in Table 1. Table 1: The chemical composition of the investigated alloy (in mass fractions w/%) Tabela 1: Kemi~na sestava preiskovane zlitine (v masnih dele`ih w/%) Si Fe Mn Mg Ti B Sc Al 0.0064 0.0151 0.6400 4.054 0.0189 0.0024 0.329 Bal. The ingots in the as-cast condition were homo- genized for 4 h at 440 °C and for 4 h at 460 °C, and then air cooled. The scalped ingots with a thickness of 25 mm were hot rolled at 400 °C to a thickness of 8.8 mm, annealed for 4 h at 475 °C, and then subsequently cold rolled to a final sheet thickness of 1.4 mm with a reduction of 84 %. The samples for the tensile tests were machined from cold-rolled sheet along the rolling direction with a gauge section of 10 mm of length and 5.4 mm of width. The samples were annealed for 2 h at 500 °C to obtain a recrystallized microstructure. The average size of the recrystallized grains in the rolling direction was about 14 µm, and in the traverse section the size was about 8 µm. The tensile tests of the investigated alloy were con- ducted on a Zwick Z250 testing machine with a 500 N load cell. The machine was equipped with a three-zone electrical resistance furnace. The testing chamber with a controlled temperature was over 300 mm in length. The testing procedure was conducted with the TestXpert II software system. The measurements included determinations of the flow stresses, the maximum elongations to failure and the strain-rate sensitivity index m. The testing tempe- ratures and strain rates ranged from 470 °C to 570 °C and from 3 × 10–4 s–1 to 1 × 10–2 s–1. The tensile tests were conducted at constant strain rates (CSRs) and at constant cross-head speeds (CCHSs). The strain-rate sensitivity indexes were determined with the multi- strain-rate jump test. The microstructures of the tested samples were examined with light microscopy. 3 RESULTS AND DISCUSSION The superplastic properties of the material were characterised by the flow behaviour during the tensile test. The flow stresses and the shapes of the flow curves are dependent on the temperature and the initial strain rate during the CCHS test. Figure 1 shows a series of true- stress, true-strain curves for the investigated alloy at various temperatures in the range from 470 °C to 550 °C at an initial strain rate of 1 × 10–3 s–1. The stress exhibits a sharp peak after loading, followed by a softening at lower temperatures (<490 °C), and then by a continuous hardening to failure at higher temperatures. The stresses were lower than 12 Nmm–2 for all the tested conditions and no steady state occurred. A similar course of stress-strain curves was observed for various initial strain rates at a temperature of 550 °C (Figure 2). After a rapid increase of the stresses to approximately 5 % strain, the tests performed at faster initial strain rates show no, or very little, increase of the flow stresses, whereas there is an indication of material hardening at lower initial strain rates (<1 × 10–3 s–1). The reason for the strain hardening of this alloy at higher temperatures and lower strain rates is the dynamic grain growth during the pulling of the samples.17,18 Generally, the shapes of the true-stress, true-strain curves A. SMOLEJ ET AL.: SUPERPLASTICITY OF THE 5083 ALUMINIUM ALLOY ... 300 Materiali in tehnologije / Materials and technology 43 (2009) 6, 299–302 Figure 2: True-stress, true-strain curves for various initial strain rates at 550 °C Slika 2: Odvisnosti dejanska napetost – dejanska deformacija pri razli~nih preoblikovalnih hitrostih in temperaturi 550 °C Figure 1: True-stress, true-strain curves for various tested tempe- ratures at an initial strain rate of 1 × 10–3 s–1 (CCHS test) Slika 1: Odvisnosti dejanska napetost – dejanska deformacija pri razli~nih preizkusnih temperaturah in za~etni preoblikovalni hitrosti 1 × 10–3 s–1 (CCHS preizkus) of the investigated Al-4Mg-0.6Mn-0.3Sc alloy are comparable with the curves of alloys with similar compositions, like Al-Mg-Mn,3,14,15 Al-Mg-Sc17,18 and Al-Mg-Mn-Sc.6 The elongations to failure were measured with a tensile test under constant cross-head speed (CCHS) at temperatures in the range from 470 °C to 570 °C and at initial strain rates from 5 × 10–4 s–1 to 1 × 10–2 s–1. The elongation to failure depended strongly on the test tem- peratures (Figure 3) and on the strain rate (Figure 4). An elongation of over 1000 % was achieved at initial strain rates up to 1 × 10–3 s–1 and 550 °C (maximum elongation of 1455 % at 7.5 × 10–4 s–1). Since a 200 % elongation can be considered as an initial indicator of superplasticity,8,20 elongations at higher strain rates up to 1 × 10–2 s–1 at 550 °C and lower temperatures in the range from 470 °C to 510 °C are still in the superplastic regime. The strain-rate sensitivity index m is one of the most important parameters that characterize the superplastic behaviour of a material. In this work the m values as a function of the strain rate at a temperature of 550 °C were estimated with the multi-strain-rate jump test. These tests were conducted by increasing and decreasing the strain rate by 20 % for every 100 % increment of elongation. The indexes m are plotted as a function of the strain rate for strains in the range from 1.1 (200 %) to 2.1 (700 %) in Figure 5. The index m changes at all strains with the strain rate. The m plots show peaks that occur within a narrow range of strain rates from 3 × 10–4 s–1 to 5 × 10–4 s–1. A maximum value of m = 0.67 was obtained in this range at a true strain of 1.1 and m = 0.46 at  = 2.1 and at strain rate 5 × 10–4 s–1. The peaks of the m-plots are shifted to a lower strain rate at higher strains. The microstructure of the alloy was examined with regard to the crystal grains after pulling the samples at an initial strain rate of 7.5 × 10–4 s–1 and a temperature of 550 °C to various elongations in the range from 200 % to 1200 % (Figure 6). The initial microstructure consisted of recrystallized grains grown during the two hours of annealing prior to the tensile test. The static and dynamic grain growth in the grip and in the gauge sections of the samples as a function of annealing or of pulling time during the tensile test are shown in Figure 7. The A. SMOLEJ ET AL.: SUPERPLASTICITY OF THE 5083 ALUMINIUM ALLOY ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 299–302 301 Figure 5: Strain-rate sensitivity index m as a function of the strain rate for various strains at 550 °C Slika 5: Indeks ob~utljivosti za preoblikovalno hitrost m pri razli~nih preoblikovalnih hitrostih in temperaturi 550 °C Figure 4: Elongation to failure as a function of initial strain rate and the samples after tensile testing at 550 °C Slika 4: Razteznost pri razli~nih za~etnih preoblikovalnih hitrostih in preizku{anci po nateznem preizkusu pri 550 °C Figure 3: Elongation to failure as a function of the tested temperature at an initial strain rate of 1 x 10–3 s–1 Slika 3: Razteznost pri razli~nih preizkusnih temperaturah in za~etni preoblikovalni hitrosti 1 x 10–3 s–1 dynamic grain growth is, especially at longer pulling times (at elongations over 900 %), greater than the static one. The grains in the gauge section were slightly elongated with a grain aspect ratio of about 1.4, which remained nearly constant for all the elongations. The cavitation that occurred during the superplastic forming in the gauge section was examined with the same samples and under the same testing conditions as shown in Figure 6. The fraction of cavitation increased with the increasing strain. However, the volume share of the cavitation did not exceed a value of 20 % at larger elongations up to 1200 %. 4 CONCLUSIONS An Al-4Mg-0.6Mn-0.3Sc alloy sheet with a thickness of 1.4 mm produced with a simple thermomechanical treatment including hot and cold rolling, exhibited good superplastic properties, reflected in large elongations to failure, high strain-rate sensitivity indexes and low flow stresses. Elongations over 1000 % were achieved at initial strain rates up to 1 × 10–3 s–1 and temperatures higher than 530 °C (maximum elongation of 1455 % at 7.5 × 10–4 s–1 and 550 °C). The strain-rate sensitivity indexes varied with the strain rate and have the highest values within a narrow range of strain rates from 3 × 10–4 s–1 to 5 × 10–4 s–1. The dynamic grain growth and the fraction of cavitation increase with the increasing strain. The Al-4.0Mg-0.6Mn-0.3Sc alloy sheet with a thickness of 1.4 mm, produced with a conventional rolling process, makes it possible to obtain a good, low-strain-rate superplasticity characterised by an elongation of over 1000 % at a temperature higher than 530 °C and a strain rate up to 1 × 10–3 s–1. This work was supported by Slovenian Research Agency (ARRS) of the Government of the Republic of Slovenia. 5 REFERENCES 1 R. Grimes, M. J. Stowell, B. M. Watts, Metals Technology, 3 (1976), 154–160 2 J. A. Wert, N. E. Paton, C. H. Hamilton, M. W. Mahoney, Metallur- gical Transactions A, 12A (1981), 1267–1276 3 R. Verma, P. A. Friedman, A. K. Ghosh, S. Kim, C. Kim, Metallur- gical and Materials Transactions A, 27A (1996), 1889–1898 4 T. G. Langdon, Metallurgical Transactions A, 13A (1982), 689–701 5 K. A. Padmanabhan, R. A. Vasin, F. U. Enikeev, Superplastic flow: phenomenology and mechanics, Springer Verlag, Berlin, Heidelberg, New York, 2001, 5–26 6 I. C. Hsiao, J. C. Huang, Scripta Materialia, 40 (1999), 697–703 7 T. G. Langdon, Materials Transactions, JIM, 40 (1999), 716–722 8 K. Higashi, Materials Science and Technology, 16 (2000), 1320– 1329 9 T. G. Langdon, Journal of Materials Science, 42 (2007) 10, 3388– 3397 10 P. B. Berbon, S. Komura, A. Utsunomiya, Z. Horita, M. Furukawa, M. Nemoto, T. G. Langdon, Materials Transactions, JIM, 40 (1999)8, 772–778 11 M. Furukawa, A. Utsunomiya, K. Matsubara, Z. Horita, T. G. Langdon, Acta Materialia, 49 (2001), 3829–3838 12 R. Verma, S. Kim, Journal of Materials Engineering and Performance, 16 (2007)2, 185–191 13 J. S. Vetrano, C. A. Lavender, C. H. Hamilton, M. T. Smith, S. M. Bruemmer, Scripta Metallugica et Materiala, 30 (1994), 565–575 14 R. Verma, A. K. Ghosh, S. Kim, C. Kim, Materials Science and Engineering, A 191 (1995), 143–150 15 P. A. Friedman, W. B. Copple, Journal of Materials Engineering and Performance, 13 (2004)3, 335–347 16 R. R. Sawtell, G. L. Jensen, Metallurgical Transactions A, 21A (1990), 421–430 17 T. G. Nieh, L. M. Hsiung, J. Wadsworth, R. Kaibyshev, Acta Materialia, 46 (1998), 2789–2800 18 F. Musin, R. Kaibyshev, Y. Motohashi, G. Itoh, Metallurgical and Materials Transactions A, 35A (2004), 2383–2392 19 Y. Peng, Z. Yin, B. Nie, L. Zhong, Transactions of Nonferrous Metals Society of China, 17 (2007), 744–750 20 T. Sakuma K. Higashy, Materials Transactions JIM, 40 (1999), 702–715 A. SMOLEJ ET AL.: SUPERPLASTICITY OF THE 5083 ALUMINIUM ALLOY ... 302 Materiali in tehnologije / Materials and technology 43 (2009) 6, 299–302 Figure 7: Static and dynamic grain growth in the longitudinal grip and gauge sections of the samples at an initial strain rate of 7.5 ×1 0–4 s–1 and at 550 °C Slika 7: Stati~na in dinami~na rast kristalnih zrn v vzdol`nih prerezih glav in merilnih dol`in preizku{ancev pri za~etni preoblikovalni hitrosti 7,5 × 10–4 s–1 in 550 °C Figure 6: Samples after tensile testing at various elongations with microstructures and cavitations in the gauge length at 550 °C and 7.5 x 10–4 s–1 Slika 6: Preizku{anci po nateznem preizkusu pri razli~nih raztezkih in posnetki mikrostruktur ter kavitacij v vzdol`nih prerezih merilnih dol`in pri 550 °C in 7,5 x 10–4 s–1 R. BIDULSKÝ ET AL.: WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS OBRABNA OBSTOJNOST KROMOVIH SINTRANIH JEKEL Róbert Bidulský1, Marco Actis Grande1, Jana Bidulská2, Tibor Kva~kaj2 1Politecnico di Torino – Alessandria Campus, Viale T. Michel 5, 15100 Alessandria, Italy 2Department of Metal Forming, Faculty of Metallurgy, Technical University of Ko{ice, Vysoko{kolská 4, 042 00 Ko{ice, Slovakia tibor.kvackaj@tuke.sk Prejem rokopisa – received: 2009-05-04; sprejem za objavo – accepted for publication: 2009-06-19 This paper deals with the influence of the processing conditions on the material properties and wear characteristics of chromium pre-alloyed sintered steels. Three different processing conditions were used, involving different cooling rates from the sintering temperatures of 1180 °C and 1240 °C. A conventional (slow) cooling condition and a new progressive condition, sinter hardening, were examined. The results showed that the typical microstructure characteristics of sintered steels represent an important parameter affecting their wear behaviour. Key words: pre-alloyed sintered steel, sinter hardening, sliding wear, porosity, microstructure V ~lanku je predstavljen vpliv pogojev procesiranja na mehanske lastnosti in obrabne zna~ilnosti kromovih sintranih jekel. Uporabljeni so bili trije razli~ni pogoji procesiranja z razli~no hitrostjo ohlajanja s temperatur 1180 °C in 1240 °C. Opredeljena sta vpliv po~asnega (konvencionalnega) ohlajanja in naprednega kaljenja sintra. Rezultati so pokazali, da so za vedenje pri obrabi pomembne zna~ilnosti mikrostrukture sintranih jekel. Klju~ne besede: sintrano jeklo, kaljenje sintra, drsna obraba, poroznost, mikrostruktura 1 INTRODUCTION Powder metallurgy (PM) is a well-established pro- cessing route for the production of near-net-shape com- ponents of complex geometry. The traditional uniaxial powder consolidation process is still widely employed for the production of ferrous parts, especially for the au- tomotive industry. In this field the typical components (i.e., gears, cams) face working conditions giving rise to sliding, rolling or abrasion. Therefore, an understanding of the wear phenomena and characteristics is very impor- tant. The dry sliding behaviours of sintered ferrous alloys have been investigated in several previous studies 1,2,3,4,5,6, which indicated that the wear mechanisms are similar to wrought materials under the same conditions. Neverthe- less, sintered materials contain a variable quantity of pores, as well as (eventually) heterogeneous microstruc- tures, which create peculiar wear characteristics for PM products. As a matter of fact, pores represent the first sites for microplastic deformation and they are potential sites for the formation of the first microcracks7,8,9. The use of chromium in PM may create some diffi- culties in reducing the oxides present at the surface and acting as a barrier to interparticle diffusion; nevertheless, chromium is a widely used hardening element in ferrous sintered products10,11,12,13. Molybdenum is also commonly used in low-alloy PM steels because of the easily reduc- ible oxides. Chromium and molybdenum are very effec- tive in promoting increased strength and toughness. Sinter hardening requires controlled cooling after sintering in the austenite range (1120–1240 °C). A new approach to sinter hardening has been proposed using vacuum furnaces14,15,16. They show enhanced cooling ca- pabilities, with several advantages related to cost effec- tiveness, reducing the problems of oil entrapment and distortion, determining the improved dimensional stabil- ity and consequently higher yield and quality of the pro- duction lots. Moreover, vacuum furnaces may reduce the decarburation typical of continuous furnaces and can be programmed to perform quenching and tempering inte- grated in the same cycle, thus reducing the internal stresses that cause excessive notch sensitivity and brittleness17,18. The main aim of this paper is to show the influence of various sintering conditions on the wear resistance of chromium pre-alloyed sintered steels. 2 MATERIAL AND EXPERIMENTAL PROCEDURE The investigated chromium pre-alloyed system was Fe + 1.5 % Cr + 0.65 % C + 0.6 % AW. The powders were homogenised in a Turbula mixer. Specimens with a green density of  7.0 g cm–3 were obtained using a 2000 kN hydraulic press, in a disc-shaped mould ( = 40 mm) applying a pressure of 600 MPa. The sintering was carried out in a TAV vacuum furnace with argon back-filling at 1180 °C and 1240 °C for 1 h. The cooling rate was 0.05 °C/s, while the rapid cooling rate (sinter Materiali in tehnologije / Materials and technology 43 (2009) 6, 303–307 303 UDK 621.762.5:620.18 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)303(2009) hardening) was 6 °C/s (Table 1). The densities were evaluated using the water-displacement method. Table 1: Sintering conditions of the chromium pre-alloyed sintered steels Tabela 1: Pogoji sintranja jekel Alloy No Sintering conditions A Temperature: 1180 °C; time: 1 h; coolingcondition: 0.05 °C/s B Temperature: 1180 °C; time: 1 h; coolingcondition: 6 °C/s (sinter hardening) C Temperature: 1240 °C; time: 1 h; coolingcondition: 6 °C/s (sinter hardening) The wear tests were carried out using a pin-on-disc apparatus. The disc was made of the investigated mate- rial. As a counter face, a WC-Co pin was used, having a rounded shape on top with a diameter of 3 mm. The counter-pin was changed after the end of each test, in or- der to preserve the roundness of its top. All the wear tests were performed in air and without any lubricant. The applied loads were 25 N, and the rotation speed of the disc was 140 r/min. The distances of the pin position from the disc centre were 34 mm. Prior to testing, the surface was polished with abrasive papers in order to de- termine a medium surface roughness equal to (or less than) 0.8 µm, as specified in the ASTM G99–95a. Each test was interrupted after (300, 600, 900, 1200 and 2000) m of sliding distance and the discs were weighed using a precision balance with a sensitivity of 10–5 to determine the evolution of the wear during each test. The wear characterization of the chromium pre-al- loyed sintered steels was carried out with optical micros- copy, also determining the volume mass and the inter- connected (open) porosity (according to UNI 7825). Wear-track observations were carried out using an SEM JEOL 7000F. Vickers hardness measurements were performed on cross-sections of the samples and the im- pact-testing procedure using Charpy tests was carried out on un-notched samples. 3 EXPERIMENTAL RESULTS AND DISCUSSION 3.1 Microstructures The microstructure of the chromium pre-alloyed sintered specimens (A in Table 1) consisted predomi- nantly of a pearlite microstructure (HV0.010  240) with small areas of ferrite (HV0.010 = 125–140), Figure 1. The system B determines the dominant bainite (formed by a mixture of upper (HV0.010 = 330–370) and lower (HV0,010 = 260–285 bainite), with some martensite (HV0.010 = 580–648), Figure 2. Increasing the sintering temperature to 1240 °C (system C) resulted in the formation of a dominant martensitic microstructure (HV0.010 = 580–692) with small, upper bainite networks (HV0.010  415), Fig- ure 3. Different cooling rates did not result, in terms of hardness, in a large difference between systems sintered at 1180 °C. On the contrary, using a higher sintering temperature (1240 °C/s) resulted in harder microstruc- ture constituents with a dominant martensitic micro- structure. 3.2 Friction coefficient Figure 4 shows a plot of the values of the steady-state friction coefficient measured for the chro- mium pre-alloyed sintered steels tested under different conditions. The values ranged from about 0.90 to 0.82, gradually decreasing as the sliding distance was in- creased. Higher values of the coefficient of friction were generally measured for samples with higher porosity lev- R. BIDULSKÝ ET AL.: WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS 304 Materiali in tehnologije / Materials and technology 43 (2009) 6, 303–307 Figure 2: Microstructure of B steel, 1180 °C / 1 h; sinter hardening, cooling rate 6 °C/s Slika 2: Mikrostruktura jekla A, 1180 °C/1h, kaljeno, hitrost ohlajanja 6 °C/s Figure 1: Microstructure of A steel, 1180 °C / 1 h; cooling rate 0.05 °C/s Slika 1: Mikrostruktura jekla A, 1180 °C/1h, hitrost ohlajanja 0,05 °C/s els (specimens sintered at 1180 °C), as a cumulative ef- fect of a higher resistance to plastic flow and a slightly greater contact area. The present results of the friction coefficient ranged from 0.7 to 0.9, in accordance with the literature data for sintered materials in the untreated condition19. 3.3 Wear characteristics The mass losses were expressed as material removal during the test and were recorded as a function of the sliding distance. The wear of PM materials is more com- plicated than that of wrought steels and depends on dif- ferent factors related to the sintered microstructures (such as plasticity and strength) of the different phases, as well as the porosity. Hence, the evaluation of the wear resistance (as the reciprocal value of the amount of wear) R. BIDULSKÝ ET AL.: WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS Materiali in tehnologije / Materials and technology 43 (2009) 6, 303–307 305 Figure 6: Typical, mild oxidative wear regime, which was observed for all tested specimens, specimen C; 1240 °C / 1 h; sinter hardening, cooling rate 6 °C/s Slika 6: Rahlo oksidativen re`im obrabe zna~ilen za vse preizku{ance, preizku{anec C, 1240 °C/ 1h, kaljeno, hitrost ohlajanja 6 °C/s Figure 4: Friction coefficient of investigated materials Slika 4: Koeficienti trenja za preiskane materiale Figure 5: (a) Wear rates for investigated specimens. (b) Wear rates for specimens cooled with greater cooling rate Slika 5: (a) Hitrosti obrabe za preizku{ance, (b) hitrosti obrabe za preizku{ance, ohlajene z ve~jo hitrostjo Figure 3: Microstructure of C steel, 1240 °C / 1 h; sinter hardening, cooling rate 6 °C/s Slika 3: Mikrostruktura jekla A, 1240 °C/1h, kaljeno, hitrost ohlajanja 6 °C/s is better expressed in terms of wear rate. The wear rate was calculated using the equation: W m L Fs N = ⋅ ⋅ ∆  (1) where: Ws is the wear rate [m3/(N m)], m is the mass loss of the test samples during the wear test [g],  is the density of the test materials [g/cm3], L is the total sliding distance [m], FN is the normal force on the pin [N]. The wear rates for the investigated specimens are shown in Figure 5. The results show that the wear resistances of chromium pre-alloyed sintered steels using higher temperatures and cooling rates (sinter hardening) were improved due to the shift of the ferrite-bainite to the dominant martensitic microstructure. Useful information on the wear mechanisms of the sintered steels was obtained by SEM observations. The investigation demonstrated the mechanism of delamina- tion: deformed layers and tracks along the direction of sliding during the wear. Plastic deformation took place on the wear surfaces during the wear tests. The contact R. BIDULSKÝ ET AL.: WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS 306 Materiali in tehnologije / Materials and technology 43 (2009) 6, 303–307 Figure 8: (a) Microstructural discontinuities as pore agglomerates with sharp edges, A specimens. (b) Microstructural discontinuities as pore ag- glomerates with slightly sharp edges, B specimens. (c) Rounded pores, C specimens. Slika 8: (a) Diskontinuitete mikrostrukture kot aglomerati por z ostrimi oblikami, preizku{anci A, (b) diskontinuitete mikrostrukture kot aglomerati por z rahlo izostreno obliko, preisku{anci B, (c) zaobljene pore, preizku{anci C Figure 7: (a) Oxide layers on the chromium pre-alloyed sintered steels (scanning microscopy) and (b) EDX spectra of oxide layers Slika 7: (a) Oksidna plast na sintranem kromovem jeklu (vrsti~ni mikroskop) in (b) EDX-spektri oksidne plasti Table 2: Material properties of the tested alloys Tabela 2: Materialne lastnosti raziskanih zlitin Alloy No P* S* PTotal TRS UTS IE Hardness HRA Microhardness range; average HV0.010g/cm 3 g/cm3 % MPa MPa MPa A 6.987 7.002 8.64 893 447 22.86 46.45 ± 0.15 (125−240); 189 B 6.983 6.973 9.01 1335 1035 13.29 63.70 ± 3.60 (260−648); 520 C 7.002 7.113 7.19 1421 1217 10.60 65.55 ± 0.65 (414−692); 589 *P-Pressing, *S-Sintering pressure of the wear surfaces increased with the increas- ing amount of porosity in accordance with 20. The sliding tests carried out on samples sintered at 1180 °C and cooled at 0.05 °C/s were, in any case, typi- cal of a mild oxidative wear regime, Figure 6. Detailed analyses revealed (Figure 7 (a) and (b)) oxide layers on the chromium pre-alloyed sintered steels in accordance with the literature data14,15,16. Therefore, delamination and oxidation wear seems to be the main wear mecha- nisms. 3.4 Material properties The sintered material characteristics of a given alloy (i.e., its porosity content and microstructure) also influ- ence the charpy impact energy, as shown by the values reported in Table 2. The important parameters that spec- ify the role of porosity are the amount of porosity and the pore size. Earlier studies1,4,6 have suggested that an amount of porosity higher than 10 % and a pore size that is larger than 12 µm constitute a dominant intercon- nected porosity. These pores are filled with debris parti- cles during wear. This may enhance the wear resistance of the samples by increasing the real contact area and de- creasing the contact pressure. A dominant role can be played by isolated pores and their shapes. Sharp-edged pores can give rise to considerable stress-concentration effects that favour the nucleation and propagation of microcracks, leading to the easier formation of wear fragments. This interpretation is underlined by the lower Charpy impact values measured for the specimens with a higher porosity content, along with the results at the higher sintering temperature of 1240 °C that reduced the negative effects of the porosity by means of roundness, so promoting an increase of the wear resistance. Speci- mens sintered at a sintering temperature of 1240 °C (HS) present more rounded pores than those sintered at a lower temperature, Figure 8 (a)-(c), along with higher impact energies. The lowest impact values were shown by the specimens sintered at the lower temperature and then slow cooled. The increase in the sintering tempera- ture and cooling rates strongly influenced the micro- structure and hardness to the shifting of the microstruc- tures from pearlite to dominant martensite micro- structures. Sinter hardening increases the martensite con- tent in the microstructure and this results in a further in- crease in the strength with a decrease of the ductility and toughness (the plasticity properties represent the im- pact-energy values). The results suggested that sinter hardening can have a practical interest in view of compo- nents where wear resistance can play a decisive role. 4 CONCLUSIONS The main results obtained in this paper may be sum- marised as follows: • A higher cooling rate (sinter hardening), supporting a bainite-martensitic microstructure, and a higher sintering temperature increase both the strength and ductility, • delamination and oxidation are the main wear mecha- nisms, • microstructure and hardness represent the dominant effect influencing the mechanical properties as well as the wear resistance, • higher temperature sintering (1240 °C) reduces the negative effects of porosity due to the evident effect of pore roundness, if compared to a lower sintering temperature and cooling rates. Acknowledgment R. Bidulský thanks the Politecnico di Torino and the Regione Piemonte for co-funding of a fellowship. This work was supported by the VEGA No. 1/4136/07. 5 REFERENCES 1 Dubrujeaud B., Vardavoulias M., Jeandin M.: Wear, 174 (1994), 155–161 2 Wang J., Danninger H.: Wear, 222 (1998), 49–56 3 Molinari A., Straffelini G.: Wear, 181–183 (1995), 334–341 4 Straffelini G., Molinari A.: Powder Metall., 44 (2001), 248–252 5 Khorsand H., Habibi S. M., Yoozbashizadea H., Janghorban K., Reihani S. M. S., Rahmani Seraji H.: Mater. Design, 23 (2002), 667–670 6 Simchi A., Danninger H.: Powder Metall., 47 (2004), 73–80 7 Hadrboletz A., Weiss B.: Int. Mater. Reviews, 42 (1997), 1–44 8 Dudrová E., Kabátová M., Bidulský R.: Fractography of Sintered Iron and Steels: A Review. RoPM 2005. Cluj-Napoca, Romania, 1 (2005), 101–113 9 Dudrová E., Kabátová M.: Fractography of Sintered Steels: A Re- view. Proc. PM World Congress, Vienna, Austria, EPMA, Shrews- bury, 3 (2004), 193–198 10 Bidulský R., Actis Grande M.: High Temp. Mater. Process., 27 (2008), 249–256) 11 Karlsson H., Nyborg L., Bergman O.: Surface Interactions during Sintering of Water atomised Pre-alloyed Steel Powder. Proc. PM World Congress, Vienna, Austria, EPMA, Shrewsbury, 3 (2004), 24–29 12 Karlsson H., Nyborg L., Berg S.: Powder Metall., 48 (2005), 51–58 13 Hryha E., Cajková L., Dudrová E.: Powder Metall. Prog., 7 (2007), 181–197 14 Blais C., Serafini R.E., L’Esperance G.: Int. J. Powder Metall., 41 (2005), 33–41 15 Actis Grande M., Bidulský R., Dudrová E., Kabátová M., Rosso M.: Powder Metal. Prog., 8 (2008), 101–108 16 Zendron M., Girardini L., Molinari A.: Powder Metall., 51 (2008), 237–244 17 Ceniga L.: J. Therm. Stresses, 31 (2008), 728–758 18 Ceniga L.: J. Therm. Stresses, 31 (2008), 862–891 19 Candela N., Plaza R., Rosso M., Velasco F., Torralba J. M.: J. Mater. Proc. Technol., 119 (2001), 7–13 20 Gulsoy H. O., Bilici M. K., Bozkurt Y., Salman S.: Mater. Design, 28 (2007), 2255–2259 R. BIDULSKÝ ET AL.: WEAR RESISTANCE OF CHROMIUM PRE-ALLOYED SINTERED STEELS Materiali in tehnologije / Materials and technology 43 (2009) 6, 303–307 307 V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC ... PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC AND Mg2Si-TiC/TiB2 COMPOSITES PRIPRAVA IN PREIZKU[ANJE PROTOTIPNIH KOMPOZITOV Mg2Si-Mg-TiC/TiB2 IN Mg2Si-TiC/TiB2 Varu`an Kevorkijan1, Sre~o Davor [kapin2 1Independent Researching plc, Betnavska cesta 6, 2000 Maribor, Slovenia 2Institut »Jo`ef Stefan«, Jamova 39, 1000 Ljubljana, Slovenia varuzan.kevorkijan@siol.si Prejem rokopisa – received: 2009-05-25; sprejem za objavo – accepted for publication: 2009-07-07 In this work, the preparation of various light weight Mg-Mg2Si–TiC metal matrix composites and Mg2Si–TiC/TiB2 ceramic composites has been described and the influence of their structure on mechanical response was discussed. Mg-Mg2Si-TiC composites with continuous magnesium matrix densified to >95 % T.D. were fabricated by pressureless reactive infiltration of performs made from Mg2Si and TiC powders. Infiltration was performed in an argon atmosphere at temperatures 700, 800 and 900 °C for 1 h. Trials made with Mg2Si preforms reinforced with TiB2 were unsuccessful. Mg2Si–TiC/TiB2 ceramic composites densified to >97 % T.D. were prepared by pressureless reactive sintering of tablets made from Mg2Si and TiC or TiB2 powders. The reactive sintering was performed at 1020 °C for 0.5–1 h under a protective argon atmosphere. The phases present in the obtained composite samples have been identified by scanning electron microscopy/energy dispersive X-ray spectroscopy. In addition, room temperature tensile tests (Rm, Rp0.2, A) and hardness measurements (HV) were also undertaken. The results have shown that Mg-Mg2Si−TiC composites are with tensile properties superior to that of conventional magnesium alloys while Mg2Si–TiC/TiB2 samples combined high hardness (9–10 GPa) and low density (2.2. –2.5 g/cm3). Key words: Mg-Mg2Si–TiC and Mg2Si–TiC/TiB2 composites, reactive pressureless infiltration, reactive pressureless sintering, microstructural examination, tensile test, advanced, low-weight engineering materials V delu opisujemo pripravo lahkih kompozitov Mg-Mg2Si-TiC s kovinsko matrico in kerami~ne kompozite Mg2Si-TiC/TiB2 ter preu~evanje vpliva njihove strukture na mehanske lastnosti. Kompozite Mg-Mg2Si-TiC s kontinuirno matrico iz magnezija, zgo{~ene do >95 % T.G., smo izdelali po postopku reakcijske infiltracije pri atmosferskem tlaku predoblik, stisnjenih iz prahov Mg2Si in TiC. Inflitracija je potekala v atmosferi argona, 1h pri temperaturah (700, 800 in 900) °C. Poskusi infiltracije predoblik Mg2Si, oja~enih s TiB2 niso bili uspe{ni. Kerami~ne kompozite Mg2Si–TiC/TiB2, zgo{~ene do >97 % T.G., smo izdelali z reakcijskim sintranjem pri atmosferskem tlaku tablet, stisnjenih iz prahov Mg2Si in TiC ali TiB2. Vzorce smo reakcijsko sintrali pri 1020 °C 1h v za{~itni atmosferi argona. Mikrostrukturo in fazno sestavo pripravljenih vzorcev smo analizirali z vrsti~nim elektronskim mikroskopom in XRD. Mehanske preiskave: natezni preizkus (Rm, Rp0.2, A) in merjenje trdot (HV) smo izvajali s standardnimi metodami pri sobni temperaturi. Rezultati nateznega preizkusa so pokazali, da imajo kompoziti Mg-Mg2Si–TiC veliko bolj{e mehanske lastnosti kot navadne magnezijeve zlitine, medtem ko vzorci Mg2Si–TiC/TiB2 zdru`ujejo visoko trdoto (9–10 GPa) in nizko specifi~no maso (2.2.–2.5 g/cm3). Klju~ne besede: kompoziti Mg-Mg2Si–TiC in Mg2Si–TiC/TiB2, reakcijska infiltracija pri atmosferskem tlaku, reakcijsko sintranje pri atmosferskem tlaku, preiskave mikrostrukture, mehanske preiskave, lahki in`enirski materiali prihodnosti 1 INTRODUCTION Magnesium alloys and Mg-based composites are pro- spective candidates for light-weight structural materials 1–2. However, most Mg alloys are of limited use in high performance applications due to their low mechanical properties 3. Improvement of their mechanical properties could be achieved by reinforcement with different ce- ramic particulates, which has already been well demon- strated 4,5, or by applying new magnesium-based com- pounds (such as Mg2Si) as the matrix constituent 6. Among these, magnesium silicide (Mg2Si) is particularly attractive because of its superior characteristics such as high melting point (1085 °C), low density (1.99 g/cm3), high hardness (350–700 HV) and elastic modulus (120 GPa) 7. On the other hand, the major disadvantage of Mg2Si is its brittleness 8–9, limiting the usage of bulk (sintered or hot pressed) Mg2Si as a structural material in engi- neering applications. A possible solution considered in this work is the formulation of ultra-light composite ma- terials with a Mg2Si-Mg matrix reinforced with ceramic particulates (TiC, TiB2, B4C) in order to achieve an im- provement in mechanical properties and brittleness. 2 EXPERIMENTAL In the first set of experiments, Mg2Si-Mg-TiB2 and Mg2Si-Mg-TiC composite samples were fabricated by pressureless infiltration of porous preforms with molten magnesium. Preforms were isostatically pressed from the various mixtures of commercial Mg2Si (99.5 %, 30 µm) Materiali in tehnologije / Materials and technology 43 (2009) 6, 309–313 309 UDK 669.018:621.762.5:620.17/.18 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)309(2009) and TiC (99.5 %, 30 µm) or TiB2 (99.5 %, 30 µm) pow- ders, as listed in Table 1. Samples were cylinders 30 mm high and 20 mm in diameter. Infiltration was performed in a vacuum furnace in an argon atmosphere at tempera- tures of (700, 800 and 900) °C for 1 h. Table 1: The volume fractions of various Mg2Si-TiC and Mg2Si-TiB2 mixtures used for preforms in infiltration, and tablets in sintering ex- periments Tabela 1: Sestava razli~nih zmesi Mg2Si-TiC in Mg2Si-TiB2 v volumenskih dele`ih (f/%), uporabljenih za izdelavo predoblik za infiltracijo in tablet za sintranje Mixture Composition, f/% Mg2Si TiC TiB2 A 90 10 – B 80 20 – C 90 – 10 D 80 – 20 In the second set of experiments, composite samples were prepared by pressureless sintering of isostatically pressed tablets made from the same Mg2Si-TiC and Mg2Si-TiB2 mixtures listed in Table 1. Sintering was performed at 1020 °C, for 0.5–1 h in a protective argon atmosphere. The as-synthesized composite samples were cut, ma- chined and polished in accordance with standard proce- dures. Microstructural characterization of fabricated com- posites was performed by optical and scanning electron microscopy (OM and SEM), whereas X-ray diffraction (XRD) measurements were applied to the samples to identify the phases and their crystal structure. Quantitative determination of the volume percentage of Mg2Si, secondary phases and ceramic particles in the matrix, as well as the retained porosity, was performed by analysing the optical and scanning electron micro- graphs of as polished composite bars using the point counting method and image analysis and processing soft- ware. Composite density measurements were carried out in accordance with Archimedes’ principle, applying dis- tilled water as the immersion fluid. The initial density of the green compacts (preforms and tablets) was calculated from the mass and geometry of the samples. Tensile tests were conducted on cylindrical ten- sion-test specimens 5 mm in diameter and 25 mm gauge length using an automated servo-hydraulic tensile testing machine with a crosshead speed of 0.254 mm/60 s. Vickers hardness (HV) measurements were per- formed at room temperature on polished composite sam- ples as an average of 15 indentations. These measure- ments were made on an automatic digital tester using a pyramidal diamond indenter with a facing angle of 136° a 0.025 kg indenting load, 50 µm/s load applying speed, and a 15 s load holding time. 3 RESULTS AND DISCUSSION Composites made by pressureless infiltration The calculated porosity of the preforms used was within the range of (30–35 ± 5) %. Based on the experi- mental findings, the pressureless infiltration of Mg2Si-TiC preforms with molten magnesium did not oc- cur below 900 °C. At 900 °C, the infiltration was com- plete within 1h, resulting in composite samples with less than 5 % of retained porosity. At the same time, under the applied experimental conditions, the pressureless in- filtration of Mg2Si-TiB2 preforms was unsuccessful. The microstructure and phase composition of the composite samples obtained is presented in Figure 1 a, b, c. V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC ... 310 Materiali in tehnologije / Materials and technology 43 (2009) 6, 309–313 Figure 1: (a, b) SEM micrograph of a pressurelessly infiltrated preform with the initial composition of the preform skeleton of the volume fraction of 70 % Mg2Si-20 % TiC and an initial porosity of (30 ± 5) %. The phases detected are Mg, Mg2Si and TiC; (c) XRD of the sample shown in the Figure 1a-c. Slika 1: (a, b) SEM posnetek mikrostrukture pri atmosferskem tlaku infiltrirane predoblike za~etne sestave v volumenskih dele`ih 70 % Mg2Si-20 % TiC ter za~etne poroznosti (30 ± 5) %. Ugotovljene faze so: Mg, Mg2Si in TiC; (c) XRD vzorcev, prikazanih na sliki 1 a–c. V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 309–313 311 Figure 2: (a) SEM micrograph of pressurelessly sintered composite simple with the inital volume composition 90 % Mg2Si and 10 % TiC, (b) XRD of the sample Slika 2: (a) SEM-posnetek mikrostrukture vzorcev kompozitov za~etne volumenske sestave 90 % Mg2Si in 10 % TiC, sintranih pri atmosferskem tlaku, (b) XRD vzorca Figure 3: (a) SEM micrograph of pressureless sintered composite sample with the initial volume composition 80 % Mg2Si and 20 % TiC, (b) XRD of the sample Slika 3: (a) SEM-posnetek mikrostrukture vzorca kompozita za~etne volumenske sestave 80 % Mg2Si in 20 % TiC, (b) XRD vzorca Table 2: Average room temperature tensile properties and Vickers hardness of pressurelessly infiltrated composite samples Tabela 2: Povpre~ne vrednosti nateznih lastnosti in Vickersove trdote, izmerjenih pri sobni temperaturi, pri vzorcih kompozita, infiltriranih pri atmosferskem tlaku Composite initial composition f/% Retained porosity (%) Density /(g/cm3) E/ (GPa) Tensile strength /MPa Vickers Hardness HV/GPa 63%Mg2Si+30%M g+7%TiC 3.6 ± 0.4 2.03 ± 0.1 88 ± 9 186 ± 19 4.9 ± 0.5 56%Mg2Si+30%M g+14%TiC 4.7 ± 0.5 2.32 ± 0.1 97 ± 10 197 ± 20 5.1 ± 0.5 Table 3: Average room temperature tensile properties and Vickers hardness of pressureless sintered composite samples Tabela 3: Povpre~ne vrednosti nateznih lastnosti in Vickersove trdote, izmerjenih pri sobni temperaturi, pri vzorcih kompozita, sintranih pri atmosferskem tlaku Iinitial composi- tion f/% Retained porosity (%) Density /(g/cm3) E/ (GPa) Tensile strength /MPa Vickers Hardness HV/GPa Mg2Si+10%TiC 1.8 ± 0.2 2.25 ± 0.1 132 ± 13 487 ± 49 9.1 ± 1 Mg2Si+20%TiC 2.2 ± 0.2 2.53 ± 0.1 141 ± 14 532 ± 53 9.9 ± 1 Mg2Si+10%TiB2 2.3 ± 0.2 2.22 ± 0.1 134 ± 13 477 ± 48 9.6 ± 1 Mg2Si+20%TiB2 2.9 ± 0.3 2.43 ± 0.2 146 ± 15 528 ± 53 10.3 ± 1 Large block-shaped Mg2Si particles of about 50 µm in size can be observed. The distribution of Mg2Si particles is in principle homogeneous with no agglo- meration. The Mg matrix is continuous with dispersed fine TiC particles. Composites made by pressureless sintering Pressureless sintering at 1020 °C for 1 h of Mg2Si-TiC and Mg2Si-TiB2 samples made from mixtures A, B, C and D (Table 1) resulted in almost fully dense composite species with a retained porosity of less than 3 %. The microstructure of the composite samples ob- tained is presented in Figures 2, 3 and 4. As illustrated in Figure 2, in pressureles sintered samples with the initial volume composition 90 % Mg2Si and 10 % TiC, the ceramic reinforcement reacted with Mg2Si transforming completely the initial TiC aggre- gates to dense TiSi2 secondary grains. According to the X-ray diffraction patterns (Figure 2 b) of pressureless sintered Mg2Si samples with 10 % of TiC reinforcement, the main product of chemical reaction between Mg2Si and TiC is TiSi2. The presence of elemental silicon was also confirmed, while magnesium and carbon did not detected by XRD, Reaction 1: 3Mg2Si + TiC = TiSi2 + Si + 6Mg + C (1) The additional SEM investigation confirmed the pres- ence of Mg-Si-C precipitates, most probably formed by further chemical reactions between elemental silicon, magnesium and carbon. However, by increasing the amount of TiC reinforce- ment to 20 %, the reaction path was changed resulting in the formation of Ti3SiC2, TiSi2 and SiC phases, Figure 3a, b, as well as the elemental magnesium, Reaction 2: 7Mg2Si + 4TiC = Ti3SiC2 + TiSi2 + 14Mg + 4SiC (2) In pressurelessly sintered composite samples rein- forced with TiB2 particles large chunky Mg2Si particles were detected, Figure 4. During reactive pressureless sintering, these Mg2Si particles melt incongruently, forming a peritectic. Further densification of the samples proceeds via pressureless reactive liquid sintering. On cooling the samples, the molten phase crystallizes in the form of a continuous lace network with an average com- position of Mg0.15Si0.85, with dispersed, fine TiB2, Figure 4 a. 4 CONCLUSION The effect of fabrication techniques (reactive infiltra- tion or pressureless reactive sintering) and processing conditions on the phase formation, microstructures and mechanical properties of Mg2Si-TiC and Mg2Si-TiB2 composites was examined. It was found that pressureless reactive infiltration is effective in production of Mg2Si-Mg-TiC composites, whereas in the case of Mg2Si-Mg-TiB2 samples, it was unsuccessful. The composite samples obtained by pressureless reactive infiltration of molten magnesium into a porous preform of Mg2Si with TiC ceramic rein- forcement were designed to consist of a continuous mag- nesium matrix discontinuously reinforced with Mg2Si and TiC. Such a design was selected in order to reduce the well known brittleness of the Mg2Si phase, thereby creating an ultra-light structural material with excellent tensile properties. On the other hand, pressurelessly reactive sintered Mg2Si-TiC and Mg2Si-TiB2 composites were designed to provide the improved hardness (9–10 GPa). Although further experimental work is necessary to identify the real mechanism of pressureless densification of Mg2Si-TiC and Mg2Si-TiB2 samples as well as the me- chanical response of reinforced samples, the results ob- tained clearly demonstrate that routinely performed pressureless densification resulted in samples with al- most theoretical density, proving at the same time the great industrial potential of this low-cost and highly pro- ductive fabrication method. Acknowledgement This work was supported by funding from the Public Agency for Research and Development of the Republic V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC ... 312 Materiali in tehnologije / Materials and technology 43 (2009) 6, 309–313 Figure 4: (a) Microstructure of pressurelessly sintered composite sample with the inital volume composition 90 % Mg2Si and 10 % TiB2, (b) XRD of the sample Slika 4: (a) Mikrostruktura vzorce kompozitov za~etne volumenske sestave 90 % Mg2Si in 10 % TiB2, sintranih pri atmosferskem tlaku, (b) XRD vzorca of Slovenia, as well as the Impol Aluminium Company and Bistral, d. o. o., from Slovenska Bistrica, Slovenia, under contract No. 1000-07-219308. 5 REFERENCES 1 K. U. Kainer, F. von Buch, In: Magnesium alloys and technology, Ed. K. U. Kainer, DGM, Wiley-VCH, 2003; pp. 1 2 F. Moll, K. U. Kainer, In: Magnesium alloys and technology, Ed. K. U. Kainer, DGM, Wiley-VCH, 2003; pp. 197 3 W. Blum, B. Watzinger, P. Weidinger, In: Magnesium alloys and their applications, Eds. B. L. Mordike, K. U. Kainer, Werkstoff- Informationsgesellschaft mbH, 1998; pp. 49 4 H. Muramatsu, K. Kondoh, E. Yuasa, T. Aizawa, JSME, 46 (2003) 3, 247 5 L. Lu, K. K. Thong, M. Gupta, Composite science and technology, 63 (2003), 627–632 6 L. Wang, X. Y. Qin, W. Xiong, X. G. Zhu, Mater. Sci and Eng. A, 459 (2007), 216 7 J. M. Munoz-Palos, M. C. Cristina, P. Adeva, Mater. Trans. JIM, 37 (1996), 1602 8 J. Zhang, Z. Fan, Y. Q. Wang, B. L: Zhou, Scripta Mater., 42 (2000), 1101–1106 9 V. Milekhine, M. I. Onsoen, J. K. Solberg, T. Skaland, Intermetallics, 10 (2002), 743 V. KEVORKIJAN, S. D. [KAPIN: PREPARATION AND TESTING OF PROTOTYPE Mg2Si-Mg-TiC ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 309–313 313 M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR OF EAF SLAG FROM STAINLESS STEEL PRODUCTION VPLIV VODNEGA HLAJENJA NA IZLU@EVALNE KARAKTERISTIKE BELE EOP-@LINDRE Mojca Loncnar1, Marija Zupan~i~2, Peter Bukovec2, Anton Jakli~1 1Acroni, d. o. o., Cesta Borisa Kidri~a 44, SI-4270 Jesenice, Slovenia 2Faculty of Chemistry and Chemical Technology, University of Ljubljana, A{ker~eva 5, SI-1000 Ljubljana, Slovenia mojca.loncnar@acroni.si Prejem rokopisa – received: 2009-06-24; sprejem za objavo – accepted for publication: 2009-07-20 The object of this study was the investigation of the influence of cooling methods of hot electric arc furnace (EAF) slag from stainless steel production on the leaching behaviour of the slag. EAF slags from four different grades of stainless steel were sampled and water or air cooled. Leaching tests were done according to the SIST EN 12457–4:2004 one-stage batch test. It was confirmed that the cooling method has a significant effect on the leaching behaviour of slags. In EAF water cooled slag samples, a decrease of Ca, Al, Ba and Se concentrations in the leachate was observed. On the other hand, water cooling caused an increase in leaching concentrations of Si and Mg. Key words: EAF slag, leaching, metals, stainless steel, water cooling Namen raziskave je bil ugotoviti, kako razli~ni na~ini hlajenja bele EOP–`lindre, ki nastane pri proizvodnji nerjavnih jekel, vpliva na izlu`evalne karakteristike kovin in drugih prete`no anorganskih parametrov. Preu~ili smo `lindre, nastale pri izdelavi {tirih razli~nih kvalitetah nerjavnih jekel. Izlu`evalne preizkuse smo izvedli po standardu SIST EN 12457–4:2004. Ugotovili smo, da razli~ni na~ini hlajenja vplivajo na dele` izlu`evanja kovin in drugih prete`no anorganskih parametrov. Izlu`evanje Ca, Al, Ba in Se je bilo pri vodno hlajenih belih EOP-`lindrah ni`je kot pri hlajenju belih EOP–`linder na zraku, obenem pa se je pri hlajenju z vodo koncentracija Si in Mg v izlu`kih belih EOP-`linder pove~ala. Klju~ne besede: bela EOP-`lindra, izlu`evanje, kovine, nerjavna jekla, vodno hlajenje 1 INTRODUCTION Steel slag is a by-product from the elaboration of steel. According to Proctor et al.1, slags represent about 10–15 % by weight of the steel output. Slag is necessary in all metallurgical processing steps of liquid metal treat- ment. Steel slags include slags that are produced in the oxygen steel converter process, in electric arc furnace (EAF) steel elaboration and slags from secondary metallurgy2. Various alloy steel slags are generated in the alloy steel making processes. They usually contain high amounts of alloying elements, such as Cr, Ni, Mn, V, Ti and Mo. Since stainless steel slags contain a high amount of potentially toxic elements, it is necessary to treat them prior to their application or use as landfill3. Historically, slags have been used for the construc- tion of roads and as fill material. However, more recently, the use of slags has been expanded as cement additives, landfill cover material and for a number of agricultural aplications1. In spite of the fact that many of the above mentioned applications are nowadays common practice, significant quantities of slag are still being dumped in landfills or stockpiled for long periods at steel plants. The environmental impact must be taken into account when slags are disposed in a landfill. Steel slags are often enriched in toxic elements, in particular metals (Cu, Pb and Zn) and metalloids (As and Sb) which can be released into the environment through ageing processes and leaching4. The release of metals and toxic elements from slags can cause environmental problems such as water and soil pollution and a toxicological risk to humans through inhalation of small slag particles (<10 µm)3. Quick cooling of EAF slags is recommended as steel slag treatment before disposal or use in other applica- tions5. Quick cooling is a common practice for carbon steel EAF slag, but it can also be used for stainless steel EAF slags. It is used to avoid or to minimise the disinte- gration of slag. Disintegration in slags is probably the re- sult of conversion of unstable polymorphous Ca2SiO4 to the low () temperature form of Ca2SiO4, which is ac- companied by an increase of 10 % in volume and leads to disintegration of slags5. Disintegration also occurs in some slags investigated in this work. It has been reported that if slags are quenched in water thereby producing an amorphous structure, the resulting metal extraction is substantially lower6. The glassy amorphous structure possesses better chemical resistance to decomposition by acid than the crystalline structure6. In some reported studies, the effect of the cooling mode of the molten slag on its leaching charac- Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 315 UDK 669.181:669.14.018.8 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)315(2009) teristics was investigated through re–melting slag and cooling tests6,7,8. In our study the leaching characteristics of steel slags in relation to different modes of cooling of hot EAF slag were investigated in order to estimate the effect of water interactions on possible waste disposal. 2 EXPERIMENTAL PROCEDURES The materials used in our study were slags from stainless steel production. Four electric arc furnace slags from four different stainless steel grades were selected in order to represent different types of EAF slag: A. Electric arc furnace slag from stainless steel X2 CrNi 18–9; symbol: EX B. Electric arc furnace slag from stainless steel AISI 304 H; symbol: E304 C. Electric arc furnace slag from stainless steel AISI 316 L, symbol: E3 D. Electric arc furnace slag from stainless steel MKM CrAl 4; symbol: EM The chemical composition of stainless steel after the EAF procedure was determined during the process of production of stainless steel by optical emission spec- trometry (OES ARL MA-310) and by IR adsorption spectroscopy (CS 344, LECO, Michigan, USA) for C and S determination. Each type of EAF slag was emptied below the furnace, excavated and sampled while still hot. One part of a representative sample of EAF slag was left to cool down in air (1 stands for air cooled samples), whereas another part of the representative hot sample was jetted with water (2 stands for water cooled samples). Sampling of representative EAF slag samples (10–20 kg) was made according to SIST EN 15002:2006. In the case of E304 a different mode of water cooling was used, in which the slag was immersed in a bucket of cold water. A few pieces of hot E304 slag were dropped into a beaker with 500 mL deionised water to evaluate the leaching of slag components during cooling. The solution was filtered and analysed by ICP–AES (OPTIMA 2000 DV, Perkin Elmer) to determine metal concentrations (Al, Mn, Cr, Zn, Cd, Cu, Pb, Sn), by IC (761 COMPACT IC, Metrohm) for Cl–, F– and SO42–, by FAAS for Mg and Ca and by UV–VIS spectrophoto- metry (Cary 1E (UV VIS), Varian) to determine Si and Cr(VI). To determine the total composition of slag, XRF spectroscopy (MAGI´X FAST, PANALYTICAL) was used for major components, IR adsorption spectroscopy for C and S (CS 244 W, LECO, Michigan, USA), ther- mal decomposition in tube furnace and measuring F– with electrochemical method, ICP–AES (OPTIMA 2000 DV, Perkin Elmer) and ICP-MS (4500, Agilent) for trace elements in acid digested slag samples. To determine their leaching characteristics, slag samples were crushed to a particle size of <10 mm and leached according to the SIST EN 12457–4 one-stage batch test (24 h water extraction of slag samples at an L/S ratio of 10). The leaching tests were done in tripli- cate. The leachate samples were centrifuged and filtered through a 0.45 µm filter. pH, EC, redox potential and the concentration of elements were determined in the leachates. ICP–MS (Agilent 4500) was used for determi- nation of Be, Mg, Ti, V, Crtot, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sb, Tl, Ba and Pb concentrations, ICP–AES (OPTIMA 2000 DV, Perkin Elmer) for Al and Ca, spectrophotometry (Cary 1E (UV VIS), Varian) for Si and Cr(VI), IC (761 COMPACT IC, Metrohm) for Cl–, SO42– and F– and TOC analyzer (Multi N/C 2100S, Analytik Jena) for DOC. 3 RESULTS AND DISCUSSION The chemical composition of EAF slag depends on the metallurgical process used during steel production and also depends on the steel grade. The elemental com- position of the steel types from which the slag samples used in our study originated is presented in Table 1. As can be seen from Table 1, steel M showed the most different composition values comparing to other steel types resulting in different EM slag composition (see Table 2) and furthermore different composition of EM slag leachate (see Figures 1–3). According to Shen et al.3 the mineral phases of stainless steel slag are dicalcium and tricalcium silicate, calcium-aluminium silicate, periclase and chromites. The M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... 316 Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 quality of steel, w/% element X 304 3 M C 1,037 0,593 0,816 0,067 Si 0,38 0,01 0,17 0,01 Mn 0,97 0,89 0,98 0,04 P 0,033 0,039 0,043 0,003 S 0,011 0,013 0,011 0,005 Cr 19,67 18,89 17,15 0,02 Cu 0,42 0,38 0,32 0,03 Ni 6,38 7,38 7,27 0,04 Al 0,01 0,004 0,008 0,275 Sn 0,015 0,013 0,011 0,005 Mo 0,36 0,38 1,54 0,01 V 0,097 0,053 0,064 0,005 Ti 0,016 0,005 0,006 0,005 Nb 0,014 0,006 0,005 0,005 W 0,031 0,054 0,05 / Co 0,107 0,117 0,154 0,01 Zr / / / 0,003 B 0,001 0,001 0,001 0,001 Pb 0,001 0,002 0,002 0,004 Sb / / / 0,005 Ca 0,0005 0,0008 0,0009 0,0013 Table 1: Elemental composition of stainless steel after EAF process in mass fractions w/%. Preglednica 1: Elementna sestava nerjavnih kvalitet jekel po EOP-po- stopku v masnih dele`ih w/%. mineral composition and mineral grain size are variable with chemical composition, mode of cooling and so on. Chemical phase analysis of steel slag indicated that Fe and Cr are mainly (about 70 %) in the form of oxides while Ni and Mo are in the form of metal9. The chemical composition of the EAF slag samples used in our study is reported in Table 2. The mass fractions of main components of EAF slag were CaO (35.40–43.62 %), SiO2 (10.78–22.95 %), Al2O3 (6.59–15.55 %), MgO (8.69–13.81 %), Fetot (4.40–10.60 %), MnO (1.45–3.63 wt %) and Cr2O3 (1.54–12.70 wt %). The amount of Cr2O3 was higher than that reported 1,8,9,10. The slag samples were also enriched in metals: Mo (158–2100 mg kg–1), Ba (248–560 mg kg–1), Cu (112–450 mg kg–1) and Zn (30–270 mg kg–1). It is well known that the leaching characteristic of metals is strongly related to the structure and chemical composition of the slag. During smelting, reduction conditions are needed to produce metals and metalloids from scrap. The absence of O2 prevents any oxidation reactions. In the slags themselves, the elements are zerovalent or occur in more reduced valence states, often incorporated in the spinel structure, if the trivalent oxidation state is stable, as in the case of CrIII, SbIII and VIII. Spinels are oxides of the form (M2+)(Fe3+)2O4 where M2+ and Fe3+ are the divalent and trivalent cations, respectively, occupying tetrahedral and octahedral inter- stitial positions in the lattice formed by O2–. The ele- ments are thus also leached as more reduced species compared to other waste11. The leaching tests showed high and comparable pH values of leachate in the range from 11.67 to 12.75 (see Table 3). Shen et al.9 reported high and similar pH values in leachate in the range from 10.28 to 10.81. It has been suggested that the release of Ca from slag may be the main reason for the increase in pH according to the chemical composition of the water9. Cornelis et al.11 reported that freshly produced alkaline wastes have a M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 317 Sample w/% CaO SiO2 Al2O3 MgO Cr2O3 MnO Fe EX1 37,46 ± 0,07 20,24 ± 0,06 6,59 ± 0,06 8,690 ± 0,002 12,0 ± 0,1 3,54 ± 0,038 6,7 ± 0,2 EX2 35,4 ± 0,4 19,5 ± 0,2 6,65 ± 0,04 9,10 ± 0,04 12,7 ± 0,3 3,63 ± 0,018 7,3 ± 0,5 E3041 41,425 ± 0,002 18,82 ± 0,04 8,856 ± 0,001 9,55 ± 0,04 9,18 ± 0,04 3,03 ± 0,01 4,4 ± 0,1 E3042 38,2 ± 0,2 18,52 ± 0,05 8,08 ± 0,03 9,59 ± 0,02 10,61 ± 0,01 3,579 ± 0,004 5,2 ± 0,1 E31 36,4 ± 0,1 22,4 ± 0,2 7,47 ± 0,09 13,8 ± 0,1 5,91 ± 0,06 3,29 ± 0,014 8,0 ± 0,2 E32 37,34 ± 0,01 22,95 ± 0,02 7,845 ± 0,004 13,6 ± 0,1 5,24 ± 0,06 3,23 ± 0,006 6,0 ± 0,2 EM1 43,6 ± 0,1 10,78 ± 0,03 15,55 ± 0,07 10,73 ± 0,04 1,540 ± 0,002 1,45 ± 0,032 10,6 ± 0,2 EM2 35,4 ± 0,2 18,83 ± 0,04 11,13 ± 0,08 8,70 ± 0,03 3,04 ± 0,03 1,76 ± 0,002 10,5 ± 0,1 Sample w/% F– TiO2 Ni V2O5 S C EX1 0,64 ± 0,01 0,99 ± 0,01 0,71 ± 0,06 0,283 ± 0,001 0,166 ± 0,003 0,16 EX2 0,50 1,03 ± 0,02 0,65 ± 0,09 0,285 ± 0,003 0,150 ± 0,001 0,23 E3041 1,19 ± 0,02 1,01 ± 0,01 0,30 ± 0,03 0,243 ± 0,005 0,296 ± 0,003 0,17 ± 0,01 E3042 0,81 ± 0,01 0,842 ± 0,001 0,43 ± 0,04 0,266 ± 0,006 0,256 ± 0,004 0,18 E31 0,122 ± 0,005 0,78 ± 0,01 0,76 ± 0,09 0,139 ± 0,001 0,095 ± 0,001 0,15 E32 0,129 ± 0,002 0,755 ± 0,003 0,76 ± 0,06 0,137 ± 0,002 0,112 ± 0,003 0,21 ± 0,005 EM1 0,83 ± 0,01 0,327 ± 0,003 0,11 ± 0,01 0,042 ± 0,001 0,593 ± 0,005 0,13 EM2 0,84 ± 0,02 0,473 ± 0,004 0,18 ± 0,03 0,074 ± 0,001 0,417 ± 0,003 0,37 ± 0,01 Sample c/(mg kg–1) P Co Cu Zn As EX1 137 ± 2 114 ± 8 412 ± 30 226 ± 5 7,6 ± 0,5 EX2 164 ± 2 120 ± 10 450 ± 40 87 ± 4 7,6 ± 0,7 E3041 137 ± 2 43 ± 2 145 ± 8 150 ± 20 6,2 ± 0,4 E3042 120 ± 7 60 ± 4 200 ± 1 58 ± 4 6,0 ± 0,1 E31 161 140 ± 20 290 ± 40 30 ± 1 9 ± 1 E32 127 ± 4 150 ± 20 310 ± 60 38 ± 6 9 ± 2 EM1 648 ± 7 23,2 ± 0,2 112,3 ± 0,7 270 ± 40 6,9 ± 0,2 EM2 630 ± 20 35 ± 2 150 ± 10 246 ± 5 7,0 ± 0,6 Sample c/(mg kg–1) Se Mo Cd Ba Pb EX1 6,4 ± 0,9 470 ± 20 1,27 ± 0,03 251 ± 5 42 ± 1 EX2 10,9 ± 0,6 440 ± 40 0,93 ± 0,08 270 ± 2 8,1 ± 0,1 E3041 11,5 ± 0,4 250 ± 30 0,42 ± 0,03 259 ± 1 5,5 ± 0,1 E3042 6,800 ± 0,003 320 ± 10 0,50 ± 0,01 248 ± 1 6,4 ± 0,2 E31 <4 2100 ± 200 0,83 ± 0,07 560 ± 10 <1 E32 <4 2100 ± 100 0,7 ± 0,2 548 ± 1 2,11 ± 0,04 EM1 7 ± 2 158 ± 7 0,41 ± 0,02 309 ± 1 17 ± 3 EM2 <4 290 ± 60 0,69 ± 0,01 314 ± 6 30,2 ± 0,7 Table 2: Total chemical composition of EAF slags. Results are presented as the mean value of duplicate analysis with the standard deviation. Preglednica 2: Kemijska sestava EOP–`linder. Rezultati so podani kot povpre~je dveh paralelk ± standardni odmik. narrow pH distribution (between 10 and 13), because the leachate pH is mainly controlled by dissolution of a limited set of minerals containing Ca, such as portlandite (Ca(OH)2), calcium monosulfoaluminate (Ca4[Al(OH)6]2 SO4·13H2O), hydrocalumite (Ca4[Al(OH)6]2·6H2O), ettringite (Ca6[Al(OH)6](SO4)3·32H2O), calcium silicate hydrate (CSH) and calcite (CaCO3). The quantities of these minerals, however, may vary, as reflected in the acid neutralization capacity (ANC). According to Cornelis et al.11 the minerals containing Ca mentioned above, exert control over leaching. In our study a narrow pH distribution and high pH values were also found. The high pH values in leachates are a consequence of the high content of Ca in the leachate (see Figure 1), probably due to Ca minerals in slags such as portlandite and calcite. The main elements in slags were Ca, Mg, Si, Al, Mn and Fe. Although they are not mentioned in Slovenian M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... 318 Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 Figure 2: Results of the leaching test of minor elements (Ba, Se, Mo, Cr) in air and water cooled EAF slags in mg kg–1. Results are presented as the mean value of triplicate analysis with the standard deviation as error bars. Slika 2: Primerjalno izlu`evanje elementov v sledovih (Ba, Se, Mo, Cr) v EOP–`lindrah, hlajenih na zraku in z vodo v mg kg–1. Rezultati so podani kot povpre~je treh paralelk in standardni odmik. Figure 1: Results of the leaching test of major elements in air and water cooled EAF slags in mg kg–1 (Ca, Al, Si, Mg, Ni, Fe). Results are presented as the mean value of triplicate analysis with the standard deviation as error bars. Values that are not presented in the Figure are under the limit of detection; for Mg (0.05 mg kg–1); for Si (0.1 mg kg–1); for Ni (0.005 mg kg–1); for Fe (0.025 mg kg–1). Slika 1: Primerjalno izlu`evanje glavnih elementov (Ca, Al, Si, Mg, Ni, Fe) v EOP–`lindrah, hlajenih na zraku in z vodo v mg kg–1. Rezultati so podani kot povpre~je treh paralelk in standardni odmik. Rezultati, ki v grafih niso podani so pod mejo detekcije, ki je za Mg (0.05 mg kg–1); za Si (0.1 mg kg–1); za Ni (0.005 mg kg–1); za Fe (0.025 mg kg–1). Figure 3: Leaching of F–, Cl– and DOC according to the one–stage batch leaching test. Results are presented as the mean value of triplicate analysis with the standard deviation as error bars. Values that are not presented in the Figure are under the limit of detection; for Cl– (2.5 mg kg–1); for DOC (10 mg kg–1). Slika 3: Izlu`evanje F–, Cl– in DOC z enostopenjskim {ar`nim preskusom. Rezultati so podani kot povpre~je treh paralelk in standardni odmik. Rezultati, ki v grafih niso podani, so pod mejo detekcije, ki je za Cl– (2.5 mg kg–1); za DOC (10 mg kg–1). waste legislation12, they were also investigated in leaching tests because of the strong dependence between major element concentrations present in slag and the leaching characteristics of trace elements.13 The most leachable element from air cooled slag is Ca, in the range from (1620 ± 80) mg kg–1 (E31) to (7000 ± 400) mg kg–1 (E3041) which represents 0.62 % and 2.36 % of the total Ca concentration, respectively. The amount of Al leached compared to the total Al concentration is in most cases even higher than for Ca, namely from 1.77 % (E31) to 4.88 % (EX1) of the total concentration, respectively, but in the case slag E3041 leaching of Al is negligible. The leaching of Si, Mg, Ni and Fe from air cooled slags was small (see Figure 1). Mn concentrations in the leachate were under the detec- tion limit of method (0.025 mg kg–1) and are not pre- sented in Figure 1. The leaching of Ca decreased in rapidly water cooled slag samples, with the exception of slag EM. The leaching of Al also decreased in all samples except E304, when cooled by water. The leaching of Al after rapid water cooling decreased significantly, especially in slag EX by 92.35 % and in slag EM by 78.57 % in comparison with air cooled samples. As can be seen from Table 4 the concentration of Ca and Al in water after several pieces of hot E304 slag were dropped into a beaker containing 500 mL deionised water was quite high (252 mg L–1 and 72.1 mg L–1, respectively). How- ever those values could not be directly compared to leaching values due to the different amount of slag samples in both cases. It is impossible to weigh hot slag to determine the S/L ratio. Nevertheless, it can be con- cluded that leaching of Al and Ca decreased when rapid water cooling was used due to ability of Ca and Al to solubilize in water after jetting hot slag samples. In the case of Si and Mg, water cooling caused an increase in leaching of elements from slags. The leaching of Si increased in all samples cooled with water. Leaching of Mg increased at all samples, too, except for slag E304 and slag EM, compared to air cooled samples. As can be seen from Table 4, the concentration of Si and Mg in water after a several E304 slag were dropped into water were negligible compared to the concentration of Ca and Al. The opposite effect was observed in leaching of Mg and Si in comparison to the concentration of Mg and Si in water after dropping several of hot slag into water. Tossavainen el at.8 reported that leaching of Si increased in many cases, while Al leaching decreased when cooled rapidly. Different methods of cooling M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 319 c/(mg kg–1) Sample Crtot Cr(VI) EX1 0,074 ± 0,007 <0.1 EX2 0,39 ± 0,04 0,44 ± 0,02 E3041 0,012 ± 0,002 <0.1 E3042 0,30 ± 0,04 0,28 ± 0,08 E31 0,42 ± 0,04 0,36 ± 0,04 E32 0,3552 ± 0,0004 0,35 ± 0,02 EM1 0,0064 ± 0,0008 <0.1 EM2 0,028 ± 0,008 <0.1 < LOD = less then LOD Table 5: Results of leaching test for Cr and Cr(VI) in mg kg–1. Results are presented as the mean value of triplicate analysis with the standard deviation. Preglednica 5: Rezultati izlu`ilnega testa za parameter Cr in Cr(VI). Rezultati so podani kot povpre~je treh paralelk ± standardni odmik. Parameter Unit EX1 EX2 E3041 E3042 pH 11,85 ± 0,09 11,85 ± 0,10 12,75 ± 0,07 12,43 ± 0,03 EC mS cm–1 1,80 ± 0,10 1,02 ± 0,09 6,40 ± 0,30 2,77 ± 0,08 Redox potential mV 217,0 ± 0,6 223 ± 7 142 ± 8 186 ± 4 Parameter Unit E31 E32 EM1 EM2 pH 12,03 ± 0,03 11,67 ± 0,01 11,89 ± 0,05 12,37 ± 0,01 EC mS cm–1 1,41 ± 0,07 0,65 ± 0,07 1,5 ± 0,1 2,6 ± 0,1 Redox potential mV 148 ± 3 56 101 115 ± 8 Table 3: Results of standard leaching test SIST EN 12457–4 presented as the mean value of triplicate analysis with the standard deviation. Preglednica 3: Rezultati nekaterih parametrov izlu`evalnega preizkusa SIST EN 12457–4. Rezultati so podani kot povpre~je treh paralelk ± standardni odmik. Parameter c/(mg L–1) Ca 252 Al 72,1 Si 0,26 Mg 0,005 Mn <0.01 Fe <0.025 Cr 0,240 Cr(VI) 0,233 Zn <0.01 Cd <0.01 Cu <0.01 Pb <0.03 Sn <0.1 Cl– 4,00 F– 5,65 SO42– 1,12 < LOD = less then LOD Table 4: Chemical composition of water after dropping several pieces of hot slag E304 into 500 mL of deionized water. Preglednica 4: Rezultati analize vode, potem ko smo v 500 mL deionizirane vode potopili par kosov vro~e `lindre E304. (re-melting and water granulation or re-melting and cooling in a crucible) were used by Tossavainen el at.8, but the results obtained were similar to those in our study. Due to the considerable amount of data obtained for leaching of minor elements, only the most significant ones are presented in Figure 2. The leaching from EAF stainless steel slag was generally very low. However some elements in air cooled slags exceeded the legal limit for inert waste material12: the leaching concentra- tion of Se from slag E3041 was (0.24 ± 0.03) mg kg–1 (limit value: 0.1 mg kg–1) and of Mo from slag EX1 was (1.4 ± 0.3) mg kg–1 and from slag E31 was (1.44 ± 0.07) mg kg–1 (limit value: 0.5 mg kg–1). Leaching concen- trations of Ba from EM1 slag was (20 ± 2) mg kg–1 and is at the limit value (limit value: 20 mg kg–1). As is shown in Figure 2, in comparison to air cooled slag, water cooling decreased the leaching of Ba and Se, with the exception of slag EM. Water cooling decreased the leaching of Ba in the range from 1.44 to more than 150– fold in comparison to air cooling. The leachable concentration of Ba from air cooled slag was in the range from (2.0 ± 0.3) mg kg–1 (E3041) to (20 ± 2) mg kg–1 (EM1) representing 0.77 % and 6.47 % of the total Ba concentration, respectively. A similar trend was observed in leaching of Mo and Cr on water cooling. Leaching of Mo in the water cooling mode decreased for slag E3, while it increased for slag E304 and slag EM, but in the case of EX it was similar to air cooled samples. A similar result was obtained in the case of Cr leaching where in all three slags (EX, E304 and EM) it increased, while, a decrease of leaching in slag E31 was observed in comparison to air cooled slags. Cr(VI) was also analysed in all leachate samples and the results (see Table 5) showed that almost all of the total Cr in leachate was present in form of Cr(VI). Soluble Cr is almost always hexavalent because equilibrium with insoluble Ca–CrIII minerals causes the Cr(OH)4– con- centration to be very low9. The leaching characteristics of F–, Cl–, DOC are presented in Figure 3. The leaching of SO42– was negligible and is not shown in Figure 3. The leaching of F– is the highest in slag EX1, (210 ± 10) mg kg–1. In the cases of slag EX and slag E3 a decrease in leachate F– concentrations was observed when cooled with water. On the other hand, an increase of F– concen- trations was observed in water cooled slag E304 and slag EM samples. Water cooling in most cases caused a decrease of Cl– concentrations (an exception was slag EX) and also a decrease of DOC concentrations. The results of our investigation showed that different modes of cooling affected the leaching behaviour of slags. Mainly it affects the leaching characteristics of major elements such as Ca, Al, Si, Mg and significantly the leaching of Ba and Se. Some similarities in leaching of Mo and Cr were also observed. The results from the single batch leaching test were compared to limits set by Slovenian legislation for the acceptance of inert waste for landfilling12. From the com- parison it can be concluded that most potentially hazardous elements did not exceed the established criteria, except for air cooled slag, where Mo (in slag E31 and slag EX1), F– (in slag EX1, slag E3041 and slag E31), Se (in slag E3041) where concentrations in leachate exceeded the limit values. Leaching concen- trations of Ba from EM1 slag was at the limit value. Although F– concentrations in leachate from air cooled slag in most cases exceeded the legal regulation (10 mg kg–1), it represents only from 0.63 % (E31) to 3.23 % (EX1) of the total fluoride concentration in slag. Procter et al.1 reported that the Sb, As, Ba, Be, Cd, Crtot, Cr(VI), Pb, Mn, Hg, Ni, Se, Ag, Tl and Zn con- centrations in leachates of steel slag, using the TCLP test for leaching evaluation, were very low. The only metals that were detected at concentrations higher than 1 mg L–1, were Ba and Mn. These metals were also found at much higher concentrations in the slag samples. Also in our study, although using different standard procedure, high values for Ba in leachtate were observed (see Figure 2). 4 CONCLUSION The results of our study showed that leaching of metals from EAF slag is generally very low. These results indicate that metals are very tightly bound and are not released from the matrix. Nevertheless, some exceptions exist. Relatively high leachate concentrations were observed for Ba and Mo. F– is the most problematic anion in leachate. The solubility of metals in slag depends on the solubility of the major phase. Leaching of major elements (for example Ca) is more extensive. Due to the high content of Ca in slags, EAF slags are alkaline solid waste. Water cooling had an effect on the leaching beha- viour of the investigated slags. Water cooling caused a decrease in leaching of Ca, Al, Ba and Se, and on the other hand, increased leaching of Si and Mg. Some similarities in leaching of Mo and Cr after water cooling were observed. Mo and Cr leaching in all three slags (EX2, E3042 and EM2) increased, while for slag E32 a decrease in leachable metal concentrations comparable to air cooled slags were observed. According to Sloot14, the single step extraction test is very limited in its capability to provide answers to complex questions such as: whether a material can be disposed in a particular type of landfill or it the material been sufficiently treated to meet requirements for disposal or beneficial applications. Future research will be focused on more sophisticated testing that will provide insight into the mechanistic aspects of leaching of EAF slag and on the effect of the rate of cooling on slag leaching behaviour. M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... 320 Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 To investigate the cooling effect on the leachability of slag in detail the mineralogical characteristics of water and air cooled slags will be included in further studies. ACKNOWLEDGEMENTS The operational part of this study was financed by the European Union, European Social Fund. Operation implemented in the framework of the Operational Programme for Human Resources Development for the Period 2007–2013, Priority axis 1: Promoting entre- preneurship and adaptability, Main type of activity 1.1.: Experts and researchers for competitive enterprises. 5 REFERENCES 1 D. M. Proctor, K. A. Fehling, E. C. Shay, J. L. Wittenborn, J. J. 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Vandecasteele, Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review, Appl. geochem., 23 (2008), 955–976 12 Decree on the landfill of waste, Official Gazette of Republic of Slovenia, 32/2006, amendment 98/2007, 62/2008 13 M. Tossavainen, E. Forssberg, Leaching behavior of rock material and slag used in road construction – a mineralogical interpretation, Process metallurgy, Steel res. 71, 11 (2000), 442–448 14 H. A. van der Sloot, Developments in testing for environmental impact assessment–editorial, Waste manage., 22 (2002), 693–694 M. LONCNAR ET AL.: THE EFFECT OF WATER COOLING ON THE LEACHING BEHAVIOUR ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 315–321 321 A: VESEL ET AL.: MODIFIKACIJA POLIMERA POLIETILEN NAFTALAT ... MODIFIKACIJA POLIMERA POLIETILEN NAFTALAT Z OBDELAVO V KISIKOVI PLAZMI MODIFICATION OF A POLYETHYLENE NAPHTHALATE POLYMER USING AN OXYGEN PLASMA TREATMENT Alenka Vesel, Kristina Eler{i~, Ita Junkar, Barbara Mali~ Institut "Jo`ef Stefan", Jamova 39, 1000 Ljubljana, Slovenija alenka.vesel@ijs.si Prejem rokopisa – received: 2009-03-09; sprejem za objavo – accepted for publication: 2009-08-25 We have studied the surface modification of a polyethylene naphthalate (PEN) foil with an oxygen plasma. The samples of PEN were treated in an inductively coupled RF plasma with a frequency of 27.12 MHz and at an output power of about 200 W. The gas pressure was 75 Pa. The samples were exposed directly to the glow region of the plasma. The samples were treated for different periods, ranging from 3 s to 60 s. Chemical changes in the surface composition after the plasma treatments were studied using high-resolution XPS (X-ray Photoelectron Spectroscopy), while the wettability was determined by water-contact-angle measurements (WCA). The untreated surface was hydrophobic with a water contact angle of about 90°. After 10 s of treatment the surface became very hydrophilic, with a contact angle of only about 3°. The oxygen concentration was increased from an initial mole fraction 21 % to about 35–38 %, depending on the treatment time. The surface oxidation resulted in the formation of different chemical bonds between the carbon and the oxygen, e.g., C=O, O–C–O, O–C=O and –C(=O)–O–C(=O)–. Key words: XPS, PEN, PET, polymer, plasma, oxygen, modification, surface, functionalization, hydrophilic V ~lanku opisujemo modifikacijo povr{ine polimera PEN (polyethylene naphthalate) s kisikovo plazmo. Plazmo smo generirali z induktivno sklopljenim radiofrekven~nim generatorjem s frekvenco 27,12 MHz in izhodno mo~jo okoli 200 W. Tlak kisika je bil 75 Pa. Vzorci polimera PEN so bili izpostavljeni plazmi razli~no dolgo ~asa: od 3 s do 60 s. Spremembe v kemijski sestavi povr{ine smo ugotavljali z metodo XPS (rentgenska fotoelektronska spektroskopija), spremembe v omo~jivosti povr{ine pa z meritvijo kontaktnega kota vodne kapljice. Ta je bil na neobdelani povr{ini 90°. Po 10-sekundni obdelavi v kisikovi plazmi je povr{ina polimera postala mo~no hidrofilna s kontaktnim kotom le okoli 3°. Pri {e dalj{ih izpostavah plazmi je bil kontaktni kot {e manj{i, tako da je bil `e pod mejo merljivosti. Iz XPS-meritev izhaja, da je koncentracija kisika na povr{ini narasla od za~etnih molskih dele`ih 21 % na 35–38 %, odvisno od ~asa obdelave. Posledica vezave kisika na povr{ino polimera je nastanek novih funkcionalnih skupin, kot npr. C=O, O–C–O, O–C=O in –C(=O)–O–C(=O)–. Klju~ne besede: XPS, PEN, PET, polimer, plazma, kisik, modifikacija, povr{ina, funkcionalizacija, hidrofili~en 1 INTRODUCTION Polymer materials are known to be hydrophobic. They have very poor adhesion properties and wettability. Therefore, they must be modified before applications like printing, painting, coating, to improve the biocom- patibility, etc. One of the most promising methods for modifying the surface properties of polymer materials is plasma treatment.1–9 Plasma treatment is an ecologically suitable method and it is replacing the traditional wet chemical techniques, which can involve harmful chemi- cals. Plasma treatment affects only the first few nano- meters of a material without changing the bulk properties.1 It is a very quick method, because usually for surface functionalization only a few seconds of treatment are necessary. Using a treatment in a plasma of different gases we can achieve a wide range of surface wettability, from moderate hydrophilicity to significant hydrophobicity. This hydrophobicity can be achieved by a treatment in plasma created in halogens, while for achieving the hydrophilicity of the surface it is best to use an oxygen plasma. In some applications, especially biological, when we want to coat the substrate with proteins or DNA, for example, a nitrogen or ammonia plasma is more desirable than an oxygen plasma.2 It should be noted that plasma treatment does not produce a unique functionality on a polymer surface. Typically, a distribution of several different functional groups is produced. Some of the functional groups may be important and some may actually be detrimental. Thus, it is desirable to determine which of the functional groups is important for a given application and to attempt to shift the distribution in favour of a specific functionality by changing the plasma gas or other plasma parameters.3 In an oxygen plasma different functional groups, like C–O, O–C–O, C=O, O=C–O, or even more exotic groups, can be produced on the surface.3–6 When the polymer is exposed to plasma the first effect that appears at the polymer surface is actually just removing of contaminants, which may also lead to improved wettability. With a further treatment time the insertion of oxygen atoms from the plasma into the polymer surface appears to lead to the formation of various functional groups that change the surface wettability. With a prolonged treatment time, etching of the surface occurs, which leads to an increased surface roughness and changes in the surface morphology. Materiali in tehnologije / Materials and technology 43 (2009) 6, 323–326 323 UDK 678.742:620.179.11 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 43(6)323(2009) In the present paper we present a study on the func- tionalization of polymer PEN (Polyethylene Naphthalate (Teonex®)) by low-pressure radio-frequency (RF) oxygen plasma. The surface of the treated polymer was characterized by applying XPS (X-ray Photoelectron Spectroscopy) and WCA (Water Contact Angle) measu- rements. According to a literature review, a modification of the polymer PEN has already been studied by using RF nitrogen plasma10 and atmospheric-pressure micro- wave8 and RF9 plasma. The authors found that the polarity of the PEN surface increased 10 times, but the contact angle on the treated surface was still relatively large (21.7°).9 2 EXPERIMENTAL 2.1 Plasma modification The samples of polymer Teonex® Polyethylene Naphthalate (PEN) were treated in the experimental system shown in Figure 1. The chemical structure of the PEN is shown in Figure 2. The system is pumped with a two-stage oil rotary pump with a pumping speed of 16 m3/h. The discharge chamber is a Pyrex glass cylinder with a length of 50 cm and an inner diameter of 3.6 cm. The plasma is created inside the discharge chamber with an inductively coupled RF generator, operating at a frequency of 27.12 MHz and an output power of about 200 W. The plasma’s parameters are measured with a double Langmuir probe and a catalytic probe. The Langmuir probe is placed into the discharge chamber, while the catalytic probe is mounted in the afterglow chamber. Commercially available oxygen is leaked into the discharge chamber. The pressure is measured with an absolute vacuum gauge and is adjusted during conti- nuous pumping using a precise leak valve. During our experiments the pressure was fixed at 75 Pa, where the density of the oxygen atoms was the highest. Using these discharge parameters an oxygen plasma with an ion density of 8 × 1015 m–3, an electron temperature of 5 eV, and a density of neutral oxygen atoms of 4 × 1021 m–3 was obtained. 2.2 XPS characterization The samples were exposed to air for a few minutes after the plasma treatment and then mounted in the XPS instrument (TFA XPS Physical Electronics). The base pressure in the XPS analysis chamber was about 6 × 10–10 mbar. The samples were excited with X-rays over a 400-µm spot area with monochromatic Al K1,2 radiation at 1486.6 eV. The photoelectrons were detected with a hemispherical analyzer positioned at an angle of 45° with respect to the normal to the sample surface. The energy resolution was about 0.6 eV. Survey-scan spectra were made at a pass energy of 187.85 eV, while for C1s and O1s individual high-resolution spectra were taken at a pass energy of 23.5 eV and a 0.1-eV step. Since the samples are insulators, we used an additional electron gun to allow for surface neutralization during the measu- rements. The spectra were fitted using MultiPak v7.3.1 software from Physical Electronics, which was supplied with the spectrometer. The curves were fitted with symmetrical Gauss-Lorentz functions. The peak width (FWHM) was fixed during the fitting process. The main C 1s peak was shifted to 284.8 eV.11 A Shirley-type background subtraction was used. 2.3 Contact angle measurements The wettability was examined immediately after the plasma treatment by measuring the water contact angle with a demineralised water droplet of volume 3 µL. Homemade apparatus equipped with a CCD camera and a PC computer was used to take high-resolution pictures of the water drop on the sample surface. Each deter- mination was obtained by averaging the results of five measurements. The relative humidity (45 %) and tempe- rature (25 °C) were monitored continuously and were found not to vary significantly during the contact-angle measurements. The contact angles were measured by our own software, which enables the fitting of the water drop on the surface in order to allow a relatively precise determination of the contact angle. The results of the water-contact measurements are shown in Table 1. A: VESEL ET AL.: MODIFIKACIJA POLIMERA POLIETILEN NAFTALAT ... 324 Materiali in tehnologije / Materials and technology 43 (2009) 6, 323–326 Figure 2: Chemical structure of PEN Slika 2: Kemijska struktura PEN Figure 1: The plasma chamber for treating the samples Slika 1: Plazemski sistem za obdelavo vzorcev Table 1: Contact angles of a water drop (WCA) on the surface of the PEN foil Tabela 1: Kontaktni kot vodne kapljice na povr{ini folije PEN Sample WCA (°) untreated 88° − 95° treated for 3 s 11° − 14° treated for 10 s  3° treated for 30 s Not measurable treated for 60 s Not measurable 3 RESULTS Figure 3 shows a comparison of the carbon C 1s peaks for samples of PEN polymer that were exposed to plasma for different times. We can see a large difference in the intensity of the high-energy peaks between the untreated polymer and the one treated for 3 s. With treat- ment times longer than 3 s the difference is less pro- nounced, indicating surface saturation with oxygen. The surface composition of the untreated and treated samples is shown in Table 2. We can see that after plasma treatment the oxygen concentration increased from the mole fraction 21 % to 35 % or to 38 % for 3 s or 60 s of treatment, respectively. The other elements N, Na, S and Si that were also found on the surface are impurities. Figure 4 shows the detailed structure of the carbon C 1s peak for the untreated sample. The peak consists of three sub-peaks belonging to the –C=C bond (C1), to the C–O bond (C2) and to the O=C–O bond from the ester group (C3). Figure 5 shows an example of a carbon peak for a sample treated for 3 s. This peak consists of five sub-peaks. In comparison with the untreated sample two new sub-peaks are observed: C23, corresponding to the C=O or O–C–O bond; and C4, which according to its very high binding energy, corresponds the –C(=O)–O–C(=O)– group. Similar functional groups were also observed on other PEN samples treated for longer times. Table 3 summarizes the concentrations of the different types of functional groups that were obtained for the PEN samples for different treatment times. 4 DISCUSSION From the XPS results shown in Table 3 we can see that the concentration of the sub-peak C1 belonging to the –C=C bonds from the aromatic rings decreased after the plasma treatment. We can conclude that the oxygen atoms probably destroy the aromatic rings by scission of the –C=C bonds, which leads to opening of the aromatic rings. Furthermore, the concentration of the sub-peak C2 A: VESEL ET AL.: MODIFIKACIJA POLIMERA POLIETILEN NAFTALAT ... Materiali in tehnologije / Materials and technology 43 (2009) 6, 323–326 325 Figure 3: Comparison of high-resolution XPS peaks of carbon C1s peaks for different treatment times. Slika 3: Primerjava visokolo~ljivih XPS-spektrov ogljika za razli~ne ~ase obdelave Table 2: Surface composition of PEN samples at different treatment times (in moll fractions, x/%) Tabela 2: Sestava povr{ine vzorcev polimera PEN v odvisnosti od ~asa obdelave v plazmi (v molskih dele`ih, x/%) Sample C O N Na S Si untreated 74.9 21.0 1.9 1.1 0.8 0.4 treated for 3 s 63.8 35.0 0.8 / / 0.4 treated for 10 s 62.6 36.5 / / 0.1 0.9 treated for 30 s 61.7 37.2 0.6 / / 0.5 treated for 60 s 58.1 38.3 / 2.1 0.4 1.0 Figure 5: Carbon C 1s peak of PEN sample treated in plasma for 3 s with five sub-peaks Slika 5: Ogljikov vrh C 1s plazemsko obdelane (3 s) folije PEN s petimi podvrhovi Figure 4: Carbon C 1s peak of untreated PEN sample with three sub-peaks Slika 4: Ogljikov vrh C 1s neobdelane folije PEN s tremi podvrhovi belonging to the C–O ether bond decreased as well. Therefore, not only the carbon atoms from the aromatic rings, but also carbons from the ether part of the PEN are attacked by oxygen atoms from the plasma. The oxidation of these carbon atoms resulted in the formation of C=O, O–C–O, O=C–O and –C(O)–O–C(O)– bonds. We can see that the concentration of these groups increases with the increasing treatment time, especially for the C=O, O–C–O and –C(O)–O–C(O)– groups, while for O=C–O an increase in the concentration is less pronounced, except in first 3 s of the treatment. The incorporation of new, oxygen functional groups to the PEN surface resulted in an increased surface wettability. As shown in Table 1, the water contact angle on the untreated PEN surface was about 90°. Such a surface is hydrophobic with poor wettability. After 10 s of treatment the surface became very hydrophilic with a contact angle of only about 3°. At longer treatment times, the contact angle was so small that it was below the detection limit. In this case, the water drop completely wetted the polymer surface. Here it is also worth mentioning the plasma treatment of the polymer PET (Polyethylene Terephthalate).6 This polymer is similar to PEN, but it has only one aromatic ring. In the case of the PET polymer, the wettability of surface after the treatment was lower (less hydrophilic) than for the PEN. Namely, after 10 s of treatment of the PET, the water contact angle decreased from an initial 74° to 15°, while perfect wettability was achieved for treatment times longer than 60 s. The same was also found by Gonzales et al.9 The concentration of oxygen at the PET surface was a little higher: 39 % and 42 % for 3 s and 60 s of treatment, respectively. The surface oxidation of the polymer PET resulted mostly in the formation of only C=O, O–C–O and O=C–O bonds.9 5 CONCLUSIONS We have shown that by an appropriate treatment of the polymers PEN and PET in plasma it is possible to change the hydrophobic surface to a very hydrophilic one, which was proved by water-contact-angle measurements. For such a modification, usually a few seconds of treatment in a low-pressure oxygen plasma are adequate. Treatment in an oxygen plasma resulted in the incorporation of oxygen atoms from the plasma into the polymer surface, leading to the formation of different chemical bonds between the carbon and oxygen atoms, e.g., C=O, O–C–O, O–C=O and –C(=O)–O–C(=O)–, which are responsible for the observed changes in the surface wettability. 6 REFERENCES 1 Chan C-M, Ko T-M, Hiraoka H, Surf. Sci. Rep., 24 (1996), 1 2 Meyer-Plath A, Schröder K, Finke B, Ohl A, Vacuum, 71 (2003), 391 3 Gerenser LJ, Surface Chemistry of Plasma-Treated Polymers, in Handbook of Thin Film Process Technology, Ed. D. A Glocker, S. I. Shah, IOP, Bristol, 1996 4 Strobel M, Lyons CS, Mittal KL, Plasma Surface Modification of Polymers: Relevance to Adhesion, VSP, Utrecht, 1994 5 U. Cvelbar, M. Mozeti~, I. Junkar, A. Vesel, J. Kova~, A. Drenik, T. Vrlini~, N. Hauptman, M. Klanj{ek-Gunde, B. Markoli, N. Krstulovi}, S. Milo{evi}, F. Gaboriau, T. Belmonte. Appl. Surf. Sci., 253 (2007), 8669. 6 Vesel A, Junkar I, Cvelbar U, Mozeti~ M, Kova~ J, Surf. Interface Anal., 40 (2008), 1444 7 Kim MS, Khang G, Lee HB, Prog. Polym. Sci., 33 (2008), 138 8 Grace JM, Zhuang HK, Gerenser LJ, Freeman DR, J. Vac. Sci. Technol., 21 (2003), 37 9 Gonzales II E, Barankin MD, Guschl PC, Hicks RF, Langmuir, 24 (2008), 12636 10 Yuji T, Urayana T, Fujii S, Mangkung N, Akatsuka H, Surf. Coat. Technol., 202 (2008), 5289 11 Beamson G, Briggs D, High Resolution XPS of Organic Polymers – The Scienta ESCA300 Database, Wiley, Chichester, 1992 A: VESEL ET AL.: MODIFIKACIJA POLIMERA POLIETILEN NAFTALAT ... 326 Materiali in tehnologije / Materials and technology 43 (2009) 6, 323–326 Table 3: Concentration of functional groups at the PEN surface versus treatment time Tabela 3: Koncentracija funkcionalnih skupin na povr{ini folije PEN v odvisnosti od ~asa obdelave v plazmi Peak designation C1 C2 C23 C3 C4 Binding energy (eV) 284.8 286.4 287.3 288.9 290.0 Assigned functional group C-C, C=C C-O C=O O-C-O O=C-O S am pl e untreated 64.4 % 30.1 % / 5.5 % / treated 3 s 45.9 % 22.1 % 9.1 % 18.0 % 5.0 % treated 10 s 44.3 % 18.2 % 12.3 % 20.3 % 4.9 % treated 30 s 40.4 % 14.0 % 19.1 % 17.7 % 8.9 % treated 60 s 40.4 % 10.6 % 21.5 % 19.3 % 8.3 % M. KRGOVI] ET AL.: THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH LASTNOSTI SINTRANEGA PRODUKTA IZ ELEKTROFILTRSKEGA PEPELA Milun Krgovi}1, Milo{ Kne`evi}2, Mileta Ivanovi}1, Ivana Bo{kovi}1, Mira Vuk~evi}1, Radomir Zejak2, Biljana Zlati~anin1, Sne`ana Ðurkovi}1 1University of Montenegro, Faculty of Metallurgy and Technology, 20000Podgorica, Montenegro 2University of Montenegro, Faculty of Civil Engineering, D`ord`a Va{ingtona bb, 20000 Podgorica, Montenegro milun@cg.ac.yu Prejem rokopisa – received: 2009-03-30; sprejem za objavo – accepted for publication: 2009-06-24 The aim of this investigation was to obtain a sintered product based on electrofilter ash as a component of the raw-material mixture with satisfactory characteristics with regard to linear and volume shrinkage, total porosity and compression strength. The second component of the raw-material mixture is illite-kaolinite clay. The product obtained by sintering this raw-material mixture, based on its mechanical properties and total porosity, can be employed as a useful building material. On the basis of the obtained results the optimum sintering regime will be defined, taking into account the economic character of the process. Keywords: electrofilter ash, clay, linear shrinkage, total shrinkage, sintering, porosity Cilj raziskave je bil pridobiti sintran produkt z elektrofiltrskim pepelom kot komponento zmesi surovin in z zadovoljivimi linearnimi ter volumenskim skr~kom, skupno poroznostjo in tla~no trdnostjo. Druga komponenta surove zmesi je bila illitno-kaolinitna glina. Produkt sintranja te zmesi je zaradi mehanskih lastnosti in skupne poroznosti primeren za uporabo kot gradbeni material. Na podlagi rezultatov te raziskave bo opredeljen optimalen re`im sintranja z upo{tevanjem ekonomike procesa. Klju~ne besede: elektrofiltrski pepel, glina, linearni skr~ek, skupni skr~ek 1 INTRODUCTION Electrofilter ash contains silicates, carbonates and phosphates of calcium, magnesium, iron, aluminium and other elements1. Illite-kaolinite clays, apart from illite and kaolinite minerals, also contain a-quartz, Fe2O3 and CaCO32. This composition of the components from the raw-material mixture qualifies, depending on the sintering temperature, the reactions in the solid state, the polymorphic transformations of quartz and the liq- uid-phase formation3. Apart from the ceramic mass- sintering rate, i.e., the firing regime, the mineral content of the raw materials has an important role in the relations between particular microstructural elements4. The liquid phase accelerates the solid-state reactions (the diffusion coefficient in such systems increases by 1000 times)5. The new crystal phases, i.e., the compounds formed as a crystal phase during the sintering process, apart from the above-mentioned factors, were determined by the min- eral and chemical content of the clay6,7. During the sintering of the samples with electrofilter ash, as a com- ponent of the raw-material mixture, the process is based on the heating of the samples at a temperature sufficient for the oxidation of the free carbon present in the ash, which could cause surface defects and a decrease of the sintered product’s strength. In the following phase the samples are heated to the sintering temperature to obtain products with satisfactory characteristics with regard to the porosity and strength8. The content of electrofilter ash in the raw-material mixture can be 20–70 %9, de- pending on the shaping method, the sintering tempera- ture and the flux addition. 2 EXPERIMENTAL The raw-material mixture for the production of sam- ples was formed on the basis of "Pljevlja" clay as a binder, with five different mass fractions of electrofilter ash (10, 20, 30, 40 and 50 %). The samples were formed by plastic shaping in a mould corresponding to a parallelepiped with the dimensions 7.7 cm × 3.9 cm × 1.6 cm. For the components of the raw-material mixture the mineral and chemical composition, and the grain size distribution with granulometric analysis, were deter- mined. The density and humidity of the components of the raw-material mixture were also determined. For the raw, unfired products, the linear and volume shrinkage during drying in air to a constant mass and drying in a dryer at a temperature of 110 °C were determined. The sintering of the samples with different amounts of electrofilter ash (Thermal plant "Pljevlja") was per- formed at a temperature of 1100 °C. This temperature was chosen on the basis of previous investigations of the temperature’s influence on the properties of the sintered products on the basis of the composition of the raw-ma- terial mixture. Materiali in tehnologije / Materials and technology 43 (2009) 6, 327–331 327 UDK 666.3:621.762.5:662.613 ISSN 1580-2949 Professional article/Strokovni ~lanek MTAEC9, 43(6)327(2009) For the sintered products with different amounts of electrofilter ash we determined: – the total porosity, – the linear and volume shrinkage during sintering, – the compression strength, – the microscopic and X-ray analysis of the sintered products. 3 RESULTS AND DISCUSSION The mineral content of "Pljevlja" clay (Figure 1) de- termined by X-ray analyses shows that the clay is an illite-kaolinite type, with the presence of quartz, musco- vite, calcite and clinochlor. The X-ray analysis of electrofilter ash (Figure 2) shows the presence of quartz, rankinite and albite. The DTA analysis of the "Pljevlja" clay does not indicate any particularly endothermic and exothermic "peaks"; therefore, TG analyses (Figure 3) and DTG (Figure 4) analyses were performed. On the curved line of the DTG (the rate of mass change during sample heating) some changes, i.e., peaks, at a tempera- ture of 529 °C were noticed, which probably correspond to the dissolution of the illite and kaolinite, as well as peaks at a temperature of 731 °C (carbonate dissolution). The DTA analysis of the electrofilter ash (Figure 5) does not show any precisely defined peaks that correspond to endothermic and exothermic reactions. The changes in the heating were registered in the form of slight inflec- tions, where the first one was registered in the tempera- ture range (305–520) °C (MgCO3), and the second with an endothermic effect at a temperature of 728 °C, as a consequence of CO2 formation with the thermal dissocia- tion of CaCO3. The most significant mass change, ac- cording to the results of the TG analysis (Figure 5), was registered in the interval from 654.9 °C to 827.3 °C, which corresponds to the thermal dissociation of CaCO3, according to the results of the X-ray analysis. The mass loss for this temperature interval was 3.78 %. The granulometric analysis (Table 1, Table 2,) shows that the electrofilter ash has a greater average grain size (109 µm) than clay (21.90 µm). For the electrofilter ash the most common fractions are: from 99 µm to 114 µm (13.7 %); from 114 µm to 131 µm (14.3 %); and from 131 µm to 150 µm (12.4 %). For the "Pljevlja" clay the most common fractions are: from 57.2 µm to 65.7 µm (4.6 %); from 65.7 µm to 75.4 µm (4.7 %); and from 75.4 µm to 150 µm (4.4 %). The results of the chemical analysis of the "Pljevlja" clay and the electrofilter ash (Table 3 and Table 4) show a larger mass fractions of Al2O3 in the electrofilter ash (21.77 %) than in the clay (10.55 %). The amount of SiO2 is lower in the electrofilter ash (49.45 %) than in the clay (71 %). The "Pljevlja" clay does not contain the M. KRGOVI] ET AL.: THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH 328 Materiali in tehnologije / Materials and technology 43 (2009) 6, 327–331 Figure 4: DTA, TG and DTG analysis of clay sample Slika 4: DTA-, TG- in DTG-analiza vzorca gline Figure 1: X-ray diffractogram of "Pljevlja" clay Slika 1: X-difraktogram gline Pljevlja Figure 2: X-ray diffractogram of electrofilter ash from TE "Pljevlja" Slika 2: X-difraktogram elektrofiltrskega pepela iz TE Pljevlja Figure 3: DTA and TG analysis of clay sample Slika 3: DTA- in TG-analiza vzorca gline following oxides, present in electrofilter ash: MnO, TiO2, ZnO and P2O5. The granulometric content of the components of the raw-material mixture has an important influence on the volume and linear shrinkage of the product during sintering. The values of the volume shrinkage during sintering decrease with the increase in the amount of ash in the raw-material mixture (Figure 6). With the increase in the amount of electrofilter ash the linear and volume shrinkage decreases. In the components of the raw-mate- rial mixture there is no significant difference in the amount of Fe2O3, but the amount of MgO in the ash is twice as high, and therefore the increase in the amount of ash in the raw-material mixture can cause a reaction be- tween Mg (II) oxide and Fe (III) oxide, and an increase of the influence on the porosity as well as the extension of the system. The particles of soot present in electrofilter ash have an important influence on the linear and volume shrinkage. During sintering the carbon pres- ent is oxidized, defects are formed and the strength of the samples is reduced. Electrofilter ash contains TiO2 and MnO, which have the role of mineralizers and affect the polymorphic transformations of the quartz. The ac- tivity of the TiO2 is influenced by its content (0.66 %) and the sintering temperature. The total porosity during sintering increases with the increase of ash content in the raw-material mixture (Fig- ure 7). The mineral and granulometric content of the components of the raw-material mixture, as well as the shaping method, have an important influence on the po- rosity. A higher mean value of the grain of electrofilter ash with relation to the clay causes an increase in the po- rosity of the raw, unfired product, and therefore an in- crease in the porosity of the sintered product. During the formation of the raw-material mixture the flux was not added, but the content of alkalis in the clay is higher than in the electrofilter ash (chemical analysis), which causes a reduction in the amount of liquid phase with the in- M. KRGOVI] ET AL.: THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH Materiali in tehnologije / Materials and technology 43 (2009) 6, 327–331 329 Figure 6: Volume shrinkage of product during sintering on T = 1100 °C, (ash content in mass fractions w/% = (10, 20, 30, 40 and 50) Slika 6: Volumenski skr~ek zmesi pri sintranju pri T = 1100 °C (vseb- nost pepela v masnih dele`ih w/% = (10, 20, 30, 40 in 50) Figure 5: DTA and TG analysis of electrofilter ash sample Slika 5: DTA in TG analiza vzorca elektrofiltrskega pepela Table 1: Particle size distribution of clay Tabela 1: Velikostna porazdelitev zrn gline Particle size (µm) <2 <5 <20 <30 >45 >60 <80 <100 <150 Percentage (%) 9.80 25.90 48.10 56.70 33.00 24.20 14.60 8.20 1.90 Table 2: Particle size distribution of electrofilter ash Tabela 2: Velikostna porazdelitev zrn elektrofiltrskega pepela Particle size (µm) <2 <5 <20 <30 >45 >60 <80 <100 <150 Percentage (%) 1.50 1.90 5.00 7.60 88.30 80.90 73.40 58.10 18.50 Table 3: Chemical composition of clay Tabela 3: Kemi~na sestava gline Oxides SiO2 Fe2O3 Al2O3 CaO MgO Na2O K2O SO3 lg.loss w/% 71 5.51 10.55 1.42 0.62 0.45 1.86 0.25 8.34 Table 4: Chemical composition of electrofilter ash Tabela 4: Kemi~na sestava elektrofiltrskega pepela Oxides SiO2 Fe2O3 Al2O3 TiO2 CaO Na2O ZnO MgO MnO P2O5 K2O lg.loss w/% 49.45 5.23 21.77 0.66 13.34 0.46 0.004 1.29 0.02 0.24 1.40 4.35 crease in the amount of ash. The liquid phase accelerates the reactions in the solid state as a result of the increase in the diffusion coefficient. The compression-strength value decreases with the increase in the amount of ash in the raw-material mixture (Figure 8). With the increase in the amount of ash the to- tal porosity is increased, which decreases the compres- sion-strength values. The amount of mullite and sillima- nite in the sintered product decreases with the increase in the content of ash (X-ray analysis of the sintered prod- uct), which has an important influence on the mechanical characteristics of the sintered product. The X-ray diffractogram of the sintered product (40 % of ash; 60 % of clay) shows the presence of quartz, albite, hematite, mullite and sillimanite (Figure 9). Mullite is formed at temperatures from 900 °C to 1100 °C. The presence of TiO2 in the electrofilter ash (0.66 %) can partly enhance the mullitization, while the presence of a small amount of MnO (0.022 %) probably has a minor effect as a mineralizer in the polymorphic transformations of quartz. The microstructure of the sintered products (Fig- ure 10 and Figure 11) shows that it is a very complex structure: crystal phase (mullite, sillimanite, quartz) with the presence of the glass phase and pores. M. KRGOVI] ET AL.: THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH 330 Materiali in tehnologije / Materials and technology 43 (2009) 6, 327–331 Figure 10: Microstructure of sintered product (T = 1100 °C, ash 40 %, clay 60 %, enlarged 1000-times) Slika 10: Mikrostruktura sintranega produkta (T = 1100 °C, masni dele` pepela 40 %, gline 60 %) pov. 1000-kratna Figure 8: Compression strength of product during sintering at T = 1100 °C, (ash content in mass fractions w/% = (10, 20, 30, 40 and 50) Slika 8: Tla~na trdnost po sintranju pri T = 1100 °C (vsebnost pepela v masnih dele`ih w/% = (10, 20, 30, 40 in 50) Figure 9: X-ray diffractogram of sintered product (ash 40 %, clay 60 %, T = 1100 °C) Slika 9: X-difraktogram sintranega proizvoda (T = 1100 °C, masni dele` pepela 40 %, gline 60 %) Figure 7: Total porosity of products during sintering at T = 1100 °C, (ash content in mass fractions w/% = (10, 20, 30, 40 and 50) Slika 7: Skupna poroznost zmesi pri sintranju pri T = 1100 °C (vseb- nost pepela v masnih dele`ih w/% = (10, 20, 30, 40 in 50) Figure 11: Microstructure of sintered product (T = 1100 °C, ash 40 %, clay 60 %, enlarged 3000-times) Slika 11: Mikrostruktura sintranega produkta (T = 1100 °C, masni dele` pepela 40 %, gline 60 %), pov. 3000-kratna 4 CONCLUSION The investigations of the properties on the basis of the raw-material mixture of electrofilter ash and clay show that: – on the basis of this raw-material mixture satisfactory characteristics of the sintered product with regard to volume shrinkage, total porosity and compression strength are obtained; – without the presence of flux, a component for the re- duction of shrinkage and electrolytes in the raw-ma- terial mixture, the mass fraction of electrofilter ash should not be higher than 30 %; – investigations were performed without the pulveriza- tion of electrofilter ash, which would definitely have an influence on the properties of the sintered prod- uct. 5 REFERENCES 1 Lj. Kosti}-Gvozdenovi}, R. Ninkovi}, Inorganic technology, Faculty of Technology and Metallurgy, University of Belgrade, Belgrade (1997) 2 M. Krgovi}, M. Ivanovi}, N. Z. Blagojevi}, @. Ja}imovi}, R. Zejak, M. Kne`evi}, Interceram, 55 (2006) 2, 104–106 3 M. Tecilazi}-Stevanovi}, Principles of ceramic technology, Faculty of Technology and Metallurgy, University of Belgrade, Belgrade (1990) 4 J. Griffiths, Ind. Min., 272 (1990), 35–40 5 M. M. Krgovi}, Z. K. Ja}imovi}, R. Zejak, Tile & Brick Int., 17 (2001) 3, 178–181 6 B. @ivanovi}, R. Vasi}, O. Janji}, Ceramic tiles, Monograph in the Institute of Materials in Serbia, Belgrade, (1985) 7 A. Mishulovich, J. L. Evanko, Ceramic tiles from high-carbon fly ash, International Ash Symposium, Center for Applied Energy Re- search, University of Kentucky, (2003) 8 Tütünlü Ftih, Atalay Ümit, Utilization of fly ash in manufacturing of building bricks, International Ash Symposium, Center for Applied Energy Research, University of Kentucky, (2001) 9 R. H. Carty, Utilization of Illinois fly ash in manufacturing of ce- ramic tiles, Final technical report, ICCI, November, (1999) M. KRGOVI] ET AL.: THE PROPERTIES OF A SINTERED PRODUCT BASED ON ELECTROFILTER ASH Materiali in tehnologije / Materials and technology 43 (2009) 6, 327–331 331 LETNO KAZALO – INDEX Letnik / Volume 43 2009 ISSN 1580-2949 © Materiali in tehnologije IMT Ljubljana, Lepi pot 11, 1000 Ljubljana, Slovenija M EHNOLOGIJEIN AT E R IALI M A T E R I A L S A N D T E C H N O L O G Y MATERIALI IN TEHNOLOGIJE / MATERIALS AND TECHNOLOGY VSEBINA / CONTENTS LETNIK / VOLUME 43, 2009/1, 2, 3, 4, 5, 6 2009/1 Nanofoils for soldering and brazing in dental joining practice and jewellery manufacturing Nanofolije za lotanje pri zobozdravni{kem delu in izdelavi nakita K. T. Rai}, R. Rudolf, B. Kosec, I. An`el, V. Lazi}, A. Todorovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The pseudo-gradient algorithm for residual gas analysis Psevdogradientna metoda za analizo masnih spektrov I. Beli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Schemes of metal-working processes and the related tribological equations of fluid mechanics Sheme procesov predelave kovin in tribolo{ke ena~be mehanike fluidov zanje D. ]ur~ija, I. Mamuzi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 The brittle tensile fracture and cleavage strength of a structural steel with a simulated weld-affected-zone microstructure Trdnost pri krhkem prelomu in cepilna trdnost za konstrukcijsko jeklo s simulirano mikrostrukturo toplotne cone zvara G. Kosec, B. Arzen{ek, J. Vojvodi~ Tuma, F. Vodopivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The electrochemical study of duplex stainless steel in chloride solutions Elektrokemijske raziskave dupleksnega nerjavnega jekla v kloridnih raztopinah A. Kocijan, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 A numerical simulation of metal injection moulding Numeri~ne simulacije brizganja kovinskih pra{natih materialov B. Berginc, M. Brezo~nik, Z. Kampu{, B. [u{tar{i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Investigation of the behaviour in chloride solution of aluminium alloys as materials for protector protections Raziskava vedenja aluminijeve zlitine, materiala za varovalne elektrode, v kloridni raztopini D. Vuksanovi}, P. @ivkovi}, D. Radonji}, B. Jordovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Improving the process capability of a turning operation by the application of statistical techniques Izbolj{anje procesa sposobnosti stru`enja z uporabo statisti~ne tehnike A. Sagbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 2009/2 A mathematical model for the stationary process of rolling of tubes on a continuous mill Matemati~ni model procesa kontinuirnega valjanja cevi Yu. G. Gulyayev, Ye. I. Shyfrin, I. Mamuzi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 The temperature dependence of the parameters of non-linear stress-strain relations for carbon-epoxy composites Temperaturna odvisnost parametrov nelinearne odvisnosti napetost-deformacija za kompozite ogljikovo vlakno-epoksi T. Kroupa, R. Zem~ík, J. Klepá~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Numerical optimization of the method of cooling of a massive casting of ductile cast-iron Numeri~na optimizacija postopka hlajenja pri masivnem ulivanju duktilne `elezove litine F. Kavicka, B. Sekanina, J. Stetina, K. Stransky, V. Gontarev, J. Dobrovska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Electrical conductivity of sintered LSM ceramics Elektri~na prevodnost sintrane LSM-keramike M. Marin{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Modelling the characteristics of an inverted magnetron using neural networks Modeliranje karakteristike invertnega magnetrona z nevronskimi sistemi I. Beli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Carnian bauxites at Muljava in central Slovenia Karnijski boksiti na obmo~ju Muljave v osrednji Sloveniji S. Dozet, M. Godec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 An investigation of the economics of using welded layers for some parts of worm presses for the extraction of oil from sunflower seeds Raziskave uporabnosti navarjenih plasti za dele vija~nih stiskalnic za ekstrakcijo olja son~nic V. Maru{i}, M. Kljajin, S. Maru{i} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 334 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 LETNO KAZALO – INDEX Slovensko dru{tvo za materiale (SDM) popularizira {tudij in raziskave materialov Slovenian Society for Materials (SDM) encouraging youngs for study and research of materials M. Torkar: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 2009/3 Environmental catalysis from nano- to macro-scale Okoljska kataliza od nano- do makrovelikosti A. M. T. Silva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Pressureless sintering and characterization of B4C, TiC and TiB2-particle-reinforced TiAl3-matrix composites Sintranje in karakterizacija kompozitov na osnovi TiAl3, oja~anih z delci B4C, TiC in TiB2 V. Kevorkijan1, S. D. [kapin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Magnetic characteristics of isothermally aged Cr-Ni-Mo-based alloys with different -ferrite contents Magnetne lastnosti izotermno `arjenih zlitin Cr-Ni-Mo z razli~no vsebnostjo -ferita B. [u{tar{i~, B. Podmilj{ak, P. McGuiness, J. V. Tuma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 The oxidation of duplex stainless steel at moderately elevated temperatures Oksidacija dupleksnega nerjavnega jekla pri zmerno povi{anih temperaturah ^. Donik, A. Kocijan, I. Paulin, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Optimization of weld bead geometry in TIG welding process using Grey relation analysis and Taguchi method Optimizacija geometrije TIG-varkov z Greyjevo analizo in Taguchijevo metodo U. Esme, M. Bayramoglu, Y. Kazancoglu, S. Ozgun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 Primary etalonnage of negative gauge pressures using pressure balances at the Czech metrology institute Primarne kalibracijske metode za negativni relativni tlak s tla~nimi tehtnicami na ^e{kem in{titutu za metrologijo J. Tesaø, Z. Krají~ek, D. Pra`ák, F. Stanìk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 The geological record as an indicator of the mudstones thermal characteristics in the temperature range of decarbonatisation Geolo{ki zapis kot pokazatelj termi~nih lastnosti laporovcev v temperaturnem obmo~ju dekarbonatizacije @. Poga~nik, J. Pav{i~, A. Meden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Kerami~ni kompoziti na osnovi silicijevega nitrida Ceramic composites based on silicon nitride A. Maglica, K. Krnel, M. Ambro`i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Investigations of micro-alloyed cast steels Raziskave mikrolegiranih jeklenih litin B. Chokkalingam, S. S. Mohamed Nazirudeen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 2009/4 The mechanical properties of two-phase Fe-NiCrMo alloys at room temperature and 290 °C after ageing in the temperature range 290–350 °C Mehanske lastnosti dvofaznih zlitin Fe-NiCrMo pri sobni temperaturi in pri 290 °C po staranju v razponu temperature 290 °C do 350 °C J. Vojvodi~ Tuma, B. [u{tar{i~, R. Celin, F. Vodopivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Mechanisms of HF bonding in dry scrubber in aluminium electrolysis Mehanizmi vezave HF v ~istilnem sistemu pri elektrolizi aluminija I. Paulin, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 The corrosion behaviour of duplex stainless steel in chloride solutions studied by XPS XPS raziskave korozijskega vedenja dupleksnega nerjavnega jekla v kloridnih raztopinah A. Kocijan, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 The application of an artificial neural network for determining the influence of the parameters for the deposition of a zinc coating on steel tubes Uporaba umetnih nevronskih mre` za dolo~itev debeline cinkove plasti na jeklenih ceveh S. Re{kovi}, Z. Glava{ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 The application of the program QFORM 2D in the stamping of wheels for railway vehicles Uporaba programa QFORM 2D pri kovanju koles za `elezni{ka vozila A. Shramko, I. Mamuzi}, V. Danchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Influence of the working technology on Al-alloys in semi-solid state Vpliv tehnologije preoblikovanja Al-zlitin v testastem stanju M. Torkar, M. Dober{ek, I. Nagli~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Steel refining in a vacuum unit with chemical boosting Rafinacija jekla v vakuumski napravi z vpihovanjem legirnih dodatkov Z. Adolf, M. Dostál, Z. [ána . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 335 LETNO KAZALO – INDEX Historical survey of iron and steel production in Bosnia and Herzegovina Zgodovinski pregled proizvodnje `eleza in jekla v Bosni in Hercegovini S. Muhamedagi}, M. Oru~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 2009/5 Finite-difference methods for simulating the solidification of castings Simulacija strjevanja z metodo kon~nih razlik V. Grozdani} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Pressureless reactive sintering of TiAl-TiC and Ti3Al-TiC composites Reakcijsko sintranje kompozitov TiAl-TiC in Ti3Al-TiC pri atmosferskem tlaku V. Kevorkijan, S. D. [kapin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 An optical-emission-spectroscopy characterization of oxygen plasma during the oxidation of aluminium foils Karakterizacija kisikove plazme med oksidacijo aluminijevih folij z opti~no emisijsko spektroskopijo N. Krstulovi}, U. Cvelbar, A. Vesel, S. Milo{evi}, M. Mozeti~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Effect of ageing a two-phase Fe-NiCrMo alloy on the strain hardening at room temperature and at 290 °C Vpliv staranja dvofazne zlitine Fe-NiCrMo na deformacijsko utrjevanje pri sobni temperaturi in pri 290 °C R. Celin, J. Vojvodi~ Tuma, B. Arzen{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Identification of material properties of quasi-unidirectional carbon-epoxy composite using modal analysis Identifikacija materialnih lastnosti za kvazienosmerni kompozit ogljik-epoksi z modalno analizo R. Zem~ík, R. Kottner, V. La{, T. Plundrich . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Re-oxidation phenomena during the filtration of steel by means of ceramic filters Reoksidacijski procesi med filtriranjem jekla s kerami~nimi filtri K. Stránský, J. Ba`an, J. Dobrovská, A. Rek, D. Horáková . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 The use of response surface methodology for prediction and analysis of surface roughness of AISI 4140 steel Uporaba metodologije odgovora povr{ine za napoved in analizo hrapavosti pri jeklu AISI 4140 F. Kahraman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Determination of optimal ball burnishing parameters for surface hardness Dolo~itev optimalnih parametrov krogli~nega glajenja za pove~anje trdote povr{ine A. Sagbas, F. Kahraman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 2009/6 Operation mikrostructure and lifetime of gas turbine engine (GTE) components Delovna mikrostruktura in trajnostna doba sestavnih delov plinskih turbin (GTE) L. B. Getsov, G. P. Okatova, A. I. Rybnikov, D. G. Fedorchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Modeling of the piezoelectric effect using the finite-element method (FEM) Modeliranje piezoelektri~nih pojavov z metodo kon~nih elementov S. Avdiaj, J. [etina, N. Syla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 Variable thermal loading analysis of (110) single crystal tungsten Analiza spremenljive termi~ne obremenitve volframovega (100) monokristala R. Murugavel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Superplasticity of the 5083 aluminium alloy with the addition of scandium Superplasti~nost aluminijeve zlitine 5083 z dodatkom skandija A. Smolej, B. Skaza, E. Sla~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Wear resistance of chromium pre-alloyed sintered steels Obrabna obstojnost kromovih sintranih jekel R. Bidulský, M. Actis Grande, J. Bidulská, T. Kva~kaj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Preparation and testing of prototype Mg2Si-Mg-TiC and Mg2Si-TiC/TiB2 composites Priprava in preizku{anje prototipnih kompozitov Mg2Si-Mg-TiC/TiB2 in Mg2Si-TiC/TiB2 Varu`an Kevorkijan1, Sre~o Davor [kapin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 The effect of water cooling on the leaching behaviour of EAF slag from stainless steel production Vpliv vodnega hlajenja na izlu`evalne karakteristike bele EOP-`lindre M. Loncnar, M. Zupan~i~, P. Bukovec, A. Jakli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Modifikacija polimera polietilen naftalat z obdelavo v kisikovi plazmi Modification of a polyethylene naphthalate polymer using an oxygen plasma treatment A. Vesel, K. Eler{i~, I. Junkar, B. Mali~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 The properties of a sintered product based on electrofilter ash Lastnosti sintranega produkta iz elektrofiltrskega pepela M. Krgovi}, M. Kne`evi}, M. Ivanovi}, I. Bo{kovi}, M. Vuk~evi}, R. Zejak, B. Zlati~anin, S. Ðurkovi} . . . . . . . . . . . . . . . . . . . . . . . . 327 336 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 LETNO KAZALO – INDEX MATERIALI IN TEHNOLOGIJE / MATERIALS AND TECHNOLOGY AVTORSKO KAZALO / AUTHOR INDEX LETNIK / VOLUME 43, 2009, 1–6, A–@ A Adolf Z. 219 Ambro`i~ M. 165 An`el I. 3 Arzen{ek B. 31, 251 Avdiaj S. 283 B Ba`an J. 261 Bayramoglu M. 143 Beli~ I. 11, 85 Berginc B. 43 Bidulská J. 303 Bidulský R. 303 Bo{kovi} I. 327 Brezo~nik M. 43 Bukovec P. 315 C Celin R. 179, 251 Chokkalingam B. 171 Cvelbar U. 245 ] ]ur~ija D. 23 D Danchenko V. 207 Dober{ek M. 213 Dobrovská J. 73, 261 Donik ^. 39, 137, 189, 195 Dostál M. 219 Dozet S. 97 \ \urkovi} S. 327 E Eler{i~ K. 323 Esme U. 143 F Fedorchenko D. G. 277 G Getsov L. B. 277 Glava{ Z. 201 Godec M. 97 Gontarev V. 73 Grande A. M. 303 Grozdani} V. 233 Gulyayev Yu. G. 63 H Horáková D. 261 I Ivanovi} M. 327 J Jakli~ A. 315 Jenko M. 39, 137, 189, 195 Jordovi} B. 49 Junkar I. 323 K Kahraman F. 267, 271 Kampu{ Z. 43 Kavicka F. 73 Kazancoglu Y. 143 Kevorkijan V. 123, 239, 309 Klepá~ek J. 69 Kljajin M. 103 Kne`evi} M. 327 Kocijan A. 39, 137, 195 Kosec B. 3 Kosec G. 31 Kottner R. 257 Krají~ek Z. 151 Krgovi} M. 327 Krnel K.165 Kroupa T. 69 Krstulovi} N. 245 Kva~kaj T. 303 L La{ V. 257 Lazi} V. 3 Loncnar M. 315 M Maglica A. 165 Mali~ B. 323 Mamuzi} I. 23, 63, 207 Marin{ek M. 79 Maru{i} S. 103 Maru{i} V. 103 McGuiness P. 129 Meden A. 157 Milo{evi} S. 245 Mozeti~ M. 245 Muhamedagi} S. 223 Murugavel R. 293 N Nagli~ I. 213 Nazirudeen M. S. S. 171 O Okatova G. P. 277 Oru~ M. 223 Ozgun S. 143 P Paulin I. 137, 189 Pav{i~ J. 157 Plundrich T. 257 Podmilj{ak B. 129 Poga~nik @. 157 Pra`ák D. 151 R Radonji} D. 49 Rai} K. T. 3 Re{kovi} S. 201 Rek A. 261 Rudolf R. 3 Rybnikov A. I. 277 S Sagbas A. 55, 271 Sekanina B. 73 Shramko A. 207 Shyfrin Ye. I. 63 Silva A. M. T. 113 Skaza B. 299 Sla~ek E. 299 Smolej A. 299 Stanìk F. 151 Stetina J. 73 Stránský K. 73, 261 Syla N. 283 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 337 LETNO KAZALO – INDEX Š [ána Z. 219 [etina J. 283 [kapin S. D. 123, 239, 309 [u{tar{i~ B. 43, 129, 179 T Tesaø J. 151 Todorovi} A. 3 Torkar M. 109, 213 V Vesel A. 245, 323 Vodopivec F. 31, 179 Vojvodi~ Tuma J. 31, 129, 179, 251 Vuk~evi} M. 327 Vuksanovi} D. 49 Z Zejak R. 327 Zem~ík R. 69, 257 Zlati~anin B. 327 Zupan~i~ M. 315 @ @ivkovi} P. 49 338 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 LETNO KAZALO – INDEX MATERIALI IN TEHNOLOGIJE / MATERIALS AND TECHNOLOGY VSEBINSKO KAZALO / SUBJECT INDEX LETNIK / VOLUME 43, 2009, 1–6 Kovinski materiali – Metallic materials Nanofoils for soldering and brazing in dental joining practice and jewellery manufacturing Nanofolije za lotanje pri zobozdravni{kem delu in izdelavi nakita K. T. Rai}, R. Rudolf, B. Kosec, I. An`el, V. Lazi}, A. Todorovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Schemes of metal-working processes and the related tribological equations of fluid mechanics Sheme procesov predelave kovin in tribolo{ke ena~be mehanike fluidov zanje D. ]ur~ija, I. Mamuzi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 The brittle tensile fracture and cleavage strength of a structural steel with a simulated weld-affected-zone microstructure Trdnost pri krhkem prelomu in cepilna trdnost za konstrukcijsko jeklo s simulirano mikrostrukturo toplotne cone zvara G. Kosec, B. Arzen{ek, J. Vojvodi~ Tuma, F. Vodopivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 The electrochemical study of duplex stainless steel in chloride solutions Elektrokemijske raziskave dupleksnega nerjavnega jekla v kloridnih raztopinah A. Kocijan, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 A numerical simulation of metal injection moulding Numeri~ne simulacije brizganja kovinskih pra{natih materialov B. Berginc, M. Brezo~nik, Z. Kampu{, B. [u{tar{i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Investigation of the behaviour in chloride solution of aluminium alloys as materials for protector protections Raziskava vedenja aluminijeve zlitine, materiala za varovalne elektrode, v kloridni raztopini D. Vuksanovi}, P. @ivkovi}, D. Radonji}, B. Jordovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Improving the process capability of a turning operation by the application of statistical techniques Izbolj{anje procesa sposobnosti stru`enja z uporabo statisti~ne tehnike A. Sagbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 A mathematical model for the stationary process of rolling of tubes on a continuous mill Matemati~ni model procesa kontinuirnega valjanja cevi Yu. G. Gulyayev, Ye. I. Shyfrin, I. Mamuzi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Numerical optimization of the method of cooling of a massive casting of ductile cast-iron Numeri~na optimizacija postopka hlajenja pri masivnem ulivanju duktilne `elezove litine F. Kavicka, B. Sekanina, J. Stetina, K. Stransky, V. Gontarev, J. Dobrovska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 An investigation of the economics of using welded layers for some parts of worm presses for the extraction of oil from sunflower seeds Raziskave uporabnosti navarjenih plasti za dele vija~nih stiskalnic za ekstrakcijo olja son~nic V. Maru{i}, M. Kljajin, S. Maru{i} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Slovensko dru{tvo za materiale (SDM) popularizira {tudij in raziskave materialov Slovenian Society for Materials (SDM) encouraging youngs for study and research of materials M. Torkar: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Pressureless sintering and characterization of B4C, TiC and TiB2-particle-reinforced TiAl3-matrix composites Sintranje in karakterizacija kompozitov na osnovi TiAl3, oja~anih z delci B4C, TiC in TiB2 V. Kevorkijan1, S. D. [kapin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 Magnetic characteristics of isothermally aged Cr-Ni-Mo-based alloys with different -ferrite contents Magnetne lastnosti izotermno `arjenih zlitin Cr-Ni-Mo z razli~no vsebnostjo -ferita B. [u{tar{i~, B. Podmilj{ak, P. McGuiness, J. V. Tuma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 The oxidation of duplex stainless steel at moderately elevated temperatures Oksidacija dupleksnega nerjavnega jekla pri zmerno povi{anih temperaturah ^. Donik, A. Kocijan, I. Paulin, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Optimization of weld bead geometry in TIG welding process using Grey relation analysis and Taguchi method Optimizacija geometrije TIG-varkov z Greyjevo analizo in Taguchijevo metodo U. Esme, M. Bayramoglu, Y. Kazancoglu, S. Ozgun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 LETNO KAZALO – INDEX MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 339 Investigations of micro-alloyed cast steels Raziskave mikrolegiranih jeklenih litin B. Chokkalingam, S. S. Mohamed Nazirudeen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 The mechanical properties of two-phase Fe-NiCrMo alloys at room temperature and 290 °C after ageing in the temperature range 290–350 °C Mehanske lastnosti dvofaznih zlitin Fe-NiCrMo pri sobni temperaturi in pri 290 °C po staranju v razponu temperature 290 °C do 350 °C J. Vojvodi~ Tuma, B. [u{tar{i~, R. Celin, F. Vodopivec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Mechanisms of HF bonding in dry scrubber in aluminium electrolysis Mehanizmi vezave HF v ~istilnem sistemu pri elektrolizi aluminija I. Paulin, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 The corrosion behaviour of duplex stainless steel in chloride solutions studied by XPS XPS raziskave korozijskega vedenja dupleksnega nerjavnega jekla v kloridnih raztopinah A. Kocijan, ^. Donik, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 The application of an artificial neural network for determining the influence of the parameters for the deposition of a zinc coating on steel tubes Uporaba umetnih nevronskih mre` za dolo~itev debeline cinkove plasti na jeklenih ceveh S. Re{kovi}, Z. Glava{ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 The application of the program QFORM 2D in the stamping of wheels for railway vehicles Uporaba programa QFORM 2D pri kovanju koles za `elezni{ka vozila A. Shramko, I. Mamuzi}, V. Danchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Influence of the working technology on Al-alloys in semi-solid state Vpliv tehnologije preoblikovanja Al-zlitin v testastem stanju M. Torkar, M. Dober{ek, I. Nagli~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Steel refining in a vacuum unit with chemical boosting Rafinacija jekla v vakuumski napravi z vpihovanjem legirnih dodatkov Z. Adolf, M. Dostál, Z. [ána . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Historical survey of iron and steel production in Bosnia and Herzegovina Zgodovinski pregled proizvodnje `eleza in jekla v Bosni in Hercegovini S. Muhamedagi}, M. Oru~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 Finite-difference methods for simulating the solidification of castings Simulacija strjevanja z metodo kon~nih razlik V. Grozdani} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 Pressureless reactive sintering of TiAl-TiC and Ti3Al-TiC composites Reakcijsko sintranje kompozitov TiAl-TiC in Ti3Al-TiC pri atmosferskem tlaku V. Kevorkijan, S. D. [kapin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 An optical-emission-spectroscopy characterization of oxygen plasma during the oxidation of aluminium foils Karakterizacija kisikove plazme med oksidacijo aluminijevih folij z opti~no emisijsko spektroskopijo N. Krstulovi}, U. Cvelbar, A. Vesel, S. Milo{evi}, M. Mozeti~. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 Effect of ageing a two-phase Fe-NiCrMo alloy on the strain hardening at room temperature and at 290 °C Vpliv staranja dvofazne zlitine Fe-NiCrMo na deformacijsko utrjevanje pri sobni temperaturi in pri 290 °C R. Celin, J. Vojvodi~ Tuma, B. Arzen{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 Re-oxidation phenomena during the filtration of steel by means of ceramic filters Reoksidacijski procesi med filtriranjem jekla s kerami~nimi filtri K. Stránský, J. Ba`an, J. Dobrovská, A. Rek, D. Horáková . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261 The use of response surface methodology for prediction and analysis of surface roughness of AISI 4140 steel Uporaba metodologije odgovora povr{ine za napoved in analizo hrapavosti pri jeklu AISI 4140 F. Kahraman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Determination of optimal ball burnishing parameters for surface hardness Dolo~itev optimalnih parametrov krogli~nega glajenja za pove~anje trdote povr{ine A. Sagbas, F. Kahraman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Operation mikrostructure and lifetime of gas turbine engine (GTE) components Delovna mikrostruktura in trajnostna doba sestavnih delov plinskih turbin (GTE) L. B. Getsov, G. P. Okatova, A. I. Rybnikov, D. G. Fedorchenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Variable thermal loading analysis of (110) single crystal tungsten Analiza spremenljive termi~ne obremenitve volframovega (100) monokristala R. Murugavel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Superplasticity of the 5083 aluminium alloy with the addition of scandium Superplasti~nost aluminijeve zlitine 5083 z dodatkom skandija LETNO KAZALO – INDEX 340 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 A. Smolej, B. Skaza, E. Sla~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Wear resistance of chromium pre-alloyed sintered steels Obrabna obstojnost kromovih sintranih jekel R. Bidulský, M. Actis Grande, J. Bidulská, T. Kva~kaj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Preparation and testing of prototype Mg2Si-Mg-TiC and Mg2Si-TiC/TiB2 composites Priprava in preizku{anje prototipnih kompozitov Mg2Si-Mg-TiC/TiB2 in Mg2Si-TiC/TiB2 Varu`an Kevorkijan1, Sre~o Davor [kapin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 The effect of water cooling on the leaching behaviour of EAF slag from stainless steel production Vpliv vodnega hlajenja na izlu`evalne karakteristike bele EOP-`lindre M. Loncnar, M. Zupan~i~, P. Bukovec, A. Jakli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Anorganski materiali – Inorganic materials Electrical conductivity of sintered LSM ceramics Elektri~na prevodnost sintrane LSM-keramike M. Marin{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Carnian bauxites at Muljava in central Slovenia Karnijski boksiti na obmo~ju Muljave v osrednji Sloveniji S. Dozet, M. Godec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 The geological record as an indicator of the mudstones thermal characteristics in the temperature range of decarbonatisation Geolo{ki zapis kot pokazatelj termi~nih lastnosti laporovcev v temperaturnem obmo~ju dekarbonatizacije @. Poga~nik, J. Pav{i~, A. Meden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Kerami~ni kompoziti na osnovi silicijevega nitrida Ceramic composites based on silicon nitride A. Maglica, K. Krnel, M. Ambro`i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Identification of material properties of quasi-unidirectional carbon-epoxy composite using modal analysis Identifikacija materialnih lastnosti za kvazienosmerni kompozit ogljik-epoksi z modalno analizo R. Zem~ík, R. Kottner, V. La{, T. Plundrich . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Modeling of the piezoelectric effect using the finite-element method (FEM) Modeliranje piezoelektri~nih pojavov z metodo kon~nih elementov S. Avdiaj, J. [etina, N. Syla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 The properties of a sintered product based on electrofilter ash Lastnosti sintranega produkta iz elektrofiltrskega pepela M. Krgovi}, M. Kne`evi}, M. Ivanovi}, I. Bo{kovi}, M. Vuk~evi}, R. Zejak, B. Zlati~anin, S. Ðurkovi} . . . . . . . . . . . . . . . . . . . . . . . . 327 Polimeri – Polymers The temperature dependence of the parameters of non-linear stress-strain relations for carbon-epoxy composites Temperaturna odvisnost parametrov nelinearne odvisnosti napetost-deformacija za kompozite ogljikovo vlakno-epoksi T. Kroupa, R. Zem~ík, J. Klepá~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Modifikacija polimera polietilen naftalat z obdelavo v kisikovi plazmi Modification of a polyethylene naphthalate polymer using an oxygen plasma treatment A. Vesel, K. Eler{i~, I. Junkar, B. Mali~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 Vakuumska tehnika – Vacuum technique The pseudo-gradient algorithm for residual gas analysis Psevdogradientna metoda za analizo masnih spektrov I. Beli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Modelling the characteristics of an inverted magnetron using neural networks Modeliranje karakteristike invertnega magnetrona z nevronskimi sistemi I. Beli~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Primary etalonnage of negative gauge pressures using pressure balances at the Czech metrology institute Primarne kalibracijske metode za negativni relativni tlak s tla~nimi tehtnicami na ^e{kem in{titutu za metrologijo J. Tesaø, Z. Krají~ek, D. Pra`ák, F. Stanìk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 LETNO KAZALO – INDEX MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342 341 Varovanje okolja – Environmental protection Environmental catalysis from nano- to macro-scale Okoljska kataliza od nano- do makrovelikosti A. M. T. Silva . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 LETNO KAZALO – INDEX 342 MATERIALI IN TEHNOLOGIJE 43 (2009) 6, 333–342