VSEBINA – CONTENTS
PREGLEDNI ZNANSTVENI ^LANKI – REVIEW ARTICLES
Plazemska sterilizacija bakterij s kisikovo plazmo
Oxygen plasma sterilization of bacteria
D. Vujo{evi}, Z. Vranica, A. Vesel, U. Cvelbar, M. Mozeti~, A. Drenik, T. Mozeti~, M. Klanj{ek-Gunde, N. Hauptman . . . . . . . . . . . . 227
IZVIRNI ZNANSTVENI ^LANKI – ORIGINAL SCIENTIFIC ARTICLES
A comparison of experimental results and computations for cracked tubes subjected to internal pressure
Primerjava eksperimentalnih rezultatov in izra~una za cevi z razpoko, ki so obremenjeni z notranjo razpoko
J. Capelle, I. Dmytrakh, J. Gilgert, Ph. Jodin, G. Pluvinage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Fatigue problems of transmission belts: a viscoelastic analysis of the strain-accumulation process
Problem utrujanja pogonskih jermenov: viskoelasti~na analiza procesa akumuliranja deformacije
I. Emri, J. Kramar, A. Nikonov, U. Florjan~i~, A. Hribar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
A micro-macro analysis of the tool damage in precision forming
Mikro-makroanaliza po{kodb orodja za natan~no kovanje
T. Rodi~, J. Korelc, A. Pristov{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
The stability of cast alloys and CVD coatings in a simulated biomass-combustion atmosphere
Stabilnost zlitin in CVD-prevlek v simulirani atmosferi zgorevanja biomas
D. A. Skobir, M. Spiegel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Nastanek LaCrO3 med zgorevalno sintezo
LaCrO3 formation during combusttion synthesis
K. Zupan, M. Marin{ek, S. Pejovnik, T. Hrobat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Dinami~ne mehani~ne lastnosti elastomernih kompozitov s polnili nanovelikosti
Dynamic mechanical properties of elastomeric composites with nano-scale fillers
Z. [u{teri~, T. Kos, M. [u{tar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Fracture toughness of a high-strength low-alloy steel weldment
@ilavost loma zvara visokotrdnega malolegiranega jekla
J. Tuma, N. Gubeljak, B. [u{tar{i~, B. Bundara . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Solidification and fracture of an as-cast Ni alloy
Strjevanje in prelom lite nikljeve zlitine
M. Torkar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
STROKOVNI ^LANKI – PROFESSIONAL ARTICLES
Laboratory accreditation – confidence in the activities of conformity assessment of products
Laboratorijska akreditacija- zaupanje v aktivnost ocene ustreznosti proizvodov
A. Klobodanovi}, M. Oru~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
LETNO KAZALO, LETNIK 40, 2006 – INDEX, VOLUME 40, 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
ISSN 1580-2949
UDK 669+666+678+53 MTAEC9, 40(6)225–285(2006)
MATERIALI IN
TEHNOLOGIJE
LETNIK
VOLUME 40
[TEV.
NO. 6
STR.
P. 225–285
LJUBLJANA
SLOVENIJA
NOV.-DEC.
2006

D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO
PLAZMO
OXYGEN PLASMA STERILIZATION OF BACTERIA
Danijela Vujo{evi}1, Zoran Vranica1, Alenka Vesel 2, Uro{ Cvelbar2,
Miran Mozeti~2, Aleksander Drenik2, Tatjana Mozeti~3, Marta Klanj{ek-Gunde4,
Nina Hauptman4
1Center za medicinsko mikrobiologijo, In{titut za zdravje Crne gore, Ljubljanska bb, 8100 Podgorica, ^rna gora
2Laboratorij za plazmo F4, Institut "Jo`ef Stefan", Jamova 39, 1000 Ljubljana, Slovenija
3Srednja zdravstvena {ola, Poljanska 61, 1000 Ljubljana, Slovenija
4Kemijski in{titut, Hajdrihova 19, 1000 Ljubljana, Slovenija
alenka.vesel@ijs.si
Prejem rokopisa – received: 2006-08-16; sprejem za objavo – accepted for publication: 2006-11-13
Prikazane so osnovne zna~ilnosti reaktivnih plazem in njihova uporabnost za sterilizacijo razli~nih materialov. Kisikova plazma
uni~uje in razgrajuje mikroorganizme (tj. bakterije) z UV–sevanjem, kemijsko razgradnjo in lokalnim ogrevanjem. V prispevku
kratko opi{emo vse tri na~ine delovanja plazme na mikroorganizme in ugotavljamo primernost razli~nih metod za sterilizacijo
zraka in trdih materialov s poudarkom na sterilizaciji biokompatibilnih materialov. Pri uporabi sterilizacije s kisikovo plazmo se
moramo zavedati nekaterih omejitev in te`av, ki pri tem nastopajo.
Klju~ne besede: sterilizacija, plazma, kisik, bakterija, spore
The main reactive plasma characteristics are presented with their applications for sterilization of different materials. Oxygen
plasma destroys and erodes microorganism with UV radiation, chemical reactions and local heating. Tree mechanisms of
interaction with microorganism are described. Advantages of plasma sterilization for air sterilization and solid materials
including biocompatible materials are discussed, baring in mind the limitations and disadvantages of the same method.
Key words: sterilization, plasma, oxygen, bacteria, spore
1 UVOD
Sterilizacija razli~nih materialov je eden od
najstarej{ih problemov v medicini in biologiji. Zdravniki
so `e v starem veku ugotovili, da se rane celijo veliko
hitreje, ~e obveze in podobni material pred uporabo
izpostavijo son~nemu obsevanju. Mnogo pozneje so
ugotovili, da komplikacije pri po{kodbah povzro~ajo
dolo~eni mikroorganizmi. Ti so lahko plesni, bakterije in
virusi. Za u~inkovito zdravljenje po{kodb bolezni in
napak je treba zagotoviti sterilnost uporabljenih mate-
rialov. Tako kot je raslo znanje o povzro~iteljih oku`b, je
raslo tudi znanje o prepre~evanju oku`b. Ugotovljeno je
bilo, da je za prepre~itev oku`b klju~nega pomena
uni~enje mikroogranizmov, ki oku`be povzro~ajo. Iz
tega spoznanja se je rodila panoga, ki jo danes
imenujemo sterilizacija. Sterilizacija pomeni popolno
uni~enje vseh mikroorganizmov, ki so ali bi lahko bili na
dolo~enem materialu. Ker prav vseh mikroorganizmov
pogosto ni mogo~e uni~iti, danes velja nekoliko bla`ji
standard: material je steriliziran, ~e je koncentracija
mikroorganizmov na dolo~enem materialu zmanj{ana za
faktor 106. Sterilizacija je ve~ni problem medicine, saj
mnogih materialov preprosto ne moremo sterilizirati.
Primer je npr. medicinska postelja. V zadnjem ~asu je
problem sterilizacije postal {e posebej pere~ ne le zaradi
potencialnih gro`enj teroristov z biolo{kim oro`jem,
ampak tudi zaradi uvajanja novih materialov, ki niso
primerni za sterilizacijo s klasi~nimi postopki. Na tem
mestu omenjamo predvsem razli~ne biokompatibilne
materiale, ki se `e danes uporabljajo v sodobni medicini,
kot so razli~ne proteze in implanti, in katerih uporaba se
bo v naslednjih letih in desetletjih v razvitih dr`avah {e
mo~no pove~ala.
Znanost o sterilizacija je torej z novimi zahtevami in
gro`njami dobila nove izzive, katerim se klasi~ni
postopki za sterilizacijo ne morejo postaviti po robu.
Popolnoma jasno je, da bo treba razviti nove, u~inkovite
metode za sterilizacijo razli~nih trdnih materialov, pa
tudi plinov, skupaj z zrakom.
Za sterilizacijo se sedaj najve~ uporabljata termi~na
in kemi~na metoda. Pri termi~ni sterilizaciji izpostavimo
vzorce visoki temperaturi – navadno za prenos toplote
uporabimo vodno paro, ki je segreta na okoli 130 °C.
Voda je odli~en medij za prenos toplote, saj je izparilna
toplota izredno visoka. Teko~o vodo s primernim
grelnikom uparimo, pare pa se potem kondenzirajo na
povr{ini vzorcev, pri ~emer se sprosti izparilna toplota.
Tako je prenos toplote bistveno hitrej{i, kot ~e bi
ogrevali vzorce s suhim zrakom. Pomanjkljivost metode
je prav visoka temperatura – mnogi materiali je ne
prenesejo. Predstavljajmo si samo, da bi poskusili s to
metodo sterilizirati `ivila – vzorci bi se preprosto
skuhali. Prav tako metoda ni primerna za sterilizacijo
velikih prezra~evalnih sistemov, saj jih je prakti~no
nemogo~e ogreti na 130 °C.
Druga metoda je kemi~na. Vzorce izpostavimo zelo
strupenemu plinu. Najbolj{i je etilen dioksid. Pri tem ni
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 227
UDK 539.2:533.9 ISSN 1580-2949
Pregledni znanstveni ~lanek/Review article MTAEC9, 40(4)227(2006)
treba vzorcev dodatno ogrevati, saj je plin izredno
strupen in deluje `e pri sobni temperaturi. Tudi ta
metoda ni primerna za sterilizacijo prezra~evalnih
sistemov, ker bi poleg bakterij pomrla {e vsa druga bitja,
ki bi pri{la v stik s plinom. Tak{ne nesre~e so se `e
zgodile tudi v bolni{nicah.
Sterilizacijo lahko dose`emo tudi z razli~nimi
sevanji. Na voljo so vsa sevanja, katerih osnovni kvanti
imajo zadostno energijo – ve~jo od 4 eV. Pri elektro-
magnetnem sevanju lahko uporabimo UV-, X- in
g-`arke. V praksi se najve~ uporablja UV-sevanje, saj
poznamo mo~ne izvire: nizkotla~ne plazme. Poleg
elektromagnetnega sevanja lahko uporabimo tudi curke
hitrih delcev. Najve~ se uporabljajo elektroni, pospe{eni
do energije okoli 1 MeV. Sterilizacijo s sevanjem najve~
uporabljajo v `ivilski industriji, medtem ko za uni~e-
vanje bakterij v ve~jih sistemih ni primerna, saj je s to
metodo prakti~no nemogo~e enakomerno obdelati velike
povr{ine.
V zadnjem ~asu so raziskovalci ugotovili, da bi lahko
prednosti termi~nega, kemijskega in sevalnega na~ina
sterilizacije zdru`ili tako, da bi kot sterilizacijski medij
uporabili plazmo. Plazma je namre~ mo~an izvir
UV-sevanja, obenem pa v njej nastajajo z vidika
mikroorganizmov zelo strupeni radikali, ki so bolj ali
manj kratko`ivi.
2 PLINSKA PLAZMA
Plinska plazma je stanje plina, v katerem v splo{nem
ne veljajo osnovni zakoni plinske termodinamike (slika
1). To pomeni,
– da temperatura kot termodinamska veli~ina sploh ni
definirana;
– da je popre~na kineti~na energija plinskih delcev
("kineti~na temperatura") za razli~ne delce v plinu
razli~na;
– da je popre~na porazdelitev stanj plinskih delcev
("notranja temperatura") za razli~ne delce v plinu
razli~na.
Na Zemlji tak{nega stanja plina ni najti, lahko pa ga
ustvarimo v laboratorijih. Najpogostej{a metoda za pre-
hod plina v stanje plazme je elektri~na plinska razelek-
tritev. Plini pri navadnih pogojih sicer ne prevajajo
elektri~nega toka, pri dolo~enih okoli{~inah pa ste~e
skozi plin tok, ki je posledica migracije elektronov in
plinskih ionov med elektrodama. To se najpogosteje
zgodi pri plinu pri nizkem tlaku med dvema elektro-
dama. V elektri~nem polju med elektrodama se
pospe{ujejo tako elektroni kot pozitivni ioni, vendar pa
pozitivni ioni pri elasti~nih trkih z molekulami plina
izgubijo preve~ energije, da bi lahko sodelovali pri
vzdr`evanju plazme. Pozitivni ioni v razelektritvi tako
skrbijo le za prostorski naboj, ki prepre~uje hitro difuzijo
elektronov na stene posode, medtem ko elektroni pri
trkih z molekulami povzro~ajo prehod plina v stanje
plazme. Elektroni pri trkih z nevtralnimi molekulami
povzro~ajo reakcije, ki so za primer kisika prikazane na
tabeli 1.
Tabela 1: Prikaz najpomembnej{ih reakcij, ki potekajo v kisikovi
plazmi
Table 1: Some most important reactions in the oxygen plasma
O2 + e– ® O2+ + 2e– O + e– ® O+ + 2e–
O2 + e– ® O+ + O + 2e– O + e– ® O* + e–
O2 + e– ® O+ + O+ + 3e– O* + e– ® O+ + 2e–
O2+ + e– ® O+ + O + e– O2 + e– ® O2* + e–
O2 + e– ® O + O + e– O2 + e– ® O2– + 2e–
O2+ + e– ® O + O O2+ + O2– ® O3 + O
Posledica prevajanja elektri~nega toka skozi plin je
torej vzbujanje molekul v visoka vzbujena stanja.
Pogosto se zgodi, da v plazmi sploh niso prisotne plinske
molekule, temve~ prevladujejo disociirana (nascentni
kisik) in ionizirana stanja. Plazme, v katerih je
koncentracija navadnih molekul O2 precej manj{a od
koncentracije vzbujenih delcev, imenujemo reaktivne
plazme. Povpre~na notranja energija plinskih delcev v
reaktivnih plazmah pogosto dosega ve~ elektron-voltov,
kar ustreza povpre~ni notranji temperaturi delcev okoli
50.000 °C!
3 OSNOVNI MEHANIZMI STERILIZACIJE S
PLAZMO
S plazemsko sterilizacijo so se pri~eli ukvarjati {ele
pred dobrim desetletjem1. Prvi poskusi so bili opravljeni
z vodikovim peroksidom. O~itno gre torej za mehak
prestop iz ~iste kemijske sterilizacije v kombinirano
plazemsko. Vodikov peroksid je mo~an oksidant in je `e
sam brez plazme dober sterilizant. Plazmo so uporabili
predvsem za detoksifikacijo sistema po opravljeni
sterilizaciji s peroksidom.
Kasneje so se raziskavam pridru`ili kemiki in fiziki,
in plazemska sterilizacija je do`ivela nov zagon. Za
za~etek so ugotovili, da lahko podobne ali bolj{e uspehe
kot s peroksidom dose`ejo z razli~nimi popolnoma
netoksi~nimi plini: voda, kisik, vodik, argon, helij, du{ik.
Ugotovili so, da je hitrost in u~inkovitost sterilizacije
mo~no odvisna od plazemskih parametrov, kot so
temperatura elektronov, gostota pozitivnih in negativnih
ionov, gostota metastabilnih atomov in molekul, vrsta in
koncentracija radikalov...
Danes je plazemska sterilizacija ena najbolj inten-
zivnih raziskovalnih podro~ij2-15. Oglejmo si osnovne
mehanizme, ki omogo~ajo sterilizacijo v plazmi.
3.1Radiacijske po{kodbe. Plazma je mo~an izvir
UV-sevanja. Absorpcija UV-`arkov v tkivu povzro~a
razpad kompleksnih organskih molekul in s tem
po~asno uni~evanje `ivega tkiva. Z UV-obsevanjem
pa je `al te`ko odstraniti razpadne produkte, ki so
lahko tudi toksi~ni. Radiacijske po{kodbe povzro~a
tudi obstreljevanje vzorcev z energijskimi ioni,
vendar pa je zna~ilna kineti~na energija ionov
prenizka, da bi ioni prodrli skozi bakterijsko ovoj-
nico.
3.2Kemijske po{kodbe. Plazma je vir razli~nih vzbujenih
molekul in radikalov, ki so kemijsko zelo aktivni.
D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
228 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Kot primer si oglejmo kisikovo plazmo. V njej
nastajajo pozitivni in negativni ioni, enoelektronsko
vzbujene molekule, ozon in nevtralni kisikovi atomi.
Nekateri delci (npr. negativni ioni) se kemijsko
ve`ejo na kompleksne organske molekule in povzro-
~ajo njihov razpad na manj{e molekule. Nevtralni
kisikovi atomi se navadno ne ve`ejo na molekule,
ampak povzro~ijo takoj{njo oksidacijo. Reakcijski
produkt je CO ali H2O, ki se v vakuumu desorbirata s
povr{ine. Proces je podoben gorenju, le da poteka
oksidacija `e pri sobni temperaturi.
3.3 Termi~ne po{kodbe. Mnogi plazemski delci imajo
precej{njo potencialno energijo. Pri relaksaciji delcev
na povr{ini se spro{~a precej{nja energija. Druga, {e
pomembnej{a metoda ogrevanja bakterije je oksida-
cija s kisikovimi atomi (glej zgornjo alinejo), ki je
izredno eksotermna reakcija. Zato bakterija v reak-
tivni plazmi v hipu (pogosto manj kot v 1 s) prepro-
sto zgori. Te`je je ogreti bakterije v porah in na
drugih nedostopnih mestih.
Podrobneje si oglejmo primer kemijskega jedkanja
bakterijske ovojnice v kisikovi plazmi. V zunanjem
ovoju endospor so ogljikovi obro~i vezani s kisikovo
vezjo:
Anionski radikal O2– iz plazme reagira s kisikovo
vezjo:
Nastala struktura nadalje reagira z molekulo vode:
Kompleksna molekula tako razpade na dve manj{i.
Nastali kisikov atom lahko spet reagira z negativnim
ionom, kar bi lahko pomenilo vzdr`evanje cikla, dokler
se atomi ne bi izgubili pri kak{ni druga~ni reakciji.
Razmerje med {tevilom razcepljenih vezi in adsorbiranih
radikalov O2– naj bi bilo po trditvi nekaterih avtorjev
(Ref 13) kar od 100 do 1000. Morebiti so avtorji
spregledali {e kak{no drugo mo`nost cepitve vezi,
vsekakor pa opisani primer lepo ponazarja kemijsko
plazemsko razgradnjo celi~ne stene mikrobov.
Oglejmo si {e primer termi~nega uni~evanja mikro-
bov v plazmi. Temperatura plina je sobna, ogrevamo le
bakterije. V prvem pribli`ku vzamemo bakterijo za oval,
ki je name{~en na podlagi. V tem primeru je toplotni stik
med bakterijo in podlago zanemarljiv. Bakterijo obdelaj-
mo s plazmo, kakr{no sicer uporabljamo za razma{~eva-
nje elektronskih komponent in plazemsko aktivacijo16,17.
Gre za visoko disociirano kisikovo plazmo, ki jo
ustvarimo v radiofrekven~i (RF) ali mikrovalovni (MW)
razelektritvi. Gostota toka kisikovih atomov (j) na
povr{ino bakterije je reda 1024 m–2 s–1. Verjetnost za
oksidacijo18 (reakciji Corg + O ® CO in 2Horg + O ®
H2O) je pri sobni temperaturi med 0,01 in 0,1. Z
indeksom "org" smo ozna~ili organsko vezan ogljik in
vodik. Reakciji sta eksotermni – energija, ki se sprosti, je
skoraj 10 eV na kisikov atom. Gostota energijskega toka
(P) je torej:
P = j · h · W
kjer je j gostota toka delcev na povr{ino bakterije, h
verjetnost za oksidacijo in W spro{~ena energija na
atom, ki reagira na povr{ini. Z vstavitvijo numeri~nih
vrednosti dobimo:
P = 1024 m–2 s–1 × 0,01 × 10–18 J = 104 W m–2
Sprememba notranje energije bakterije je enaka
produktu gostote energijskega toka in povr{ine bakterije,
enaka pa je tudi produktu mase, specifi~ne toplotne
kapacitete in spremembi temperature bakterije:
DW = P · S = m · cp · DT/Dt
Sprememba temperature bakterije v ~asovni enoti je
torej:
DT/Dt = (P · S)/(m · cp) = 10
4 K/s
Pri tem smo vzeli za povr{ino bakterije S = 1 µm2,
maso m = 10–15 kg in specifi~no toplotno kapaciteto cp =
1000 J kg–1 K–1.
Izoliranim bakterijam na gladki podlagi se torej v
kisikovi plazmi slabo pi{e. Bakterije, ki lebdijo v plinu, s
plazmo uni~imo `e v nekaj stotinkah sekunde, za tiste na
podlagi pa potrebujemo ve~ ~asa. Pri zgornjem izra~unu
smo namre~ predpostavili, da je bakterija toplotno izo-
lirana, v resnici pa je povr{ina, s katero se dotika
podlage, vendarle kon~no velika. Termi~no uni~evanje
bakterij s kisikovo plazmo je torej odli~na metoda, ~e so
bakterije dobro izpostavljene plazmi. Pri tem velja {e
enkrat omeniti, da je okolica na sobni temperaturi.
Ogrevamo samo bakterije.
@al se mnoge bakterije zadr`ujejo v re`ah, kjer je
toplotni stik s podlago bolj{i, predvsem pa je v re`ah
te`ko zagotoviti zadostno koncentracijo atomov kisika.
Zaradi tega je zna~ilni ~as za sterilizacijo v kisikovi
plazmi reda velikosti ene ure.
4 KRITI^NA OCENA PLAZEMSKE
STERILIZACIJE
Sterilizacija biokompatibilnih materialov zaenkrat
tehnolo{ko {e ni zadovoljivo re{ena. Tudi raziskave s
plazemsko sterilizacijo teh materialov {e niso privedle
do komercializacije tega postopka. Bistvena te`ava je v
tem, da je s plazemskega vidika biokompatibilni material
zelo podoben mikroogranizmom, ki jih je treba uni~iti.
^e je plazma zadosti agresivna, da lahko jedka mikro-
organizme, je navadno tudi dovolj agresivna, da jedka
podlago. V tem smislu samo kemijsko jedkanje ne more
prinesti zadovoljive sterilizacije. Tudi samo UV–sevanje
ni posebej primerno za sterilizacijo biokompatibilnih
materialov, saj po{koduje tudi podlago. Zaradi tega je
sedaj ve~ina raziskav za sterilizacijo biokompatibilnih
D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 229
materialov s plazmo osredinjena na kombinirano
delovanje vseh treh bistvenih na~inov sterilizacije s
plazmo. Biokompatibilni materiali imajo pogosto dovolj
gladko povr{ino, da je termi~ni stik med bakterijami in
povr{ino razmeroma slab (slika 2). Zaradi tega lahko v
splo{nem ra~unamo, da je temperatura bakterije ve~ja od
podlage. Pri povi{ani temperaturi postane pomembno
kemijsko jedkanje. Znano je namre~, da je hitrost
oksidacije organskih materialov z nekaterimi plinskimi
radikali mo~no odvisna od temperature. @e nekoliko
(reda nekaj 10 °C) povi{ana temperatura lahko povzro~i
porast verjetnosti za oksidacijo tudi za ve~ velikostnih
redov.
Sterilizacija biokompatibilnih materialov se zaplete,
~e imamo na povr{ini tanko plast, na kateri so bakterije
(slika 3). Neposredna hladna sterilizacija ni mogo~a, saj
se z jedkanjem bakterij na povr{ini dogaja tudi erozija
tanke plasti, ki je navadno bolj odporna proti eroziji z
atomi. Posledice zelo kratke obdelave povr{ine so
prikazane na slikah 4 in 5, kjer se poleg ovojnice
bakterije pri~ne degradacija plasti. ^e je plast debelej{a,
se sorazmerno pove~a dol`ina obdelovanja, ki lahko traja
tudi ve~ ur. Razlog za to je izogibanje lokalnemu
segrevanju, ki ga povzro~ajo rekombinacije delcev na
povr{ini. Ker temperatura za polimerne materiale, iz
katerih so narejeni nekateri implantati, ne sme presegati
temperature 100 °C, je treba reakcije omejevati s
hlajenjem plinskega toka molekul, ki v vakuumski
posodi odna{ajo odve~no toploto s povr{ine. Zaradi tega
smo omejeni na pulzno delovanje, pri ~emer hladimo
vzorec v intervalih.
Plazemsko sterilizirani vzorci imajo po sterilizaciji
pove~ano povr{insko energijo, kjer so na povr{ini nastale
polarne in razcepljene vezi, ki so dovzetne za vezavo
katerega koli materiala. To je zelo ugodna lastnost za
vezavo materiala z tkivi, ki se tak{nega materiala bolje
oprimejo.
D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
230 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Slika 4: Slika spor "Bacillus subtilis" po uni~enju s kisikovo plazmo
pri obdelavi s 5 pulzi po 10 s
Figure 4: SEM picture of the spores of Bacillus subtilis after being
destroyed by the oxygen plasma treatment in 5 pulses for 10 s
Slika 2: Aktivna bakterija Bacillus subtilis slikana z elektronskim
mikroskopom (SEM) pri 10.000-kratni pove~avi
Figure 2: SEM picture of an active bacteria Bacillus subtilis
Slika 3: Spore "Bacillus subtilis" na podlagi v tanki plasti
Figure 3: Spores of Bacillus subtilis on the substrate
Slika 1: Primer kisikove plazme, ki nastane z radiofrekven~nim
vzbujanjem v steklenem reaktorju 30 l
Figure 1: An example of RF oxygen plasma created in a glass reactor
with the volume of 30 l
Bistvene raziskave, ki danes potekajo v svetu na
temo plazemske sterilizacije, so namenjene ugotavljanju
vpliva plazemskih parametrov na hitrost sterilizacije in
na po{kodovanje biokompatibilnih materialov. V
idealnem primeru bi plazma popolnoma uni~ila bakte-
rije, podlaga pa sploh ne bi bila po{kodovana. Idealne
re{itve verjetno ne bomo nikdar dosegli, lahko pa se
idealu pribli`amo s pravilno izbiro plazemskih para-
metrov. Pri tem mislimo predvsem na primerno koncen-
tracijo razli~nih plazemskih radikalov. Znano je namre~,
da razli~ni radikali razli~no reagirajo z mikroorganizmi
in podlagami. Te`ava je le v tem, da je na dana{njem
nivoju znanja zelo te`ko individualno spreminjati
koncentracije radikalov. ^e `elimo npr. povi{ati koncen-
tracijo ionov, se navadno pove~a tudi koncentracija
atomov in vzbujenih molekul.
Mo`na re{itev je posredna uporaba plazme. Namesto
plazme, ki vsebuje razli~ne radikale, uporabimo stanja
plina po prehodu skozi plazmo. Splo{ni izraz za tak{na
stanja plina je "afterglow". Plin vodimo najprej skozi
plazmo, da dose`emo visoko koncentracijo vseh
radikalov. Pozneje pa s katalizo na izbranih povr{inah
relaksiramo samo dolo~ene radikale, druge pa pustimo
bolj ali manj nedotaknjene. Tako lahko v kon~ni fazi
pridobimo tak{no stanje plina, v katerem imamo prak-
ti~no samo eno vrsto radikalov. @al je tudi poznanje
selektivne relaksacije plazemskih radikalov na povr{inah
{e vedno izredno pomanjkljivo.
Pri sterilizaciji mikroorganizmov s plazmo nastopa {e
vrsta te`av, ki se v literaturi redko omenja. Na tem mestu
omenjamo samo najpomembnej{e: (1) zagotavljanje
enakomernosti plazme, (2) generiranje plazme v porah,
(3) toksi~ni plini v plazmi in (4) toksi~ni plini kot
reakcijski produkti.
Ker je hladna plazma neravnovesno stanje plina, je
prakti~no nemogo~e zagotoviti homogenost plazme v
celotnem plazemskem reaktorju. Posledica tega je
neenakomernost sterilizacije. Podro~ja, kjer je plazma
mo~nej{a (vsebuje ve~ radikalov ali pa je energija
radikalov pove~ana) se hitro sterilizirajo, podro~ja, kjer
je plazma {ibkej{a, pa se sterilizirajo po~asneje. Tisti
predeli, kjer je sterilizacija `e potekla, so brez potrebe
izpostavljeni radikalom, ki pogosto povzro~ajo ne`elene
spremembe tudi na materialih, ki jih steriliziramo.
Podro~ja, izpostavljena {ibkej{i plazmi, pa se sterilizi-
rajo po~asneje in lahko tudi po dolgotrajni izpostavi
plazmi vsebujejo `ive mikroorganizme ali vsaj spore.
Problem nehomogenosti plazme je izredno pere~ in sedaj
{e ni zadovoljive re{itve. Ve~ina plinskih razelektritev, s
katerimi je mogo~e generirati plazme, namre~ ustvarja
nehomogeno plazmo ali pa plazmo z nezadovoljivo
koncentracijo radikalov. To je posledica osnovnih
procesov v plinskih razelektritvah, v katere se na tem
mestu ne spu{~amo. Da bi premostili problem neho-
mogenosti, so raziskovalci po svetu razvili razli~ne
razelektritve, ki omogo~ajo vsaj pribli`no enakomernost
plazme. Pri nizkih tlakih je plazma v marsikateri
razelektritvi pribli`no enakomerna, vendar pa vsebuje
premajhno gostoto radikalov za uspe{no sterilizacijo.
Druga skrajnost je uporaba plazme pri navadnem
zra~nem tlaku, kjer je koncentracija radikalov zadostna,
razmeroma hladno plazmo pa je sicer mogo~e generirati
z enosmerno ali nizkofrekven~no razelektritvijo z
dielektri~no pregrado (angle{ko: dielectric-barrier glow
discharge), vendar pa je tak{na plazma pogosto nehomo-
gena, vselej pa izrazito neizotropna in s tega vidika
popolnoma neuporabna za sterilizacijo predmetov z
zapleteno obliko. Ve~ina raziskovalcev zato i{~e re{itve
v uporabi razelektritev pri grobem vakuumu, kjer je
plazma za silo izotropna in vsebuje zadostno koncentra-
cijo radikalov. Ker plazma vselej vsebuje ionizirane
delce, ki s prostorskim nabojem zastirajo elektri~no
polje, so za generiranje plazme z visoko koncentracijo
radikalov pri grobem vakuumu najprimernej{e visoko-
frekven~ne razelektritve, pri katerih je omogo~eno
pribli`no enakomerno vzbujanje radikalov po celotnem
volumnu. Sedaj je najbolj perspektivna radio–frekven~na
induktivno sklopljena razelektritev, ki jo uporabljamo
tudi v na{ih laboratorijih.
Generiranje plazme v porah ali ozkih re`ah je te`ava,
na katero so opozorili fiziki, davno preden so se pojavile
prve ideje o sterilizaciji materialov s plazmo. Plazma
namre~ slabo prodira v pore. Zna~ilno se koncentracija
radikalov hitro zmanj{uje z globino pore. Za to sta odgo-
vorna dva procesa: majhna koncentracija energijskih
radikalov v porah, kar vodi k zmanj{anju generiranja
radikalov, in relaksaciji radikalov na notranjih stenah
por. Prvi pojav je mogo~e popolnoma izni~iti z uporabo
dodatne razelektritve, ki delujejo po principu votle
katode: v pori, ki jo nabijemo negativno proti plazmi, se
zaradi prostorskega naboja ustvari mo~an radialni
gradient elektri~nega polja, ki povzro~i nihanje
elektronov v pori. Posledica tega je lokalna oja~itev
plazme, ki lahko izni~i pojave, ki sicer prepre~ujejo
normalno koncentracijo radikalov. ^e so materiali, ki jih
nameravamo sterilizirati, elektri~no prevodni, lahko z
D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 231
Slika 5: Pove~ava spore, ki ka`e u~inkovitost kisikove plazme pri
eroziji ovojnice spore, kjer jedkamo prete`no s kisikovimi atomi
Figure 5: SEM picture of one spore showing the efficiency of oxygen
plasma treatment. The spore’s protective layer is eroded by its etching
mainly with the oxygen atoms created in the plasma
dodatno razelektritvijo z votlo katodo dose`emo odli~ne
rezultate. Te`ava je v tem, da ve~ina materialov, ki jih
`elimo sterilizirati s plazmo, ni elektri~no prevodna. V
teh primerih si z razelektritvijo z votlo katodo ne
moremo prav ni~ pomagati. Delno lahko pojav oja~itve
plazme v porah izolatorjev nadomestimo z uporabo
radiofrekven~nega nabijanja materiala, kar pa je sedaj {e
vedno v fazi znanstvenih eksperimentov. Navadno
radiofrekven~no nabijanje ne vodi k pojavu oja~itve
razelektritve v votli katodi.
Naslednja te`ava pri plazemski sterilizaciji je
zna~ilnost vseh plazem. V njih vselej nastajajo toksi~ni
plini. Vrsta tak{nih plinov in njihova koncentracija je
vselej odvisna od vrste plazme. V ~isti kisikovi plazmi
ne najdemo posebej toksi~nih plinov. Izjema je ozon,
katerega koncentracija je odvisna od vrste razelektritve.
Koncentracija ozona v kisikovi plazmi lahko dose`e
prostorninski dele` 10 %, kar je ve~ velikostnih redov
nad dovoljeno koncentracijo. V tehnolo{kih procesih je
navadno te`ko dose~i obdelavo materialov s ~istim
kisikom. ^etudi je zagotovljena laboratorijska ~istota
kisika iz jeklenke (ve~ kot 99,999 %), je v procesni
komori vselej residualna atmosfera, ki pogosto vsebuje
du{ik in vodno paro. V plazmi kisik reagira z obema
plinoma in tvori du{ikove okside in vodikov peroksid.
Posebej to velja za razelektritve pri navadnem zra~nem
tlaku, kjer je vsaj delno me{anje kisika z zrakom
obi~ajen pojav.
Pri plazemski sterilizaciji poleg plinov, zna~ilnih za
plazmo v ne~istem kisiku, nastajajo tudi drugi radikali,
ki so lahko bistveno bolj toksi~ni od ozona, du{ikovih
oksidov in vodikovega peroksida. Interakcija kisika z
ogljikovodiki (ki so prete`na sestavina `ivih bitij) je
navadno nepopolna oksidacije: namesto CO2 (ki je
produkt popolne oksidacije) ve~inoma nastaja CO, ki je
toksi~en plin. Poleg obilice vodikovega peroksida, ki je
prav tako posledica nepopolne oksidacije ogljiko-
vodikov, nastajajo med plazemsko oksidacijo organskih
materialov tudi nekateri drugi toksi~ni plini. Poleg
du{ikovih oksidov so to lahko bolj kompleksne mole-
kule, kamor spada tudi vodikov cianid, poleg tega pa
tudi `veplov oksid in podobni plini. Plazemska obdelava
organskih snovi torej lahko vodi k sintezi razli~nih
plinov, ki so ve~inoma toksi~ni, vendar pomenijo nizek
volumenski dele` (manj od 10 %). Te`ava je {e ve~ja pri
uporabi zraka za sterilizacijo. V tem primeru je koncen-
tracija razli~nih (pogosto zelo toksi~nih) plinskih
molekul, ki vsebujejo C, N, H in druge elemente, lahko
velika.
Plazemska sterilizacija torej kot ve~ina plazemskih
procesov vodi k sintezi razli~nih toksi~nih plinov in
radikalov. Le-ti se delno absorbirajo v vakuumski ~rpalki
(~e proces poteka v pri zni`anem tlaku), v splo{nem pa
bi lahko postali resen problem. Z uporabo katalizatorjev
za toksi~ne pline je mogo~e ta problem bistveno
zmanj{ati ali celo odpraviti19.
5 SKLEP
Opisali smo osnovne mehanizme sterilizacije s
plazmo. Plazemska sterilizacija temelji na termi~nih,
kemijskih in radiolo{kih efektih. V vsakem primeru
lahko najdemo dovolj agresivno plazmo, s katero
steriliziramo poljubne materiale. Te`ava nastopi tedaj,
ko `elimo sterilizirati temperaturno ob~utljive biokom-
patibilne materiale. V tem primeru je treba izbrati tak{no
plazmo, ki je dovolj reaktivna, da uni~i bakterije, vendar
{e vedno dovolj ne`na, da ne po{koduje podlage. Zaradi
nasprotnosti obeh zahtev je tak{no plazmo pogosto zelo
te`ko generirati, in to je verjetno razlog, zaradi katerega
plazemska sterilizacija {e ni komercializirana.
Zahvala
Ta ~lanek je rezultat skupnega dela slovenskih in
~rnogorskih raziskovalcev pri projektu BI-SCG/04-05-{t.
28 v okviru SLO-CG znanstveno-tehni~nega sodelo-
vanja.
6 LITERATURA
1 M. C. Krebs, P. Becasse, D. Verjat, J.C. Darbot, Int. J. Pharm., 160
(1998), 75–81
2 M. Mozeti~, T. Mozeti~, P. Panjan, Vakuumist, 21 (2001), 10–12
3 A. Vesel, M. Mozeti~, Vakuumist, 23 (2003), 9–14
4W. Bar, G. M. de Bar, A. Naumann, S. Rusch-Gerdes, Amer. J.
Infec. Contr., 29 (2001), 306–311
5M. Moisan, J. Barbeau, S. Moreau, J. Pelletier, M. Tabrizian, L. H.
Yahia, Int. J. Pharm., 226 (2001), 1–21
6 S. D. Ferreira, W. S. Dernell, B. E. Powers, R. A. Schochet, C. A.
Kuntz, S. J. Withrow, R. M. Wilkins, Clin. Orth. Rel. Res., 388
(2001), 233–239
7M. Moisan, J. Barbeau, J. Pelletier, Du Vide, 56 (2001), 15–28
8 S. Cariou-Travers, J. C. Darbord, Du Vide, 56 (2001), 34–46
9 P. Koulik, S. Krapivina, A. Saitchenko, M. Samsonov, Du Vide, 56
(2001), 117–125
10 D. A. Mendis, Physica Scripta T89 (2001), 173–175
11 C. E. Holy, C. Chen, J. E. Davies, M. S. Shoichet, Biomater., 22
(2001), 25–31
12 R. Ben Gadri , J. R. Roth, T. C. Montie, K. Kelly-Wintenberg, P. P.
Y. Tsai, D. J. Helfritch, P. Feldman, D. M. Sherman, F. Karakaya, Z.
Y. Chen, Surf. Coat. Techol., 131 (2000), 528–542
13 A. Kakligin, P. Koulik, S. Krapivinina, G. Norman, E. Petrov, A.
Ricard, M. Samsonov, Proc. 13th Int. Coll. Plasma Processes, (2001),
28–32
14 T. K. Subramanyam, R. Schwefel, P. Awakovitz, Proc. 13th Int. Coll.
Plasma Processes, (2001), 33–36
15 M. Moisan, J. Barbeau, J. Pelletier, N. Philip, B. Saoudi, Proc. 13th
Int. Coll. Plasma Processes, (2001), 12–18
16 A. Vesel, M. Mozeti~, Vacuum, 61 (2001), 373–377
17 D. Babi~, I. Poberaj, M. Mozeti~, Rev. Sci. Instr., 72 (2001),
4110–4114
18 M. Mozeti~, A. Zalar, P. Panjan, M. Bele, S. Pejovnik, R. Grmek,
Thin Solid Films, 376 (2000), 5–8
19 M. Mozeti~, G. A. Evangelakis, U. Cvelbar, Plazemska sterilizacija
preto~nega zraka, SI21448. Urad za intelektualno lastnino Republike
Slovenije (2004)
D. VUJO[EVI] ET AL.: PLAZEMSKA STERILIZACIJA BAKTERIJ S KISIKOVO PLAZMO
232 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
J. CAPELLE ET AL.: A COMPARISON OF EXPERIMENTAL RESULTS AND COMPUTATIONS ...
A COMPARISON OF EXPERIMENTAL RESULTS AND
COMPUTATIONS FOR CRACKED TUBES SUBJECTED
TO INTERNAL PRESSURE
PRIMERJAVA EKSPERIMENTALNIH REZULTATOV IN
IZRA^UNA ZA CEVI Z RAZPOKO, KI SO OBREMENJENI Z
NOTRANJO RAZPOKO
Julien Capelle1, Igor Dmytrakh2, Joseph Gilgert1, Philippe Jodin1, Guy Pluvinage1
1Laboratoire de Fiabilité Mécanique, ENIM & Université de Metz, Île du Saulcy F-57045 Metz cedex, France
2Karpenko Physico-Mechanical Institute of National Academy of Sciences of Ukraine, (KPhMI), Department of Physical
Fundamentals of Fracture and Strength of Materials, Lviv, Ukraine
jodin@univ-metz.fr
A cylindrical pipe that is used for gas transportation is mainly submitted to stresses originating from internal pressure. Other
stresses are due to weight and the unexpected movements of supports and/or the ground. The first give rise to circumferential
stresses, the second to longitudinal bending stresses. Here, we study the case of pipes that are joined by welding. This weld is an
eventual source of defects, where cracks can originate. But there are other kinds of defects that can come from corrosion pits or
accidental notches caused by diving machines, or in the case of work on the pipe. In this last case, the notch corresponds to a
reduction of the section, which is enhanced by the stress-concentration factor. The objective of this work is to compare the
prediction of finite-element computations with fracture experiments on such notched pipes. The results are given in terms of
stress-concentration factors and show some discrepancy with the experimental results. As the mechanical properties have been
measured on standard plane specimens, a transfer problem to curved structures is suspected to be at the origin of the difference,
because with the dimensions of the pipe it is not possible to have standard and curved specimens in the same direction of
rolling, and the mechanical properties of this pipe are different in the circumferential and transverse directions.
Key words: pressure pipe, notch fracture mechanics, transferability
V valjasti cevi za pretok plina so napetosti zaradi notranjega pritiska. Druge napetosti nastanejo zaradi gravitacije in
nepri~akovanih premikov podpor ali zemlji{~a. Prve napetosti so obodne, druge pa podol`ne in upogibne. V tem delu
obravnavamo primer cevi, ki so povezane z varjenjem. Zvar je eventualni vir napak, na katerih nastanejo razpoke. Druge vrste
napak lahko nastanejo zaradi korozijskih zajed ali odrgnin, ki jih povzro~ijo gradbeni stroji ali nastanejo `e pri izdelavi cevi. V
tem primeru zareza ustreza zmanj{anju prereza, napetost pa je pove~ana zaradi zarezne koncentracije napetosti. Cilj tega dela je
primerjava napovedi na podlagi izra~una z metodo kon~nih elementov s preizkusi preloma cevi z napako. Rezultati izra~unov,
ki so predstavljeni v obliki faktorja intenzitete napetosti, se ne ujemajo popolnoma z rezultati preizkusov. Ker se mehanske
lastnosti dolo~ijo pri standardnih ravninskih preizku{ancih, predpostavljamo, da je vzrok za razliko prenos na ukrivljeno
strukturo. Zaradi izmer cevi ni mogo~e izdelati standardnih in ukrivljenih preizku{ancev v enaki smeri valjanja in so mehanske
lastnosti cevi druga~ne v obodni kot v pre~ni smeri.
Klju~ne besede: cev pod pritiskom, mehanika loma, prenos
1 INTRODUCTION
The computation of circumferential stress, also called
hoop stress, in cylindrical pipes subjected to internal
pressure is well known, and the general relationship is
given as follows:
σ θ =
⋅p r
t
i (1)
where sθ is the hoop stress, pi is the internal pressure, r
is the radius of the tube and t is the thickness of the
tube. This relationship is valid if t ≤ r/10, in other cases
the relationship (1) is corrected as:
σ θ =
⋅
−
⋅ +












a p
b a
b
r
2
2 2
2
2
1i
( )
(2)
where a is the internal radius, b is the external radius, r
is the radius of the computed point in the cylinder wall
and pi is the internal pressure.
These relationships are accurate enough to design
pressure pipes if no defect is present in the tube. But, if
the tube is realized by welding, misalignment or lack of
penetration can occur, or if there are corrosion pits, or if
the diving equipment causes damage to the external
envelope of the tube, a reduction of section occurs and
the stress is increased as a consequence. However, the
reduction of section is not the only effect that causes a
stress increase, and the notch-concentration-factor effect
brings the majority of the increase. The objective of this
work was to compute the actual hoop stress when an
external notch is present and to compare with a fracture
test under gas pressure that was made with the three
coded methods, i.e., the ASME B31 G, the modified
ASME B31 G and the DNV RP-F101. This work is
based on a study of the pipeline and has resulted in
several publications and presentations at international
congresses 1,2.
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 233
UDK 539.42:621.774.2 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)233(2006)
2 CODED METHODS
2.1 ASME B31 G 3
This is a code for evaluating the remnant strength of
corroded pipelines. It is a supplement of the ASME B31
code for pressure piping. The code was developed in the
late nineteen-sixties and early seventies at the Battelle
Memorial Institute and provides a semi-empirical proce-
dure for the assessment of corroded pipes. Based on an
extensive series of full-scale tests on corroded pipe
sections, it was concluded that line pipe steels have an
adequate toughness and that the toughness is not a
significant factor. The failure of blunt corrosion flaws is
controlled by their size and the flow stress or yield stress
of the material. The input parameters include the pipe’s
outer diameter (Dext) and the wall thickness (t), the
specified minimum yield strength (SMYS), the
maximum allowable operating pressure (MAOP), the
longitudinal extent of corrosion (2c) and the defect depth
(a). According to this code, a failure equation for the
corroded pipelines is proposed by means of the data
from a bursting experiment and expressed by consi-
dering the two conditions below:
• First, the maximum hoop stress cannot exceed the
yield strength of the material.
• Second, short corrosion defects are projected with a
parabolic shape, and long corrosion defects are
projected with a rectangular shape on the shape of a
rectangular one (Figure 1 and 2).
The failure pressure equation for a corroded pipeline
with a parabolic defect is:
08
2
4
2
.
c
D
D
text
ext









≤ (3)
P
t
D
a/t
a/t /Mult
y
ext
=
⋅ ⋅
⋅ −
−




2 11 1 066
1 066
( . ) . ( )
. ( )
σ
 (4)
with M
c
D
D
t
= +










1 08
2
2
.
ext
ext (5)
M is the so-called bulging factor.
2.2 Modified ASME B31 G
This includes the modified flow stress and the
bulging factor. The flow stress sult is taken as:
σ σult yMPa/ .= +11 69 (6)
where sy is the yield strength.
Two cases are considered:
Case 1
2
50
2
c
D
D
text
ext









≤ (7)
P
t
D
a/t
a/t /Mult
y
ext
=
⋅ + ⋅
⋅ −
−


2 11 69 1 085
1 085
( . ) . ( )
. ( )
σ



(8)
The bulging factor is equal to:
M
c
D
D
t
c
D
= +





 


−

1 0 6275
2
0 003375
2
2
. .
ext
ext
ext



 


4 2
D
t
ext (9)
Case 2
2
50
2
c
D
D
text
ext









> (10)
P
t
D t
a/t
a/t /Qult
ult
ext
=
⋅ ⋅
−
⋅ −
−






2 1
1
( ) ( )
( )
σ
(11)
The bulging factor is equal to:
M
c
D
D
t
= +










3 3 0 032
2
2
. .
ext
ext (12)
It is necessary to recall that the ASME B31G is
limited to low stress-concentration factors and internal
pressure loading conditions.
The assessment procedure considers the maximum
depth and the longitudinal extent of the corroded area,
but ignores the circumferential extent and the actual
profile. If the corroded region is found to be
unacceptable, B31G allows the use of a more rigorous
analysis or a hydrostatic pressure test in order to
determine the pipe’s remaining strength. Alternatively, a
lower maximum allowable operating pressure may be
imposed.
2.3 DNV RP-F101 4
This is the first comprehensive and extensive code on
pipeline-corrosion defect assessment. It prepares
guidance on the pipeline under internal pressure and
combined loading. Furthermore, it provides a codified
formulation for pressure and bending and area depth.
DNV RP-101 proposes two methods to find the failure
pressure.
The first method is named the partial safety factor,
and the second is classified as the allowable stress
design. The allowable-stress-design method that
considers non-interacting defects is discussed here. To
pursue the design procedure via DNV RP-101 it is
necessary to determine the loading type (pressure only
J. CAPELLE ET AL.: A COMPARISON OF EXPERIMENTAL RESULTS AND COMPUTATIONS ...
234 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 2: Corrosion defects projected with a rectangular shape
Slika 2: Korozijske po{kodbe, predstavljene s pravokotno obliko
Figure 1: Corrosion defects projected with a parabolic shape
Slika 1: Korozijske po{kodbe, predstavljene s paraboli~no obliko
and combined loading), and consequently the failure
pressure can be obtained as:
P
t
D t
a/t
a/t /Qult
ult
ext
=
−
⋅ −
−






2 1
1
σ ( )
( )
(13)
where Q is the correction factor:
Q
D t
= +





1 0 31
1
.
ext
(14)
According to this code, the failure pressure should
not exceed the maximum allowable stress design
operating pressure (MAOP); otherwise, the corroded
pipe will have to be repaired or replaced before returning
to service.
3 FINITE-ELEMENT COMPUTATION
3.1 Meshing the model
The model tube is a rolled steel cylindrical pipe with
an external diameter of 219.1 mm and a thickness of
6.1 mm. A quasi-semi-ellipsoidal notch represents an
accidental external defect. The major axis of the
ellipsoid is parallel to the axis of the tube and the length
of the notch is 30.5 mm.
The depth of the notch is 3.05 mm and the width is
also 3.05 mm. The radius of the notch tip is 0.15 mm, as
shown in Figures 3 and 4.
As the defect has two perpendicular planes of
symmetry, only a quarter of the whole structure was
meshed. A schematic view of the notched tube is given
in Figure 4. For our computations, the CAST3M pro-
gramme was used. Such a structure is not very easy to
model exactly, as the very small notch-tip radius implies
very strong geometrical constraints.
Figure 5 shows the mesh of an ellipsoidal notch with
the approximate notch radius. Due to the program’s
constraints, simple linear elements were used.
3.2 Boundary conditions and loading
As the model represents a quarter of the whole
structure, and no pressure effect on the ends is assumed,
symmetrical boundary conditions were applied on each
section of the models. The loading is applied as a
15 MPa uniform pressure on the internal face of the tube.
3.3 Material behaviour and properties
The material constituting the tube is rolled steel. A
Young’s modulus of 203000 MPa was deduced from
previous tests on a "Roman-tiles-type" specimen 5.
J. CAPELLE ET AL.: A COMPARISON OF EXPERIMENTAL RESULTS AND COMPUTATIONS ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 235
Figure 5: Details of the mesh at the notch
Slika 5: Detajl mre`e pri zarezi
Figure 4: Plan of the grinding part
Slika 4: Na~rt bru{enja
Figure 3: Notch on the pipe
Slika 3: Zareza na cevi
The yield strength was estimated to be 528 MPa. The
Ludwik's law will make it possible to introduce the
actual behaviour of the steel into its plastic range, where
the hardening parameter is n = 0.0446, and the resistance
coefficient is K = 587.3 MPa.
σ ε= K np (15)
3.4 Post-processing of results
The results of the computations were given in terms
of the hoop stress distribution on the ligament surface
between the notch tip and the inner surface of the tube.
The figures were obtained with the help of the home-
made SCILAB® programme.
4 RESULTS
4.1 Finite-element computations
The results are shown in Figure 6. The hoop stress
field is represented over the mesh where it is computed.
The hottest point is on the small axis of the ellipsoid. But
the hoop stress does not take into account the degree of
triaxiality, when the ligament is reduced, just under the
small axis of the ellipse. Consequently, the Von Mises
stress was computed and represented in Figure 7. It is
clear that if the stress level far from the notch is about
the same as the hoop stress at the same place, the stress
along the notch tip and, particularly at the deepest point
of the notch, is much higher.
For comparison, the hoop stress is computed using
the relationships (1) and (2). The results are the
following:
• (1): hoop stress at mid thickness: 174.6 MPa
• (2): hoop stress at inner face: 174.7 MPa
• (2): hoop stress at outer face: 164.7 MPa
From the FE computation (Figure 8) we can extract
the values of the hoop stress on the outer face, far from
the notch, 148.5 MPa, and on the inner face, 189.9 MPa.
The value at the mid thickness is, therefore, 169.2 MPa.
This value is quite similar to that obtained for the usual
analytical relationships of cylindrical tubes (174.6 MPa).
This validates the FE computation.
For this particular notch we have estimated the
stress-concentration factor using the relationship:
K ep
max, pl
G, pl
=
σ
σ
(16)
In this case, we obtain:
K ep = =
386
186
2 07. (17)
4.2. Experimental results
Some tubes containing a notch with the dimensions
given here were loaded with a gas up to failure. With the
ground tubes the fracture occurs under a pressure of
about 12 MPa. Only two results are available, but they
give fracture pressures that are close together. These
results seem to be in agreement with the tests carried out
by a South Korean team6, although these tests used a
J. CAPELLE ET AL.: A COMPARISON OF EXPERIMENTAL RESULTS AND COMPUTATIONS ...
236 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 8: The variation of the hoop stress around the notch. L04 is the
ligament line prolonging the small axis of the ellipse, L02 is the notch
front line
Slika 8: Variacija hoop-napetosti okoli zareze. L04 je ~rta ligamenta
podalj{ek male osi elipse, L02 je ~elna ~rta zareze
Figure 6: Variation of the hoop stress on the surface of the ligament
Slika 6: Variacija hoop-napetosti na povr{ini ligamenta
Figure 7: Von Mises stress on the ligament under the notch for
different pressures
Slika 7: Von Misesova napetost v ligamentu pod zarezo pri razli~nem
pritisku
pipe in X65 with different dimensions. Moreover, this
type of burst test with gas is rare, as are papers on this
subject. So it is very difficult to properly compare our
results.
5 COMPARISON OF RESULTS
If we consider the hoop stress, it appears that the
computation gives a maximum value that is less than the
yield strength. The hoop stress acts along the circular
direction of the tube, but the stress in a perpendicular
direction acts in the longitudinal direction of the tube,
and the strains in this direction are constrained by the
great length of the tube. Consequently, a triaxiality effect
is induced, and the stress to be observed is the Von
Mises stress (Figure 7). This triaxiality effect induces an
over stress to obtain the yield of the material. Here, the
overstress factor is t = sVM/sY = 760/528 = 1.44. The
maximum value is about 760 MPa for an internal
pressure of 12 MPa.
Calculated codes give other results:
Table 1: Different ultimate pressure
Tabela 1: Razli~ne kon~ne napetosti
Pult/MPa
Error compared
between experimental
result (%)
ASME B31 G 11.3 5.8
Modified ASME B31 G 10.8 10
DNV RP-F101 6.6 45
To take account of the grinding in these calculations,
we reduced the value of the ligament under the notch to
2 mm. According to the experimental result, it seems
that the ASME B31G code is the closest. The DNV
RP-F101 is the most conservative code.
6 CONCLUSION
It has been shown in this paper that the construction
of a meshed structure that conveniently represents a
notched pressure pipe is quite difficult. However, the
results of the FE computations give consistent results
with respect to the experimental data.
To improve the prediction of fracture of the notched
pressure pipes it is necessary now to improve the
meshing of the notch. Moreover, experiments provided
different data that will be compared with further FE
computation predictions.
7 REFERENCES
1 J. Capelle, J. Gilgert, G. Pluvinage, Ch. Schmitt: Calcul du facteur de
sécurité associé à la ténacité d’un tuyau de faible epaisseur, Paper
presented at the conference IFCAM01, (2006)
2 J. Capelle, M. Lebienvenu, G. Pluvinage: Hydrogen effect on fatigue
life of a pipe steel, Paper presented at the conference ICMFM XIII,
(2006)
3 ASME B31G-1991: Manual for determining the remaining strength
of corroded pipelines, The American Society of Mechanical
Engineers, New York, USA, (1991)
4 DNV-RP-F101: Corroded pipelines, Det Norske Veritas, 1999
5 G. Pluvinage, J. Capelle: Etude d’un dimensionnement de conduite
de gaz basée sur la mécanique de rupture et l’analyse limite, Paper
presented at the 5ème Journée de Mécanique de l’Ecole Militaire
Polytechnique, 2006
6 J. B. Choi, B. K. Goo, J. C. Kim, Y. J. Kim, W. S. Kim: Develop-
ment of limit load solutions for corroded gas pipelines, International
Journal of Pressure Vessels and Piping 80 (2003), 121–128
J. CAPELLE ET AL.: A COMPARISON OF EXPERIMENTAL RESULTS AND COMPUTATIONS ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 237

I. EMRI ET AL.: FATIGUE PROBLEMS OF TRANSMISSION BELTS
FATIGUE PROBLEMS OF TRANSMISSION BELTS:
a viscoelastic analysis of the strain-accumulation process
PROBLEM UTRUJANJA POGONSKIH JERMENOV:
viskoelasti~na analiza procesa akumuliranja deformacije
Igor Emri, Janez Kramar, Anatolij Nikonov, Ur{ka Florjan~i~, Anton Hribar
University of Ljubljana, Faculty of Mechanical Engineering, A{ker~eva 6, 1000 Ljubljana, Slovenia
igor.emri@fs.uni-lj.si
Prejem rokopisa – received: 2006-05-17; sprejem za objavo – accepted for publication: 2006-10-09
We performed an analysis of the time-dependent behaviour of drive belts under the loading conditions to which they are
exposed during normal operation. They are dynamically loaded with a tooth-like periodic (cyclic) load. Within each loading
cycle the elastomeric material undergoes a combination of creep and retardation processes. Under certain conditions, the
retardation process between two loadings cannot be fully completed. Thus, the material enters the second phase of loading with
a residual strain state. Consequently, the strain state starts to accumulate, which leads to hardening of the material, crack
formation, and ultimately to the failure of the belt.
We recognized that drive belts exhibit the accumulation of strain when exposed to normal operation at certain critical angular
velocities. The strain accumulated in each consecutive cycle depends on the geometry of the belt, the angular velocity of the
pulleys, the number of completed cycles, and the retardation spectrum of the material. In this paper we discuss the effect of the
number of loading cycles to which the material is exposed in the strain-accumulation process. For a given belt geometry the
critical angular velocity increases with the number of loading cycles. At the same time the magnitude of the accumulated strain
decreases non-linearly as the number of loading cycles increases. Hence, the strain-accumulation process slows down with the
increasing number of loading cycles. However, if the belt operates at, or in the close vicinity of, its critical angular velocity, it
will almost certainly fail. Since the critical angular velocity is directly related to the retardation time of the material, and the
magnitude of the accumulated strain depends on the strength of the corresponding discrete spectrum lines, we can conclude that
the time-dependent mechanical properties of the elastomersic material from which the belt is constructed are the most critical
parameters for predicting the durability of drive belts and other dynamically loaded elastomeric products.
Key words: time-dependent constitutive modelling, power transmission belts, synchronous belts, failure, viscoelastic analysis,
strain accumulation, elastomers, time-dependent behaviour, mechanical spectrum
V delu predstavljamo viskoelasti~no analizo ~asovno odvisnega vedenja pogonskih jermenov, ki so med obratovanjem motorja
dinami~no obremenjeni s kora~no spremembo. V ~asu enega obremenitvenega cikla je posamezna viskoelasti~na komponenta
jermena izpostavljena kombiniranemu procesu lezenja in relaksacije. Pri dolo~enih pogojih, ki jih opredeljujeta geometrija
jermena in kotna hitrost jermenice, se proces retardacije med dvema obremenitvenima cikloma ne zaklju~i. To pomeni, da
material vstopi v naslednjo obremenitveno fazo s preostalo deformacijo. Postopoma se za~ne deformacija akumulirati, kar vodi
do utrjevanja materiala, nastanka razpoke in posledi~no do propada jermena.
Analiza poka`e, da se akumulacija deformacije v jermenu pojavi pri dolo~enih kriti~nih vrednostih kotne hitrosti. Proces
akumuliranja deformacije v vsakem zaporednem obremenitvenem ciklu je odvisen od geometrije jermena, kotne hitrosti
jermenice, {tevila zaklju~enih obremenitvenih ciklov in retardacijskega spektra materiala, iz katerega je narejen jermen.
Predstavljeno delo obravnava vpliv {tevila obremenitvenih ciklov na proces akumuliranja deformacije v pogonskem jermenu
med obratovanjem motorja. Pri dani geometriji jermena kriti~na kotna hitrost nara{~a s pove~evanjem {tevila obremenitvenih
ciklov, medtem ko velikost akumulirane deformacije nelinearno pojema, kar ka`e, da se z nara{~anjem {tevila ciklov
obremenjevanja proces akumuliranja deformacije upo~asni. Rezultati ka`ejo, da bo jermen med obratovanjem pri kriti~ni kotni
hitrosti (oz. v njeni bli`ini) zelo verjetno odpovedal. Z ozirom na to, da je kriti~na kotna hitrost povezana z retardacijskim
~asom materiala in je velikost akumulirane deformacije odvisna od jakosti pripadajo~e diskretne spektralne linije, lahko
sklepamo, da so ~asovno odvisne mehanske lastnosti elastomernega materiala, iz katerega je narejen jermen, kriti~ni parameter
za napoved trajnosti jermenov in drugih dinami~no obremenjenih elastomernih produktov.
Klju~ne besede: ~asovno odvisno konstitutivno modeliranje, pogonski jermeni, utrujanje, propad jermena, viskoelasti~na
analiza, akumulacija deformacije, elastomeri, ~asovno odvisno vedenje, mehanski spekter
1 THE LOADING CONDITIONS OF A
SYNCHRONOUS BELT
The loading conditions of a synchronous belt were
determined with the commercial FEM program called
ANSYS, assuming the elastic behaviour of all belt
components. The belt was pre-stressed with a force F
and loaded with a desired torque M so that the pre-
stressing force was adequately divided into the strand on
the tension side, F1, and the strand on the slack side F2,
as schematically shown in Figure 1. The distance
between the two pulleys is indicated as l, the radius of
both pulleys is R, and the times t1 and t2 indicate when
the belt enters and leaves the driving pulley.
The driving pulley and the driven pulley were then
rotated such that a selected point on the belt would return
to its initial position. Such a movement we designated as
a complete loading cycle of the belt. For a further
analysis of the strain accumulation, we selected the
location on the tooth where the shear stress state within
the loading cycle, calculated with the FEM program, has
the form of an impulse function. This location is
indicated as point A in Figure 2a. The corresponding
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 239
UDK 539.42:678 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)239(2006)
calculated time-dependent evolution of the stress state is
shown in Figure 2b.
As a first approximation the shear stress may be
modelled as the difference between two step functions
with the shear stress intensity t0. Hence,
τ τ( ) ( ) ( )t h t= +0
+ τ ξ ξ0 1 2
1
1 1{ [ ] [ ]}h t t n h t t n
n
n N
− − − − − − −
=
=
∑ ( ) ( ) (1)
The times t1 and t2 and the duration of one loading
cycle x are functions of the geometry and the angular
velocity of the belt drive, w. Here, N is the number of
cycles to which the belt has been exposed, and t(0) is the
shear stress at t = 0. Hence, t1 = (l+πR)/(wR),
t2 = (l+2πR)/(wR), and x = (2l+πR)/(wR).
2 ANALYSIS OF THE STRAIN
ACCUMULATION
The time-dependent strain response of a rubber
material can be expressed as 1,
γ τ
τ
( ) ( ) ( ) ( )
( )
t J t J t s
s
s
s
t
= + −∫0
0
∂
∂
d (2)
where J(t) is the shear creep compliance. Assuming the
material is simple and can be modelled with a single
spectrum line, the material function is expressed as
J(t) = Jg + L1e(–t/l1), where Jg denotes the glassy com-
pliance and l1 is the retardation time where the
corresponding spectrum line L1 = (l1) is located.
Let us analyse the accumulated strain at the end of N
completed cycles at t = tN = Nx. Substituting Equation
(1) into Equation (2), and considering the geometry of
the drive belt as l/R = π, we obtain
γ τ
ω
( ) ( ) ( )N J
N
NN=




+0 4π Γ , Γ ΓN n
n
N
N n( ) ( )=
=
∑ ∆
1
(3)
where
∆Γ n n L
n
( ) exp exp= −





 − −










τ
ωλ ωλ1 1
0 1
4 3
1
π π( )

 (4)
denotes the strain accumulation for each consecutive
cycle. Equation (3) describes the time-dependent
evolution of the strain field in the material when
exposed to cyclic loading. Figure 3 shows the strain
accumulation in each consecutive cycle, expressed by
Equation (4), as a function of lg w for different numbers
of completed cycles. From Figure 3 it is clear that the
strain accumulation has its maximum at a certain critical
angular velocity.
The location of the critical angular velocity, wCR(n),
can be obtained by equating the two last terms in
Equation (4),
1 – exp(–π/wCR(n)l1) = exp[π(4n–3)/wCR(n)l1] (5)
The critical angular velocity at which the accumu-
lated strain has a peak magnitude is a close form solution
of Equation (5) and can be expressed as
ω
λ
CR ( )
ln
n
n
n
=
−
−
π
1
4 2
4 3
(6)
It is important to note that the critical angular
velocity is directly related to the retardation time of the
I. EMRI ET AL.: FATIGUE PROBLEMS OF TRANSMISSION BELTS
240 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 3: The effect of different numbers of loading cycles on the
strain accumulated in the material
Slika 3: Vpliv {tevila obremenitvenih ciklov na akumulacijo defor-
macije v materialu
,
/M
P
a
τ
S
h
ea
r
S
tr
es
s
Figure 2: Shear stresses at point A within a complete loading cycle
Slika 2: Spreminjanje stri`ne napetosti v to~ki A v enem obremenit-
venem ciklu
Figure 1: Schematic diagram of the belt-loading conditions and the
geometry
Slika 1: Shemati~en prikaz obremenjevanja jermena in njegove
geometrije
material, which clearly emphasizes the importance of the
material’s time-dependent properties. By combining
Equations (3) and (6) we obtain the corresponding peak
value of the accumulated strain in each loading cycle,
∆Γ n
n
n L
n
n
n
max
( )
( , )ω τCR = −
−
−




−
0 1
4 3
1
4 2
4 3
4 2
;
n = 1, 2, 3 ..., N (7)
The critical angular velocity and the corresponding
peak value of the accumulated strain in each loading
cycle as a function of n for l1 = 100 s 2 are shown in
Figure 4. From the figure we can clearly see that the
critical angular velocity shifts towards higher
frequencies for each consecutive loading cycle, and that
the relation is almost linear. At the same time the
corresponding accumulated strain decreases for each
consecutive cycle.
Providing the drive belt can operate at the critical
angular velocity at all times, the maximum strain that
could be accumulated over N cycles would be,
Γ Γn n
n
n N
n n L
n
n
n
max max( , ) ( , )ω ω = τCR CR= −
−
−=
=
∑∆
1
0 1
1
4 2
4 3
4 2
4 3
1






−
=
=
∑
( )n
n
n N
(8)
It is important to stress that
lim ( , , ) limmax
n
n
n
n L
n
n
n→∞ →∞
= =
−
−
−


∆Γ ω κ τCR π 0 1
1
4 2
4 3
4 2



−( )4 3n
= 0 (9)
which means that the strain accumulated during each
cycle will tend towards zero value as n ® µ. However
lim ( , ) limmax
(
n
n
n
N L
n
n
n→∞ →∞
=
−
−
−





∆Γ ω τCR 0 1
1
4 2
4 3
4 2
4 3
1
n
n
n N
−
=
=
∑
)
= ∝ (10)
which means that if a belt were to operate all the time at
the critical angular velocity it would always fail.
The total accumulated strain, expressed by Equation
(8), as function of the cumulative number of loading
cycles is shown in Figure 5.
3 CONCLUSIONS
From the presented analysis we can conclude that
drive belts will exhibit the accumulation of strain when
exposed to normal operation at certain angular velocities.
For a given belt geometry the critical angular velocity
increases with the number of loading cycles. At the same
time the magnitude of the accumulated strain decreases
non-linearly as the number of loading cycles increases.
Hence, the strain-accumulation process slows down with
the increasing number of loading cycles, and will be
negligible after a certain number of loading cycles, as
shown in Figure 4.
However, if the belt operates at, or in the close
vicinity of, its critical angular velocity, it will almost
certainly fail. The critical angular velocity depends on
the material’s retardation time (i.e., the location of the
mechanical spectrum), while the magnitude of the
accumulated strain depends on the strength of the
corresponding discrete spectrum lines. Thus, the
time-dependent mechanical properties of the elastomeric
material from which the belt is constructed are the most
critical parameters for predicting the durability of drive
belts and other dynamically loaded elastomeric products.
ACKNOWLEDGEMENTS
We would like to acknowledge the support provided
by the Slovenian Research Agency under the contract
L2-66000-0782. The contribution to the numerical
calculations, data processing and the preparation of the
figures by R. Cvelbar is greatly appreciated.
4 REFERENCES
1 N. W. Tschoegl, The phenomenological theory of linear viscoelastic
behavior: an introduction, Springer-Verlag, Berlin Heidelberg, 1989
2 I. Emri, T. Prodan, A measuring system for bulk and shear charac-
terization of polymers, Experimental Mechanics 46 (2004), 429–439
I. EMRI ET AL.: FATIGUE PROBLEMS OF TRANSMISSION BELTS
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 241
Figure 4: The critical angular velocity and the maximum strain
accumulation as a function of the number of loading cycles
Slika 4: Kriti~na kotna hitrost in najve~ja akumulirana deformacije v
odvisnosti od {tevila obremenitvenih ciklov
Figure 5: The total accumulated strain as a function of the cumulative
number of loading cycles
Slika 5: Celotna akumulirana deformacija v odvisnosti od kumula-
tivnega {tevila obremenitvenih ciklov

T. RODI^ ET AL.: A MICRO-MACRO ANALYSIS OF THE TOOL DAMAGE IN PRECISION FORMING
A MICRO-MACRO ANALYSIS OF THE TOOL DAMAGE
IN PRECISION FORMING
MIKRO-MAKROANALIZA PO[KODB ORODJA ZA NATAN^NO
KOVANJE
Toma` Rodi~1,3, Jo`e Korelc2, Anton Pristov{ek3
1Naravoslovnotehni{ka fakulteta, Oddelek za materiale in metalurgijo, A{ker~eva 12, 1000 Ljubljana, Slovenia
2Fakulteta za gradbeni{tvo in geodezijo, Jamova 2, Ljubljana, Slovenia
3C3M, d. o. o, Vandotova 55, 1000 Ljubljana, Slovenia
tomaz.rodic@c3m.si
Prejem rokopisa – received: 2006-05-17; sprejem za objavo – accepted for publication: 2006-10-05
A micro-macro finite-element model for predicting the cyclic stress-strain response and damage evolution in tool-steel materials
is presented. The elasto-plastic constitutive model at the macro-scale combines isotropic and kinematic hardening with
continuum damage. This permits relatively precise modelling of the critical regions in the tooling systems over a large number
of loading cycles. The macroscopic stress-strain fields are coupled with representative volume elements at the micro-level,
where interactions between the primary carbides (M6C, MC, V8C7) and the martensitic matrix are evaluated. This provides a
detailed insight into the stress-strain fields at the micro-level and reveals the damage mechanisms at the micro-scale. The
performance of the model is demonstrated on an industrial example of a tool for the cold precision forming of metals.
Key words: damage, micro-macro, finite element method, tool steels, precision forming of metals
Predstavljen je numeri~ni model za analizo cikli~nih napetostno-deformacijskih odzivov in razvoja po{kodb orodnih jekel na
razli~nih dimenzijskih skalah po metodi kon~nih elementov. Makroskopski elasto-plasti~ni konstitutivni model povezuje
izotropno in kinemati~no utrjevanje s po{kodbami kontinuuma. To omogo~a razmeroma natan~no modeliranje kriti~nih obmo~ij
v sistemu orodij za veliko {tevilo obremenitvenih ciklov. Makroskopska napetostno-deformacijska polja so povezana z
reprezentativnimi volumenskimi elementi na mikroravni, kjer analiziramo medsebojne vplive med primarnimi karbidi (M6C,
MC, V8C7) in martenzitno osnovo. S tem dobimo podroben vpogled v napetostno-deformacijska polja in po{kodbene
mehanizme na mikroravni. Uporabnost mikro-makromodela je prikazana na industrijskem primeru orodja za natan~no
preoblikovanje kovin v hladnem.
Klju~ne besede: po{kodbe, mikro-makro, metoda kon~nih elementov, orodna jekla, natan~no preoblikovanje kovin
1 INTRODUCTION
The tooling systems applied in production of cold
forged components are repetitively subjected to very
high loads. Despite of the high strength materials and
prestressing applied to die inserts, these loads often
cause local plastic deformation of the dies. Even though
the plastic deformations caused by each forming cycle
are relatively small they accumulate during the
production and can eventually lead to the initiation of
fatigue cracks. Once a fatigue crack is initiated it can
grow and lead to the failure of tooling system. Statistical
investigations show that more than eighty percent of cold
forging tools fail in this way.
The designers are therefore interested in identifying
and optimising those design parameters that have strong
impact on the fatigue response of tooling systems. In this
work the response is modeled by an elasto-plastic
constitutive model, which combines isotropic and
kinematic hardening with continuum damage. This
permits relatively precise modelling of stress/strain
response of tool steels over large number of loading
cycles and estimation of accumulated damage. A method
for evaluating the sensitivity 1 of damage to material
parameters and optimisation 2 can be combined with this
approach.
2 CONSTITUTIVE MODEL
The elasto-plastic material model developed by
Pedersen 3 is considered. This model takes into account
simultaneous evolution of isotropic and kinematic
hardening and damage. Since the strains in the tool are
expected to be small (<1) an additive decomposition of
the strain tensor eij into elastic and plastic parts is
assumed;
ε ε εij ij
e
ij
p= + (1)
The elastic stress strain relationship is given by
σ εij ijkl kl
eL= ⋅ (2)
where Lijkl is the tensor of elastic moduli. The summa-
tion convention is adopted for repeated indices. It is
noted that experimental investigations of tool steel
materials do not reveal significant effect of damage on
their elastic response. The rate of plastic strain is
derived from the normality rule
&
&ε λ
σ
p
ij
f= ∂
∂
(3)
where f is the yield surface and &λ is the plastic multiplier
derived from the consistency condition, &f = 0. The flow
rule implicitly comprises damage D as follows:
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 243
UDK 669.14.018.25:621.73 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)243(2006)
(4)
where
(5)
(6)
(7)
(8)
In the above equations Xij is represents kinematic
hardening while the scalars R and k describe isotropic
hardening.
2.1 Kinematic hardening
The back stress tensor Xij is the centre of the yield
surface in stress space, it is defined by the following
evolution equations
(9)
and (10)
(11)
2.2 Nonlinear isotropic hardening
The scalar k is assumed to be constant while evo-
lution equation for R is defined by
(12)
where b is a material parameter and R8(?,q) represents
the limit of isotropic hardening or softening.
2.3 Continuum damage
Many different evolution equations have been
proposed in the literature to describe irreversible damage
development. For the industrial example described in
this paper the following equation has been applied
(13)
where
α( )p
p p
p p
d
d
=
≥
<



1
0
, za
, za
(14)
&
&
p
D
=
−
λ
1
(15)
p pD D= =Max( )( )0 (16)
D DC p= Max( )( ) (17)
3 COMPUTER IMPLEMENTATION
The material model has been implemented into a
specialised commercial finite element system 4 by using
the code development concept 4-6 shown in Figure 1.
The symbolic system 5,6 for automatic code
generation is based on the Mathematica package and
allows constitutive models, element formulations and
response functionals to be described on a highly abstract
level. The formulations are automatically processed by
computer, to derive consistently linearised element
stiffness matrices, loading vectors and sensitivity terms
for either direct differentiation method or adjoint
method. From these expressions the computer code is
automatically generated for different languages
including C and FORTRAN; this code can then be
integrated into a finite element environment which
performs both direct and sensitivity analyses on a global
structural level. An optimisation shell is also build
around the finite element software to allow automatic
optimisation of design parameters. The interactions
between the symbolic system, the finite element
environment and the optimisation shell are indicated in
Figure 1.
4 INDUSTRIAL APPLICATION
The computational model has been applied to
multi-scale damage analysis an industrial tool (Figure
2a) for production of an automotive precision part 7. In
the first step the macro-mechanical tool loads have been
T. RODI^ ET AL.: A MICRO-MACRO ANALYSIS OF THE TOOL DAMAGE IN PRECISION FORMING
244 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 1: Code development concept
Slika 1: Koncept za razvoj programske kode
evaluated by the finite element simulation of the forming
process. These loads were then repetitively applied to the
working surface of the prestressed die insert. In Figure
2c the macroscopic stress-strain response of the tool at
the most critical location is shown for the first fifty
forming cycles. These loading cycles were then mapped
to the to the representative volume element (RVE) of a
high strength powder metalurgical tool steel in order to
evaluate stress-strain fields at the micro level where
interactions between spherical primary carbides (M6C,
MC, V8C7) and martensitic matrix occur. In Figure 2b
the stress levels in carbides are shown. The model 8 can
be extended to tribological problems where damage and
wear of tool surfaces can be evaluated by taking into
account stress concentrations due to surface roughness,
temperature changes due to dissipation of plastic work
and friction, internal stresses at the microstructure due to
different thermal expansion of the carbides and the
martensitic matrix as well as cooling effects due to the
presence of lubricants.
5 REFERENCES
1 S. Stupkiewicz, J. Korelc, M. Dutko, T. Rodi~: Shape sensitivity
analysis of large deformation frictional contact problems. Comput.
methods appl. mech. eng. 191 (2002) 33, 3555–3581
2 Doltsinis I. St., Rodic T.: Process design and sensitivity analysis in
metal forming processes: Computational methods and applications,
International Journal for Numerical Methods in Engineering 45
(1999), 661–692
3 Pedersen T. O.: Cyclic plasticity and low cycle fatigue in tool
materials. Ph. D. Thesis. DCAMM, Report No. S 82, November
1998
4 www.c3m.si
5 Korelc J.; Automatic generation of finite-element code by simul-
taneous optimization of expressions, Theoretical Computer Science,
187 (1997a), 231–248
6 Korelc J.; Automatic generation of numerical codes with intro-
duction to AceGen 4.0 symbolic code generator, www.fgg.uni-lj.si/
Symech/
7 Grønbæk J., Hinsel C.: The importance of optimized prestressing
with regard to the tool performance in precision forging (Keynote
Paper). Kuzman, K. (Edtr.): 3rd International Conference on
Industrial Tools, ICIT 2001, Roga{ka Slatina, April 22-26, 2001
8 A. Ibrahimbegovi}, I. Gre{ovnik, D. Markovi~, S. Melnyk, T. Rodi~:
Shape optimization of two-phase material with microstructure,
Engineering Computations: International Journal for Computer-
Aided Engineering and Software, 22 (2005) 5/6, 1108
T. RODI^ ET AL.: A MICRO-MACRO ANALYSIS OF THE TOOL DAMAGE IN PRECISION FORMING
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 245
Figure 2: Micro-macro analysis of an industrial tool for cold precision forming of metals: (a) real macro-micro problem; (b) stress fields in
virtual FE model at macro and micro levels; (c) cyclic stress-strain response of RVE of tool steel.
Slika 2: Mikro-makroanaliza industrijskega orodja za natan~no preoblikovanje kovin v hladnem: (a) relni makro-mikroproblem; (b) napetostno
polje v virtualnem MKE-modelu na makro- in mikroravni; (c) cikli~ni napetostno-deformacijski odziv RVE orodnega jekla

D. A. SKOBIR, M. SPIEGEL: THE STABILITY OF CAST ALLOYS AND CVD COATINGS ...
THE STABILITY OF CAST ALLOYS AND CVD
COATINGS IN A SIMULATED BIOMASS-COMBUSTION
ATMOSPHERE
STABILNOST ZLITIN IN CVD-PREVLEK V SIMULIRANI
ATMOSFERI ZGOREVANJA BIOMAS
Danijela A. Skobir1, Michael Spiegel2
1Institute of Metals and Technology, Lepi pot 11, SI-1000 Ljubljana, Slovenia
2Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D-40237 Düsseldorf, Germany
danijela.skobir@imt.si
Prejem rokopisa – received: 2006-09-29; sprejem za objavo – accepted for publication: 2006-10-13
The corrosion resistance in a biomass-combustion environment was studied for the following materials: cast alloys (Alloy 800,
Inconel 617, 1.4910, HCM 12 and P91), Fe-9 % Cr model alloys with and without additions of Al, Si and Mo, and cast alloys
coated using the pack-cementation process with Al and Al-Si. The simulated atmosphere for the biomass-combustion
environment contained 200 µg/g HCl, volume fractions 13 % CO2, 22 % H2O and 5 % O2. The samples were covered with a salt
mixture of mass fractions of 52.4 % KCl and 47.6 % K2SO4 in order to simulate the corrosion beneath the deposits. The
specimens were exposed for 1000 h at the test temperature of 550 °C.
Keywords: hot corrosion, biomass combustion, CVD-coatings, deposits
S korozijskimi preizkusi v simulirani atmosferi za zgorevanje biomas smo raziskovali korozijsko obstojnost naslednjih
materialov: lite zlitine (zlitina 800, Inconel 617, 1.4910, HCM 12 in P91), modelne zlitine Fe-9 % Cr z dodatki Al, Si in Mo in
brez njih ter lite zlitine, na katere je bila s CVD-postopkom nanesena plast Al oziroma Al-Si. Simulirana atmosfera za
zgorevanje biomas je vsebovala 200 µg/g HCl in prostorninske dele`e: 13 % CO2, 22 % H2O in 5 % O2. Vzorci so bili prekriti s
solno me{anico z masnima dele`ema 52,4 % KCl in 47,6 % K2SO4 za simulacijo korozije pod depoziti. Preizkusi so potekali pri
temperaturi 550 °C, ~as trajanja preizkusov pa je bil 1000 h.
Klju~ne besede: visokotemperaturna korozija, zgorevanje biomas, CVD-prevleke, depoziti
1 INTRODUCTION
One of the most important problems of modern
society is the removal of waste and biomass, stemming
mainly from the production of highly developed indu-
strial products. An effective and useful way of removing
biomass is combustion, connected with the production of
steam used for the production of electrical energy.
Nowadays, approximately 23 % of the total amount of
waste in Europe is burned; the rest is deposited in
landfills1,2. In Western Europe, nearly 600 combustion
plants are in operation, and the number is still increasing.
Until 2010 an increase in the total amount of energy
from renewable sources, from 6 % to 12 %, is expected,
as well as a substantial increase in the efficiency of
thermal power plants.
Corrosion is a major issue concerning the limited
lifetime of tube materials and the plant efficiency in
biomass- and waste-incineration plants. In biomass-fired
plants, high contents of potassium and chlorine are
present in the combustion environment, causing early
failure of the thermal components, such as superheater
tubes3,4. Solid and/or liquid chloride salts, together with
their vapours, can destroy the protective surface oxide
scales of high-temperature materials, even at tempera-
tures well below the melting points of the salts2, 5-7.
Rapid corrosion results from the complicated chemical
reactions between tube materials and the gaseous species
(HCl, SO2, etc.) and, especially, the low melting point of
the eutectic salts of heavy metals (Sn, Pb, Zn) and
alkali-metal (K, Na) chlorides, as well as sulfates2, 8-10.
The most corrosive species in the flue gas is HCl. There
is generally more HCl than SO2; however, the HCl/SO2
ratio strongly depends on the waste being burned. A
generally accepted model for chlorine-induced corrosion
in waste- and biomass-fired boilers is the 'active
oxidation' mechanism, first observed and described by
Lee and McNallan11. The chlorine is produced by the
catalytic oxidation of HCl according to Deacon reaction
(Eq. 1) as well as by the reaction of the salt with the
oxide scale of the pre-oxidized metal, according to Eq. 2
and 3:
2HCl + 1/2O2 = H2O + Cl2 (1)
2NaCl + Fe2O3 + 1/2O2 = Na2Fe2O4 + Cl2 (2)
2NaCl + Cr2O3 + 1/2O2 = Na2Cr2O4 + Cl2 (3)
The chlorine diffuses through the cracks and pores of
the oxide scale to the metal/scale interface, reacting to
form FeCl2(s):
Fe + Cl2 = FeCl2(s) → FeCl2(g) (4)
As the vapor pressure of the chloride is 10–4 bar at
500 °C, it evaporates and the volatile chloride diffuses
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 247
UDK 620.193:669.14:669.245 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)247(2006)
outwards through the oxide scale. At the oxide/gas
interface the reaction to Fe2O3 takes place, releasing
chlorine again:
2FeCl2(g) + 3/2O2 = Fe2O3 + 2Cl2 (5)
The growth of the Fe2O3 in the cracks and pores of
the oxide destroys the scale and the corrosive gas can
react with the unprotected metal. Hence, a scale is
produced on the metal substrate, which is not passivating
and, for this reason, the mechanism was nominated as
active oxidation. The mechanism of this oxidation is
schematically presented in Figure 1. The chlorine plays
a catalytic role in this corrosion process because it is not
consumed. In-depth thermogravimetric studies on the
mechanism of active oxidation were carried out by Reese
and Grabke12, showing that the evaporation of FeCl2(g)
from the metal/scale interface is the rate-determining
step in NaCl-induced corrosion. In order to increase the
efficiency of combustion plants it is necessary to develop
effective protective coatings for vital components in
hostile combustion environments.
2 EXPERIMENTAL
In this study, bare metals, CVD coatings and model
alloys were tested in a simulated biomass-combustion
atmosphere. The chemical composition of the cast alloys
is presented in Table 1. All of these alloys are based on
iron, except for Inconel 617, which is a nickel-based
alloy.
With the goal to decrease the surface degradation that
occurs on exposure to high temperatures and corrosive
atmospheres the cast alloys were coated using the
pack-cementation process. The results of the exposure
tests of uncoated as well as coated alloys were
compared.
The pack-cementation process is essentially an
in-situ chemical vapour deposition (CVD) process,
which is used to deposit Al or some other elements
(Al-Si, Al-Cr and Al-B) onto metal substrates to form
aluminide diffusion coatings.
The substrates to be coated were placed in a sealed or
semi-sealed container together with a powder mixture
that consists of metal elements to be deposited (diffusion
element), a halide activator (NH4Cl) and an inert filler
(Al2O3). The substrates can be buried in, or placed
above, the powder mixture. The sealed container is
heated under a protective atmosphere of Ar to a
temperature between 650–1200 °C and held there for a
specified time. At these coating temperatures the halide
activators react with the metal elements in the powder
mixture and form a series of metal-halide vapour species
such as AlCl, AlCl2, AlCl3 and Al2Cl613. The coating is
formed via reduction reactions of the metal-halide
vapours at the substrate surface and subsequent
solid-state diffusion between the metal elements and the
substrate. For this reason, the coatings produced by using
this process are also termed diffusion coatings.
Additionally, Fe-9 % Cr model alloys with and
without additions of Al, Si and Mo were tested under the
same conditions. The chemical composition of the model
alloys is presented in Table 2.
All the materials were machined into specimens with
dimensions of about (10 × 10 × 2) mm, then ground with
400 # and 600 # SiC paper, cleaned in a ultrasonic bath
D. A. SKOBIR, M. SPIEGEL: THE STABILITY OF CAST ALLOYS AND CVD COATINGS ...
248 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 1: Schematic model of the mechanism of "active oxidation"
Slika 1: Shematski prikaz modela "aktivne oksidacije"
Table 1: Chemical composition of the cast alloys (w/%)
Tabela 1: Kemijska sestava litih zlitin (w/%)
Alloy Cr Ni Fe Mn Mo Al Co Si V
Alloy 800 19–23 30–34 bal <1.5 - 0.1–0.6 - 0.5 -
Inconel 617 20–24 bal max 3 max 1 8–10 - 10–15 max 1 -
1.4910 16–18 12–14 bal <2 2–2.5 - - <0.75 -
HCM 12 11.2 0.66 bal 0.50 0.86 - - - 0.25
P 91 8.6 0.26 bal 0.41 0.93 - - 0.3 0.21
Table 2: Chemical composition of the model alloys (w/%)
Tabela 2: Kemijska sestava modelnih zlitin (w/%)
Alloy Fe Cr Mo Al Si
VI811 bal 9 - 2.5 2.5
VI813 bal 9 10 - -
VI814 bal 9 10 2.5 2.5
VI815 bal 9 5 2.5 2.5
of acetone and weighed. After drying, each sample was
covered with a salt mixture of mass fractions 52.4 %
KCl and 47.6 % K2SO4 to simulate the corrosion beneath
deposits.
The exposure experiments were performed in a
flue-gas, using a horizontal furnace equipped with a
quartz working tube. The furnace was connected to
gas-mixing equipment; however, the N2–5 % O2–200
µg/g HCl mixture was supplied as a premixed
commercial gas. The gas was dried by passing it through
columns filled with P2O5 before entering the furnace.
Because of the large constant-temperature zone it was
possible to test 20 samples at the same time. The
exposure experiments were carried out at 550 °C. The
extent of the corrosion was determined by measuring the
mass loss after 1000 h of reaction after the removal of
the corrosion products by chemically etching in a
KMnO4-NaOH solution at 80 °C. After exposure,
metallographic cross-sections were prepared by dry
grinding the samples in order to prevent the dissolution
of the chloride products from the scale. Scanning
electron microscopy (SEM) and energy-dispersive X-ray
analysis (EDX) were used to study the morphology and
the chemical composition of the corrosion products.
3 RESULTS AND DISCUSSION
Figure 2 shows the extent of the corrosion on the
investigated alloys, expressed in terms of mass change in
mg/cm2. The model alloys, VI814 and VI815, show a
relatively small mass loss for the samples in the
biomass-combustion environment due to their high
content of Al, Si and Mo. The corrosion layer on the
SEM micrograph of a cross-section of the VI815 alloy
(Figure 3a) is very thin, about 52 µm. The corrosion
layer consists of an Fe-rich layer and closer to the metal
there is a scale interface, with an increasing amount of
Cr, Al, Si and Mo being detected. The inner part is a
Cr-rich layer with a large amount of Cl (Figure 3b).
Slightly worse corrosion behavior was shown by the
VI811 alloy, whereas the VI813 alloy with a high Mo
content was almost completely corroded. The analysis of
the deposited layer of the VI813 alloy shows that the
corrosion layer consists of two sublayers and is very
thick, about 622 µm (Figure 4a). In the upper layer is
the remainder of the salt on the top, and below an
Fe-oxide was formed, where no chromium was found.
The underneath layer is the layer of the inner corrosion
products. Figure 4b shows a detailed view of the
internal oxidation zone, which is relatively deep and
therefore responsible for the large mass loss. The outer
part of the scale of inner corrosion products is an Fe-rich
layer, and towards the metal-scale interface an increasing
content of Cr, Cl and Mo and no sulphur were detected.
From Figure 2 it can also be seen that the corrosive
attack on the nickel-based Inconel 617 alloy and on the
800 alloy with the high Ni content is much smaller than
on the iron-based cast alloys. From Figure 5a it is clear
that the corrosion layer on the exposed Inconel 617 is
extremely thin, only about 3.6 µm, which shows that this
alloy is just slightly corroded. The corrosion layer
consists of two layers (Figure 5b): the first layer is the
Ni-rich layer, and the second is the Cr-rich layer below.
No chlorides were detected in this layer.
The corrosion layer for the cast P91 alloy (Figure
6a), which has the lowest corrosion resistance among the
D. A. SKOBIR, M. SPIEGEL: THE STABILITY OF CAST ALLOYS AND CVD COATINGS ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 249
Figure 3: SEM micrograph from a metallographic cross-section of the
VI815 model alloy after corrosion beneath the KCl-K2SO4 salt
mixture in N2-5 % O2-200 µg/g HCl at 550 °C for 1000 h. (a)
overview image; (b) detailed image of the internal part of the
corrosion layer
Slika 3: SEM-posnetek metalografskega prereza za modelno zlitino
VI815 po koroziji pod solno me{anico KCl-K2SO4 v N2-5 % O2-200
µg/g HCl pri 550 °C in po 1000 h. (a) pregledna slika; (b) detajlna
slika notranjega dela korozijske plasti
Figure 2: Mass loss of the materials exposed in a flue gas for 1000 h
at 550 °C and covered with the KCl-K2SO4 salt mixture
Slika 2: Sprememba mase preizku{ancev po 1000-urnem korozijskem
preizkusu na 550 °C pod depozitom solne me{anice KCl-K2SO4
D. A. SKOBIR, M. SPIEGEL: THE STABILITY OF CAST ALLOYS AND CVD COATINGS ...
250 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Figure 7: SEM micrograph from a metallographic cross-section of
Al-coated Inconel 617 alloy after corrosion beneath the KCl-K2SO4
salt mixture in N2-5 % O2-200 µg/g HCl at 550 °C for 1000 h. (a)
overview image; (b) detailed image of the internal part of the
corrosion layer
Slika 7: SEM-posnetek metalografskega prereza za zlitino Inconel
617, prevle~eno z Al po koroziji pod solno me{anico KCl-K2SO4 v
N2-5 % O2-200 µg/g HCl pri 550 °C in po 1000 h. (a) pregledna slika;
(b) detajlna slika notranjega dela korozijske plasti
Figure 5: SEM micrograph from a metallographic cross-section of the
Inconel 617 alloy after corrosion beneath the KCl-K2SO4 salt mixture
in N2-5 % O2-200 µg/g HCl at 550 °C for 1000 h. (a) overview image;
(b) detailed image of the internal part of the corrosion layer
Slika 5: SEM-posnetek metalografskega prereza za zlitino Inconel
617 po koroziji pod solno me{anico KCl-K2SO4 v N2-5 % O2-200
µg/g HCl pri 550 °C in po 1000 h. (a) pregledna slika; (b) detajlna
slika notranjega dela korozijske plasti
Figure 4: SEM micrograph from a metallographic cross-section of the
VI813 model alloy after corrosion beneath the KCl-K2SO4 salt
mixture in N2-5 % O2-200 µg/g HCl at 550 °C for 1000 h. (a)
overview image; (b) detailed image of the internal part of the
corrosion layer
Slika 4: SEM-posnetek metalografskega prereza za modelno zlitino
VI813 po koroziji pod solno me{anico KCl-K2SO4 v N2-5 % O2-200
µg/g HCl pri 550 °C in po 1000 h. (a) pregledna slika; (b) detajlna
slika notranjega dela korozijske plasti
Figure 6: SEM micrograph from a metallographic cross-section of the
P91 alloy after corrosion beneath the KCl-K2SO4 salt mixture in N2-5
% O2-200 µg/g HCl at 550 °C for 1000 h. (a) overview image; (b)
detailed image of the internal part of the corrosion layer
Slika 6: SEM-posnetek metalografskega prereza za zlitino P91 po
koroziji pod solno me{anico KCl-K2SO4 v N2-5 % O2-200 µg/g HCl
pri 550 °C in po 1000 h. (a) pregledna slika; (b) detajlna slika
notranjega dela korozijske plasti
cast alloys, is much thicker (244 µm) than that on the
Inconel 617. On the SEM micrograph, again an Fe-rich
layer was detected on the top, and an increasing amount
of Cr and Cl was detected towards the metal-scale
interface (Figure 6b).
The exposure tests of Al-coated Inconel 617 and
Al-Si-coated 800 alloy did not show any improvement in
corrosion resistance compared to the uncoated material
(Figure 2). In the case of the Inconel 617, coated with
Al, there is almost no corrosion layer formed (Figure
7a). The aluminised layer (Figure 7b) has the chemical
composition 36.2 % Al, 35.4 % Ni, 13.7 % Cr, 7.3 % Co,
6.6 % Mo and 0.77 % Fe. Just below this layer an
enrichment of Cr was detected. The chemical
composition of this layer is 33.9 % Cr, 4.6 % Al, 27.6 %
Ni, 11.6 % Co and 19.1 % Mo. Below this layer is the
metal substrate.
For all the other coated cast alloys an improvement in
the corrosion resistance was observed (Figure 2).
Figures 8a and b show the corrosion layer of the P91
alloy, coated with Al-Si.
In spite the fact that the Al-Si coatings were not as
thick as the Al coatings (the Al coatings were about 80
µm and Al-Si about 30–40 µm) no significant differences
in the corrosion resistance were observed.
4 CONCLUSIONS
Exposure tests were carried out to compare the
corrosion resistance of several iron- and nickel-based
alloys, as well as the same alloys coated with Al, Al-Si
and Fe-9 % Cr model alloys beneath a salt mixture of
KCl and K2SO4 in N2–5 % O2 atmosphere with the
addition of 200 µg/g HCl. In this atmosphere, which is
typical for a biomass-combustion environment, active
oxidation by the HCl and alkali-chlorides plays a major
role in the corrosion of this material. The results showed
that among the model alloys (Fe-9Cr) the most
corrosion-resistant are the VI814 and VI815 alloys, due
to their large amount of Al, Si and Mo. In the group of
cast alloys, the Inconel 617 nickel-based alloy has the
best corrosion resistance, followed by the 800 alloy,
which also contains quite large amounts of Ni. The
Inconel 617 alloy coated with Al, and the 800 alloy
coated with Al-Si do not show any improvement in
corrosion resistance compared to the uncoated alloys. It
can therefore be summarized that the alloying elements
Ni, Mo, Al and Si have a beneficial effect on the
corrosion resistance of the model and cast alloys. The
coatings on the alloys that do not include these alloying
elements do not improve the corrosion resistance. The
formation of deposits significantly contributes to the
corrosion by solid and liquid salts (i.e., chlorides and
sulphates).
ACKNOWLEDGEMENTS
This work was carried out within the SUNASPO-
Research Training Network at the Department of
Interface Chemistry and Surface Engineering of the
Max-Planck-Institut für Eisenforschung GmbH, Düssel-
dorf, Germany. The author would like to thank PD Dr.
Michael Spiegel for the opportunity of working in the
field of High Temperature Corrosion, and especially for
his support. The financial support of the European
Commission is gratefully acknowledged.
5 REFERENCES
1 Statistisches Bundesamt Wiesbaden (1992), Statistik der öffentlichen
Abfallbeseitigung von 1990
2 Spiegel M.: Materials and Corrosion 50 (1999), 373–393
3 Sander B.: Biomass and Bioenergy 122 (1997), 177
4 Nielsen H. P., Frandsen F. J., Dam-Johansen K. and Baxter L. L.:
Prog Energy Combust Sci. 26 (2000), 283
5 Grabke H. J.: Incinerating municipal and industrial waste in Bryers
(ed.), Hemisphere Publ. Corp., (1991), 161–176
6 Li Y. S., Niu Y. and Wu W. T.: Mater. Sci. Eng A345 (2003), 64
7 Shinata Y.: Oxid. Met. 27 (1987), 315
8 Montgomery M. and Karlsson A.: Materials and Corrosion 50
(1999), 579
9 Miller P. D. and Krouse H. H.: Corrosion 28 (1972), 274
10 Grabke H. J., Reese E. and Spiegel M.: Corros. Sci. 37 (1995), 1023
11 Lee Y. Y., McNallan M. J.: Metallurg. Trans. 18A (1987), 1099
12 Reese E., Grabke H. J.: Materials and Corrosion 43 (1992), 547
13 Xiang Z. D., Burnell-Gray J. S. and Datta P. K.: Journal of Material
Science 36 (2001), 5673
D. A. SKOBIR, M. SPIEGEL: THE STABILITY OF CAST ALLOYS AND CVD COATINGS ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 251
Figure 8: SEM micrograph from a metallographic cross-section of the
P91 alloy, coated with Al-Si after corrosion beneath the KCl-K2SO4
salt mixture in N2-5 % O2-200 µg/g HCl at 550 °C for 1000 h. (a)
overview image; (b) detailed image of the internal part of the
corrosion layer
Slika 8: SEM-posnetek metalografskega prereza za zlitino P91,
prevle~eno z Al-Si po koroziji pod solno me{anico KCl-K2SO4 v N2-5
% O2-200 µg/g HCl pri 550 °C in po 1000 h. (a) pregledna slika; (b)
detajlna slika notranjega dela korozijske plasti

K. ZUPAN ET AL.: NASTANEK LaCrO3 MED ZGOREVALNO SINTEZO
NASTANEK LaCrO3 MED ZGOREVALNO SINTEZO
LaCrO3 FORMATION DURING COMBUSTTION SYNTHESIS
Klementina Zupan, Marjan Marin{ek, Stane Pejovnik, Teja Hrobat
Univerza v Ljubljani, Fakulteta za kemijo in kemijsko tehnologijo, A{ker~eva 5, 1000 Ljubljana, Slovenija
klementina.zupan@fkkt.uni-lj.si
Prejem rokopisa – received: 2006-01-23; sprejem za objavo – accepted for publication: 2006-10-09
Med vrsto postopkov mokre kemije, s katerimi posku{ajo zagotoviti v produktu ve~jo homogenost na atomskem nivoju, ve~jo
~istost ter ve~jo aktivnost prahov, je zgorevalna sinteza iz raztopin tista metoda, ki v zadnjem ~asu hitro pridobiva na pomenu.
Pri zgorevalni sintezi lantanovega kromita lahko izhajamo iz kovinskih nitratov, izbiramo pa lahko med razli~nimi reducenti
(tetraformaltrisazin-TFTA, urea, glicin citronska kislina). V prispevku primerjamo nastanek lantanovega kromita med
kalcinacijskim postopkom in v procesu zgorevalne sinteze iz citratno-nitratnega gela. Pri obeh postopkih smo pogoje za
pripravo intermediatov izbrali na osnovi razultatov termi~ne analize reakcijskih zmesi. Sestavo faz ter morfologijo vmesnih in
kon~nih produktov smo dolo~ali z rentgensko pra{kovno in SEM-analizo.
Klju~ne besede: zgorevalna sinteza, lantanov kromit, nastanek
Several methods for the low-temperature synthesis of LaCrO3 have been developed to achieve the compositional homogeneity,
purity and activity of powders including combustion synthesis from the solutions. The reaction mixtures usually employ metal
nitrates and different reducing agents, e.g., TFTA (teraformal trisazine), urea, glycine, and citric acid. In the present work the
formation of LaCrO3 in the calcining and in the combustion process was compared. In both procedures, intermediate formation
temperatures were determined by thermal analysis. The intermediates and the final products were characterized by X-ray
powder diffraction and by scanning electron microscopy.
Key words: combustion synthesis, lanthanum chromite, formation
1 UVOD
Lantanov kromit spada zaradi svojih dobrih lastnosti
(obstojnost pri visokih temperaturah, elektri~na prevod-
nost) med spojine za pripravo materialov za elektrodo ali
vmesnik v visokotemperaturnih gorivnih celicah s trdnim
elektrolitom. Vmesnik med seboj povezuje posamezne
dele gorivne celice (katoda / trdni elektrolit / anoda).
Uporabljajo ga tudi kot grelni element ali oblogo v
visokotemperaturnih pe~eh1.
Materiale na osnovi lantanovega kromita navadno
pripravljamo s kalcinacijsko metodo iz oksidov, hidro-
ksidov in karbonatov s ponavljanjem operacij mletja in
`ganja. Hitrost reakcij v trdnem je omejena z difuzijo,
zato v novej{em ~asu za pripravo teh materialov
preizku{ajo in uvajajo t. i. metode mokre kemije, npr.
sol-gel-postopki2, koprecipitacijska metoda3, metoda
trdnih raztopin prekurzorjev4, zgorevalna sinteza5 in
druge metode.
V primerjavi z enostavno reakcijo zgorevalne sinteze
v trdnem je potek zgorevalne sinteze iz raztopin veliko
bolj komleksen. Kljub {tevilnim raziskavam in enostav-
nemu osnovnemu principu pogosto ostane nepojasnjen.
Pri reakciji (ena~ba 1) trdnih komponent A in B v trdno
komponento AB z dovolj visokim tali{~em se reakcijska
toplota redoks reakcije porabi izklju~no za nastanek
enofaznega produkta in njegovo segrevanje. Pri zgore-
valni sintezi iz raztopin pa se reakcijska toplota ne
porablja le za nastanek in segrevanje kon~nih produktov
(ena~ba 2), ampak tudi za vse transformacije in fazne
spremembe, ki v sistemu potekajo. Med zgorevalno
sintezo iz citratno-nitratnega gela lahko poteka ve~
zaporednih ali vzporednih reakcij6, ~eprav jih med samo
sintezo ne lo~imo zaradi eksotermnosti in avtokatalitske
narave procesa. Predvsem pa nanje poka`e analiza
vmesnih in kon~nih produktov. Pri tovrstnih sintezah
moramo ra~unati tudi s toplotnimi izgubami ter
temperaturnimi gradienti v reakcijski zmesi
A+ B→ AB (1)
3La(NO3)3 + 3Cr(NO3)3 + 5H8C6O7 = 3LaCrO3 +
+ 30CO2 + 9N2 + 20H20 (2)
Da bi razjasnili potek sinteze lantanovega kromita iz
citratno-nitratnega gela, je bilo smiselno, da raziskave
izvajamo v nedopiranem sistemu (LaCrO3), kjer je
{tevilo kristalnih faz, ki med reakcijo nastajajo, ~im
manj{e. Nastanek lantanovega kromita smo posku{ali
pojasniti z analizo vmesnih produktov reakcije. Za
primerjavo smo lantanov kromit sintetizirali s kalcinacijo
iz lantanovega hidroksida in kromovega oksida.
2 EKSPERIMENTALNO DELO
Gele, intermediate ter kon~ni produkt smo pripravili
iz citratno-nitratnih za~etnih snovi. Reakcijske zmesi
smo pripravili tako, da smo kovinske nitrate lantana in
kroma raztopili v minimalni koli~ini vode ter dodali
vodno raztopino citronske kisline. Molsko razmerje med
citronsko kislino in nitratnimi ioni je bilo 0,18. Reak-
cijsko zmes smo prenesli v 500-mililitrsko bu~ko ter jo
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 253
UDK 546.654:54.057 ISSN 1580-2949
Izvirni znanstveni ~lanek/Original scientific article MTAEC9, 40(6)253(2006)
su{ili pri temperaturi 60 °C in ni`jem tlaku (vodna
~rpalka 2,7 kPa). Po su{enju smo citratno-nitratni gel
uporabili za pripravo vmesnih produktov. Segrevali smo
miligramske koli~ine gelov do izbranih temperatur (170
°C, 310 °C, 380 °C, 600 °C in 800 °C) ter tako
prepre~ili, da bi reakcija potekla avtokatalitsko do konca.
Lantanov kromit smo pripravili tudi po kalcinacijskem
postopku iz lantanovega hidroksida in kromovega
oksida. Obe komponenti smo zatehtali v ustreznem mol-
skem razmerju ter zmes ob dodatku etanola homogeni-
zirali v ahatni ferilnici. Nato smo reakcijsko zmes stisnili
v tablete (60 MPa, Φ = 6 mm) ter jih `gali 4 h pri
izbranih temperaturah (600 °C, 800 °C, 1000 °C).
Lastnosti reaktantov ter reakcijskih zmesi smo
spremljali s termi~no analizo s termoanalizatorjem
Mettler 3000. Rentgensko pra{kovno analizo vzorcev
smo izvedli z difraktometrom tipa D4 ENDEAVOR
X-ray Diffractometer (Bruker). Morfologijo vmesnih in
kon~nih produktov smo spremljali z vrsti~nim elektron-
skim mikroskopom JEOL T300.
3 REZULTATI IN DISKUSIJA
TG/DTG-analizo smo uporabili za dolo~anje ter-
mi~nih lastnosti reakcijskih zmesi za kalcinacijski
postopek in za zgorevalno sintezo. V primeru kalcinacij-
skega postopka smo analizirali tudi izhodni komponenti
lantanov hidroksid ter kromov oksid (Slika 1).
Pri segrevanju kromovega oksida v izbranem
temperaturnem obmo~ju med 20 °C in 950 °C pri~ako-
vano ni opaziti spremembe mase, nasprotno od lantano-
vega hidroksida, ki izgublja maso v ve~ stopnjah. V prvi
se pretvori oksid v hidroksid. Dejanska izguba mase je
9,3 % in je v skladu s teoreti~no izra~unano vrednostjo
9,5 %. Druga stopnja naj bi ustrezala nastanku lantano-
vega oksida,7 vendar v na{em primeru ta reakcija pote~e
v temperaturnem intervalu med 440 °C in 740 °C, ko se
izguba mase 4,6 % dobro ujema s teoreti~no izgubo 4,7
%. V reakcijski zmesi LCkalc je potek do temperature 600
°C enak kot pri lantanovem hidroksidu, ko pri~ne masa
nara{~ati. Nastaja z lantanom bogata faza La2CrO6 pri
reakciji oksidov s kisikom. Nad temperaturo 750 °C
vzorec ponovno izgublja maso, kar pripisujemo reakciji
La2CrO6 s Cr2O3. Po podatkih Kikkikawe in soavtorjev8
lantanov kromit pri kalcinacijskem postopku nastaja nad
temperaturo 900 °C, pri hidrazinskem postopku pa v
temperaturnem intervalu med 780 °C in 840 °C. Pri na{i
sintezi iz hidroksida in oksida je temperatura nastanka
ni`ja, kar je lahko posledica razlik v za~etni stopnji
priprave reakcijske zmesi in s tem nekoliko spremenje-
nega mehanizma nastanka perovskitne faze.
Citratno-nitratni gel prav tako izgublja maso v ve~
stopnjah. Prvi dve sta posledica reakcije med nitratnimi
ioni in citronsko kislino, tretja pa je gorenje organskega
ostanka z zrakom, kar smo `e obravnavali v pretklih
raziskavah9. Pri temperaturi 530 °C kristalizira lantanov
kromat (LaCrO4). Nad temperaturo 744 °C poteka
reakcija razpada lantanovega kromata po reakciji:
LaCrO4 →LaCrO3 + ½O2 (3)
Z rentgensko strukturno analizo vmesnih in kon~nih
produktov smo dolo~ili zaporedje nastanka faz pri obeh
sinteznih postopkih. Pri vzorcu LCkalc smo sestavo
kristalnih faz dolo~ili po kalcinaciji pri 600 °C, saj pri
temperaturah, ni`jih od te, najprej pote~e pretvorba
lantanovega hidroksida v oksid. Vzorec je slabo krista-
liziran in vsebuje z lantanom bogato fazo La2CrO6 ter
Cr2O3 ter LaCrO4. Po kalcinaciji pri 800 °C je v vzorcu
le perovskitna modifikacija. Citratno-nitratni geli
(Gel018) so po segrevanju do 170 °C, 310 °C in 380 °C
amorfni, po segrevanju do 600 °C pa je v njih le LaCrO4
v monoklinski modifikaciji. Po segrevanju do 800 °C
vzorec Gel018 vsebuje le perovskitno modifikacijo
lantanovega kromita. Rezultati rentgenske pra{kovne
analize so skladni s termi~no analizo in ka`ejo na razliko
v mehanizmu nastanka lantanovega kromita pri obeh
uporabljenih sinteznih metodah. LaCrO4 v vzorcu LCkalc
po kalcinaciji pri 600 °C dopu{~a mo`nost, da lantanov
kromit nastaja po dveh mehanizmih. Po prvem nastaja
lantanov kromit v reakciji faze, bogate z lantanom
(La2CrO6), s kromovim oksidom, v drugi pa z razpadom
LaCrO4. Po podatkih iz literature v reakciji lantanovega
hidroksida z amorfnim kromovim oksidom prevladuje
K. ZUPAN ET AL.: NASTANEK LaCrO3 MED ZGOREVALNO SINTEZO
254 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Slika 1: a) TG- in b)DTG-analize Cr2O3, La(OH)3 in reakcijskih
zmesi LCkalc ter Gel018 v zraku
Figure 1: a) TG and b) DTG curves of Cr2O3, La(OH)3 and reaction
mixtures LCkalc and Gel018 in air
prvi mehanizem8. Navzo~nost LaCrO4 v produktih,
pripravljenih s kalcinacijo, je mo`na zaradi uporabe
etanola pri pripravi reakcijske zmesi. Reducent prepre-
~uje oksidacijo kroma iz 3+ v 6+ ter s tem prepre~uje
nastanek lantanovega kromita izklju~no preko vmesnega
La2CrO6. Pri zgorevalni sintezi blizu stehiometrijskega
citratno-nitratnega razmerja je mehanizem nastanka
lantanovega kromita vezan na reakcijo razpada lanta-
novega kromata (ena~ba 3). V predhodnih raziskavah
smo perovskitno fazo potrdili v vseh vzorcih, priprav-
ljenih z zgorevalno sintezo za citratno nitratna razmerja
c/n od 0,18 do 0,2810. Druge faze pa so bile vezane na
obliko reakcijske zmesi pri zgorevalni sintezi. Pri sintezi
v plasti je stik med delci gela nepopoln, v produktu je
podobno kot pri kalcinacijskem postopku navzo~ tudi
La2CrO6, ki lahko nastane zaradi temperaturnih
gradientov in zaradi kratkih ~asov pri temperaturi
sinteze.
Tabela 1: Kristalne faze v intermediatih, pripravljenih s kalcina-
cijskim postopkom in iz citratno-nitratnega gela
Table 1: Crystalographic modifications in intermediates prepared by
calcining and citrate-nitrate
Vzorec Tkalcinacije
°C
Glavne kristalne faze
Gel018 170 amorfen
Gel018 310 amorfen
Gel018 380 amorfen
Gel018 600 LaCrO4
Gel018 800 LaCrO3
LCkalc 600 La2CrO6,Cr2O3, LaCrO4
LCkalc 800 LaCrO3
Slika 3 prikazuje vzorca LCkalc in Gel018 po toplotni
obdelavi pri temperaturah 600 °C in 800 °C. Vzorec
LCkalc, kalciniran pri 600 °C, je v obliki mikrometrskih
zrn, ki se deloma povezujejo v aglomerate, medtem ko je
vzorec LCkalc po kalcinaciji pri 800 °C sestavljen
prete`no iz aglomeratov, ve~jih od 2 µm. V tempera-
turnem intervalu od 600 °C do 800 °C se La2CrO6 in
LaCrO4 pretvorita v perovskitno modifikacijo, kar pa se
ne izra`a v spremembi morfologije. Vzorec Gel018,
segret do 600 °C, ima zna~ilno cevasto zgradbo volumi-
noznih aglomeratov, ni pa opaziti izrazitej{e zrnate
strukture. Pri segrevanju vzorca Gel018 do 800 °C enako
kot pri kalcinacijskem postopku nastane perovskitna
modifikacija, ki jo spremlja o~itna sprememba morfo-
logije vzorca. Vzorec sestavljajo zrna velika do 0,5 µm,
ki niso povezana v aglomerate. Skladno z drugimi
metodami karakterizacije se razlika v mehanizmu na-
stanka lantanovega kromita pri kalcinacijskem postopku
in pri zgorevalni sintezi izra`a tudi pri morfologiji.
4 SKLEP
Nastanek lantanovega kromita pri zgorevalni sintezi
iz citratno-nitratnega gela smo posku{ali pojasniti z
analizo vmesnih produktov reakcije. Za primerjavo smo
lantanov kromit sintetizirali s kalcinacijo iz lantanovega
hidroksida in kromovega oksida.
V reakcijski zmesi kalcinacijskega postopka so
termi~ne lastnosti do temperature 600 °C enake kot pri
lantanovem hidroksidu, ki v tem temperaturnem inter-
valu izgublja vodo. Nara{~anje mase, ki sledi, je
povezano z nastankom z lantanom bogate faze La2CrO6
pri reakciji kovinskih oksidov s kisikom. Nad tempera-
turo 750 °C vzorec ponovno izgublja maso, kar pripisu-
jemo reakciji La2CrO6 s Cr2O3. Temperatura nastanka
lantanovega kromita je v na{em primeru ni`ja od pri~a-
kovane, kar je lahko posledica razlik v pripravi
reakcijske zmesi pri kalcinacijskem postopku.
V citratno-nitratnih gelih pri segrevanju sledi ve~
stopenj. V prvih dveh te~eta reakciji med nitratnimi ioni
in citronsko kislino, tretja pa je gorenje organskega
K. ZUPAN ET AL.: NASTANEK LaCrO3 MED ZGOREVALNO SINTEZO
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 255
Slika 3: Posnetki vzorcev LCkalcin in Gel018 po razli~ni toplotni
obdelavi
Figure 3: SEM micrographs samples LCkalcin in Gel018 after different
thermal treatment
Slika 2: Pra{kovni posnetki LCkalc in gela018 po kalcinaciji pri 600
°C
Figure 2: Phase development of samples LCkalc and Gela018 during
thermal treatment at 600 °C
ostanka z zrakom. Kromatna faza kristalizira pri tempe-
raturi 530 °C, nad temperaturo 744 °C pa razpada do
kromita.
Mehanizem nastanka lantanovega kromita se pri
sinteznih metodah kalcinacije in zgorevalne sinteze
razlikuje. Pri zgorevalni sintezi lantanov kromit nastane
v reakciji razpada lantanovega kromata. Ta je tudi v
vzorcu, pripravljenem s kalcinacijo po segrevanju pri
600 °C, kar ka`e na to, da lantanov kromit nastaja po
dveh mehanizmih. Pri prvem nastaja v reakciji faze,
bogate z lantanom (La2CrO6), s kromovim oksidom, pri
drugem pa z razpadom LaCrO4. Navadno pri rekacijeh
hidroksidov z oksidi prevladuje prvi mehanizem.
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7 A. Neumann, D. Walter, The thermal transformation from lanthanum
hydroxide to lanthanum hydroxide oxide, Thermochimica Acta, 445
(2006), 200–204
8 T. Kikkiawa, M. Yoshinava, K. Hirota and O. Yamaguchi, Synthesis
of LaCrO3 by the Hydrazine Method, J. Mater. Sci. Lett., 14 (1995),
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K. ZUPAN ET AL.: NASTANEK LaCrO3 MED ZGOREVALNO SINTEZO
256 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Z. [U[TERI^ ET AL.: DINAMI^NE MEHANI^NE LASTNOSTI ELASTOMERNIH KOMPOZITOV ...
DINAMI^NE MEHANI^NE LASTNOSTI
ELASTOMERNIH KOMPOZITOV S POLNILI
NANOVELIKOSTI
DYNAMIC MECHANICAL PROPERTIES OF ELASTOMERIC
COMPOSITES WITH NANO-SCALE FILLERS
Zoran [u{teri~, Toma` Kos, Marija [u{tar
Savatech, d. o. o., Razvojni in{titut, [kofjelo{ka 6, 4502 Kranj, Slovenija
zoran.susteric@sava.si
Prejem rokopisa – received: 2006-09-18; sprejem za objavo – accepted for publication: 2006-10-12
V delu je prikazan na~in preu~evanja reolo{kih lastnosti elastomernih kompozitov z organsko modificirano montmorillonitno
glino kot nanopolnilom z uporabo deformacijskih, temperaturnih in koli~inskih odvisnosti njihovih dinami~nih mehani~nih
funkcij, tj. dinami~nega pro`nostnega modula in modula izgub. Pri tem je uporabljen teoreti~ni model, ki poleg razlage vedenja
dinami~nih funkcij omogo~a tudi dolo~itev zna~ilnih energij za deformacijski in toplotni razpad notranje sekundarne strukture
teh nanokompozitov.
Klju~ne besede: elastomer, glina, nanokompozit, reolo{ke lastnosti
The work presents an approach of studying rheological properties of elastomeric composites with organically modified
Montmorillonite clay, as nanofiller, by deformational, temperature and content dependence of their dynamic mechanical
functions, i.e. the storage and loss moduli. Within this frame a theoretical model has been used, which, apart from elucidation of
dynamic functions, also enables determination of characteristic energies for deformational and thermal breakdown of the
nanocomposite internal secondary structure.
Keywords: elastomer, clay, nanocomposite, rheological properties
1 UVOD
V zadnjih nekaj letih se je zanimanje za uporabo
nanopolnil, posebno dolo~enih vrst gline1 kot oja~e-
valnih in toplotnostabilizacijskih dodatkov elastomerom
mo~no pove~alo. Nanopolnila imajo veliko specifi~no
povr{ino in zato lahko v elastomerih `e v razmeroma
majhnih koli~inah u~inkovito nadomestijo klasi~na
aktivna polnila, na primer saje ali siliko. Poleg kemijske
sestave, zgradbe, velikosti in povr{inskih zna~ilnosti
delcev nanopolnil to dejstvo potrjujejo tudi reolo{ke
analize nastalih elastomernih nanokompozitov1,2.
To delo podaja rezultate reolo{kega preu~evanja
kompozitov iz naravnega kav~uka in organsko modifi-
cirane montmorillonitne gline, dobljenih z me{anjem v
talini. S sekundarnimi interakcijami delci gline med
seboj in s kav~ukovimi molekulami ustvarjajo vezi ter
tako sekundarno mre`o. Ker je zaradi povr{insko aktivne
gline gostota nastalih vezi velika, so pro`nostni moduli
tak{nih mre` pri majhnih deformacijah in zmernih
temperaturah visoki. Vendar zaradi {ibkosti sekundarnih
vezi z ve~anjem deformacije in/ali temperature za~ne
mre`a razpadati v energijsko disipacijskem procesu, kar
je reolo{ko mo`no spremljati. V ta namen je posebno
primerna periodi~na deformacija z merjenjem kompo-
zitovih dinami~nih mehani~nih funkcij, to je dina-
mi~nega pro`nostnega modula in modula izgub, v odvis-
nosti od deformacije in temperature. Za razumevanje
rezultatov je uporabljen statisti~nomehani~ni model3,4, s
katerim je omogo~ena tudi dolo~itev zna~ilnih energij
mehani~nega in toplotnega razpada mre`e in s tem
kvantitativna ozna~ba teh nanovelikostnih u~inkov v
elastomerih.
2 TEORETI^NI DEL
Z interkalacijo elastomernih molekul v glini in
eksfoliacijo delcev gline med me{anjem se zaradi
medsebojnih elektrostati~nih interakcij v snovi ustvarijo
multifunkcionalne vezi in s tem ustrezna tridimen-
zionalna mre`a. Ker so tovrstne interakcije kratkega
dosega van der Waalsove vrste, so nastale vezi v
primerjavi s kovalentnimi ali ionskimi vezmi {ibke5 z
zna~ilnimi energijami v obmo~ju 5–50 kJ mol–1.
Mehani~ni in toplotni u~inki zato mo~no vplivajo na
stabilnost posledi~ne sekundarne mre`e. @e pri majhnih
deformacijskih in/ali temperaturnih dvigih za~nejo vezi
in s tem sekundarna mre`a razpadati, kar je jasno
razvidno iz poteka dinami~nih mehani~nih funkcij
nanokompozita, saj je po teoriji gumene pro`nosti
pro`nostni modul sorazmeren z gostoto vezi6, modul
izgub pri danih pogojih pa z njeno spremembo. Za
tak{ne mre`e pa je pri tem zna~ilno, da se v mirovanju
po dolo~enem ~asu reformirajo, kar se sicer pri
poru{enih mre`ah s kovalentno vezavo ne zgodi nikoli.
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 257
UDK 691.4:620.17 ISSN 1580-2949
Izvirni znanstveni ~lanek/Original scientific article MTAEC9, 40(6)257(2006)
2.1 Vpliv deformacije
Na~elno je vseeno, katere vrste oscilirajo~a defor-
macija se uporabi pri preu~evanju odvisnosti dinami~nih
mehani~nih funkcij nanokompozitov od njene velikosti.
Da bi se izognili dolo~enim teoreti~nim in tudi merilnim
nerodnostim, zlasti pri velikih deformacijah, je ugoden
strig, saj so stri`ni pro`nostni moduli, nasprotno od
nateznih ali kompresijskih, dobro definirani v znatno
{ir{em deformacijskem obmo~ju7.
Tako ima pri majhnih (stri`nih) deformacijah dina-
mi~ni (stri`ni) pro`nostni modul kompozita G' visoko
vrednost, saj je gostota sekundarnih vezi visoka. Z
nara{~ajo~o deformacijo (ker gre za periodi~no defor-
miranje, je mi{ljena amplituda stri`ne deformacije g) se
zaradi razpadanja vezi njihova gostota manj{a in G'
monotono pojema z za~etne proti nizki kon~ni vrednosti,
ko je sekundarna mre`a v celoti poru{ena. Ker je razpad
sekundarne mre`e disipacijski proces, pa (stri`ni) modul
izgub G'' po drugi strani, z za~etne nizke vrednosti
naraste in preide maksimum, ko je razpad najmo~nej{i,
ter nato pojema, podobno kot G'. Pri tem pa je treba
opozoriti tudi na disipacijo energije zaradi notranjega
trenja, ki je mo~no odvisna od frekvence in vpliva na
vrednost G'', zlasti pri majhnih deformacijah. Defor-
macijski potek dinami~nih mehani~nih funkcij pri
razpadu sekundarne mre`e je shemati~no prikazan na
sliki 1.
S statisti~no mehaniko verigastih molekul in stati-
stiko razpada sekundarne mre`e je mo`no priti do
naslednjih analiti~nih izrazov deformacijske odvisnosti
dinami~nih mehani~nih funkcij G'(g) in G''(g)3,4:
G'(g) = G'(0) (1+Wrg/RT)exp(–Wrg/RT) (1)
G''(g) = G''(gmax) (Wrg/RT)exp(1–Wrg/RT) (2)
kjer sta G'(0) in G''(gmax) maksimalni vrednosti dina-
mi~nih stri`nih modulov, R plinska konstanta, T tem-
peratura in Wr zna~ilna energija za deformacijski razpad
sekundarne mre`e, ki jo je mo`no dolo~iti iz ena~b (1)
in (2) ter meritev G'(g) in G''(g). Energija Wr je odvisna
{e od vsebnosti polnila in temperature, vendar je de-
formacijsko neodvisna pri majhnih deformacijah. Z
ve~anjem deformacije postane odvisna tudi od slednje
Wr = Wr(g):
Wr(g) = Wr(¥) + {1/[Wr(0) – Wr(¥)] + g/3RT]
–1 (3)
kjer sta Wr(0) in Wr(¥)za dano sekundarno mre`o od
deformacije neodvisni konstanti s pri~akovanimi vred-
nostmi v obmo~ju, zna~ilnem za energije sekundarnih
interakcij.
Ena~bi (1) in (2) napovedujeta asimptoti~no defor-
macijsko pojemanje stri`nih modulov proti ni~li, na-
mesto proti nizkima, vendar kon~nima vrednostima
G'(¥) in G''(¥). Strogo vzeto bi bilo to treba upo{tevati,
v resnici pa je nebistveno, ker sta ti vrednosti zelo
majhni in praviloma dose`eni zunaj merilnega obmo~ja
prakti~nega pomena.
2.2 Vpliv temperature
Pri dani temperaturi sekundarne vezi nastajajo in
razpadajo v dinami~nem ravnovesju, tako da njihova
povpre~na gostota ostane konstantna. S spremembo
temperature se gostota ustali pri drugi vrednosti, ni`ji, ~e
je temperatura vi{ja, saj je med spremembo zaradi
mo~nej{ega termi~nega gibanja molekul razpad vezi
verjetnej{i od nastanka. Za tak{no dogajanje statisti~na
mehanika napoveduje termi~no aktivacijsko tempera-
turno odvisnost gostote vezi n(T) Arrheniusove oblike:
n(T) µ exp(Ea/RT), kjer je Ea aktivacijska energija za to-
plotni razpad sekundarne mre`e.
Po drugi strani teorija gumene pro`nosti napoveduje
premo sorazmernost pro`nostnega modula z gostoto vezi
in temperaturo6 G' µ nT. Z upo{tevanjem n(T) za tempe-
raturno odvisnost modula izhaja4:
G'(T) µ T exp(Ea/RT) (4)
Izka`e se, da ta zveza dr`i z visoko natan~nostjo.
Vrednosti aktivacijske energije za toplotni razpad mre`e
Ea so prav tako v obmo~ju, zna~ilnem za energije sekun-
darnih interakcij. Podobna temperaturna odvisnost velja
tudi za G'', le da ima aktivacijska energija zaradi notra-
njega trenja nekoliko druga~no vrednost.
2.3 Vpliv vsebnosti polnila
Glina kot nanopolnilo v elastomeru deluje oja~e-
valno, tako zaradi nastanka sekundarnih vezi kot tudi
zaradi pove~anega notranjega trenja. Delovanje je
obenem toplotno stabilizacijsko, saj vezi omejujejo
molekulsko gibljivost. Podrobna analiza poka`e, da je za
ne prevelike koncentracije polnila oja~evalni u~inek,
izra`en z odvisnostjo dinami~nega pro`nostnega modula
kompozita od volumenskega dele`a gline fV, naslednji4:
G'(fV) » G'(0) exp(kfV) (5)
kjer je k snovna konstanta, zna~ilna za sistem elastomer/
nanopolnilo.
Z. [U[TERI^ ET AL.: DINAMI^NE MEHANI^NE LASTNOSTI ELASTOMERNIH KOMPOZITOV ...
258 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Slika 1: Deformacijska odvisnost dinami~nih mehani~nih funkcij
nanokompozitov
Figure 1: Deformational dependence of nanocomposites’ dynamic
mechanical functions
3 EKSPERIMENTALNI DEL
Eksperimentalni del zajema pripravo vzorcev nano-
kompozitov in merjenje dinami~nih mehani~nih funkcij
v razli~nih odvisnostih.
3.1 Snovi in priprava vzorcev
Vzorci so bili pripravljeni z me{anjem elastomerne
taline z organsko modificirano montmorillonitno glino in
premre`evalnim sistemom v gnetilnem me{alniku (Bra-
bender Plastograph) 10 min ob za~etni temperaturi glave
me{alnika 60 °C in hitrosti 60 r/min, pri ~emer so bile
uporabljene naslednje snovi:
– naravni kav~uk SMR 10 z viskoznostjo po Mooneyu
(ML (1+4) 100 °C) 89
– kemijsko modificirana montmorillonitna glina
(Dellite 67G)
– nemodificirana glina (Dellite LVF)
– premre`evalni sistem (`veplo, cinkov oksid, stearin-
ska kislina, TBBS)
Tako so bili narejeni kompoziti z 10, 25 in 35 mas-
nimi deli gline na 100 delov kav~uka, koli~inska sestava
premre`evalnega sistema pa je bila v skladu s stan-
dardom ISO 1659. Za odpravo morebitnih notranjih
napetosti, nastalih med me{anjem, so vzorci po~ivali
najmanj 24 h pred presku{anjem.
3.2 Merjenje
Merjenje dinami~nih mehani~nih funkcij je bilo
izvedeno z instrumentom Rubber Process Analyser RPA
2000 (Alpha Technologies) v obmo~ju amplitud stri`ne
deformacije 0,01–10 ter v temperaturnem obmo~ju
40–100 °C, vse pri frekvenci 0,3 Hz. Ta frekvenca je
dovolj nizka, da lahko med meritvijo molekulski deli
med topolo{ko sosednjimi vezmi nemoteno spreminjajo
svoje konformacije, s ~imer je zagotovljena varnost pred
ne`elenimi pojavi, na primer elasti~nim izbruhom8.
Predhodno premre`enje (vulkanizacija) vzorcev je
bilo izvedeno z istim instrumentom pri temperaturi 160
°C v trajanju do dosega 90-odstotne stopnje premre`enja
(t90).
4 REZULTATI IN DISKUSIJA
4.1 Vpliv deformacije
Na slikah 2 in 3 sta prikazani dinami~ni mehani~ni
funkciji G'(g) in G''(g) kovalentno premre`enih nano-
kompozitov z razli~nimi vsebnostmi gline, pri ~emer so
to~ke dobljene eksperimentalno, krivulje pa so izra~u-
nane z ena~bama (1) in (2). Razmeroma dobro ujemanje
modela z eksperimentom je dose`eno v primeru G'(g),
ujemanje G''(g) pa je slab{e, in pri nizkih deformacijah
ga sploh ni. Razlog je v tem, da model ne zajema notra-
njega trenja, ki je pri nizkih deformacijah znatno, pri
visokih pa se manj{a. Zaradi tega je ujemanje izra~una-
nega G''(g) z izmerjenim nekoliko bolj{e pri vi{jih
deformacijah.
S slike 2 je razviden mo~an vpliv vsebnosti gline na
G'(g) pri nizkih deformacijah. Poleg oja~evalnega
u~inka, ki je sicer eksplicitno opisan z ena~bo (5), je
opazno hitrej{e pojemanje G' pri deformiranju kompo-
zitov z vi{jimi vsebnostmi gline. To je posledica gostej{e
sekundarne mre`e, v kateri je povpre~na razdalja med
vezmi kraj{a, porazdelitev razdalj pa o`ja kot pri
redkej{ih mre`ah. Zato za~ne gostej{a mre`a razpadati
pri ni`jih deformacijah in hitreje. To se izra`a tudi v
velikostih za mehani~ni razpad zna~ilnih energij Wr(0)
(slika 2). Odvisnost od vsebnosti gline pa se z
nara{~ajo~o deformacijo manj{a in pri velikih deforma-
cijah popolnoma izgine. To je razumljivo, saj je v tem
deformacijskem stanju mre`a prakti~no poru{ena in
Z. [U[TERI^ ET AL.: DINAMI^NE MEHANI^NE LASTNOSTI ELASTOMERNIH KOMPOZITOV ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 259
Slika 3: Deformacijska odvisnost modula izgub elastomernih
nanokompozitov z razli~nimi vsebnostmi gline pri frekvenci 0,3 Hz in
temperaturi 40 °C
Figure 3: Deformational dependence of loss modulus for elastomeric
nanocomposites of different clay contents at frequency of 0.3 Hz and
temperature of 40 °C
Slika 2: Deformacijska odvisnost dinami~nega pro`nostnega modula
elastomernih nanokompozitov z razli~nimi vsebnostmi gline pri
frekvenci 0,3 Hz in temperaturi 40 °C
Figure 2: Deformational dependence of storage modulus for
elastomeric nanocomposites of different clay contents at frequency of
0.3 Hz and temperature of 40 °C
nizke vrednosti zna~ilne energije Wr(¥) so za razli~ne
vsebnosti gline enake.
Z vidika aktivnih polnil v elastomerih so nekoliko
presenetljivi poteki G''(g), predvsem vrednosti G''(gmax),
glede na vsebnost gline. Pri kompozitih s sajami ali
siliko G''(gmax) z vsebnostjo nara{~a, tako zaradi razpada
vezi kot zaradi notranjega trenja. Pri kompozitih z
organsko modificirano glino pa velike gostote nastalih
sekundarnih vezi o~itno tako omejijo notranje trenje, da
so G''(gmax) kompozitov z ve~jimi vsebnostmi gline,
kljub obse`nej{emu deformacijskemu razpadanju vezi in
s tem ustrezni energijski disipaciji, ni`ji od G''(gmax)
manj{ih vsebnosti. Tak{no vedenje je {e ena reolo{ka
posebnost elastomernih nanokompozitov.
4.2 Vpliv temperature
Na sliki 4 je predstavljena temperaturna odvisnost
dinami~nega pro`nostnega modula elastomernih kompo-
zitov z razli~nimi vsebnostmi gline. Glede na sorazmerje
(4) je odvisnost podana v obliki ln[G'(T)/T] kot funkcija
1/RT, pri ~emer so za G' vzete za~etne deformacijske
vrednosti, tj. pri g = 0.
Kot prikazuje slika, je eksperimentalno ujemanje s
sorazmerjem (4) dobro, z visoko korelacijo. Aktivacijske
energije, podane na sliki, so v zna~ilnem obmo~ju
energij vezi van der Waalsove vrste, dobro ujemanje pa
obenem potrjuje napoved, da je toplotna poru{itev
sekundarne mre`e termi~no aktiviran proces. Pri tem
podobne vrednosti aktivacijske energije za kompozite
razli~nih vsebnosti gline pomenijo, da vsebnost
nanopolnila bistveno ne vpliva na kinetiko toplotnega
razpada.
4.3 Vpliv vsebnosti polnila
Oja~evalni u~inek gline v elastomeru je podan v
obliki eksponentne odvisnosti dinami~nega pro`nostnega
modula G' od volumenskega dele`a gline fV z ena~bo
(5). V sistemih elastomer/polnilo je volumenske dele`e
polnila te`ko dolo~iti z merjenjem, enostavno pa jih je
izra~unati z masnim dele`em fV in gostoto. Vendar, ker
se gostote kompozitov z razli~nimi vsebnostmi gline
med seboj le malo razlikujejo, je razlika med fV in fm
dovolj majhna, da je fV mo`no nadomestiti z fm. Zato je
na sliki 5 odvisnost G' (vrednosti pri g = 0) od vsebnosti
gline podana kar z napovedano (z ena~bo 5) linearno
zvezo ln G'–fm, pri ~emer naklon podaja za dan sistem
elastomer/glina zna~ilno konstanto k.
S slike je razvidno, da je napoved potrjena z visoko
korelacijo, kar je dodatni pokazatelj ustreznosti modela
za obravnavo reolo{kih lastnosti mre` s sekundarno
vezavo.
5 SKLEP
Na~in reolo{kega preu~evanja nanokompozitov
elastomer/glina z dinami~nima mehani~nima funkcija-
ma, tj. z dinami~nim pro`nostnim modulom in modulom
izgub, se je pokazal kot primeren. Vsaka sprememba v
sekundarni tridimenzionalni mre`i, ki jo z van der
Waalsovo vezavo glina ustvarja z elastomernimi mole-
kulami in ki je glavni nosilec obremenitev nanokom-
pozita, se izra`a v vedenju dinami~nih funkcij, kar je
eksperimentalno mo`no u~inkovito spremljati.
Za razumevanje dogajanja na nanoravni je pri tem
prav tako u~inkovita uporaba teoreti~nega modela defor-
macijskega in toplotnega razpada sekundarnih mre` v
elastomernih sistemih z nanopolnilom, saj razmeroma
dobro ujemanje njegovih napovedi z izmerjenimi dina-
mi~nimi mehani~nimi funkcijami, posebno v primeru
dinami~nega pro`nostnega modula, potrjuje ne le obstoj
tak{nih mre`, temve~ tudi verodostojnost samega
modela. Vsekakor pa je ob tem najpomembnej{e, da
model, sprejet z navedenimi pokazatelji kot prepri~ljiv,
omogo~a zanesljivo dolo~itev dveh energij, ki kvanti-
Z. [U[TERI^ ET AL.: DINAMI^NE MEHANI^NE LASTNOSTI ELASTOMERNIH KOMPOZITOV ...
260 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Slika 4: Temperaturna odvisnost dinami~nega pro`nostnega modula
elastomernih kompozitov z razli~nimi vsebnostmi gline pri amplitudi
deformacije ni~ in frekvenci 0,3 Hz
Figure 4: Temperature dependence of storage modulus for elasto-
meric composites of different clay contents at zero strain amplitude
and frequency of 0.3 Hz
Slika 5: Odvisnost dinami~nega pro`nostnega modula elastomernih
kompozitov od vsebnosti gline pri amplitudi deformacije ni~ in
frekvenci 0,3 Hz
Figure 5: Dependence of storage modulus for elastomeric composites
on clay content at zero strain amplitude and frequency of 0.3 Hz
tativno ozna~ujeta sekundarne mre`e: zna~ilne energije
za mehani~ni razpad in aktivacijske energije za toplotno
poru{itev mre`e. Njune vrednosti so v obmo~ju, zna-
~ilnem za energije sekundarnih interakcij.
Kon~no, izkazalo se je, da je z uporabljenim mo-
delom mo`na tudi kvantitativna karakterizacija tovrstnih
nanokompozitov z ozirom na vsebnost gline, kar lahko
neposredno koristi pri na~rtovanju uporabe.
6 LITERATURA
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cations, Wiley, New York, 1994, Chap. 1
8 M. Kralj Novak et al., Kovine zlit. tehnol. 29 (1995), 251
Z. [U[TERI^ ET AL.: DINAMI^NE MEHANI^NE LASTNOSTI ELASTOMERNIH KOMPOZITOV ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 261

J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
FRACTURE TOUGHNESS OF A HIGH-STRENGTH
LOW-ALLOY STEEL WELDMENT
@ILAVOST LOMA ZVARA VISOKOTRDNEGA
MALOLEGIRANEGA JEKLA
Jelena Tuma1, Nenad Gubeljak2, Borivoj [u{tar{i~1, Borut Bundara3
1Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
2University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000 Maribor, Slovenia
3Institute of Metals Constructions, Mencingerjeva 7, 1000 Ljubljana, Slovenia
jelena.tuma@imt.si
Prejem rokopisa – received: 2006-05-17; sprejem za objavo – accepted for publication: 2006-11-15
The use of high-strength low-alloy steels for high-performance structures, e.g., pressure vessels and pipelines, requires often
high-strength consumables to produce an overmatched welded joint. This globally overmatched welded joint contains local
mis-matched regions, which can affect the unstable fracture behaviour of the welded joint and the welded structure itself. If
local mis-matched regions are present in the vicinity of a crack tip, then the fracture toughness of the weld metal can be
significantly lower than that of the base metal. In this paper, the influence of the weld-metal microstructure on the fracture
behaviour is estimated enabling an evaluation of the resistance to stable crack growth through different microstructures. The
lower bound of the fracture toughness for different microstructures was evaluated using a modified Weibull distribution. The
results, obtained using specimens with a through thickness crack front, indicated a low fracture toughness, caused by the
strength mis-matching interaction along the crack front. In the case of through-the-thickness specimens, at least one local brittle
zone (LBZ) or a local soft region is incorporated into the process zone in the vicinity of the crack tip. Hence, an unstable
fracture occurred with small stable crack propagation, or without it. Despite the fact that the differences between the impact
toughness of the weld metal and the base metal can be insignificant, the fracture toughness of a weld metal can be significantly
lower.
Key words: fracture mechanics, welded joint, crack-tip opening displacement, resistance curves
Uporaba visokotrdnih malolegiranih jekel za zelo obremenjene strukture, npr. posode pod pritiskom in cevovode, zahteva
uporabo varilnega materiala, ki ustvari zvar z ve~jo trdnostjo. Taki zvari vsebujejo lokalna podro~ja z me{ano trdnostjo, ki
lahko vplivajo na nestabilno lomno vedenje zvara in zvarjene strukture. ^e me{ana podro~ja le`ijo v bli`ini vrha razpoke, je
lahko `ilavost loma pomembno manj{a kot pri osnovnem materialu. V tem delu je ocenjen vpliv mikrostrukture zvara na
vedenje pri lomu, kar omogo~a oceno odpornosti proti stabilnem {irjenju razpoke skozi razli~ne mikrostrukture. Ni`ja vrednost
`ilavosti loma je bila ocenjena za razli~ne mikrostrukture z modificirano Weibullovo porazdelitvijo. Rezultati, ki so bili
dose`eni pri vzorcih z razpoko preko debeline, so pokazali nizko `ilavost loma zaradi razli~ne trdnosti vzdol` ~ela razpoke. V
primeru vzorcev z razpoko preko debeline je vsaj eno lokalno krhko podro~je (LBZ) ali lokalno mehko podro~je vklju~eno v
procesno podro~je v bli`ini vrha razpoke. Zato se je stabilna propagacija razpoke izvr{ila z majhnim stabilnim {irjenjem ali brez
njega. ^eprav so majhne razlike med udarno `ilavostjo zvara in osnovnega materiala, je lahko `ilavost loma zvara pomembno
manj{a.
Klju~ne besede: mehanika loma, zvarni spoj, premik vrha odprtja razpoke, krivulje odpornosti
1 INTRODUCTION
Strength-overmatched welded joints are designed to
ensure the safe service of a welded structure by keeping
the flaws, e.g., planar defects, in an elastic weld metal,
while the base metal starts to yield. Such an approach
ensures that a welded structure can sustain local plastic
deformation, important when temporary overloading or
geometrical changes occur. These changes can be caused
by temperature variations during a structures service life.
The strength-overmatching requirement presents no
special problems for steel with yield strength of less than
600 MPa 1, but in case of steels with higher yield
strengths, e.g., above 700 MPa, locally undermatched
regions can occur. Such an overmatched weld joint is
quite sensitive to planar cracks developing from defects.
Thus, a higher stress concentration around the planar
defects in a weld metal in locally undermatched regions
can cause unstable fracture behaviour2. In this case a
significant range of experimentally fracture-toughness
values is obtained. It is possible, however, to overcome
this problem by determining the lower bound fracture
toughness, which can ensure the structural integrity and
a safe service life. The lower-bound fracture-toughness
value represents the value where the crack propagation
occurred. If the stress intensity factor (caused by applied
load) is lower than the lower-bound fracture toughness,
than crack propagation does not appear. This paper
presents a procedure for determining the lower-bound
fracture toughness of laboratory specimens cut from a
critically overmatched weld joint. The influence of the
weld-metal microstructure on the fracture behaviour is
estimated, enabling an evaluation of the resistance to
stable crack growth through different microstructures, as
well as an evaluation of the relevant value of the lower
bound of the fracture toughness. Reasons for the range of
experimentally measured fracture-toughness values are
also presented.
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 263
UDK 539.42:621.791.05:669.14.018.298 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)263(2006)
2 MATERIALS AND WELDING
The base metal is a high-strength low-alloy steel,
corresponding to grade HT80. The steel, with a thickness
of 40 mm, was delivered in quenched-and-tempered (Q
+ T) condition. Different mechanical properties can be
obtained for such a steel by using different tempering
temperatures (600–700 °C). The microstructure of the
steel of tempered martensite and lower bainite provides a
high strength and a high impact toughness. The welding
was done on plate samples (500 × 250 × 40) mm and
(1000 × 250 × 40) mm using the flux-cored arc-welding
(FCAW) process. The edge preparation was X-shaped,
Figure 1, as is usual for the welding of steel plates with
a thickness of 40 mm. The consumables were filled
wires (f 1.2 mm), suitable for welding with mixed-gas
shielding (82 % Ar and 18 % CO2). The cooling times
from 800 °C to 500 °C (Dt8/5) were approximately of 9 s,
with heat inputs of 1.8–2.0 MJ m–1, while the preheating/
inter-pass temperature was of 100 °C. The cooling time
was chosen because faster cooling rates (Dt8/5 = 6 s)
reduce the toughness in the intercritical region, and the
slower cooling rates (Dt8/5 > 12 s) reduce the toughness
due to the formation of a martensite-austenite consti-
tuent3. The welding parameters are given in Table 1. The
first passes of the welded joint were made using
preheating at 120 °C 4.
The chemical compositions of the base metal (BM)
and the different weld regions are listed in Table 2.
These compositions indicate a more pronounced alloying
effect from the BM in the root region than in the filler
regions. Local tempering or quenching caused by
reheating and cooling during the deposition of
subsequent passes is also present in the root and filler
weld regions. This is the main reason why the local
mis-matching through the weld thickness varied, even in
the case of a homogeneous weld.
J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
264 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
2
4
0
2
60 o
Figure 1: The "X" shaped groove used in this investigation
Slika 1: @leb z X-obliko, uporabljen pri tej raziskavi
Table 1: Welding parameters for each weld pass
Tabela 1: Varilni parametri za vsak varek
Welding pass Current
A
Voltage
V
Speed of
welding
cm/min
Interpass
temperature
°C
Heat input
kJ/cm
Dt8/5
s
Weld joint
region
1 155 24.5 11.5 120 19.813 10.61
2 185 23.5 13.7 135 19.040 10.82 root
3 250 24 16.0 30 22.500 8.78
4 250 24 15.0 65 24.000 10.47
5 240 23 10.5 105 31.543 15.65
6 240 23 11.1 120 29.784 15.66
7 220 23 15.9 65 19.130 8.43
8 220 23.5 14.6 85 21.203 9.96 filler
9 210 23 14.2 120 20.481 10.95 part
10 220 23 13.9 125 21.763 11.83
11 210 24 15.4 80 19.662 9.11
12 250 24 14.8 110 24.342 12.43
13 220 25 15.8 95 20.899 10.18
14 230 25 19.5 125 17.692 9.70
average 210 24 14.0 88 21.338 10.17 root
average 226 24 15.0 103 22.648 11.39 filler
Table 2: Chemical composition of the base metal, the pure weld metal and the actual weld metal of the filler and the root regions
Tabela 2: Kemi~na sestava osnovnega materiala, ~istega vara, realnega vara v obmo~ju polnitve in korena v masnih dele`ih w/%
Material C w/% Si w/% Mn w/% P w/% S w/% Cr w/% Ni w/% Mo w/% CE/%
Base metal 0.09 0.27 0.25 0.015 0.004 1.12 2.63 0.25 0.366
Weld metal (pure) 0.06 0.35 1.43 0.011 0.008 0.86 3.01 0.56 0.448
WMfill (filler part) 0.07 0.33 1.27 0.008 0.006 0.86 2.21 0.47 0.404
WMroot 0.08 0.32 0.78 0.012 0.007 0.99 2.50 0.35 0.388
The content of carbon is very low in the base metal
and the weld metals and the temperature of martensite
transformation is higher. Thus, the time interval for
self-tempering from the temperature of martensite
transformation up to room temperature is larger. In this
case a brittle hard microstructure does not appear. This is
the reason for the high toughness of the microstructure.
Table 2 presents the change of the carbon equivalent
(CE) during the welding process. The low CE and the
low strength hinder the hydrogen-assisted cold cracking.
The mechanical properties of the welds were determined
using round tensile specimens (f 5 mm) extracted from
the root and the cap region of the X-groove welds in
longitudinal direction. The tensile tests were performed
at room temperature and at the fracture-toughness testing
temperature, i.e., –10 °C. The results are listed in Table
3, with the data in brackets representing the designed
values (theoretical) of the mis-matching factor, which do
not correspond to the real welds. The differences
between the designed values and real mis-matching
factors are a consequence of the weld-pool dilution/
alloying by molten BM (see chemical compositions in
Table 2). It should also be pointed out that the cooling
rate in these experiments (Dt8/5 » 9 s) was obviously
different from that used during the all-weld metal sample
preparation by the consumable producer.
Table 3: Average mechanical property values of the base metal and
the weld metal
Tabela 3: Povpre~ne mehanske lastnosti osnovnega materiala in vara
Material Temp.
°C
E
GPa
RP0.2
MPa
Rm
MPa
At
%
Cv+
J
M
Base 20° 201 711 838 19.6 54-40 °C –
metal –10° 209 712 846 19 85-10 °C –
WM 20° 210* 770 845 16 56-10 °C (1.08)
WMfill
20° 205 861 951 11.7 56-10 °C 1.21
–10° 211 873 1041 10.8 33-40 °C 1.22
WMroot
20° 221 807 905 15.3 61-10 °C 1.14
–10° 212 824 902 16.5 50-40 °C 1.16
+ mean value of three Charpy-V notched impact-toughness specimens
* value has been estimated because an accurate experimental value
was not available
The impact-toughness V-notch specimens and the
single-edge notch bend SE(B) specimens were also
extracted from the welded joints. Different testing
temperatures were used to evaluate the impact
toughness. It can be concluded that the impact toughness
corresponds to the brittle-to-ductile transition region of
the weld joint, see Table 3. In spite of higher dilution/
alloying by the molten BM in the root region, a better
impact toughness is achieved in that region than in the
filler part of the WM.
The mis-match factor M is defined as:
M
y,
y,
=
σ
σ
WM
BM
(1)
The mechanical properties listed in Table 3 are the
average values of the region from where the tensile
specimens were taken. Hence, an empirical relationship
was used to obtain the local mis-matching values of
mechanical properties.
3 METALLOGRAPHIC INVESTIGATION
The cross-sections of the welded joints were polished
and etched (3 % nital) to reveal the microstructure 5,
shown in Figure 2. Previously performed fracture-
toughness testing 6,7 showed that in the case of unstable
crack propagation, the fracture-toughness value
depended on the microstructure of the crack-tip region.
Hence, a fracture-toughness analysis of unstable crack
propagation requires the classification of the fracture
toughness data connected to the microstructures at the
crack tip.
Figure 3 shows a welded joint cross-section
indicating two different regions inside a weld pass – one
region, with a dendritic structure (’as-welded’), and the
other one showing evidence of being re-heated at the
subsequent welding pass. The darkened regions in the
weld metal correspond to the partially transformed
J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 265
Figure 3: The re-heated and as-welded region within a welded pass,
×20
Slika 3: Pogreto in kot varjeno podro~je v varku, pove~ano 20-krat
Figure 2: Macrograph of the cross-section of the welded joint, ×1.5
Slika 2: Makroposnetek prereza zvara, pove~ano 1,5-krat
regions, re-heated above Ac1. The temperature of the
subsequent weld pass was between Ac1 and the self-
tempering temperature.
4 FRACTURE-TOUGHNESS TESTING
Specimen and Location of Machined Notch
The critical crack-tip opening displacement (CTOD)
value in the case of unstable crack propagation strongly
depends on the microstructures at the crack tip. Different
microstructures are formed in the weld metal, depending
on the thermal cycles and the chemical composition. For
this reason, the notch positioning in the welded joint is
very important. The effect of different microstructure on
the fracture behaviour was assessed by testing CTOD B
× 2B specimens (thickness B = 36 mm) with a through-
the-thickness notch tip in the weld metal. The CTOD B ×
B specimens, with the surface notch in the weld metal,
were used to assess the effect of different micro-
structures on the fracture behaviour of the welded joint.
Crack-tip opening displacement testing
The fatigue pre-cracking of the specimens was
performed according to the step-wise high-ratio R
"SHR" technique 8. The CTOD testing was performed on
the fracture-toughness specimen in accordance with the
BS 7448 standard 9. The testing temperature was of –10
°C, according to the recommendations of the Offshore
Mechanics and Arctic Engineering (OMAE) 10. A
single-specimen method was used with the DC
potential-drop technique applied to monitor the stable
crack growth 11. The specimens were loaded using a
constant cross-head velocity of 1 mm/min, i.e., in
displacement control. Base-metal BxB specimens with a
shallow crack (a/W = 0.1) and a deep crack (a/W = 0.5)
were also tested. In both cases the maximum CTODm
values were observed: CTODm = 1.08 mm (for a/W =
0.1) and CTODm = 0.604 mm (for a/W = 0.5).
5 ANALYSIS OF THE FRACTURE-TOUGHNESS
RESULTS
Figure 4 shows the resistance curves for almost the
same crack lengths (a/W = 0.27), but with a different
microstructure at the crack tip. The critical value of the
CTOD during crack-growth initiation is lower for the
’as-welded’ microstructure, denoted WM(B), than for
the ’re-heated’ microstructure, denoted WM(A). The
stable crack growth through WM(B) is characterised by
a low slope of the resistance curve and thus by a low
resistance to stable crack growth. The shallow-cracked
specimen with a shorter crack (a/W = 0.28) exhibited a
higher value of CTOD initiation than in the case of the
longer crack (a/W = 0.4). In the latter case, local
instability occurred (’pop-in’) during crack-tip blunting,
followed by crack arrest in the WM(A). The same slope
for the resistance curves obtained from the two spe-
cimens with different crack lengths (a/W = 0.27 and a/W
= 0.4) indicates to a stable crack growth through the
same WM(A) microstructure.
Figure 5 shows the values of the CTOD as a
fracture-toughness parameter for both series of
specimens, B × 2B and B × B, with the notch in the weld
metal and the base metal. Significant differences
between the fracture-toughness values of the base metal
and weld metal were observed. Also, all critical values
for the B × 2B specimens were within the same interval.
This is a consequence from the incorporation of at least
one local brittle zone (LBZ) or local soft region in the
process zone in the vicinity of the crack tip.
The results for the critical CTOD, obtained using
BxB specimens, are classified according to the micro-
structure, WM(A) and WM(B), depending on the
position of the fatigue crack tip at the beginning of the
CTOD testing. Since, the higher critical CTOD values
were measured for the specimens with a crack tip in the
WM(A), it is clear that the critical CTOD values for the
specimens with a crack tip in the WM(B) can be divided
J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
266 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
0
0.05
0.1
0.15
0.2
0.25
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
∆a / mm
C
T
O
D
/
m
m
∆ajump
δjump
a/W=0.3
Crack tip in WM(B)
"Stable" crack growth from
WM(B) towards WM(A)
Crack arrested
in WM(A)
Crack tip in
WM(A)
a/W=0.27
a/W=0.27
Figure 4: CTOD resistance curves of B × B specimens with the crack
tip in different microstructure
Slika 4: CTOD odpornostne krivulje za B × B vzorce s konico razpoke
v razli~ni mikrostrukturi
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
C
T
O
D
/
m
m
W We el ld dm me et ta al l
c
δ
δ
u
δm
B×B
B
B
×
×
2
2
B
B
B×B
B
WM(A) WM(B)
ase metal
a/W= 0.20 0.20
0.28 0.20
0.27 0.20
0.27 0.32
0.24
0.27
0.27
a/W = 0.5
a/W = 0.5
Figure 5: Compilation of the critical CTOD values
Slika 5: Pregled kriti~nih vrednosti CTOD
into two groups, depending on the crack depth.
Obviously, the scatter of the critical CTOD values and
the relatively small amount of data prevented a more
reliable estimation of the fracture-toughness lower-
bound value for different microstructures.
A modified Weibull distribution was used for the
statistical interpretation of the measured and corrected
critical CTOD values. Zerbst et al. 12 proposed a
modified Weibull distribution for estimating the
lower-bound fracture toughness in terms of the J-integral
13. The distribution function referring to this is given by:
P
J
J J P
J
J
f
C l. b. f
C
,
=
− ≤
− −










ln
( ) .
exp
2
05
1
0
0
2 



≥






 , fP 05.
(2)
with the lower bound, Jl.b., as the toughness for a failure
probability of zero.
The term J can be replaced with CTOD = d by using
the relation between d and J 14:
d
J
m
=
⋅σ ys
m
a
W
R= − + + ⋅0111 0817 136. . . *;
R
n
n
*
.
= ⋅



500
2 718
or R* =
σ
σ
m
y
(3)
The terms m and R* were introduced by Kirk and
co-workers [14] on the basis of finite-element analysis
results. The lower bound fracture toughness can be
derived by considering the condition of continuity for Pf.
As a result, the lower bound is simply obtained from the
mean value by the expression:
δ β δl. b. c,mean= ⋅ ⋅0 26.
with (4)
β = + − +1 2 737 2 327 125802 3. . .p p p
where p is the fraction of data that is rejected by the size
criterion.
The results of this analysis are two curves of Weibull
distribution that are in good agreement with the
experimental results for each individual microstructure,
as shown in Figure 6. The lower-bound fracture-
toughness value is represented by the CTOD value at the
intersection point of the Weibull distribution curve with
the x-axis. Although the Weibull distribution curves are
for different microstructures, it is worth pointing out that
the fracture-toughness lower-bound value is low for both
of them 7.
6 CONCLUSION
In spite of the fact that the differences between the
impact toughness of the weld metal and the base metal
are insignificant, the fracture toughness of the weld
metal can be significantly lower. The overmatched weld
metal exhibited unstable crack propagation, while the
base metal is ductile at the same test temperature. From
the analysis performed on the B x B specimen it can be
concluded that the critical value of the fracture toughness
and the fracture behaviour of the weldment as a whole,
depend on the crack depth and the microstructure at the
crack tip, and also on the microstructure toward which
the crack is growing. The influence of these parameters
is reflected in pronounced differences in the
experimentally obtained values. The higher reliability for
estimating the fracture-toughness lower bound was
achieved by using a modified Weibull distribution with
the CTOD parameter. The B x 2B specimens also
indicated low critical CTOD values, but with lower
scatter. The reason for this is the increased constraint,
since the ligament profile is of square shape, and also the
fact that the stress state at the crack tip causes an
interaction between strength-mis-matched microstruc-
tures, which are inevitably crossed by the crack front. In
the case of through-the-thickness specimens at least one
local brittle zone (LBZ) or a local soft region is
incorporated in the process zone in the vicinity of the
crack tip. Hence, the unstable fracture occurred with
small stable crack propagation, or without. The
statistically determined lower-bound fracture toughness
takes account of this effect, which causes an increased
scatter of experimental results. Therefore, for structural
integrity procedures, it is possible to use the present
approach to determine relevant fracture-toughness
values.
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J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 267
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
CTOD /mm
P
ro
b
a
b
ili
ty
,
P
f
Lower bound toughness
of WM(A) microstructure
Lower bound
toughness of
WM(B) mic.
Figure 6: Failure probability with lower bound values classified by
microstructures WM(A) and WM(B)
Slika 6: Verjetnost preloma pri spodnji vrednosti za mikrostrukturi
WM(A) in WM(B)
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K.-H.: Engineering estimation of the lower bound toughness in the
transition regime of ferritic steels, Fatigue & Fracture of engineering
materials & Structures, (1998) 21, 1273–1278
13 Anderson, T. L.: Fracture mechanics fundamentals and applications,
Second edition, 1994
14 Kirk, M. T., Dodds, R. H.: J and CTOD estimation equations for
shallow cracks in single edge notch bend specimens, J. of Testing
and Evaluation, 21 (1993) 4
J. TUMA ET AL.: FRACTURE TOUGHNESS OF A HIGH-STRENGTH LOW-ALLOY STEEL WELDMENT
268 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
M. TORKAR: SOLIDIFICATION AND FRACTURE OF AN AS-CAST Ni ALLOY
SOLIDIFICATION AND FRACTURE OF AN AS-CAST Ni
ALLOY
STRJEVANJE IN PRELOM LITE NIKLJEVE ZLITINE
Matja` Torkar
Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
matjaz.torkar@imt.si
Prejem rokopisa – received: 2006-05-17; sprejem za objavo – accepted for publication: 2006-11-06
The investigation was carried out on samples cut from 20-kg as-cast ingots of a Ni alloy. The as-cast microstructures were
examined, the intensity of the segregations were determined, and the fracture surfaces of the specimens, cooled in liquid
nitrogen, were examined. It was found that with slow solidification, carbide particles precipitate on the grain boundaries,
diminishing the grain-to-grain cohesion and influencing the morphology of fracture. In the areas of columnar solidification the
fracture propagates along the dendrite boundaries.
Key words: Ni alloy, solidification structure, segregation intensity, fracture surface
Izceje v zlitini z lito strukturo poslab{ujejo preoblikovalnost v vro~em. Za preiskavo so bili odrezani vzorci iz litih ingotov
zlitine na osnovi niklja z maso 20 kg. Preiskana je bila strjevalna struktura in dolo~ena intenziteta izcej. Vzorci so bili
prelomljeni v hladnem in preiskana je bila morfologija povr{ine preloma. Med po~asnim strjevanjem nastajajo po mejah zrn
karbidni delci, ki zmanj{ujejo kohezijo med zrni in vplivajo na morfologijo preloma. Na vrsto preloma vplivajo stebrasta
strjevalna zrna zaradi poti preloma vzdol` mej dendritov.
Klju~ne besede: nikljeva zlitina, strjevalna struktura, intenziteta izcej, povr{ina preloma
1 INTRODUCTION
Most as-cast Ni-based superalloys have a low hot
workability1. The hot-workability window depends on
the microstructural characteristics, the yield strength2, the
deformation rate and the dynamic and static recry-
stallization. The Ni-based alloy with about 75 % Ni, 20
% Cr, 2.5 % Ti, 1.4 % Al and 0.08 % C is strengthened
by sub-micron precipitates of γ' phase (Ni3Al) and, with
a sufficient content of carbon, also by carbide
precipitates. During solidification, primary carbide and
carbo-nitride particles of the M(C,N) type are formed,
while the secondary carbides, M7C3 and M23C6,
precipitate at dendrite boundaries during the cooling of
the solid alloy, because of the decreased solubility of
carbon in austenite with decreasing temperature. The
presence of carbides and the intermetallic precipitates
greatly increases the creep resistance of the alloy, which
depends on the size, quantity and distribution of the
precipitates. The basic mechanism of hot deformation
consists of the gliding and climbing of dislocations. The
resulting strain hardening is decreased by dynamic
recovery and recrystallization, which also affect the
kinetics of precipitation and the temperature of phase
transformation. With a higher content of alloying
elements, the yield strength of the alloy and the acti-
vation energy, Ea, for recrystallization are greater. The
yield strength of the alloy also depends on the defor-
mation rate, according to the Zener-Hollomon equation3 .
For this reason the intercrystalline hollows and
segregations decrease the workability until the moment
when the microstructure is modified by recrystallization.
Sufficient dynamic recrystallization also stops the
propagation of the microcracks formed on non-defor-
mable inclusions and on the triple points of the grains. If
a grain-boundary crack is oriented orthogonally to the
flow of the metal it propagates until a grain boundary of
a very different orientation is met, at which point the
propagation of the crack is arrested4.
To obtain the optimal properties for Ni-based
superalloys a heat treatment, specific to the particular
alloy5, is necessary. During the heat treatment two
essential operations are included:
– The solution of the g' phase and most of the carbide
particles. The solution of the g' occurs in the range
960–980 °C. This range of temperature increases
with the increasing content of Ti in the alloy. M23C6
precipitates are dissolved in the temperature range
1040–1095 °C and M7C3 particles in the range
1095–1150 °C.
– The controlled precipitation of g' and carbide parti-
cles during cooling from the solution temperature
and during holding at 700 °C.
The two-step heat treatment produces an over
saturation of the matrix of the alloy with carbon, which
increases the tensile strength at lower temperatures, but
leads, however, to a more unstable microstructure at
higher temperatures.
The grain size of nickel superalloys also affects the
proper relation between the tensile strength and the
low-cycle fatigue. The resistance to low-cycle fatigue
requires a small grain size (forged material), while the
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 269
UDK 669.245:539.42 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 40(6)269(2006)
resistance to creep requires a coarse grain size (as-cast
material). For this reason, modern turbine blades are
mostly produced by casting6. As a compromise, a
thermo-mechanical treatment giving a "necklace"
structure7 has been developed. This structure consists of
coarse, slightly elongated grains, surrounded by small
grains, and ensures the best balance of properties.
As-cast Ni alloys usually have a microstructure of
coarse, columnar grains, which requires careful starting
reductions during the hot-working process. During
dendritic solidification, strong segregations of elements
are formed in the interdendritic pockets. The intensity of
the segregations and the size of the dendrites depend on
the rate of solidification: the slower the cooling rate, the
coarser are the dendrites and the greater are the
segregations.
The aim of this work was to characterise the as-cast
microstructure of a Ni-based alloy.
2 EXPERIMENTAL PROCEDURE
The alloy was prepared by melting in air in an
induction furnace and casting into 20-kg ingots. The
ingots were forged, and during the forging a great
number of cracks were formed. Specimens were cut from
several places in the ingot and areas containing
segregations were assessed by using a scanning electron
microscope (SEM) equipped with a wavelength-
dispersive spectrometer (WDS). The microstructures
were also examined using optical microscopy. The
coefficient of segregation was calculated from the
difference in the content of elements within the grain and
in the interdendritic region. Prior to fracturing the
samples were cooled in liquid nitrogen. In addition, the
resulting fracture surfaces were examined in the SEM.
3 RESULTS AND DISCUSSION
From the solidification microstructure (Figure 1),
with coarse, columnar grains near the surface and
equiaxed crystal grains in the middle of the ingot, the
content of Cr, Co, Al and Ti was determined in the
region of the equiaxed grains with point analysis within
the grain and in the interdendritic region. The contents of
M. TORKAR: SOLIDIFICATION AND FRACTURE OF AN AS-CAST Ni ALLOY
270 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
a
b
c
Figure 2: Columnar and equiaxed grains with dendrites in as-cast
Ni-based alloy. Etched with Marble’s reagent.
Slika 2: Stebrasta in enakoosna zrna z dendriti v liti nikljevi zlitini;
jedkano z Marblovim jedkalom
Table 1: Concentration of elements in and between the solidification
grains
Tabela 1: Masni dele` elementov v strjevalnih zrnih in med njimi
Element Concentration, w/% Coef. of
segregation
K = cmax/cmin
In the grain In the inter-
dendritic pocket
Cr 20.08 26.04 1.29
Co 1.14 1.39 1.21
Ni 69.88 69,72 -
Al 0.43 0.46 1,06
Ti 2.03 4.45 2.19
Fe 1.12 1.29 1.15
a
b
Figure 1: Dendrites and interdendritic segregations of as-cast
Ni-based alloy. Etched with Marble’s reagent.
Slika 1: Dendriti in meddendritne izceje v liti nikljevi zlitini; jedkano
z Marblovim jedkalom
analysed elements and the calculated segregation
coefficients in Table 1 confirm the expected strong
segregation.
The segregation intensity increases from iron to
cobalt to chromium, and it is much greater for titanium.
The segregations make the alloy chemically inhomoge-
neous and cause a difference in the hot deformability.
The morphology of the as-cast microstructure
depends on the cooling rate; however, it is also related to
the segregation intensity. Several samples were cut from
the as-cast ingots and the microstructures were examined
M. TORKAR: SOLIDIFICATION AND FRACTURE OF AN AS-CAST Ni ALLOY
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 271
a
b
Figure 5: Detail of brittle-fracture surface with triangles and
tetrahedra and a mixture of brittle and ductile fracture with dimples
(SEM)
Sliki 5: Detajl krhke povr{ine preloma s trikotniki in tetraedri ter
duktilni prelom z jamicami (SEM)
Figure 3: Stringer of carbide particles on the grain boundary in
as-cast ingot (SEM)
Slika 3: Niz karbidnih delcev na meji zrn v ingotu z lito strukturo
Figure 6: Fracture along the columnar grains
Slika 6: Prelom vzdol` stebrastih zrn
a
b
c
Figure 4: Ductile and brittle fracture of as-cast sample in the region of
equiaxed grains (SEM)
Slika 4: Duktilen in krhek prelom v litem vzorcu v obmo~ju
enakoosnih zrn (SEM)
using optical microscopy. The as-cast microstructure
reveals a dendritic solidification (Figure 1) with coarse,
columnar and equiaxed grains (Figure 2), with inter-
dendritic segregations and stringers of carbide particles
on the grain boundaries (Figure 3).
The examination of the cold fracture of the as-cast
alloy (Figures 4, 5) revealed a mixed fracture surface,
with both ductile- and brittle-fracture areas being
present. Since the alloy is very tough, the fracture was
obtained by bending samples that were cooled in liquid
nitrogen. As shown in Figure 5, on the relatively smooth
surface of the brittle fracture, triangles or tetrahedra were
observed, indicating that the fracture occurred on the
{111} lattice plane. The stacking-fault tetrahedra are
special forms of point-defect agglomerates8. They are
formed by dissociated glide or climb and the aggregation
of vacancies. In face-centred cubic metals and alloys the
vacancies can group in three-dimensional faults in the
form of stacking faults on four {111} planes with six n
edges of the tetrahedron.
On the fracture surface a ductile area with trans-
crystalline dimples prevails (Figures 4, 5), with carbide
particles at the bottom of the dimples. The fracture along
the boundaries of the columnar grains is similar. The
mixture of ductile and brittle fracture is shown in
Figures 4b, c and 5b. The fractures are mostly trans-
crystalline. In some areas a quasi-ductile and
quasi-brittle micromorphology was observed, which
does not permit a proper interpretation of the prevailing
fracturing process.
4 CONCLUSIONS
The Ni alloy had a poor hot workability and a large
number of hot cracks appeared during the hot forging.
The metallography revealed dendritic solidification with
coarse, columnar grains near the surface, equiaxed grains
in the centre of the ingot and interdendritic segregation
of the alloyed elements and carbide particles on the grain
boundaries.
The stringers of the carbide particles are the main
reason for the poor grain-to-grain cohesion and represent
an easy path for crack propagation during the hot
working. They also affect the fracture propagation
during cold fracture. The precipitation of carbide
particles at the grain boundaries occurs during the slow
cooling after solidification or during a too-low soaking
temperature prior to hot working.
The examination of the cold fractures revealed
quasi-ductile and quasi-brittle areas, partly transcry-
stalline and partly intercrystalline. On the brittle-fracture
surfaces triangles and tetrahedra were observed,
suggesting a fracture on the {111} lattice planes.
For improved hot workability of the alloy it is
necessary to decrease the grain size and the amount of
segregation and to avoid the precipitation of carbide
particles on the grain boundaries.
ACKNOWLEDGEMENT
The Ministry of Higher Education, Science and
Technology of the Republic of Slovenia sponsored this
research.
5 REFERENCES
1 Schindler, I., Machá~ek, J., Spittel, M., Intermetallics 7 (1999),
83–87
2 Torkar, M., [u{tar{i~, B., Vodopivec, F., Kovine, zlit., tehnol., 27
(1993) 4, 289–294
3 Long, Z., Zhuang, J., Lin, P., Zhong, Z., Advanced Technologies for
Superalloy Affordability, ed. K. M. Chan, S. K. Srivastava, D. U.
Furrer, K. R. Bain, The Minerals, Metals&Materials Society, 2000,
187–196
4 Ryan, N. D., McQueen, H. J. J. of Mech. Work. Technol., 12 (1986),
279–296
5Mc Queen, H. J., Bourell, D. L. J. of Metals, (1987), Sept., 28–35
6 Ryan, N. D., McQueen, H. J. J. of Mech. Work. Technol.,12 (1986),
323–349
7Wright, D. C., Smith D. J. Mat. Sci. And Technol., (1986) 2,
742–747
8Matsukawa, Y., Zinkle S.J., Dynamic observation of the collapse
process of a stacking fault tetrahedron by moving dislocations,
Journal of Nuclear Materials, 329–333 (2004), 919–923
M. TORKAR: SOLIDIFICATION AND FRACTURE OF AN AS-CAST Ni ALLOY
272 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
A. KLOBODANOVI], M. ORU]: LABORATORY'S ACCREDITATION – CONFIDENCE IN THE ACTIVITIES ...
LABORATORY ACCREDITATION – CONFIDENCE IN THE
ACTIVITIES OF CONFORMITY ASSESSMENT OF PRODUCTS
LABORATORIJSKA AKREDITACIJA- ZAUPANJE V AKTIVNOST
OCENE USTREZNOSTI PROIZVODOV
Azemina Klobodanovi}, Mirsada Oru~
Institute of Metallurgy "Kemal Kapetanovi}", Travni~ka cesta 7, 72000 Zenica, Bosnia and Herzegovina
miz@miz.ba
Prejem rokopisa – received: 2005-08-29; sprejem za objavo – accepted for publication: 2006-10-19
The role of accredited laboratories is to verify the quality of products. This is particularly important for those products intended
for export. The activities of the laboratories of the Institute of Metallurgy and their significance for industrial activity in Bosnia
and Herzegovina are presented.
Key words: accreditation, products quality control, quality management
Naloga akreditiranih laboratorijev je preverjanje kakovosti proizvodov. To je posebno pomemebno za izdelke, namenjene za
izvoz. Predstavljena je aktivnost laboratorijev na Institutu za metalurgijo in njegov pomen za industrijsko dejavnost v Bosni in
Hercegovini.
Klju~ne besede: akreditacija, kontrola kakovosti proizvodov, upravljanje kakovosti
1 INTRODUCTION
The prime task of Central and East European
Countries is to achieve the required level of quality for
products and services that are exported to the countries
of the European Union. A considerable amount of work
and knowledge are needed to bring the quality of
products to a higher level, and much effort is necessary
to improve the quality and responsibility of the work of
all the people involved in the processes of production,
control and quality assurance. The first difficulty to
overcome is the barriers related to the conformity of the
national legal framework, metrology, standardisation and
of quality assessment with EU regulations. This is a
major and complex task, since it involves the adoption of
rules and processes prescribed in about 200 legal
directives and about 7000 European standards related to
metrology systems, methods of testing and certification,
all necessary in order to have a comparable and
transparent system of quality and procedures in all the
involved countries, and which are easy to supervise1.
Also, for the placement of products in EU markets in
the non-obligatory area of certification, serious barriers
exist. First of all, certificates for the quality-management
system in accordance with the standard ISO 9001:2000
and for the environmental management systems in
accordance with ISO 14000 must be obtained, with the
aim to ensure that certificates, accreditations, test and
calibration reports are accepted throughout Europe. This
means that products intended for export must be tested in
accredited laboratories that have a certified system of
quality control.
Quality is a characteristic confirming that the product
is manufactured according to an approved procedure and
that the properties are in agreement with a standard or
with a prescription accepted by the manufacturer and the
purchaser. The word quality has also a more general
significance that may not be defined by a document in
the case when it is related to a specific activity, a process
or an organisation. With the quality system for
companies and laboratories, the rules of behaviour in
business are established, and reciprocal relations, tasks
and responsibilities of the quality management are put in
place. Therefore, good quality control for companies is
one of the attributes for survival in a competitive market.
2 QUALITY – A NEW APPROACH TO
BUSINESS
Quality is a global requirement valued in developed
countries and becoming of essential importance for
different industrial companies in Bosnia and
Herzegovina, too. The market success of a number of
products is more and more dependent on the purchaser’s
satisfaction and the price of the product. Because of the
competition, which may offer the same quality for a
lower price or an improved quality for an unchanged
price, the quality determines the competitiveness in the
market place for companies too3.
For this reason, the concept of quality has radically
changed, and at present it is completely oriented towards
the purchaser, his or her needs, expectations and
preferences. It is not enough for the supplier to have
high-quality products/services, it is also necessary to be
ready to offer an acceptable price for an increasing level
of quality. Therefore, only continuous improvements
enable the producer to stay at the front of the general
development and to be continuously competitive in the
market.
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 273
UDK 691.1:389:061.6(497.15) ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 40(6)273(2006)
At the beginning of the industrial revolution the
sellers controlled the market, and because of the limited
range of goods on offer, the purchaser was frequently
forced to accept products of insufficient quality. The
primary task of manufacturing was to ensure an
increasing quantity of goods on the market. The
saturation of the market set up the balance between
supply and demand and asserted the quality and
reliability as being significant for the market value of
products. The increased number of suppliers of goods on
the market is the cause of decreasing prices for goods of
increasing quality. Success in competitive markets forces
the producers to ensure not only that their products
conform to standards, but also to improve the extent and
reliability of the control of quality, including also
non-standardised requirements.
The increased market competition and the
strengthening of the role of the purchaser led to the
development of a quality system involving the control of
the quality of products and the inclusion of preventive
actions to provide a constant supervision of the
manufacturing process as well as the provision of an
acceptable level of interference of this process with the
environment. All the people involved in the production
process have to take part in the activities related in a
broad sense to the quality control. This understanding of
the broad significance of quality control led to the
development of the principles of the system of quality
assurance for products.
Rapid changes in the market for products put the
producers into a position in which even permanent
improvement of the product quality, process and quality
system were not sufficient to ensure success. This was
the reason for the evolution of quality with new methods
of integration and harmonization to predict the
customer’s behaviour. The processes inside an
organization based on standards and internal producer
rules were combined with continuous research and
development and led to the system of Total Quality
Management (TQM).
3 THE IMPORTANCE AND PARTICIPATION OF
ACCREDITED LABORATORIES
Frequently, in the business sections of journals in
Bosnia and Herzegovina there are reports on the
successful operation of companies that have obtained
certificates in accordance with standards from the ISO
9000 and ISO 9001 series. However, very rarely, if ever,
is the reader informed about organizations with
accredited testing and calibration laboratories, in spite of
the fact that these organisations are competitive with
different services in their domain of activity in
accordance with the European standard EN 45001 and
the ISO/IEC 17025 standard4. The value of the
accreditations according to these two standards is equal
to the value of the ISO 9000 certificates. The quality of
the system involving standards, internal company rules
and metrology and the assessment of the conformity of
products depends also on the quality of some basic
elements of the country’s infrastructure, since the rules,
standardization, and metrology for the assessment of the
conformity of products and services according to
standards are base elements of the infrastructural quality
of the country.
The differences in principles and the level of
development of the quality of the infrastructure between
different countries set up barriers and limited the growth
rate of trade on the European and world markets. It is,
for this reason, of primary importance that the level of
development of the infrastructure, especially in
less-developed countries, becomes very fast relative to
those in countries that are potential markets for products.
Testing and calibration are base elements for the
assessment of conformity and are applied widely for a
large range of products and their results are a reliable
basis for the inspection and certification of products. In
building up the EU market, it was necessary to develop
conditions for the acceptance of goods produced in one
country to be accepted in other countries without
retesting. It was, therefore, necessary to define
requirements which can be fulfilled in every certified
European laboratory for testing and calibration and make
the results of the testing and calibration acceptable in all
the countries of the EU2. The approach is based on the
European standard EN 45001. On the other hand, the
countries’ governments have a responsibility towards
consumers in terms of health, safety, the environment
and legal regulations. This requires that all of the testing
is carried out in accredited laboratories.
The rules in the standards of the EN 45000 series
have been satisfactory for Europe; however, accredited
bodies have come to the conclusion that trade is a
worldwide process and many countries cannot accept the
EU’s standards. This was one of the reasons for the
development of the new ISO/IEC 17025 standard. This
standard includes previous requirements defined in the
EN 45001 standard, but also others, which have to be
accepted by the testing and calibration laboratories, if
these laboratories want their services to be accepted
internationally.
It is the policy of the EU to remove trade barriers;
one of the basic conditions for a successful functioning
of the common market, "a new approach to technical
harmonization and standards" is defined. Part of this
policy, related to the conformity of assessment, is the
goal to abolish technical trade barriers and establish a
mutual confidence in producer competence and in the
competence of the body for the assessment of conformity
(Figure 1).
This confidence should be ensured in obligatory and
in non-obligatory areas with harmonized standards, with
the application of quality assurance methods, with the
testing, inspection and certification of products as well
as with the introduction of a modern and independent
A. KLOBODANOVI], M. ORU]: LABORATORY ACCREDITATION – CONFIDENCE IN THE ACTIVITIES ...
274 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
organization for cooperation in testing, certification and
accreditation at the European level.
The basic task is to support the establishment of
agreements on the mutual recognition of tests in the
non-obligatory area.
If accreditation bodies certify and announce that
services from bodies they have accredited are based on
the same rules and, for this reason, to be trusted and
accepted, then all services will be acceptable in all
countries that have signed the document of agreement. In
this way, it is possible to build up the "pyramid of
confidence", an example of which is shown for the EU in
Figure 2.
Accreditation is, indeed, the basis for establishing the
mutual confidence between the conformity-assessment
bodies. It ensures the transparency of the activity of
accreditation bodies at national and regional levels.
4 ACCREDITED LABORATORIES OF THE
METALLURGICAL INSTITUTE
"Kemal Kapetanovi}", d.o.o., ZENICA
The metallurgical Institute "Kemal Kapetanovi}",
d.o.o., Zenica (formerly "Hasan Brki}") has been active
in Bosnia and Herzegovina for almost 45 years, and it is,
for this field of activity, the only organization in the
country.
Several institute laboratories served initially as a
testing and analytical base for scientific investigations;
later they also provided services to outside customers,
sometimes with a smaller participation in the scientific
analysis of the experimental data. During more than 40
years a great deal of experience in laboratory work was
gained and many testing methods have been developed,
e.g., mechanical testing of different materials (metallic
and non-metallic), metallography, chemical, ceramic and
mineralogical analysis, calibration methods for force,
hardness, torque, temperature and pressure. In the time
of war, the market required laboratory services, and
priority was given to this activity and to continuous
efforts to work in accordance with European and
international standards.
In accordance with the available recourses, it was
decided to further improve the quality system. This
began with the laboratories and inspection bodies, and to
ensure an efficient and transparent operation at all levels
of the institute, taking care that the interest of the
customers is considered.
The laboratories were the first accredited laboratories
in Bosnia and Herzegovina in 1998. The accreditation
was carried out by the National Department for
Standardization, Metrology and Patents BiH (now the
Institute for Accreditation BiH) in accordance with the
EN 45001 standard. Later, the laboratories were
reaccredited according to the ISO/IEC 17025 standard,
and the institute has the following accreditations:
– LK – 02-01 (calibration scope: calibration of
equipment for force, torque and hardness);
– LI – 02-02 (testing scope: mechanical testing of
metallic materials);
– LI – 02-03 (testing scope: metallographic testing of
metallic materials);
– LI – 02-04 (testing scope: chemical analysis of
metallic materials and petroleum products, physical
and mechanical testing of construction materials,
including refractories);
– LK – 02-05 (calibration scope: calibration of
measuring instruments for temperature and
pressure).
5 CONCLUSION
From the experience of countries in transition, it is
known that a very important part of the agreement for all
the candidate countries for inclusion in the EU is the
chapter related to the free exchange of products. This
requires the conforming of the technical legislature, the
reciprocal recognition of results of assessment of
conformity and the establishment of mechanisms for the
A. KLOBODANOVI], M. ORU]: LABORATORY ACCREDITATION – CONFIDENCE IN THE ACTIVITIES ...
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 275
Figure 2: Example of the pyramid of confidence for the EU
Slika 2: Primer piramide zaupanja za EU
Figure 1: Procedure for ensuring confidence in supplier’s competence
Slika 1: Procedura za zagotovitev zaupanja v kompetenco dobavitelja
removal of trade barriers. For this reason, the compe-
tence of laboratories for testing materials and products is
very important, since it determines which test results will
be the basis for the assessment of the conformity of
products to standards. The mutual confidence in the
competence is the condition for the acceptance of the
global principle: "once tested and once certificated",
based on accreditations that are themselves based on
multi-national agreements of recognition of the equality
of results of national conformity assessments.
The Metallurgical Institute "Kemal Kapetanovi}"
Zenica has the possibility to perform, together with the
accredited laboratories, an important role in this area in
Bosnia and Herzegovina, having already gained
sufficient experience, satisfactory resources and the
confidence of customers/users of services resulting from
many years of cooperation. In recent years, the
laboratories were certified by the Croatian Register of
Shipping and Metallurgical Institute "Kemal Kapeta-
novi}" Zenica has got opportunity to be in the list of
approval service suppliers in the important areas for
conformity assessment.
6 REFERENCES
1 D. Ujevi}.: Planning and introduction of a quality system into the
manufacturing process following the ISO 9000 standards,
Proceedings – 1st Symposium, Revitalization and modernization of
metal industry of Bosnia and Herzegovina, Biha}, 1997
2 A. Me{anovi}: Accreditation – instrument for acquisition of confi-
dence in the other activities to conformity assessment, Glasnik No. 3
– Department for standardization, metrology and patents B&H, 1999
3Mirsad Begi}: Quality – New philosophy of business, NIP "Eco-
nomic newspaper" d.d., Sarajevo, 2001
4 A. Klobodanovi}: Importance of laboratory’s accreditation, Business
newspaper No 1113/1114, Sarajevo, 2003
A. KLOBODANOVI], M. ORU]: LABORATORY ACCREDITATION – CONFIDENCE IN THE ACTIVITIES ...
276 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
LETNO KAZALO – INDEX
Letnik / Volume 40 2006
ISSN 1580-2949
© Materiali in tehnologije
IMT Ljubljana, Lepi pot 11, 1000 Ljubljana, Slovenija
M
EHNOLOGIJEIN
ATERIALI
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 40, 2006/1, 2, 3, 4, 5, 6
2006/1
Inhibition of the pitting corrosion of grey cast iron using carbonate
Raziskave inhibiranja jami~aste korozije sivih litin z uporabo karbonatne me{anice
A. Kocijan, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The characterization of polymer composites by thermogravimetry
Termogravimetri~na karakterizacija polimernih kompozitov
I. G. Popovi}, L. Katsikas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The influence of copper on the decarburization and recrystallization of Fe-Si-Al alloys
Vpliv bakra na razoglji~enje in rekristalizacijo zlitin Fe-Si-Al
D. Steiner Petrovi~, M. Jenko, V. Dole~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Improving the corrosion resistance of components made from structural steels
Pove~anje korozijske odpornosti delov iz konstrukcijskih jekel
P. Jur~i, P. Stolaø . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Evolucija globularne mikrostrukture pri postopku Rheo-light
Evolution of globular microstructure at the Rheo-light process
M. Torkar, M. Godec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Poslovanje dru`b z dejavnostjo proizvodnje kovin v Sloveniji v obdobju od leta 1992 do 2004
Operation of metal producing companies in Slovenia in the period from 1992 to 2004
V. Pirih . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2006/2
Segregation and oxidation
Segregacija in oksidacija
H. J. Grabke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Small-punch testing of a weld’s heat-affected zones
Testiranje lezenja toplotno vplivanih podro~ij vara z uporabo majhnega bata
R. [turm, Y. Li . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Degradation of VOC'S by a two stage thermal and high frequency DBDC system
Degradacija VOC z dvostopenjskim termi~nim in visokofrekven~nim DBDC-sistemom
O. G. Godoy-Cabrera, A. Mercado-Cabrera, R. López-Callejas, R. Valencia A., S. R. Barocio, A. E. Muñoz-Castro, R. Peña-Eguiluz,
A. de la Piedad-Beneitez . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Determination of the deformational energy during slab-width rolling on an edger mill
Dolo~anje deformacijske energije pri valjanju slabov na kr~ilnem ogrodju
F. Vode, A. Jakli~, R. Robi~, A. Ko{ir, F. Perko, J. Novak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
B2O3 and CaO in the magnesium oxide from seawater
B2O3 in CaO v magnezijevem oksidu iz morske vode
V. Martinac, M. Labor, N. Petric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Preparation of NiO/YSZ powders using a pechini-type method
Priprava NiO/YSZ prahov s prilagojeno pechini metodo
T. Razpotnik, V. Franceti~, J. Ma~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Microstructure evaluation of an NRC-processed automotive component
Ocena mikrostrukture avtomobilske komponente, izdelane po postopku NRC
M. Torkar, B. Breskvar, M. Godec, P. Giordano, G. Chiarmetta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Properties and microstructure of very pure CrNiV steel
Lastnosti in mikrostruktura zelo ~istih jekel CrNi
S. Nìme~ek, P. Moty~ka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
2006/3
Mechanical and corrosion properties of AA8011 sheets and foils
Mehansko vedenje in korozijske lastnosti trakov in folij AA8011
K. Deliji}, V. Asanovi}, D. Radonji} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
278 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
LETNO KAZALO – INDEX
Flame temperature as a function of the combustion conditions of gaseous fuels
Temperatura plamena v odvisnosti od pogojev zgorevanja plinastih goriv
M. Lalovic, Z. Radovic, N. Jaukovic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
[tudij mikrostrukture tiskanih slojev YSZ na podlagi Ni-YSZ
Microstructure characterisation of screen-printed layers of YSZ on Ni-YSZ substrate
M. Marin{ek, B. Kapun, A. Zupan~i~ Valant, K. Zupan, G. Kapun, J. Ma~ek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Supramolekularni poliuretani z azobenzenskimi skupinami
Supramolecular azobenzene polyurethanes
G. Ambro`i~, M. @igon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Mehanske lastnosti kav~ukovih zmesi na osnovi NBR
Mechanical properties of NBR based compounds
H. [ubic ml., Z. [u{teri~, M. @umer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Influence of micro-alloying on the phase transformations in cast manganese steels
Vpliv mikrolegiranja na fazne premene v litem manganovem jeklu
P. Moty~ka, J. Drnek, L. Kraus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
2006/4
A crack growth analysis in critical structural components
Analiza rasti razpoke v kriti~nih komponentah naprav
D. Semenski, @. Bo`i}, H. Wolf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Hot ductility of austenite stainless steel with a solidification structure
Vro~a preoblikovalnost avstenitnega nerjavnega jekla s strjevalno strukturo
F. Tehovnik, F. Vodopivec, L. Kosec, M. Godec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
The extraction of raw materials for the cement industry and nature conservation
Zagotavljanje primernih materialov za cementno industrijo s ciljem ohranjanja narave
@. Poga~nik, M. Stupar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Vacuum teaching for undergraduate students at the University of Coimbra
U~enje vakuuma za {tudente na Univerzi Coimbra
J.M.F. dos Santos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Isothermal decomposition of the β' phase in Cu-Zn-Al shape-memory alloys
Izotermna razgradnja β'-faze v zlitinah s spominom Cu-Zn-Al
V. Asanovi}, K. Deliji}, N. Jaukovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Estimation of the fatigue threshold values for a crack propagating through a bi-material interface taking into account
residual stresses
Ocena utrujenostnega praga za razpoko, ki napreduje skozi vmesno ploskev med dvema materialoma z upo{tevanjem
rezidualnih napetosti
L. Náhlík . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Karakterizacija kopolimerov SEC in SEC-MALS asparaginske kisline in laktida
SEC and SEC-MALS characterization of copolymers of aspartic acid and lactide
M. Gri~ar, E. @agar, A. Kr`an, M. @igon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
2006/5
Fatigue behaviour of a cast nickel-based superalloy Inconel 792-5A at 700 °C
Utrujanje lite nikljeve superzlitine Inconel 792-5A pri 700 °C
M. Petrenec, K. Obrtlík, J. Polák, T. Kruml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
The application of linear elastic fracture mechanics to optimize the vacuum heat treatment and nitriding of hot-work tool
steels
Uporaba linearne elastomehanike loma pri optimiranju vakuumske toplotne obdelave in nitriranju orodnih jekel za delo v vro~em
V. Leskov{ek, B. [u{tar{i~, D. Nolan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
The influence of long-term service exposure on the structure and properties of high-temperature steels and alloys
Vpliv dolgotrajnega obratovanja pri visokih temperaturah na lastnosti jekel in zlitin, namenjenih uporabi v energetskih napravah
A. Rybnikov, L. Getsov, G. Pigrova, N. Dashunin, E. Manilova, N. Mozaiskaja . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
The influence of mim and sintering-process parameters on the mechanical properties of 316L SS
Vpliv procesnih parametrov brizganja in sintranja na mehanske lastnosti nerjavnega jekla 316L
B. Berginc, Z. Kampu{, B. [u{tar{i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
Behaviour and optimisation of multi-directional laminate specimens under delamination by bending
Vedenje in optimizacija ve~smernih vzorcev laminatov pri upogibu z delaminacijo
N. Ouali, A. Ahmed-Benyahia, A. Laksimi, T. Boukharouba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
LETNO KAZALO – INDEX
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 279
The behavior of fatigue-crack growth in shipbuilding steel using the ESACRACK approach
Modeliranje rasti utrujenostne razpoke jekla za ladijske plo~evine po postopku ESACRACK
M. Shehu, P. Huebner, M. Cukalla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Ocena odpornosti proti zmrzovanju gradbene keramike na podlagi direktnih in indirektnih metod
Frost resistance evaluation of building ceramics by indirect and direct methods
T. Kopar, J. Ranogajec, M. Radeka, R. Marinkovi}-Nedu~in, V. Ducman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
2006/6
Plazemska sterilizacija bakterij s kisikovo plazmo
Oxygen plasma sterilization of bacteria
D. Vujo{evi}, Z. Vranica, A. Vesel, U. Cvelbar, M. Mozeti~, A. Drenik, T. Mozeti~, M. Klanj{ek-Gunde, N. Hauptman . . . . . . . . . . . . 227
A comparison of experimental results and computations for cracked tubes subjected to internal pressure
Primerjava eksperimentalnih rezultatov in izra~una za cevi z razpoko, ki so obremenjeni z notranjo razpoko
J. Capelle, I. Dmytrakh, J. Gilgert, Ph. Jodin, G. Pluvinage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Fatigue problems of transmission belts: a viscoelastic analysis of the strain-accumulation process
Problem utrujanja pogonskih jermenov: viskoelasti~na analiza procesa akumuliranja deformacije
I. Emri, J. Kramar, A. Nikonov, U. Florjan~i~, A. Hribar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
A micro-macro analysis of the tool damage in precision forming
Mikro-makroanaliza po{kodb orodja za natan~no kovanje
T. Rodi~, J. Korelc, A. Pristov{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
The stability of cast alloys and CVD coatings in a simulated biomass-combustion atmosphere
Stabilnost zlitin in CVD-prevlek v simulirani atmosferi zgorevanja biomas
D. A. Skobir, M. Spiegel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Nastanek LaCrO3 med zgorevalno sintezo
LaCrO3 formation during combusttion synthesis
K. Zupan, M. Marin{ek, S. Pejovnik, T. Hrobat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Dinami~ne mehani~ne lastnosti elastomernih kompozitov s polnili nanovelikosti
Dynamic mechanical properties of elastomeric composites with nano-scale fillers
Z. [u{teri~, T. Kos, M. [u{tar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Fracture toughness of a high-strength low-alloy steel weldment
@ilavost loma zvara visokotrdnega malolegiranega jekla
J. Tuma, N. Gubeljak, B. [u{tar{i~, B. Bundara . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Solidification and fracture of an as-cast Ni alloy
Strjevanje in prelom lite nikljeve zlitine
M. Torkar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Laboratory accreditation – confidence in the activities of conformity assessment of products
Laboratorijska akreditacija- zaupanje v aktivnost ocene ustreznosti proizvodov
A. Klobodanovi}, M. Oru~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
LETNO KAZALO – INDEX
280 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
MATERIALI IN TEHNOLOGIJE / MATERIALS AND TECHNOLOGY
AVTORSKO KAZALO / AUTHOR INDEX
LETNIK / VOLUME 40, 2006, A–@
A
Ahmed-Benyahia A. 199
Ambro`i~ G. 99
Asanovi} V. 83, 153
B
Barocio S. R. 55
Berginc B. 193
Bo`i} @. 123
Boukharouba T. 199
Breskvar B. 73
Bundara B. 263
C
Capelle J. 233
Chiarmetta G. 73
Cukalla M. 207
Cvelbar U. 227
D
Dashunin N. 185
Deliji} K. 83, 153
Dmytrakh I. 233
Dole~ek V. 13
Drenik A. 227
Drnek J. 111
Ducman V. 211
E
Emri I. 239
F
Florjan~i~ U. 239
Franceti~ V. 69
G
Getsov L. 185
Gilgert J. 233
Giordano P. 73
Godec M. 23, 73, 129
Godoy-Cabrera O. G. 55
Grabke H. J. 39
Gri~ar M. 161
Gubeljak N. 263
H
Hauptman N. 227
Hribar A. 239
Hrobat T. 253
Huebner P. 207
J
Jakli~ A. 61
Jaukovi} N. 89, 153
Jenko M. 3, 13
Jodin Ph. 233
Jur~i P. 17
K
Kampu{ Z. 193
Kapun B. 93
Kapun G. 93
Katsikas L. 7
Klanj{ek-Gunde M. 227
Klobodanovi} A. 273
Ko{ir A. 61
Kocijan A. 3
Kopar T. 211
Korelc J. 243
Kos T. 257
Kosec L. 129
Kr`an A. 161
Kramar J. 239
Kraus L. 111
Kruml T. 175
L
Labor M. 65
Laksimi A. 199
Lalovic M. 89
Leskov{ek V. 179
Li Y. 49
López-Callejas R. 55
M
Ma~ek J. 69, 93
Manilova E. 185
Marin{ek M. 93, 253
Marinkovi}-Nedu~in R. 211
Martinac V. 65
Mercado-Cabrera A. 55
Moty~ka P. 79, 111
Mozaiskaja N. 185
Mozeti~ M. 227
Mozeti~ T. 227
Muñoz-Castro A. E. 55
N
Náhlík L. 157
Nìme~ek S. 79
Nikonov A. 239
Nolan D. 179
Novak J. 61
O
Obrtlík K. 175
Oru~ M. 273
Ouali N. 199
P
Pejovnik S. 253
Peña-Eguiluz R. 55
Perko F. 61
Petrenec M. 175
Petric N. 65
Piedad-Beneitez A. de la 55
Pigrova G. 185
Pirih V. 27
Pluvinage G. 233
Poga~nik @. 139
Polák J. 175
Popovi} I. G. 7
Pristov{ek A. 243
R
Radeka M. 211
Radonji} D. 83
Radovic Z. 89
Ranogajec J. 211
Razpotnik T. 69
Robi~ R. 61
Rodi~ T. 243
Rybnikov A. 185
S
Santos dos J. M. F. 145
Semenski D. 123
Shehu M. 207
Skobir D. A. 247
Spiegel M. 247
Steiner Petrovi~ D. 13
LETNO KAZALO – INDEX
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 281
Stolaø P. 17
Stupar M. 139
[
[turm R. 49
[u{tar M. 257
[u{tar{i~ B. 179, 193, 263
[u{teri~ Z. 107, 257
[ubic ml. H. 107
T
Tehovnik F. 129
Torkar M. 23, 73, 269
Tuma J. 263
V
Valencia A. R. 55
Vesel A. 227
Vode F. 61
Vodopivec F. 129
Vranica Z. 227
Vujo{evi} D. 227
W
Wolf H. 123
Z
Zupan K. 93, 253
Zupan~i~ Valant A. 93
@
@agar E. 161
@igon M. 99, 161
@umer M. 107
LETNO KAZALO – INDEX
282 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
MATERIALI IN TEHNOLOGIJE / MATERIALS AND TECHNOLOGY
VSEBINSKO KAZALO / SUBJECT INDEX
LETNIK / VOLUME 40, 2006
Kovinski materiali – Metallic materials
Inhibition of the pitting corrosion of grey cast iron using carbonate
Raziskave inhibiranja jami~aste korozije sivih litin z uporabo karbonatne me{anice
A. Kocijan, M. Jenko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The influence of copper on the decarburization and recrystallization of Fe-Si-Al alloys
Vpliv bakra na razoglji~enje in rekristalizacijo zlitin Fe-Si-Al
D. Steiner Petrovi~, M. Jenko, V. Dole~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Improving the corrosion resistance of components made from structural steels
Pove~anje korozijske odpornosti delov iz konstrukcijskih jekel
P. Jur~i, P. Stolaø . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Evolucija globularne mikrostrukture pri postopku Rheo-light
Evolution of globular microstructure at the Rheo-light process
M. Torkar, M. Godec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Poslovanje dru`b z dejavnostjo proizvodnje kovin v Sloveniji v obdobju od leta 1992 do 2004
Operation of metal producing companies in Slovenia in the period from 1992 to 2004
V. Pirih . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Segregation and oxidation
Segregacija in oksidacija
H. J. Grabke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Small-punch testing of a weld’s heat-affected zones
Testiranje lezenja toplotno vplivanih podro~ij vara z uporabo majhnega bata
R. [turm, Y. Li . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Degradation of VOC'S by a two stage thermal and high frequency DBDC system
Degradacija VOC z dvostopenjskim termi~nim in visokofrekven~nim DBDC-sistemom
O. G. Godoy-Cabrera, A. Mercado-Cabrera, R. López-Callejas, R. Valencia A., S. R. Barocio, A. E. Muñoz-Castro, R. Peña-Eguiluz,
A. de la Piedad-Beneitez . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Determination of the deformational energy during slab-width rolling on an edger mill
Dolo~anje deformacijske energije pri valjanju slabov na kr~ilnem ogrodju
F. Vode, A. Jakli~, R. Robi~, A. Ko{ir, F. Perko, J. Novak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Microstructure evaluation of an NRC-processed automotive component
Ocena mikrostrukture avtomobilske komponente, izdelane po postopku NRC
M. Torkar, B. Breskvar, M. Godec, P. Giordano, G. Chiarmetta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Properties and microstructure of very pure CrNiV steel
Lastnosti in mikrostruktura zelo ~istih jekel CrNi
S. Nìme~ek, P. Moty~ka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Mechanical and corrosion properties of AA8011 sheets and foils
Mehansko vedenje in korozijske lastnosti trakov in folij AA8011
K. Deliji}, V. Asanovi}, D. Radonji} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Flame temperature as a function of the combustion conditions of gaseous fuels
Temperatura plamena v odvisnosti od pogojev zgorevanja plinastih goriv
M. Lalovic, Z. Radovic, N. Jaukovic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Influence of micro-alloying on the phase transformations in cast manganese steels
Vpliv mikrolegiranja na fazne premene v litem manganovem jeklu
P. Moty~ka, J. Drnek, L. Kraus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A crack growth analysis in critical structural components
Analiza rasti razpoke v kriti~nih komponentah naprav
D. Semenski, @. Bo`i}, H. Wolf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Hot ductility of austenite stainless steel with a solidification structure
Vro~a preoblikovalnost avstenitnega nerjavnega jekla s strjevalno strukturo
F. Tehovnik, F. Vodopivec, L. Kosec, M. Godec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
LETNO KAZALO – INDEX
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 283
Isothermal decomposition of the β' phase in Cu-Zn-Al shape-memory alloys
Izotermna razgradnja β'-faze v zlitinah s spominom Cu-Zn-Al
V. Asanovi}, K. Deliji}, N. Jaukovi} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Estimation of the fatigue threshold values for a crack propagating through a bi-material interface taking into account
residual stresses
Ocena utrujenostnega praga za razpoko, ki napreduje skozi vmesno ploskev med dvema materialoma z upo{tevanjem
rezidualnih napetosti
L. Náhlík . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Fatigue behaviour of a cast nickel-based superalloy Inconel 792-5A at 700 °C
Utrujanje lite nikljeve superzlitine Inconel 792-5A pri 700 °C
M. Petrenec, K. Obrtlík, J. Polák, T. Kruml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
The application of linear elastic fracture mechanics to optimize the vacuum heat treatment and nitriding of hot-work tool
steels
Uporaba linearne elastomehanike loma pri optimiranju vakuumske toplotne obdelave in nitriranju orodnih jekel za delo v vro~em
V. Leskov{ek, B. [u{tar{i~, D. Nolan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
The influence of long-term service exposure on the structure and properties of high-temperature steels and alloys
Vpliv dolgotrajnega obratovanja pri visokih temperaturah na lastnosti jekel in zlitin, namenjenih uporabi v energetskih napravah
A. Rybnikov, L. Getsov, G. Pigrova, N. Dashunin, E. Manilova, N. Mozaiskaja . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
The influence of mim and sintering-process parameters on the mechanical properties of 316L SS
Vpliv procesnih parametrov brizganja in sintranja na mehanske lastnosti nerjavnega jekla 316L
B. Berginc, Z. Kampu{, B. [u{tar{i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
The behavior of fatigue-crack growth in shipbuilding steel using the ESACRACK approach
Modeliranje rasti utrujenostne razpoke jekla za ladijske plo~evine po postopku ESACRACK
M. Shehu, P. Huebner, M. Cukalla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
A comparison of experimental results and computations for cracked tubes subjected to internal pressure
Primerjava eksperimentalnih rezultatov in izra~una za cevi z razpoko, ki so obremenjeni z notranjo razpoko
J. Capelle, I. Dmytrakh, J. Gilgert, Ph. Jodin, G. Pluvinage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Fatigue problems of transmission belts: a viscoelastic analysis of the strain-accumulation process
Problem utrujanja pogonskih jermenov: viskoelasti~na analiza procesa akumuliranja deformacije
I. Emri, J. Kramar, A. Nikonov, U. Florjan~i~, A. Hribar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
A micro-macro analysis of the tool damage in precision forming
Mikro-makroanaliza po{kodb orodja za natan~no kovanje
T. Rodi~, J. Korelc, A. Pristov{ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
The stability of cast alloys and CVD coatings in a simulated biomass-combustion atmosphere
Stabilnost zlitin in CVD-prevlek v simulirani atmosferi zgorevanja biomas
D. A. Skobir, M. Spiegel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Fracture toughness of a high-strength low-alloy steel weldment
@ilavost loma zvara visokotrdnega malolegiranega jekla
J. Tuma, N. Gubeljak, B. [u{tar{i~, B. Bundara . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Solidification and fracture of an as-cast Ni alloy
Strjevanje in prelom lite nikljeve zlitine
M. Torkar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Laboratory's accreditation – confidence in the activities of conformity assessment of products
Laboratorijska akreditacija- zaupanje v aktivnost ocene ustreznosti proizvodov
A. Klobodanovi}, M. Oru~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Anorganski materiali – Inorganic materials
B2O3 and CaO in the magnesium oxide from seawater
B2O3 in CaO v magnezijevem oksidu iz morske vode
V. Martinac, M. Labor, N. Petric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Preparation of NiO/YSZ powders using a pechini-type method
Priprava NiO/YSZ prahov s prilagojeno pechini metodo
T. Razpotnik, V. Franceti~, J. Ma~ek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
[tudij mikrostrukture tiskanih slojev YSZ na podlagi Ni-YSZ
Microstructure characterisation of screen-printed layers of YSZ on Ni-YSZ substrate
M. Marin{ek, B. Kapun, A. Zupan~i~ Valant, K. Zupan, G. Kapun, J. Ma~ek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
LETNO KAZALO – INDEX
284 MATERIALI IN TEHNOLOGIJE 40 (2006) 6
Nastanek LaCrO3 med zgorevalno sintezo
LaCrO3 formation during combusttion synthesis
K. Zupan, M. Marin{ek, S. Pejovnik, T. Hrobat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Polimeri – Polymers
The characterization of polymer composites by thermogravimetry
Termogravimetri~na karakterizacija polimernih kompozitov
I. G. Popovi}, L. Katsikas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Supramolekularni poliuretani z azobenzenskimi skupinami
Supramolecular azobenzene polyurethanes
G. Ambro`i~, M. @igon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Mehanske lastnosti kav~ukovih zmesi na osnovi NBR
Mechanical properties of NBR based compounds
H. [ubic ml., Z. [u{teri~, M. @umer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Karakterizacija kopolimerov SEC in SEC-MALS asparaginske kisline in laktida
SEC and SEC-MALS characterization of copolymers of aspartic acid and lactide
M. Gri~ar, E. @agar, A. Kr`an, M. @igon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Behaviour and optimisation of multi-directional laminate specimens under delamination by bending
Vedenje in optimizacija ve~smernih vzorcev laminatov pri upogibu z delaminacijo
N. Ouali, A. Ahmed-Benyahia, A. Laksimi, T. Boukharouba . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Dinami~ne mehani~ne lastnosti elastomernih kompozitov s polnili nanovelikosti
Dynamic mechanical properties of elastomeric composites with nano-scale fillers
Z. [u{teri~, T. Kos, M. [u{tar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Vakuumska tehnika – Vacuum technique
Vacuum teaching for undergraduate students at the University of Coimbra
U~enje vakuuma za {tudente na Univerzi Coimbra
J.M.F. dos Santos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Plazemska sterilizacija bakterij s kisikovo plazmo
Oxygen plasma sterilization of bacteria
D. Vujo{evi}, Z. Vranica, A. Vesel, U. Cvelbar, M. Mozeti~, A. Drenik, T. Mozeti~, M. Klanj{ek-Gunde, N. Hauptman . . . . . . . . . . . . 227
Gradbeni materiali – Materials in civil engineering
The extraction of raw materials for the cement industry and nature conservation
Zagotavljanje primernih materialov za cementno industrijo s ciljem ohranjanja narave
@. Poga~nik, M. Stupar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Ocena odpornosti proti zmrzovanju gradbene keramike na podlagi direktnih in indirektnih metod
Frost resistance evaluation of building ceramics by indirect and direct methods
T. Kopar, J. Ranogajec, M. Radeka, R. Marinkovi}-Nedu~in, V. Ducman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
LETNO KAZALO – INDEX
MATERIALI IN TEHNOLOGIJE 40 (2006) 6 285

VACUUM HEAT TREATMENT
LABORATORY
Vacuum Brazing
Universally accepted as the most versatile method of joining metals. Vacuum Brazing is a precision metal joining
technique suitable for many component configurations in a wide range of materials.
ADVANTAGES
• Flux free process yields clean, high integrity joints
• Reproducible quality
• Components of dissimilar geometry or material type may be joined
• Uniform heating & cooling rates minimise distortion
• Fluxless brazing alloys ensure strong defect free joints
• Bright surface that dispense with expensive post cleaning operations
• Cost effective
Over five years of Vacuum Brazing expertise at IMT has created an unrivalled reputation for excellence and
quality.
Our experience in value engineering will often lead to the use of Vacuum Brazing as a cost effective solution to
modern technical problems in joining.
INDUSTRIES
• Aerospace • Hydraulics • Nuclear
• Mechanical • Pneumatics • Automotive
• Electronics • Marine
QUALITY ASSURANCE
Quality is fundamental to the IMT philosophy. The choice of process, all processing operations and process control
are continuously monitored by IMT Quality Control Department.
The high level of quality resulting from this tightly organised activity is recognised by government authorities,
industry and International companies.
IN[TITUT ZA KOVINSKE MATERIALE IN TEHNOLOGIJE
INSTITUTE OF METALS AND TECHNOLOGY
Lepi pot 11 • POB 431 • 1000 Ljubljana • Slovenia
tel.: +386 1 4701 800 • fax: +386 1 4701 939
www.imt.si • e-mail: imt imt.si
VACUUM HEAT TREATMENT
LABORATORY
Vacuum Heat Treatment
Vacuum Heat Treatment is recognised as a high quality cost effective and ultra clean method for processing a wide
range of components and materials currently in use in today's industry. The range of our equipment enables us to
heat treat most sizes of load, from small batches to work up to 350 mm diameter, 910 mm high, and weight up to
380 kg.
ADVANTAGES
• Clean, bright surface finish
• Minimal distortion
• Minimal post treatment operations, e.g., grinding or polishing
Five years of continual investment has ensured that VHTL maintains its position as market leader in the field of
high quality sub-contract metal processing.
We operate the latest generation of IPSEN VTTC furnace capable of processing components up to 350 mm in
diameter, which in addition to our high pressure, rapid quenching facilities increases the range of materials suitable
for Vacuum Heat Treatment.
TYPICAL APPLICATIOS
• Bright Annealing • Demagnetisation
• Bright Stress Relieving • Degassing
• Hardening/Tempering • Diffusion Treatments
• Brazing/Hardening/Tempering • Sintering
• Solution Treatment
QUALITY ASSURANCE
Quality is fundamental to the IMT philosophy. The choice of process, all processing operations and process control
are continuously monitored by IMT Quality Control Department.
The high level of quality resulting from this tightly organised activity is recognised by government authorities,
industry and International companies.
IN[TITUT ZA KOVINSKE MATERIALE IN TEHNOLOGIJE
INSTITUTE OF METALS AND TECHNOLOGY
Lepi pot 11 • POB 431 • 1000 Ljubljana • Slovenia
tel.: +386 1 4701 800 • fax: +386 1 4701 939
www.imt.si • e-mail: imt imt.si
Zavod za gradbeni{tvo Slovenije
Slovenian National Building and Civil Engineering Institute
Dimi~eva 12, 1000 Ljubljana, SLOVENIJA, Telefon: + 386 1/280 42 50, Telefaks: + 386 1/280 44 84
Elektronska po{ta: info@zag.si, WWW: http://www.zag.si/
• temeljne in uporabne raziskave
• presku{anje v akreditiranih laboratorijih (SA,
SWEDAC, PTB-DKD), potrjevanje skladnosti in certificiranje
gradbenih materialov, proizvodov in izvedenih del
• predkonkuren~ni razvoj na podro~ju gradbeni{tva
• razvoj novih metod presku{anja in meritev
• {tudije, preiskave, meritve, pregledi in opazovanja,
• ekspertno svetovanje in sodelovanje pri revizijah ter analize
stanja: gradbenih objektov, transportnih naprav,
prometnic, naravnega in bivalnega okolja
• kalibriranje in overjanje meril, etalonov in
referen~nih materialov
Materiali
mineralna veziva in malte
kamen in agregat
beton in betonski izdelki
kovine, korozija in protikorozijska za{~ita
keramika in ognjevzdr`ni materiali
polimeri
asfalti, bitumen in bitumenski proizvodi
Gradbena fizika
akustika
toplotna za{~ita
po`arna presku{anja
po`arno in`enirstvo
Konstrukcije
stavbe in mostovi
kovinske konstrukcije in transportne naprave
lesene konstrukcije
potresno in`enirstvo
dinamika konstrukcij
Geotehnika in prometnice
geomehanika in geotehnika okolja
vzdr`evanje in gospodarjenje s cestami
geotehni~no opazovanje
in`enirska geologija in mehanika hribin
Metrologija
Penjeni stekleni agregat: toplotno izolacijski
material, izdelan iz odpadnega stekla
Mineralo{ke preiskave naravnih in umetnih
nekovinskih materialov
Dolo~anje tla~ne trdnosti na preizku{ancu iz kamna
Dolo~itev dinami~nih karakteristik
nevezanih materialov s triosnim
cikli~nim aparatom

Lahkota prihodnosti
TALUM, d.d., KIDRI^EVO
Tovarni{ka ulica 10
2325 Kidri~evo, Slovenia
Telephone: +386 2 799 51 00
Telefax: +386 2 799 51 03
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NOVO!Izdal: In{titut za kovinske materiale in tehnologije, LjubljanaAvtor: Boris Ule
FIZIKALNA METALURGIJA
RE[ENE NALOGE
Delo je nekje vmesmed zbirko re{enih nalog in u~benikom
fizikalne metalurgije. Naloge v knjigi so re{ene v vseh
podrobnostih, ve~ino re{itev pa uvodoma dopolnjuje nekaj
teoreti~ne razlage. Pri vsaki nalogi sonavedeni vsi potrebni
podatki, da uporabnik pri samostojnem re{evanju ne bo
potreboval {e kak{nih drugih virov.^e pa `e, so ti navedeni
med tekstom, nekaj najbolj{ih del s podro~ja fizikalne
metalurgije pa je na{tetih v popisu literature na koncu
knjige.
Pri pripravi knjige je bilo uporabljeno obi~ajno didakti~no
na~elo, po katerem se vsako poglavje pri~ne z la`jimi,
kon~a pa z zahtevnej{imi nalogami. Nekatere izmed nalog
so zastavljene kot teoreti~ne, spet drugimpa je avtor sku{al
pridati {e prakti~no uporabnost. V zbirko so zato vklju~ene
tudi naloge, ki so pomembne za vsakdanjo in`enirsko
prakso. Tak{ne naloge na primer obravnavajo nekatera
vpra{anja toplotne obdelave ali pa dobo trajanja obreme-
njenihkovinskihmaterialov.
PRVA ZBIRKA RE[ENIH NALOG IZ FIZIKALNE METALURGIJE
Marec 2005
500 strani, 191 nalog, 221 slik in diagramov
ISBN 961-91448-1-3
Knjiga vsebuje devet poglavij:
(1) Kristalna zgradba kovin
(2) To~kaste napake
(3) Difuzija
(4) Strjevanje
(5) Dislo-kacije
(6) Mejne povr{ine
(7) Utrjevanje kovin
(8) Fazne premene
(9) Lom, utrujanje in lezenje
Temeljne informacije o najnovej{ih tehnologijah in zlitinah
Izdal: In{titut za kovinske materiale in tehnologije, Ljubljana
Avtor: Franc Vodopivec
KOVINE IN ZLITINE
kristalna zgradba, mikrostruktura, procesi, sestava in lastnosti
Kristalna zgradba in procesi
Mikrostruktura in procesi
Sestava in lastnosti kovinskih zlitin
Kristalna mre`a • to~kaste in linijske napake deformacija,
utrjevanje in spro{~anje, deformacijske energije termi~no
aktivirana plasti~na deformacija trdne raztopine, razgradnja in
utrjevanje kristalizacija taline fazne premene difuzija v
trdnem utrujenost prelom struktura in lastnosti povr{in
absorpcija in segregacije elektri~na prevodnost magnetizem
korozija in pasivnost povr{inska in notranja oksidacija.
Ravnote`ni faznim diagrami strjevanje in`enirskih zlitin;
segregacije in homogenizacija vro~a in hladna predelava jekla in
aluminijevih zlitin toplotna obdelava jekel in zlitin utrjevanje
povr{ine s termokemi~nimi in fizikalnimi postopki kovinski
kompoziti kovinska stekla mehansko legiranje nanozlitine
intermetalne spojine.
Temeljne zna~ilnosti in`enirskih zlitin obremenitve pri uporabi
metode karakterizacije jekla sive litine aluminij in zlitine
baker in zlitine titan in zlitine magnezij in zlitine cink, kositer
in svinec ter zlitine nikelj in kobalt ter zlitine kovine in zlitine
z visokim tali{~em plemenite kovine in zlitine mehko in
trdomagnetne zlitine zlitine za elektri~ne upore in kontakte
cermeti in trde kovine biokompatibilne zlitine.
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Delo povzema temeljna znanja o zgradbi kovin in zlitin na
treh redih velikosti, od atoma in kristalne mre`e do lastnosti
pri uporabi in povezavi med njihovimi lastnostmi,
mikrostrukturo in kemijsko sestavo. Dokumentirano je tudi z
izsledki iz slovenskih raziskovalnih ustanov in iz industrije,
ki proizvaja ali uporablja kovine in zlitine v Sloveniji.
Knjiga prina{a temeljne informacije o najnovej{ih tehno-
logijah in zlitinah, vse do amorfnih in nanokristalnih zlitin.
Za pripravo knjige je uporabljeno nad 30 monografij in nad
250 ~lankov iz {tevilnih najbolj kakovostnih inozemskih
strokovnih in znanstvenih revij iz let 1980 do 2001.
Opremljena je z 271 slikami in diagrami ter 167 analiti~nimi
odvisnostmi, ki opisujejo ravnote`na stanja in kinetiko
procesov. V knjigi je citirano ve~ kot 900 avtorjev, med njimi
ve~ kot 100 slovenskih. Vsebuje avtorsko in vsebinsko
kazalo. Knjiga bo dosegljiva tudi na CD plo{~ku.
PRVA SLOVENSKA ZNANSTVENA MONOGRAFIJA O TEMELJNIH ZNANJIH
ZGRADBE KOVIN IN ZLITIN
September 2002,
474 str., 271 slik, diagramov
ISBN 961-238-084-8
VSEBINA
NAVODILA AVTORJEM
BESEDILO ^LANKA (ROKOPIS IN ELEKTRONSKA OBLIKA)
Glavnemu uredniku je treba predlo`iti dve kopiji
rokopisa ~lanka, skupaj s povzetkom, klju~nimi bese-
dami in z ilustracijami. Prispevki morajo biti napisani v
slovenskem ali angle{kem jeziku; izvle~ki, klju~ne
besede, podpisi k slikam in naslovi tabel pa v obeh
jezikih.
Glavni urednik bo poskrbel za strokovno oceno
~lanka. Avtorji imajo pravico navesti imena (naslove in
telefonske {tevilke) treh ali {tirih oseb, ki so uspo-
sobljene strokovno oceniti njihov prispevek. Izbrani
recenzent ni nujno, da je iz predlo`enega seznama
avtorja. Nepopolni podatki o predlo`enih recenzentih
lahko upo~asnijo objavo rokopisa. Rokopis bo vrnjen
avtorju skupaj s pripombami recenzenta.
^e je ~lanek sprejet (po recenzentovem in lektorje-
vem pregledu), avtor vrne popravljen ~lanek uredni{tvu
(izpis na papirju, elektronska oblika, originalne slike) v
enem od bolj raz{irjenih urejevalnikov besedil: Word for
Windows ali Word Perfect. ^e avtor uporablja kak{en
drug urejevalnik, naj ga posname ali konvertira kon~ni
izdelek v navaden ASCII-format.
Priprava rokopisa
• Besedilo naj bo napisano na listih A4 z dvojnim
presledkom med vrsticami, ob levi strani s 3 cm
{irokim robom (da je mogo~e vna{ati popravke
lektorjev) na o{tevil~enih straneh.
• Formule so lahko v datoteki samo nazna~ene, na
izpisu pa ro~no izpisane.
• ^lanek v elektronski obliki lahko avtor posreduje
tudi po e-po{ti: mit@imt.si.
Opomba: V vseh primerih si izdajatelj pridr`uje pra-
vico odlo~anja, ali bo ~lanek sprejet za objavo ali ne.
Avtor prevzema vso odgovornost za svoj prispevek.
Predlo`eni prispevek ne sme biti v postopku za objavo v
kaki drugi publikaciji in avtor ne sme kr{iti pravic
kopiranja. Ko je prispevek sprejet za objavo, preidejo
avtorske pravice kopiranja na izdajatelja. Ta prenos
avtorskih pravic na izdajatelja zagotavlja naj{ir{e
reproduciranje.
Celoten rokopis ~lanka obsega:
• naslov ~lanka (v slovenskem in angle{kem jeziku)
• podatke o avtorjih
• izvle~ek (v slovenskem in angle{kem jeziku)
• klju~ne besede (v slovenskem in angle{kem jeziku)
• besedilo ~lanka (v slovenskem ali angle{kem jeziku)
• preglednice, tabele (glava tabele v slovenskem in
angle{kem jeziku)
• slike (risbe, fotografije)
• podnapise k slikam (v slovenskem in angle{kem
jeziku)
• pregled literature (v angle{kem jeziku)
^lanek naj bi bil ~im kraj{i in naj ne bi presegal 4–6
tiskanih strani, pregledni ~lanek 12 tiskanih strani,
prispevek s posvetovanj pa 2–4 tiskane strani.
Prva stran ~lanka
Naslov ~lanka naj bo natan~en toda tudi informativen
ter ne sme presegati ene vrstice teksta. Besede iz naslova
naj bodo primerne za indeksiranje in iskanje.
Sledijo podatki o avtorju(-jih), imenu in naslovu
institucije oz. laboratorija, kjer je delo nastalo.
Podatki o avtorju: ime (celo ime, ne samo za~etnica),
priimek, akademski naslov in poklic, e-po{ta, faks.
Izvle~ek
^lanek mora vsebovati izvle~ek, ki naj vsebuje
bistveno in kratko vsebino, sklepe ~lanka ter opozorilo
na kakr{nokoli novo informacijo, ki je predstavljena v
~lanku. Izvle~ek mora biti razumljiv kot samostojna
oblika. Napisan naj bo v preteklem ~asu, ker se nana{a
na delo, ki je bilo `e opravljeno. Sklicevanje na formule,
ena~be in vire literature v tekstu ni dovoljeno. Izogibati
se je treba manj znanim izrazom, kraticam in okraj{a-
vam.
Dol`ina izvle~ka naj bi bila do 250 besed.
Klju~ne besede
Avtor dolo~i do {est klju~nih besed po lastni presoji,
s katerimi natan~no dolo~i vsebino ~lanka in ki so
primerne za indeksiranje in iskanje.
Merske enote, ena~be
Obvezna je raba merskih enot, ki jih dolo~a Odredba
o merskih enotah (Ur. L. RS {t. 26/01), tj. enot medna-
rodnega sistema SI. Uporaba in pisava morata biti po tej
odredbi skladni s standardi SIST ISO 2955, serije SIST
ISO 31 in SIST ISO 1000.
Ena~be se ozna~ujejo ob desni strani besedila s
teko~o {tevilko v okroglih oklepajih.
Preglednice (tabele)
Preglednice (tabele) naj bodo napisane na lo~enih
listih in ne med besedilom, ozna~ene s primerno glavo
tabele.
V preglednicah in diagramih se ne uporabljajo izpi-
sana imena veli~in, ampak ustrezni simboli v skladu z
ISO 31. (Glavne smernice so v prispevku P. Glavi~,
Mednarodni standardi – veli~ine in enote, Materiali in
tehnologije, 37 (2003) 1–2, 79–84.)
Preglednice (tabele) morajo biti jasno citirane v
besedilu z arabskimi {tevilkami.
Preglednica (tabela) mora imeti naslov (v sloven-
skem in angle{kem jeziku), da je njen pomen razumljiv
tudi brez citiranja v besedilu.
Ilustracije
Ilustracije (risbe, diagrami, fotografije) morajo biti
o{tevil~ene, prilo`ene posebej in ne vstavljene (ali
nalepljene) med besedilom.
Diagrami in fotografije morajo biti izdelani od 1,5-
do 3-krat ve~ji od velikosti tiskanega diagrama in morajo
biti natan~no ozna~eni. Navadno so tiskani v {irini enega
stolpca (7,9 cm), razen v posebnih primerih (maks. {irina
≈16 cm). Neprimerna velikost ~rk na diagramu omogo~a
pomanj{avo le do optimalne ~itljivosti. ^rkovne oznake
na diagramu naj bodo take velikosti, da je po pomanj{avi
velikost {tevilk in (velikih) ~rk od 1,2 mm do 2,4 mm.
Pogosto so ~rte na diagramih pretanke v primerjavi s
celotnim diagramom.
Za vse slike po fotografskih posnetkih je treba
prilo`iti izvirne fotografije, ki so ostre, kontrastne in
primerno velike. Pomembno je, da fotografije niso `e
skenirane. ^e je treba, naj bo ozna~eno na hrbtni strani
slik, kje je njihov zgornji rob. Priporo~ljivo je primerno
pomanj{anje slike, ~e ni jasno, kateri njen detajl je
pomemben.
Diagrami in slike naj bodo narisani in posneti v
formatih BMP, TIF, JPG. Za risanje naj bo po mo`nosti
uporabljen program CorelDraw.
Vsi podpisi k slikam (v slovenskem in angle{kem
jeziku) naj bodo zbrani na lo~enem listu in ne med
besedilom.
Izdajatelj zahteva kvalitetne slike, ki omogo~ajo tudi
kvalitetno tiskanje. Izdajatelj praviloma ne sprejema
kopij slik in diagramov.
Ilustracije so lahko tiskane barvno, ~e uredni{tvo
presodi, da je to bistvenega pomena pri objavi. Izdajatelj
in avtor nosita vsak del dodatnih stro{kov. Nadaljnje
informacije o barvnih ilustracijah in stro{kih avtorjev so
dosegljive pri izdajatelju.
Na avtorjevo `eljo uredni{tvo vrne diagrame in slike,
ko je ~lanek objavljen.
Literatura
Literaturni viri so zbrani na koncu ~lanka in so
o{tevil~eni po vrstnem redu, kakor se pojavijo v ~lanku.
Vsak vir mora biti opremljen s podatki, ki omogo~ajo
bralcu, da ga lahko poi{~e.
Vsak literaturni vir mora biti popoln, in tako
okraj{ave ibid., idem., et al., etc., niso dovoljene.
Literaturni viri, ki se nana{ajo na {e neobjavljena ali
nesprejeta dela, naj se ne citirajo. Avtorjem pripo-
ro~amo, da ne navajajo ve~jega {tevila samocitatov.
Bibliografske navedbe naj bodo dosledno priprav-
ljene v angle{kem jeziku.
Knjige, periodi~ne publikacije, deli knjig, ~lanki v
periodi~nih publikacijah, patenti, elektronske mono-
grafije, ~lanki in drugi prispevki v elektronski obliki
morajo biti citirani kot npr.:
1. Monografije
Zgled: H. Ibach, H. Luth, Solid state physics, 2nd ed.,
Springer, Berlin 1991, 245
2. ^lanki v periodi~nih publikacijah
Zgled: H. J. Grabke, Kovine zlitine tehnologije, 27
(1993), 1–2, 9
3. Periodi~ne publikacije
Zgled: Kovine zlitine tehnologije. IMT Ljubljana,
1992–1999. Ljubljana: IMT, 1998. Text in Slovene
and English. ISSN 1318-0010
4. Prispevki v zbornikih posvetovanj
Zgled: I. Rak, M. Kocak, V. Gliha, N. Gubeljak:
Fracture behaviour of over-matched high strength
steel welds containing soft root layers, Proc. of the
2nd Inter. Symp. on Mis-Matching of Interfaces and
Welds, Reinsford, 1997, 627–641
5. ^lanki in drugi prispevki v elektronski obliki
Zgled: M. P. Wnuk: Principles of fracture mechanics
for space applications. Kovine zlitine tehnologije
[online]. 34, 1999, 6, 505–508 [cited 2000-01-30].
Available from World Wide Web:
http://www.imt.si/materiali-tehnologije/
AVTORSKI PREGLED ^LANKA
Avtorji prejmejo tiskan ~lanek v avtorski pregled.
Uredni{tvu ga morajo vrniti v dveh dneh, sicer si
uredni{tvo pridr`uje pravico, da objavi ~lanek brez
avtorskega pregleda.
SEPARATI
Avtorji prejmejo brezpla~no 20 izvodov separatov
objavljenega ~lanka. Dodatne izvode lahko avtor naro~i
po ceniku, ki ga dobi v uredni{tvu.
AVTORSKE PRAVICE
Avtor mora predlo`iti izjavo, da je besedilo njegovo
izvirno delo in ni bilo v taki obliki {e nikoli objavljeno.
Predlo`eni prispevek ne sme biti v postopku za objavo v
kaki drugi publikaciji. Deli ~lankov so lahko `e bili
predstavljeni kot referati. Z objavo preidejo avtorske
pravice na izdajatelja. Pri morebitnih kasnej{ih objavah,
mora biti periodi~na publikacija Materiali in tehnologije
navedena kot vir.
Uredni{tvo periodi~ne publikacije Materiali in
tehnologije:
• odlo~a o sprejemu ~lankov za objavo
• poskrbi za strokovne ocene in morebitne predloge za
kraj{anje ali izpopolnitev prispevka
• poskrbi za jezikovne popravke
Rokopisi ~lankov ostanejo v arhivu uredni{tva
periodi~ne publikacije Materiali in tehnologije.
DODATEK: ZGLED ZA UVELJAVLJEN NA^IN
PISANJA ^LANKA
NASLOV ^LANKA
Pravilen in dober naslov ~lanka vsebuje kar najmanj
mo`nih besed, ki najbolj ustrezno opi{ejo vsebino
prispevka.
Naslov mora
– biti natan~en in ne sme presegati ene vrstice teksta.
Naslova ne smemo
– pri~enjati z nepotrebnimi oz. odve~nimi besedami,
kot so "[tudij" ali "Preiskava"
– oblikovati v vpra{alni obliki.
IZVLE^EK
Izvle~ek naj bo skraj{ana oblika ~lanka, dol`ina ne
sme presegati 250 besed.
Napisan naj bo v preteklem ~asu, ker se nana{a na
delo, ki je bilo `e opravljeno.
Izvle~ek mora
– opisati glavni predmet in cilj preiskave
– povzeti rezultate
– oblikovati glavne sklepe
Izvle~ek ne sme
– posredovati informacije ali sklepov, ki niso del
~lanka
– citirati literature
1 UVOD
Namen pisanja uvoda je podati zadosti predhodnih
informacij, da bi bralec ~lanka lahko pravilno razumel in
ocenil rezultate {tudije. Kratko in jasno naj bo podan
namen pisanja prispevka.
Uvod naj bo napisan v sedanjem ~asu, ker se nana{a
na problem in osvojeno znanje problema na za~etku
preiskave.
Uvod mora
– jasno opisati naravo in obseg problema, ki ga
raziskuje avtor
– podati pregled najnovej{e literature, da bi pravilno
usmeril bralca
– podati uporabljeno metodo preiskave, in ~e je treba
tudi razloge za izbor dolo~ene metode
2 EKSPERIMENTALNI DEL
Eksperimentalni del prispevka mora podati vse
podrobnosti eksperimentalnih naprav in metod, ki so bile
uporabljene, da je avtor dosegel navedene rezultate.
Napisan naj bo v preteklem ~asu, pasivna oblika.
Eksperimentalni del mora
– vsebovati podrobnosti, ki se nana{ajo na opremo in
uporabljene materiale, njihovo koli~ino, tempe-
rature, ~ase itd.
– zagotoviti zadostno informacijo, ki bo omogo~ala
raziskovalcu istega znanstvenega podro~ja, da
preizkus lahko ponovi.
Eksperimentalni del ne sme
– navajati nobenih dose`enih rezultatov preiskave.
3 REZULTATI
Ta del mora podati celotno sliko vseh preizkusov, ne
da bi se ponavljale posamezne podrobnosti iz eksperi-
mentalnega dela. Podatki morajo biti jasni in natan~ni.
Avtor lahko uporabi diagrame in tabele, ~e je to
potrebno.
Ta del naj bo napisan v preteklem ~asu.
Rezultati ne smejo
– opisovati in navajati eksperimentalnih metod
– vsebovati diskusije o dose`enih rezultatih (Zaradi
narave nekaterih ~lankov je mo`no zdru`iti rezultate
in diskusijo v eno poglavje, da bi bil ~lanek bralcu
bolj jasen in la`je razumljiv.)
– vsebovati rezultatov ali podatkov, ki niso del
diskusije.
4 DISKUSIJA
Namen diskusije je podati na~ela, odnose in posplo-
{evanja, ki so bili prikazani v rezultatih.
Diskusija mora razjasniti pomen rezultatov in
primerjati sedanja dognanja s prej objavljenimi deli.
Diskusija naj bo napisana v sedanjem ali preteklem
~asu.
Diskusija mora
– razlo`iti rezultate in jih ne sme samo ponoviti
Diskusija se ne sme
– izogibati komentiranju rezultatov, ki niso povsem
ustrezni.
5 SKLEPI
Sklepi morajo biti kratki. Vsebujejo naj enega ali dva
sklepa, povzeta iz rezultatov in diskusije rezultatov.
^e je treba, naj bodo sklepi oblikovani po to~kah.
Sklepi morajo
– biti natan~ni in bralcu jasno razumljivi
Sklepi ne smejo
– biti ponovitev rezultatov
– biti enaki izvle~ku.
6 LITERATURA
INSTRUCTIONS FOR AUTHORS
SUBMISSION OF PAPERS (MANUSCRIPT + ELECTRONIC TEXT ON DISKETTE)
Two duplicate copies of the original manuscript
complete with abstract, key words and illustrations
should be submitted to the Editor-in-chief.
All contributions should be written in Slovene or
English, with title, abstract, key words and figure
captions in both languages. The Editor-in-chief will take
care of the review process.
Authors are encouraged to list the names, addresses
and telephone numbers of three or four individuals who
are qualified to serve as referees for their paper,
however, the refeeres selected by the Editor will not
necessarily be from the list suggested by the author.
Failure to provide information on several possible
referees may delay processing of the manuscript.
The manuscript will be returned to the author
together with the notes of the referees.
If the paper is accepted the author will be asked to
amend the manuscript in accordance with the referees’
comments (for both language and technical content) and
return it to the Editorial Board (hard copy plus electronic
form with original illustrations) in one of the wildely
used word-processing programs such as Word for
Windows or Word Perfect. If the author wishes to use
any other word-processing program the final product
should be converted into normal ASCII (text).
Preparation of the manuscript
• Manuscripts should be typed on A4 paper, double-
spaced, with 3 cm margins (for corrections) on
numbered pages.
• Contributions in electronic form can also be
submitted by e-mail: mit@imt.si.
Note: In all cases the Publisher reserves the right to
decide whether to accept the paper for publication.
The author should obtain all the necessary authority
for publication. Submission of an article implies it is not
under consideration for publication elsewhere and that
the author is satisfied that no copyright will be infringed.
Upon acceptance of an article, the copyright is transfered
to the publisher. This transfer will ensure the widest
possible dissemination of the article.
Style of manuscript:
• title of the paper (in Slovene and English)
• authors’ full names with affiliations
• abstract (in Slovene and English)
• key words (in Slovene and English)
• text of the paper (in Slovene or English)
• tables (table titles in Slovene and English)
• illustrations (drawings or photographs)
• captions to figures (in Slovene and English)
• references (in English)
The paper should be as short as possible and should
not exceed 4–6 print pages. Review papers may be up to
12 printed pages, papers presented at conferences should
be restricted to 2–4 printed pages.
Title page
Papers should be headed by a concise but informative
title which should not exceed one line, words from the
title should be suitable for indexing and searching.
The title should be followed by the name(s) of the
author(s) and by the name and address of the institu-
tion(s) or laboratory(ies) where the work was carried out.
Telephone and fax numbers as well as an e-mail address
for a contact author should also be supplied.
Abstract
Papers must include an abstract. This summary
should present a brief and factual account of the content
and conclusions of the paper and an indication of any
new information presented in the paper. The abstract
should be understandable in isolation. The abstract
should be written in the past tense, because it refers to
work which was already done. References to formulae,
equations and references that appear in the text is not
allowed. Uncommon expressions and abbreviations
should be avoided.
The length of the abstract should not exceed 250
words.
Key words
The author may supply up to six key words, that
describe the content of the article and are suitable for
indexing and searching.
Symbols, equations (units of measurement)
Units of measurement should comply with the Law
of Units of Measurement and Measures (Official Gazette
of the Republic of Slovenia 2001/26) i.e. international SI
units. Equations should be marked on the right-hand side
of the text with numbers in round brackets.
Tables
Tables should be typed on separate sheets.
Written names of quantities should not be used in
tables and diagrams, only the corresponding symbols,
according to ISO 2955, series ISO 31 and ISO 1000.
Tables should be clearly referred to in the text using
Arabic numerals.
Each table should have a title which makes the
general meaning understandable without reference to the
text.
Ilustrations
Ilustrations (drawings, diagrams, photographs)
should be numbered and provided separately, not
inserted in the text.
The drawings or gloss prints for the line pictures
should be 1.5–3 times larger than the printed size of the
figures and should contain carefully applied lettering.
Figures are reduced to a single-column width (7.9 cm)
except in special cases (max. printed size ≈16 cm).
Inappropriately sized lettering on a figure may
prevent its reduction to the size optimum for its
information content.
The lettering used on a figure should be chosen so
that after reduction the height of numbers and capital
letters falls within the range (1.2–2.4) mm.
Lines and arrows should also be of sufficient
thickness so as to remain clear after the reduction
process.
The photographs supplied for reproduction should be
original, sharp, with good contrast and of appropriate
size. It is important that the photographs supplied are not
already screened. When necessary, the top side of a
photograph should be marked on the back. A reduction
factor should be recommended for a photo when it is not
obvious what detail in the photo is of interest.
Diagrams and figures should be drawn and saved in
any supported format, e.g. BMP, GIF, JPG. Use Correl
Draw if available, since figures can be saved as vector
images.
Figure captions (in Slovene and English) should be
listed together at the end of the manuscript and not
inserted in the text.
The publisher reqiures a set of good quality drawings
and photographs to ensure good quality printing. Photo
copies cannot be accepted.
Illustrations can be printed in colour when they are
judged by the Editor to be essential to the presentation.
The publisher and the author will each bear part of the
extra costs involved. Further information concerning
colour illustrations and the costs to the author can be
obtained from the publisher.
Upon request original drawings and photographs will
be returned after publication of the paper.
References
The references should be collected at the end of the
article, and numbered in the order of their appearance in
the text.
Each reference should be complete, the use of ibid.,
idem., et al., etc. is not permitted.
References to unpublished or not readily accessible
reports should be avoided.
References should be cited in English.
We recommend the authors to avoid self-citing in the
references.
In the list of references monographs, articles in
journals, journals, contributions to conference proceed-
ings, patent documents, electronic monographs, articles
and other electronic documents should be cited in
accordance with the following examples:
1. Monographs
Example: H. Ibach, H. Luth, Solid State physics, 2nd
ed., Springer, Berlin 1991, 245
2. Articles in journals
Example: H. J. Grabke, Kovine zlitine tehnologije,
27 (1993), 1–2, 9
3. Journals
Example: Kovine zlitine tehnologije, IMT Ljubljana,
1992–1999, Ljubljana, IMT, 1998. Text in Slovene
and English. ISSN 1318-0010
4. Contributions to conference proceedings
Examples: I. Rak, M. Kocak, V. Gliha, N. Gubeljak:
Fracture behaviour of over-matched high strength
steel welds containing soft root layers, Proc. of the 2nd
Inter. Symp. on Mis-Matching of Interfaces and
Welds, Reinsford, 1997, 627–641
5. Articles and other contributions in electronic form
Example: M. P. Wnuk: Principles of fracture
mechanics for space applications. Kovine zlitine
tehnologije [online]. 34, 1999, 6, 505–508 [cited
2000-01-30]. Available from World Wide Web:
http://www.imt.si/materiali-tehnologije
PROOFS
Authors will receive a set of proofs. They are
requested to return the proofs with any corrections
within two days. In the case of a delay the Editorial
Board reserves the right to publish the article without the
author’s proofs.
OFFPRINTS
A total of 20 prints of each article will be supplied
free of charge to the author(s). Additional offprints can
be ordered, prices are available from the Editorial Board.
COPYRIGHT
In addition to the paper, authors must also enclose a
written statement that the paper is original work and has
not been published in this form anywhere else and that it
is not under consideration for publication elsewhere.
Parts of the paper may have been given in the form of
reports.
On publication, copyright will pass to the publisher.
The Journal of Materials and Technology must be stated
as the source in all later publications.
The Editorial Board of the Journal of Materials and
Technology:
• decide whether to accept a paper for publication;
• obtain professional reviewers for papers and decide
on any proposals to shorten or extend them;
• obtain correct terminology and edit language.
Manuscripts of papers will be kept in the archives of
the journal: Materials and Technology.
ADDITION: INSTRUCTIONS FOR AUTHORS
WRITING A TITLE
A good Title will have the fewest possible words that
adequately describe the contents of the paper.
The Title should:
– Be concise and not exceed a single line of text.
The Title should not:
– Begin with the waste words such as "Study of" or
"An investigation";
– Be in the form of a question.
PREPARING THE ABSTRACT
The Abstract should be viewed as a miniversion of
the paper and not exceed 250 words.
The Abstract should be written in the past tense,
because it refers to work already done.
The Abstract should:
– State the principal objectives and scope of the
investigation;
– Describe the methodology employed;
– Summarize the results;
– State the principal conclusions.
The Abstract should not:
– Give information or conclusions that are not
included in the paper;
– Cite references to the literature.
1 WRITING THE INTRODUCTION
The purpose of the Introduction is to supply
sufficient background information to allow the reader to
understand and evaluate the results of the present study.
If should state briefly and clearly the purpose in writing
the paper.
Much of the Introduction should be written in the
present tense, because it relates to the problem and the
established knowledge relating to the problem at the start
of the work.
The Introduction should:
– Present as clearly as possible the nature and scope of
the problem investigated;
– Review recent literature to orient the reader;
– It should state the method of the investigation, and if
necessary the reasons for the choice of a particular
method.
2 THE EXPERIMENTAL SECTION
The Experimental section of the paper must give full
details of the experimental apparatus and the methods
used in obtaining the results.
It is recommended that authors use passive language
in the past tense.
The Experimental section should:
– Include accurate details relating to the equipment
and materials used, including quantities, tempera-
tures, times etc.
– Provide sufficient information for a colleague in the
same field to reproduce the experiment.
The Experimental section should not:
– Introduce any of the results obtained.
3 WRITING THE RESULTS SECTION
The Results section should provide an overall picture
of the experiments without repeating any of the details in
the Experimental section. The data should be presented
clearly and concisely, using graphs and tables where
appropriate.
The Results section should be written in the past
tense, using a mixture of passive and active language.
The Results section should not:
– Describe any experimental methods;
– Include any discussion of the data obtained (Because
of the nature of some papers it may be appropriate to
combine the Results and Discussion sections into a
single section to improve clarity and make it easier
for the reader.);
– Contain results or data which play no part in the
Discussion.
4 THE DISCUSSION
The purpose of the Discussion is present the
principles, relationships, and generalisations shown by
the Results.
The Discussion must make clear the significance of
the Results and compare the findings with previously
published work.
The Discussion should be written using both the
present and past tenses. Active and passive language
should be used to enhance the readability.
The Discussion should:
– Discuss the results not simply repeat them.
The Discussion should not:
– Avoid commenting on results which do not quite fit.
5 THE CONCLUSIONS
The Conclusion section should be short. It will
present one or more conclusions which have be drawn
from the Results and the subsequent Discussion.
If appropriate, the conclusions should be presented in
point form.
The Conclusions should:
– Be concise and easily understood by the reader.
The Conclusions should not:
– Be a re-statement of the results;
– Be the same as the Abstract.
6 REFERENCES