Dislocation Relaxation Processes in Metals

Original contr ibut ions on d i s loca t ion re laxa t ion e f f e c t s , submitted t o t h i s conference, a r e introduced. The contr ibut ions a r e concerned with i n t r i n s i c d i s loca t ion relaxat ion e f f e c t s a s well a s with some dis locat ionpoint defect in te rac t ions , espec ia l ly hydrogen-disl ocation i n t e r a c t i o n . In f .c.c. metals, the kink-pair formation model f o r the Bordoni peaks obtained f u r t h e r support by new experiments. In b . c . c , metals, by experiments on high puri ty and hydrogen charged specimens considerable progress has been achieved i n the understanding of the mechanisms responsible f o r the numerous relaxat ion peaks: a general agreement i s obtained f o r the main i n t r i n s i c and hydrogen induced processes. 1. Introduct ion.In t h i s paper we introduce or ig ina l contributions submitted to t h i s conference, which a r e concerned with i n t r i n s i c d i s loca t ion re laxa t ion e f f e c t s a s well as with some dis locat ion-point defec t in te rac t ions . The or ig ina l contr ibut ions a r e quoted here with the names of the authors , o ther references a r e given with numbers of a reference 1 i s t . His to r ica l ly , i n f .c .c . metals a c l e a r separat ion i s we1 1 establ ished between i n t r i n s i c d i s loca t ion processes (Bordoni peaks) and dis locat ion-point defec t i n t e r ac t ion e f f e c t s . Mobile d i s loca t ion segments may i n t e r a c t with point defec t s which a r e i n t r i n s i c and mobile (Hasiguti peaks), e x t r i n s i c and mobile ( e . g . hydrogen dragging e f f e c t s o r more general Snoek-Koester peaks, o r immobile (unpinning peaks). Such a c l a s s i f i c a t i o n scheme may be i n s u f f i c i e n t f o r an exact d e f i n i t i o n of a mechanism, but i t may serve a s a f i r s t guide. A t t h i s conference a considerable number of contr ibut ions i s concerned with b.c .c . metals. Here such a c l e a r separat ion of i n t r i n s i c d i s loca t ion e f f e c t s i s par t ly a problem. Especially i n V , Nb, Ta i n t e r s t i t i a l so lu te atoms (H,O,N,C) a r e always present i n various concentration ranges (1-1000 atppm), and ul t ra-high vacuum ( U H V ) techniques a r e required t o reduce the i n t e r s t i t i a l s o l u t e content . In Nb, Ta the order of 1 atppm i n t e r s t i t i a l s o l u t e concentration can be obtained. Even a t such a low level in te rac t ion e f f e c t s with d i s loca t ions may appear. For low temperatures the in te rac t ion with mobile H has t o be considered, f o r high temperatures (T>400 K) in te rac t ions with mobile 0 , N, C may become important. Therefore i t i s much more d i f f i c u l t i n b .c .c . metals t o d i s t inguish between int r i n s i c d i s loca t ion e f f e c t s and dis locat ion-impuri ty in te rac t ions . U H V pur i f i ca t ion Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981502 C5-26 JOURNAZ. DE PHYSIQUE techniques l e t achieve considerable progress r e c e n t l y and the i n t r i n s i c d i s l o c a t i o n processes i n b.c.c. metals as w e l l as s tud ies on s p e c i f i c d i s l o c a t i o n p o i n t de fec t i n t e r a c t i o n s has become a ~ a j o r t o p i c o f t h i s session. I n t r i n s i c d i s l o c a t i o n r e l a x a t i o n e f f e c t s i n f .c.c. metals (Bordoni peaks) are p resen t l y considered as f a i r l y w e l l understood [I]. This i s r e f l e c t e d i n a lower number o f o r i g i n a l con t r ibu t ions t o t h i s top ic . However, the presented papers g ive answer t o some impor tant open questions. General ly speaking, we are i n a phase o f cons o l i d a t i o n of the k i n k p a i r formation model f o r the Bordoni peaks. Inves t iga t ions are extended a lso t o hexagonal nletals, which show s i m i l a r behaviour as f.c.c. metals. A h i g h l i g h t o f our session c e r t a i n l y i s the presentat ion o f resu l t s , obtained w i t h a new experimental technique, which can d e l i v e r d i r e c t l y in fo rmat ion on the under ly ing mechanism o f a r e l a x a t i o n e f f e c t (Gremaud, Beno i t ) . Some con t r ibu t ions are concerned w i t h extreme mate r ia l s . One paper deals w i t h s o l i d ~ e ~ , which e x i s t s under h igh pressure a t u l t r a l o w temperatures i n a b.c.c. s t ruc tu re , where d i s l o c a t i o n e f f e c t s have been studied (Iwasa, Saito, Suzuki). Less extrem, b u t s t i l l a chal lenge f o r the exper imenta l i s t a re i n v e s t i g a t i o n s on a l k a l i metal s i n g l e c r y s t a l s , on which systematic s tud ies on d i s l o c a t i o n r e l a x a t i o n e f f e c t s have been presented (Hamnerschmid, Kirchner, Schoeck). Several papers are concerned w i t h hydrogen-dislocat ion i n t e r a c t i o n s i n metals and a l l o y s o f d i f f e r e n t s t ruc tu re , p a r t l y by techniques s e n s i t i v e t o sur face condit i o n s and w i t h q u i t e d i f f e r e n t i n t e n t i o n s . We mention a lso a paper on f a t i g u e i n Cu studied by i n t e r n a l f r i c t i o n technique (Mi zubayachi , Okuda) . I n the remaininq p a r t o f t h i s paper we w i l l review some new r e s u l t obtained on b.c.c. and f . c .c . metals. 2. Dis loca t ion r e l a x a t i o n peaks i n b.c.c. metals 2.1 Nomenclature.Chambers [21 c a l l e d the peaks a,B,y i n the order o f increasing temperature, where a and y were considered as i n t r i n s i c d i s l o c a t i o n r e l a x a t i o n peaks, B as due t o d i s l o c a t i o n p o i n t de fec t i n t e r a c t i o n s . La te r a' was observed as a low temperature subpeak o f a. The Grenoble group in t roduced f u r t h e r Pa o r B f o r i n d i c a t i n g i n t e r a c t i o n e f f e c t s Y between d i s l o c a t i o n segments mobi le i n the a o r y regime respec t i ve ly and i n t e r a c t i n g w i t h i n t e r s t i t i a l so lu te atoms (H,O,N,C), and B1, B2 f o r i n t e r a c t i o n processes w i t h i n t r i n s i c p o i n t defects. Three remarks should be added: (1) The a peak i n Ho (Grau, Schul tz) , which can be s tudied i n h igh p u r i t y samples i n an convenient temperature regime, has been separated i n 4 subpeaks, c a l l e d al..a4 ( i n t h e order o f decreasing temperature), ( 2 ) I n V, Nb, Ta the peaks c a l l e d "a" i n the past are due t o hydrogen decorated d i s l o c a t i o n segments (see [ 3 ] , R i t c h i e ' s review; Maul, Schultz; Okuda, Mizubayashi e t a1 .). (3 ) R i t c h i e i n h i s review suggests t o preserve a' f o r geometrical k i n k m ig ra t ion i n screw components (GKM(B)), and a f o r k i n k p a i r formation i n non screws (KPF(1) ) . 2 . 2 Low temperature d i s l o c a t i o n r e l a x a t i o n e f f e c t s i n b.c.c. metals.D is loca t ion e f f e c t s f r e e from in te r fe rence w i t h H so lu te atoms were s tud ied i n d e t a i l i n Fe and Mo. One observes i n both metals a complex a peak, i n Fe usua l l y 2 subpeaks are re ported, i n Mo there e x i s t d i s t i n g t l y more than 2, probably 4 subpeaks [4 ] . A process, r e l a t e d t o i n t r i n s i c p o i n t defects, appears i n Mo as a h igh temperature shoulder o f a. The 6 process i n Fe shows an evo lu t ion and f i n a l l y a t ransformat ion i n t o peak a i n the cours o f anneal ing [5 ] . The c h a r a c t e r i s t i c in f luence o f anneal ing i n the temperat u r e regime o f stage 111 recovery ( p o i n t de fec t recovery) as repor ted i n [51 can be seen more o r less c lea r l y i n a l l b.c.c. metals, i nves t iga ted so f a r 163. The 6 peaks a re considered as the analogous t o the H a s i y t i peaks i n f .c .c . metals. They requ i re the presence o f i n t r i n s i c atomic defects, however, 1 ess i s known f o r the 6 peaks. Here i s an open f i e l d f o r the f u t u r e . For an deeper understanding one has t o consider the m o b i l i t y o f p o i n t defects i n b.c.c. metals. Below we g ive t h e temperatures f o r the onset o f de fec t m o b i l i t y f o r some b.c.c. metals: Fe (125 K, 250 K), Mo (35 K/500 K), W (27 K/800 K), Nb (<8 K, 250 K), Ta (<8 K, 300 K). The indecated temperatures are recovery temperatures f o r p o i n t defects created by i r r a d i a t i o n [7 ] . It should be noted t h a t i n terms o f a t w o i n t e r s t i t i a l model i t i s expected t h a t p l a s t i c deformation creates on ly i n t e r s t i t i a l atoms which become mobi l a t h igher temperatures, i n the so c a l l e d stage I 1 1 ( t h e h igher temperature i n d i c a t e d above). Whereas i n a o n e i n t e r s t i t i a l model deformation induced i n t e r s t i t i a l atoms should migrate a t the lower temperature, i nd ica ted above. The reader may note t h a t de fec t m o b i l i t y i n Fe s t a r t s a t 125 K, i n Nb below 8 K. A c r i t i c a l examination o f the e v o l u t i o n o f the low temperature d i s l o c a t i o n i n t e r n a l f r i c t i o n peaks w i l l be i n t e r e s t i n g . We t u r n s h o r t l y t o the subpeaks o f a. I n Yo, a c t i v a t i o n parameters, espec ia l l y a c t i v a t i o n volumes ( f o r d e t a i l s see [4 ] ) are compatible w i t h the f o l lowing i n t e r p r e t a t i o n : al-KPF (L), a3,aq-GKM (8) f o r two d i f f e r e n t geometr ical kinks, e.g. K: and K: [81. I n Fe two processes of a are separated. A general view s i m i l a r as i n Mo (GKM(0) and KPF (I)) has been obta ined by AstiP, Peyrade, Groh. However, Yagalas, Moser, have n o t found support f o r a GKM component. Microdeformation r e s u l t s conf i rm i n Fe t h a t a main component o f ci i s due t o KPF (I) (San Juan, No, Fantozzi, Esnouf, Vanoni). Magalas, Moser suggest t h a t d i s l o c a t i o n s w i t h d i f f e r e n t Burgers' vectors may be responsib le f o r the subst ructure o f a. I n V, Nb, Ta small amounts of hydrogen ( 2 1 atppm) create H-Snoek-Koester peaks, which were c a l l e d "a peaks" i n the past, and which mask the i n t r i n s i c d i s l o c a t i o n re l a x a t i o n e f f e c t s . I t i s hoped t h a t the d e t a i l e d i n v e s t i g a t i o n ~ o f Maul e t a l . [3 ] on Nb w i t h c o n t r o l l e d amounts of H w i l l end a long standing controversy concerning t h i s po in t . Th is view i s confirmed by Okuda, Mizubayachi, Kuramochi e t a l . . S t i l l open i s a f i n a l understanding o f the combined a c t i o n o f H and 0 on the r e l a x a t i o n s t reng th and the f i n e s t r u c t u r e o f the i n t e r a c t i o n peaks. C5-28 JOURNAL DE PHYSIQUE 2.3 H igh temperature peaks i n b .c .c . meta ls . There i s general agreement t o r e l a t e t h e y peak t o KPF (El ) , i . e . t o correspond t o t h e phenomenon c o n t r o l l i n g t h e low temp e r a t u r e p l a s t i c i t y o f b.c.c. p e t a l s . The y peak i s s t u d i e d i n Ta (Rodr ian, S c h u l t z ) , Mo (Grau, S c h u l t z ) , Nb (DeLima, B e n o i t ) , Fe ( A s t i $ , Peyrade, Groh) and p resen ts ve ry c l osed c h a r a c t e r i s t i c s : i t s temperature i s near t h e knee temperature o f t h e f l o w s t ress tempera tu re curve, i t s w i d t h i s near t h e Debye w i d t h and i t shows a tendency t o anneal o u t q u i c k l y . I n Nb [91 and Fe [ l o ] t h e i n s t a b i l i t y o f t h e y peak i s s t u d i e d i n d e t a i l and i t i s shown t h a t i t i s connected w i t h t h e i n s t a b i l i t y o f t h e screw n e t work. Long s t r a i g h t screw d i s l o c a t i o n s , as p resen t a f t e r low temperature deformat ion , a r e expected t o bow o u t under t he i n f l u e n c e o f i n t e r n a l s t resses , as soon as t h e temp e r a t u r e of t h e y peak i s reached. Thereby l o w e r i n g t h e l e n g t h o f screw components ( A s t i 6 e t a l . [ l o ] ) . Exper iments on Mo [ 4 ] a re a l s o i n l i n e w i t h these suggest ions and i n d i c a t e t h e r e d u c t i o n o f screw components as w e l l as o f i n t e r n a l s t resses i n t h e y regime. The s i t u a t i o n i n Ta [I11 i s more compl ica ted. A t t h e peak temperature 0 s o l u t e atoms become mobi leand p i n n i n g e f f e c t s i n t e r f e r e w i t h changes o f t h e screw d i s l o c a t i o n s t r u c t u r e . A subpeak, y2 i s s t a b l e i n t h e presence o f 0 s o l u t e atoms and Rodr ian [ 9 1 g i v e s arguments t h a t y2 i s due t o GKM (0), where t h e k i n k s a re decora ted w i t h mobi l oxygen atoms. A y peak can be observed a l s o i n K (Hammerschmid, K i r chne r , Schoeck) and these obse rva t i ons suppo r t t h e i d e a t h a t t h e s p e c i f i c p r o p e r t i e s of screw d i s l o c a t i o n s a r e of c r y s t a l l o g r a p h i c o r i g i n and n o t a phenomenon preserved t o t r a n s i t i o n meta ls . Some r e s u l t s on t h e Snoek-Koester peak (SK peak) o f 0 o r C a r e presented. Here an examinat ion o f a r e c e n t t h e o r y by Seeger [12 ] i s o f i n t e r e s t . Up t o now t h e expe r imen ta l r e s u l t s presented a r e n o t d e t a i l e d enough t o g i v e a f i n a l e v a l u a t i o n . Fo r Ta-0 (Rodr ian, S c h u l t z ) agreement o r a t l e a s t cons i s tency w i t h t h e t h e o r e t i c a l p red i c t i o n s has been obta ined. F o r Fe-C, Magalas, Moser c o u l d n o t f i n d agreement w i t h Seeger 's p r e d i c t i o n s . I t shou ld be n o t i c e d t h a t Rodr ian f o r Ta-0 used sma l l i m p u r i t y concen t ra t i ons (25 atppm 0 ) , whereas Magalas e t a l . worked i n range o f high concent r a t i o n s (1000 atppm C). I t i s i n t e r e s t i n q t o n o t e t h a t Magalas e t a l . c o n f i r m t h a t t h e SK peak develops a f t e r h e a t i n g t o 6 0 0 K , s u p p o r t i n n t h e sugges t i on o f Mondino, Seeger [13] on carbon-vacancy p a i r d i s s o c i a t i o n . 2.4 Conclusions f o r b . c . c . me ta l s . A t t h i s conference i t appears c l e a r l y t h a t a c h a r a c t e r i s t i c r e l a x a t i o n spectrum can be proposed f o r d i s l o c a t i o n s i n b.c.c. meta ls : 3 KPF on non-screw d i s l o c a t i o n s i s l o c a t e d a t l o w temperatures w i t h ~ = 1 0 ' p b (H a c t i v a t i o n entha lpy , p shear modulus, b Burgers v e c t o r ) KPF on screw d i s l o c a t i o n s appears near t h e knee temperature o f t h e f l o w s t r e s s temperature cu rve w i t h ~ ~ 1 0 ' p b3 GKM peaks a r e l o c a t e d a t low temperatures a t t h e low temperature s i d e o f t h e KPF peak on non-screws. Here f u r t h e r i n v e s t i g a t i o n s w i l l be app rec ia ted i n t e r a c t i o n peaks between H and d i s l o c a t i o n segments, (H-Snoek-Koester peaks), appear a t i n t e r m e d i a t e temperatures. I n V, Nb, Ta these peaks ve ry o f t e n dominate t h e l ow temperature spectrum. The Snoek-Koester peaks due t o 0, N, C i n t e r s t i t i a l s o l u t e atoms r e q u i r e f u r t h e r sys tema t i c obse rva t i ons . a t l o w e s t temperatures, below 10 K, s t i l l mob i l e d i s l o c a t i o n segments a r e present, p robab l y geometr ica l k i n k s i n non-screw d i s l o c a t i o n s . 3. D i s l o c a t i o n r e l a x a t i o n peaks i n f . c . c . meta ls . I n Cu and d i l u t e Cu-Au a l l o y s , Schulz and Lenz separa te an u l t r a s o n i c a t t e n u a t i o n (U.S.A.) spectrum w i t h d i f f e r e n t components due t o d i s l o c a t i o n resonance, KPF and phonon e l e c t r o n i n t e r a c t i o n . They f i n d t h e 2 Bordoni peaks i n t h e 10-50 YHz range and c o n f i r m i n t h i s range t h e w e l l known va lues H ~ 0 . 1 1 eV and s f o r t h e main peak. L a u z i e r and M i n i e r i nves t i g a t e t he s u b s t r u c t u r e o f t h e Bordoni peak i n Cu, w i t h t h e h e l p o f e l e c t r o n i r r a d i a t i o n s and e l e c t r o n m ic roscop i c obse rva t i ons and propose t h a t t he w i d t h o f t h e Bordoni peaks cannot be e x p l a i n e d o n l y b y a H o r r o d i s t r i b u t i o n b u t must i n c l u d e r e l a x a t i o n o f d i f f e r e n t t ypes o f d i s l o c a t i o n s as suggested by Thompson and Holmes [14l. These r e s u l t s a re i m p o r t a n t a l s o f o r p o i n t d e f e c t s t u d i e s i n i r r a d i a t e d meta ls , where d i s l o c a t i o n s a re used as a probe f o r m i g r a t i n g de fec t s . A new exper imenta l techn ique u s i n g U.S.A. measurements d u r i n g low f requency s t r a i n i n g o f t h e specimen i s presented by Gremaud and Beno i t : they c o n f i r m t h a t t h e Bordoni r e 1 a x a t i o n i n A1 must be assoc ia ted w i t h KPF on d i s l o c a t i o n s . D i r e c t measurements o f t h e i n t e r n a l s t r e s s i n s t r a i n e d A1 specimens, by d i p t e s t method, a r e per formed by Ch i co i s , Hamel, Fougcres, Esnouf, Fan tozz i , Perez; t hey c o n f i r m t h e d i r e c t amp1 i tude c o r r e l a t i o n between t h e i n t e r n a l s t r e s s and t h e Bordoni r e 1 a x a t i o n i .e. t h e Park c o n d i t i o n . By a s tudy on deformed and H charged Ni , Tanaka, Atsumi, Yamada, show t h a t H developpes a H d i s l o c a t i o n i n t e r a c t i o n peak a t t h e expense o f t h e Bordoni peak. These two peaks seem t o be s i m i l a r t o t h e X and Y peaks shownby t h e exper iments o f Besson and Boch [15], c o n f i r m i n g t h a t t h e l ower temperature peak i s t h e composed Bordoni peak (Y ) and t h e o t h e r ( X ) an e x t r i n s i c peak. The work o f Seyed Reihani , Esnouf, Fantozz i , Revel , on Mg w i t h d i f f e r e n t p u r i t i e s , show c l e a r l y t h a t t h e pure Mg spectrum i s v e r y s i m i l a r as t h e A1 spectrum a f t e r deformat ion ,on t h e c o n t r a r y w i t h t h e l a r g e peak observed i n l e s s pu re Mg; t h i s l a r g e peak i s caused by d i s l o c a t i o n dep inn ing. As a conc lus ion t h e p resen t s t u d i e s on f .c .c . me ta l s c o n f i r m t h e main cha rac te r i s t i c s o f t h e Bordoni r e l a x a t i o n peaks. F.c.c. me ta l s ( i n c l u d i n g N i ) and h.c.p. meta ls seem t o show an u n i f o r m spectrum w i t h 2 Bordoni r e l a x a t i o n peaks l o c a t e d a t low temperature, b u t exper iments on o t h e r ( t h a n Mg) h.c.p. me ta l s o f h i g h p u r i t y a r e needed t o c o n f i r m t h i s p o i n t o f view. The i n t e r p r e t a t i o n o f Bordoni r e l a x a t i o n as KPF on d i s l o c a t i o n s i s w e l l conf i rmed, b u t perhaps a t t e n t i o n must be focussed on t h e d i f f e r e n t types o f d i s l o c a t i o n s concerned w i t h Bordoni r e l a x a t i o n peaks. C5-30 JOURNAL DE PHYSIQUE References.1. G. Fantozzi, W. Benoit , C. Esnouf, and J. Perez, Annales de Physique 4, 7 (1979) 2. R. H. Chambers, Physical Acoust ics, v o l . 111 A, p. 123 (Ed. W. P. Mason) Academic Press, New York, London (1966) 3. M. Maul and H. Schultz, t o be publ . S c r i p t a Met. see a lso: M. Maul, D i s s e r t a t i o n U n i v e r s i t P t S t u t t g a r t (1981) 4. R. Grau, D i s s e r t a t i o n U n i v e r s i t a t S t u t t g a r t (1981) 5. I . G. R i t ch ie , J. F. Dufresne, and P. Moser, phys. s t a t . so l . (a) 61, 591 (1980) 6. H. Schul tz and coworker, unpubl ished 7. H. Schultz, t o be presented a t the I n t e r n . Conf. on p o i n t defects and de fec t i n t e r a c t i o n s i n Metals, Kyoto, Japan (1981) 8. A. Seeger and C. Wuthrich, I 1 Nuovo Cimento 33 B, 38 (1976) 9. L. F. P. De Lima, These, EPFL, Lausanne (1981) 10. P. Ast i6 , J. P. Peyrade e t P. Groh, S c r i p t a Met. 15, 477 (1981) see a lso: P. Ast i6 , These, Un ive rs i t k de Toulouse (1981) 11. U. Rodrian, D i s s e r t a t i o n Univers i t a t S t u t t g a r t (1980) 12. A. Seeger, phys. s t a t . so l . (a) 55, 457 (1979) 13. M. Mondino and A. Seeger, S c r i p t a Met. 11, 817 (1977) 14. D. 0. Thompson and D. K. Holmes, J. Appl. Phys. 30, 525 (1959) 15. J. L. Besson and P. Boch, I1 Nuovo Cimento 33 B, 29 (1976)