Internal Friction Associated with High-temperature Dislocation Mobility

I n t e r n a l f r i c t i o n associated w i t h d i s l o c a t i o n mobil i t y can be c las s i f i e d i n t o th ree catagor ies: (1) Those o r i g i n a t e d from t h e i n t r i n s i c p roper t ies o f s i n g l e d is loca t ions ; (2 ) those o r i g i n a t e d from the i n t e r a c t i o n between d is. l o c a t i o n s and p o i n t defects; (3 ) those o r i g i n a t e d from d i s l o c a t i o n c l imb and from the coorperat ive behavior o f groups o f d i s l o c a t i o n s (e.g., d i s l o c a t i o n p i leups, g r a i n boundaries, subgrain boundaries, e t c . ) g i ve r i s e t o r e l a xa t ion phenomena o n l y a t h igher temperatures. I t seems, thus, the t o p i c o f i n t e r n a l f r i c t i o n associated w i t h h igh temperature d i s l o c a t i o n rnobi l i t y (Theme 3) should inc lude cataoory (3) and p a r t o f catagory (2 ) concerninq w i t h the d is loca t ion -po in t -de fec t i n t e r a c t i o n a t h igh temperatures. The t e r n "h igh temperature" used here may be def ined as the range o f temperature a t wich the p inn ing po in ts o r " atmosphere" concerned are "mobile" and migrate w i t h d i s l o cat ions. The papers o f Theme 3 may be discussed under t i le f o l l o w i n g headings: I. Mobile p inn ing p o i n t s m i g r a t i n ~ w i t h d is loca t ions ; 11. d i s l o c a t i o n p i leups and d i s l o c a t i o n cl imb; 111. g r a i n boundary re laxa t ion ; I V . h igh temperature p roper t ies o f s o l i d s r e l a t e d t o d i s l o c a t i o n m o b i l i t y a t n ign temperatures. Various models and viewpoints have been proposed by d i f f e r e n t authors and i t i s h i g h l y i n t e r e s t i n g t o s t a r t a c r i t i c a l discussion. 1. Mobile Pinninp Points M ig ra t ing w i t h Dis locat ions. R i t c h i e and Sprungmann / l / a t t r i b u t e d the threelow-f requency i n t e r n a l f r i c t i o n (Q-l) peaks (P0,P1,P2) they observed i n deformed and annealed p o l y c r y s t a l l i n e 5N cl-Zr t o the rma l l y ass is ted unpinn ing o f d i s loca t ions , l o n g i t u d i n a l andtra.nsversediffusions o f the p inn ing p o i n t s (assumed t o be the 17-23 pg/g o f oxygen contained i n the U-Zr) i n the d i s l o c a t i o n core (LCG and TCD) respec t i ve ly . The authors s ta ted t h a t peaks s i e i l a r t o P0,P1 and P3 have been observedin s i l v e r /2/ and there fo re the core r e d i s t r i b u t i o n o f i m p u r i t y i n t e r s t i t i a l s appears t o be a general phenomenonwhichcontributes peaks t o the lowfrequency Q-1 spectra 0.f deformed metals. The authors claimed t h a t t h i s p a r t of the spectrum (Pp) was a t t r i b u t e d erroneouS1~1 t o g r a i n boundary (GB) re laxa t ion . It seems t h a t t h i s asser t ion may n o t be conciusive. The peaks P1 and P2 a t t r i b u t e d t o LCC and TCD may a lso be respec t i ve ly the so lu te €33 peak ( 0 i n a-Zr) associated w i t h GB s l i d i n g and the GB peak associated w i t h CB m ig ra t ion ( c f / a / ) . 2. Dis loca t ion Pi leups and D is loca t ion Climb.-In the paper by R i v i e r e , Arnirault and Woirgard /4/ , the authors claimed once and again t h a t the peaks associated w i t h the p o l y and the s ing le c r y s t a l s are i d e n t i c a l as regards the l o c a t i o n ( i n both temperat u r e and frequency) and the behavior dur ing successive annealings. So the authors asserted t h a t i t i s confirmed t h a t the geometry o f the d i s l o c a t i o n arrangement has the most important in f luence t o these peaks and the G B ' s have on ly an i n d i r e c t *on leave from I n s t i t u t e o f Sol i d S ta te Physics, Academia Sinica, Hefe i , China Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981562 65-422 JOURNAL DE PHYSIQUE i n f luence through the i n t e r a c t i o n s w i t h the d i s l o c a t i o n network. It seems t h a t the experimental r e s u l t s reoor ted by the authors i n t h i s paper and i n those publ ished p rev ious ly /5-S,2/ showing t h a t the r e l a x a t i o n peaks appeared i n s l i g h t l y deformed s ing le c r y s t a l s are i n the same temperature range as the "orthodox" GB peaks i n pol y c r y s t a l s need t o be re-examined and analysed r a t h e r c a r e f u l l y ana the asser t ion t h a t the GB peak i s due t o d i s l o c a t i o n motion i n s i d e the g ra ins has much t o be d j s cussed. It seems that , i n many cases, the authors compared the r e s u l t s o f po lycrys t a l l i n e and s ing le -c rys ta l specimens w i t h d i f f e r e n t p u r i t i e s , o r w i t h d i f f e r e n t cold-work s tates. Although the Q-1 peaks sometimes occured i n near l y the same temper a t u r e req ion i n po lyc rys ta l l i n e and "s ing le -c rys ta l " specimens, but c e r t a i n l y they are n o t i d e n t i c a l by ca re fu l analys is . The procedure adopted f o r subst ract in9 the high-temperature Q-1 background should be examined ui t k extreme care. A1 so the height o f the peak i n c r ~ l s t a l l i n e specimens i s much h igher than those i n the s ing le -c rys ta l specimens. This leads t o the quest ion t h a t whether the s ing le -c rys ta l specimens used by the authors are c r y s t a l s wi thout any GB'S. To be sure, r e a l r e l a x a t i o n peaks may a1 so appear i n deformed s i n g l e c r y s t a l S , b u t the authors are q u i t e r i g h t i n emphasizing t h a t i t i s s t i l l premature t o venture prec ise assumption as r e ~ a r d s the elementary mechanism responsib le f o r the motion o f the d is loca t ions i n s i d e the rains because o f the lack o f s u f f i c i e n t l y prec ise values o f the a c t i v a t i o n parameters. Furthermore, one should be very ca re fu l i n t a k i n ~ Q1 measurements w i t h s l i g h t l y deforned c r y s t a l s i n ascending temperatures because o f the "ambiguous" Q ~ peaks r e s u l t e d from the anneal ins e f f e c t . I t i s very d i f f i c u l t t o avoid the cold-working e f f e c t in t roduced i n mounting the h i g h l y softened s i n c l e c r y s t a l specimens fo r C-' measurements. Such e f f e c t can o n l y be "e l iminated" by a long-t ime anneal ing a t very h igh tenperatures. It i s c e r t a i n t h a t the cold-work s t a t e ano the d i s l o c a t i o n con f igu ra t ion i n the g r a i n proper would in f luence 63 beahvior and the d i s l o c a t i o n con f igu ra t ion i n the Ga'S, b u t the GB peak observed i n p o l y c r y s t a l s does n o t need t o be associated w i t h the same d i s l o c a t i o n group as t h a t responsib le f o r the poss ib le r e l a x a t i o n peaks observed i n s l i g h t l y deformed s ing le c r y s t a l S . The r e l a x a t i o n behavior o f the s l i p bands ( d i s l o c a t i o n p i leups) i n deformed s i n g l e and p o l y c r s y t a l s and o f the d is locat i o n groups i n high-angle GB'S may be s i m i l a r and may g ive r i s e t o s i m i l a r r e l a x a t i o n peaks b u t no t necessar i ly i d e n t i c a l as regards the l o c a t i o n and the behavior dur ing successive annealings. Thus i t seems premature t o consider t h a t the "orthodox" CB peak observed i n completely r e c r y s t a l l i z e d p o l y c r y s t a l l i n e specimens i s n o t o r i g i n a t e d from GB r e l a x a t i o n process. I n passing, i t may be worthwhi le t o c i t e a few examples i l l u s t r a t i n g t h a t the s t a t e i n the g r a i n proper o r the mutual o r i e n t a t i o n o f the neighbouring gra ins do inf luence the r e l a x a t i o n behavior o f the GB'S. I t has been shown f o r 99.391 A1 t h a t the amount o f co ldwork ing p r i o r t o t h e r e c r y s t a l l i z a t i o n o f t h e specimen has cons ide rab le i n f l uence on t h e GB r e l a x a t i o n behav ior . A h i g h e r amount o f p r e v i o u s co ld -work ing s h i f t s t h e GB peak t o a l ower temperature / g / . T h i s has been a t t r i b u t e d t o t h e d i f f e r e n c e i n t h e mutual o r i e n t a t i o n o f ne ighbou r i ng g r a i n s . It has a l s o been shown i n 39.97 e l e c t r o l y t i c Cu /10/ t h a t t h e h e i g h t o f t h e GB peak a t 280°C ( f = l . S tiz, g r a i n s i z e o f specimen=0.04 mm) decreased w i t h an i nc rease o f t h e amount o f c o l d r e d u c t i o n p r i o r t o annea l i ng and d isappeared a t a p r i o r c o l d r o l l e d r e d u c t i o n o f 90.3 %. And t h i s has been shown t o be r e l a t e d t o t h e f o r m a t i o n o f t h e (100) [001] c u b i c s t r u c t u r e l e a d i n g t o t h e f o r m a t i o n of low-ang le GB's i n s t e a d o f t h e h igh-ang le GB's i j h i c h g i v e r i s e t o t h e "or thodox" GB peak. I n commenting a paper e n t i t l e d " I n t e r n a l F r i c t i o n a t Very H igh Temperatures" /11/, Crussard suggested as e a r l y as i n 1950 /12/ t h a t as we observed t h a t c r y s t a l s a r e g e n e r a l l y po l ygon i zed , so as a w a l l o f d i s l o c a t i o n , must induce some Q ~ and t h e Q-l a t v e r y h i g h temperatures above t h e temperature r e g i o n o f t h e GB peak c o u l d be due t o p o l y g o n i z a t i o n . I n t h i s connect ion , t h e o b s e r v a t i o n o f medium-temperature Q-1 peaks i n s u p e r h i g h p u r i t y (99.9999) A1 and Mg p o l y c r y s t a l s as r e p o r t e d by Esnouf and Fantozz i /13/ i s notewor thy . I n commenting a p rev ious paper by Esnouf, Gabbay and Fan tozz i / l 4 / concern ing t h i s medium-temperature peak, F r i e d e l /15/ suggested t h a t t h i s v e r y h i g h Q-1 peak (about 0.08) i s o r i g i n a t e d f rom t h e s h i f t by c r o s s s l i p o f t h e nodes of po l ygon i zed w a l l s . Now Esnouf and Fan tozz i emphasize t h a t F r i e d e l ' s model cannot h o l d f o r t h e s i m i l a r case o f h i g h p u r i t y Mg as t h e a c t i v a t i o n energy f o r d i s l o c a t i o n mo t i on by c r o s s s l i p i s v e r y h i g h f o r hexagonal me ta l s . They a t t r i b u t e d t h e r e f o r e t h i s peak t o t h e d i s l o c a t i o n g l i d e c o n t r o l l e d by j o g c l i m b i n g and d i f f u s i o n o f vacancies a long d i s l o c a t i o n s . However, t h e ques t i ons r a i s e d by F r i e d e l were n o t answered, t h e most i m p o r t a n t o n e s a r e : ( l ) The assumed d i s t a n c e between j o g s o f 1500 b ( b i s t h e Burgers v e c t o r ) i n thermal e q u i l i b r i u m i s t o o l a r g e f o r A1 a t 400K; ( 2 ) i t seems s u p r i s i n g t h a t a j o g c l i m b i n g t h r u a d i s t a n c e o f 1 o r 2 b can g i v e r i s e t o such a h i g h Q ~ peak and a co r respond ing l y l a r g e modulus drop. As t h e au tho rs ment ioned t h a t t h i s peak i s absent i n 5N aluminium, i t seems t h a t these h i g h 9 -1 peaks observed i n 6N A1 and Mg p o l y c r y s t a l s a t temperature somewhat below t h e temperatures o f t h e GB peaks o f 99.991 A1 ( a t 285OC f o r f=0.8 Hz) and 99.97 Mg ( a t 220°C f o r f=0.5 Hz) /16/ may p o s s i b l y be t h e r e a l s o l v e n t GB peaks o f A1 and #g o f v e r y h i g h p u r i t y . Then t h e G3 peaks observed e a r l i e r i n l e s s pure A1 and Mg p o l y c r y s t a l s were a c t u a l l y t h e s o l u t e GB peaks. Such a p o s s i b i l i t y has been imag ined sometime ago /17/. The average g r a i n s i z e o f t h e A1 and Mg specimens used b y Esnouf e t a1 was about 1 mm which i s comparable w i t h t h e s m a l l e s t d imension o f t h e specimen. It was shown i n t h e case o f 99.991 A1 t h a t a noticeable GB peak appears even when t h e average g r a i n s i z e i s comparable t o t h e d iameter o f t h e w i r e specimen l . This g i ves an a d d i t i o n a l suppo r t t o t h e p r o p o s i t i o n t h a t t h e medium-temperat u r e peaks a r e s o l v e n t GB peaks. The con t i nued e f f o r t o f Gond i ' s group o f making KO peak a n a l y s i s by means o f C5-424 JOURNAL DE PHYSIQUE 9-1 and dynamic modulus measurements d u r i n g deformat ion i s h i g h l y i n s p i r i n g /19-23/. I n t h e paper submi t ted t o t h i s conference /24/, t h i s group repo r ted t h e r e s u l t s o f dynamic modulus and Q-1 measurements c a r r i e d o u t on 99.99 A1 d u r i n g creep deformat ion The ( 8 ) f u n c t i o n s g i v i n g t h e d i s t r i b u t i o n o f d i s l o c a t i o n segments bo th o f mobi le and immobi le d i s l o c a t i o n s were analysed u t i l i z i n g creep curves, dynamic modulus and TEN data . The conc lus ion was made t h a t t h e exper imenta l data a r e e i t h e r c o n s i s t e n t w i t h respec t t o t h e 5)-1 peak observed by Esnouf e t a1 /14/ a t 130°C ( 1 Hz) o r w i t h t h e K1 peak /25/. And t h i s was considered by t h e authors as a c o n f i r m a t i o n o f t h e assurnp t i o n made i n t h e i r p rev ious papers t h a t t h e peak K1, observed i n correspondence t o K6 peak, i s connected w i t h d i s l o c a t i o n s . I t i s t o be p o i n t e d o u t t h a t t h e peak observed by Esnouf e t a1/14/ appears o n l y i n 6N A1 ( n o t i n t h e 99.99 A1 used by t h e au tho rs ) . The a u t h o r ' s a s s e r t i o n t h a t t h e peak K1 i s observed i n correspondence t o K6 peak needs t o be analysed r a t h e r c a r e f u l l y . The K-peak (K1,K2) observed by Gendi ' S group (1976) /25/ i n 99.6 mac roc rys ta l l i n e A1 i s n o t i n correspondence t o t h e K6 peak observed by K6 (1947) /16/ ( a t 285°C f o r f=0.8 Hz). T h i s K-peak shou ld be compared w i t h t h e peak observed i n 99.2 po l yc rys t a l l i n e A1 which appeared around 220°C ( f = l H z ) /11,26/. Then i t can be seen t h a t t he K-peak ( o f macrocrys ta l l i n e A l ) appeared d e f i n i t e l y a t a temperature about 60°C h i $ h e r than t h e GB peak o f p o l y c r y s t a l l i n e A1 o f about t he same p u r i t y . The a u t h o r ' s creep da ta may be r e l a t e d t o t h e K-peak o f 99.99 m a c r o c r y s t a l l i n e A1 whichinay be con-nected w i t h d i s l o c a t i o n s , b u t t h i s conc lus ion cannot be extended t o t h e K6 peak observed i n 93.991 p o l y c r y s t a l l i n e A1 /16/. From t h e c o n d i t i o n s f o r t h e appearance and disappearance o f t he K-peak, we have reasons t o assume t h a t t h e K-peak i s r e l a t e d t o d i s l o c a t i o n anneal ing and po l ygon iza t i on . It seems t h a t t h e v a r i a t i o n and disappearance o f t h e GB peak d u r i n g p l a s t i c de fo r mat ion cannot be cons idered as a suppor t t o t h e i n t e r p r e t a t i o n o f t h e K6 peak i n terms o f t h e c o n t r i b u t i o n s o f d i s l o c a t i o n s i n s i d e t h e g ra ins . The s t r u c t u r e change a t t he GB d u r i n s p l a s t i c deformat ion nay a l s o cause t h e disappearance o f t h e GB peak /ll/. 3. Gra in Boundary Relaxat ion. A conc re te d i s l o c a t i o n model o f high-angle GB's i n terms o f t h e inhovogeneous s l i d i n n o f t h e cont inuous d i s l o c a t i o n i n t h e GB's suggest e d by Sun and K6/3/ seems t o be ab le t o e x p l a i n many exper imenta l r e s u l t s . For h i g h p u r i t y i s o t r o p i c meta ls , t h e v i s c o s i t y f o r GB s l i d i n g i s c o r r e l a t e d w i t h t h e d i f f u s i o n c o e f f i c i e n t a long GB, Db, by an express ion s i m i l a r t o E ins te in-Stokes f o r mula. The optimum temperatures o f GB Q-l peaks f o r a number o f pure meta ls c a l c u l a t e d acco rd ing t o t h i s model and s l i d i n g mechanism a r e f a i r l y c l o s e t o t h e cor responding expe r imen ta l l y observed v a l u e s . I t i s shown t h a t f o r impure meta ls , t h e v i s c o s i t y o f some GG'S i s cons ide rab l y increased by t h e s e l e c t i v e seg reg ra t i on o f i m p u r i t i e s a long them, so t h a t another Q-l peak ( t h e s o l u t e peak) appears a t a temperature above t h e ,GB peak i n pu re metal ( t h e s o l v e n t peak). The s o l u t e ~ e a k w i l l auuear a t a temperat u r e below t h a t o f t h e s o l v e n t ~ e a k o n l y when p r e c i p i t a t i o n has occured a t t h e GB's g i v i n g r i s e t o a sma l l e r CB v i s c o s i t g . Th i s has been observed p r e v i o u s l y i n t h e cases o f impure A1 Ill/, Cu c o n t a i n i n g B i /27/ , Cu c o n t a i n i n g 0 /g/ and now a l s o i n KO c o n t a i n i n g 0/28/and i n d i l u t e b i n a r y A1 -Cu, A1 -Fe and A1 -S i a1 l oys /29/. A1 so, i n a n i s o t r o p i c pure me ta l s and i n t h e presence o f i n t e r n a l s t r e s s , t h e m i g r a t i o n o f GB's may cause another h ightemperature ? l peak o r a h i g h 3 -1 back-ground i n add i t i o n t o t h e GB peak assoc ia ted w i t h GB s l i d i n g . I t i s t o be p o i n t e d o u t t h a t such a cont inunas d i s l o c a t i o n model and s l i d e mechanism can a l s o be a p p l i e d t o r e l a x a t i o n problems o f o t h e r t ypes of d i s l o c a t i o n group such as t h e s l i p bands o r d i s l o c a t i o n p i l e u p s . T h i s may be one o f t h e reasons why t h e r e l a x a t i o n phenomena s i m i l a r t o GB r e l a x a t i o n have sometimes been observed i n s l i g h t l y deformed s i n g l e c r y s t a l s . It was q u i t e a puzz le why s o l u t e peak was n o t observed w i t h t h e s o l v e n t peak i n a-Fe c o n t a i n i n g carbon /30/ . Now :!aria and Zhu /28/ observed a carbon s o l u t e peak a t t h e h i g h e r temperature s i d e of t h e i r o n GB peak f o r Fe c o n t a i n i n g 0.0002 wt% and 0.0005 wt% carbon, and t h i s s o l v e n t peak disappeared as t h e amount o f carbon i n c r e a sed up t o 0.0027 wt%. S o l u t e GB peaks have a l s o been observed by L i e t a1 i n a-Fe/31/ and i n Fe-Cr-F.l a l l o y s /32/ c o n t a i n i n g v e r y smal l amount of r a r e e a r t h elements.4. A p p l i c a t i o n s . It i s i n s p i r i n g t h a t t h e h ightemperature Q-' phenomena ( i n c l u -d i n g GB r e l a x a t i o n and t h e h ightemperature background) have been a p p l i e d t o manyproblems hav ing p r a c t i c a l s i g n i f i c a n c e such as t h e i n v e s t i g a t i o n o f t h e d i s t r i b u t i o nand t h e s t a t e o f smal l amounts o f r a r e e a r t h elements i n u i r o n /31/, t h e mechanismo f t h e improvement o f t h e h ightemperature p r o p e r t i e s of Fe-Cr-A1 a l l o y s /32/ , t h en o n d e s t r u c t i v e i n v e s t i g a t i o n o f GB seg rega t i on o f Sb and t h e growth k i n e t i c s o f t h esecondary r e c r y s t a l l i z a t i o n i n g r a i n o r i e n t e d Fe-Si a l l o y s /33/ , /34/ , t h e s teadys t a t e c reep o f 25Cr-20Ni a u s t e n i t i c s t a i n l e s s s t e e l s /35/ and t h e creep r u p t u r e be-h a v i o r o f A1 a l l o y s /29/ . References/l/I . G . R i t c h i e , K.M. 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