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HIGH-TEMPERATURE DISLOCATION MOBILITY
T. Kê
To cite this version:
JOURNAL DE PHYSIQUE
CoZZoque C 5 , suppl6ment au nOZO, Tome 42, octobre 1981 page C5-421
INTERNAL FRICTION ASSOCIATED WITH HIGH-TEMPERATURE DISLOCATION MOBILITY
T.S. ~ 8 *
Groupe drEtudes de M6taZZurgie Physique e t Physique des Mate'riaurc, INSA de Lgon, 69621 V-iZZexrbanne, France
A b s t r a c t . - 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 l a s - s i f i e d i n t o t h r e e c a t a g o r i e s : (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 r o p e r t i e s o f s i n g l e d i s l o c a t i o n s ; ( 2 ) those o r i g i n a t e d from t h e i n t e r a c t i o n between d i s - . 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 i m b and from t h e c o o r p e r a t i v e 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 l e u p s , g r a i n boundaries, subgrain boundaries, e t c . ) g i v e r i s e t o r e l a - x a t i o n phenomena o n l y a t h i g h e r 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 i g h temperature d i s l o c a t i o n rnobi l i t y (Theme 3) should i n c l u d e cataoory ( 3 ) and p a r t o f catagory ( 2 ) concerninq w i t h t h e d i s l o c a t i o n - p o i n t - d e f e c t i n t e r a c t i o n a t h i g h temperatures. The t e r n " h i g h tem- p e r a t u r e " used here may be d e f i n e d as t h e range o f temperature a t wich t h e p i n n i n g p o i n t s o r
"
atmosphere" concerned a r e "mobile" and m i g r a t e w i t h d i s l o - c a t i o n s .The papers o f Theme 3 may be discussed under tile f o l l o w i n g headings: I. Mobile p i n n i n g p o i n t s m i g r a t i n ~ w i t h d i s l o c a t i o n s ; 11. d i s l o c a t i o n p i l e u p s and d i s l o - c a t i o n climb; 111. g r a i n boundary r e l a x a t i o n ; I V . h i g h temperature p r o p e r t i e s 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 i g n 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 P o i n t s M i g r a t i n g w i t h D i s l o c a t i o n s .
-
R i t c h i e and Sprungmann / l / a t t r i b u t e d t h e t h r e e l o w - f r e q u e n c y i n t e r n a l - f r i c t i o n(Q-l)
peaks (P0,P1,P2) they ob- served 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 t h e r m a l l y a s s i s t e d unpin- n i n g o f d i s l o c a t i o n s , l o n g i t u d i n a l andtra.nsversediffusions o f t h e p i n n i n g p o i n t s (assumed t o be the 17-23 pg/g o f oxygen contained i n t h e U-Zr) i n t h e d i s l o c a t i o n core (LCG and TCD) r e s p e c t i v e l y . The authors s t a t e d t h a t peaks s i e i l a r t o P0,P1 andP3
have been observedin s i l v e r /2/ and t h e r e f o r e t h e 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 t h e low- frequency 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) r e l a x a t i o n . It seems t h a t t h i s a s s e r t i o n 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 l s o be r e s p e c t i v e l y t h e s o l u t e €33 peak ( 0 i n a-Zr) a s s o c i a t e d w i t h GB s l i d i n g and t h e GB peak associated w i t h CB m i g r a t i o n ( c f/ a / ) .
2.
D i s l o c a t i o n P i l e u p s and D i s l o c a t i o n Climb.-In t h e paper by R i v i e r e,
Arnirault and Woirgard /4/,
the authors claimed once and again t h a t t h e peaks associated w i t h t h e p o l y and t h e s i n g l e c r y s t a l s are i d e n t i c a l as regards t h e l o c a t i o n ( i n b o t h tempera- t u r e and frequency) and t h e behavior d u r i n g successive annealings. So t h e authors asserted t h a t i t i s confirmed t h a t t h e geometry o f the d i s l o c a t i o n arrangement has t h e most important i n f l u e n c e t o these peaks and t h e G B ' s have o n l y an i n d i r e c t * o n leave from I n s t i t u t e o f Sol i d S t a t e Physics, Academia Sinica, H e f e i,
China65-422 JOURNAL DE PHYSIQUE
i n f l u e n c e through t h e 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 t h e experimental r e s u l t s r e o o r t e d by t h e authors i n t h i s paper and i n those published p r e v i o u s l y
/5-S,2/
showing t h a t t h e r e l a x a t i o n peaks appeared 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 are i n t h e same temperature range as the "orthodox" GB peaks i n po- l 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 t h e a s s e r t i o n t h a t t h eGB
peak i s due t o d i s l o c a t i o n motion i n s i d e t h e g r a i n s has much t o be d j s - cussed. It seems t h a t , i n many cases, t h e authors compared the r e s u l t s o f p o l y c r y - s t a l l i n e and s i n g l e - c r y s t a 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 t a t e s . Although t h e Q-1 peaks sometimes occured i n n e a r l y t h e same tempe- r a t u r e r e q i o n i n p o l y c r y s t a l l i n e and " s i n g l e - c r y s t a l"
specimens, b u t c e r t a i n l y they a r e n o t i d e n t i c a l by c a r e f u l a n a l y s i s . The procedure adopted f o r s u b s t r a c t i n 9 t h e high-temperature Q-1 background should be examined ui t k extreme care. A1 so t h e h e i g h to f the peak i n c r ~ l s t a l l i n e specimens i s much h i g h e r than those i n t h e s i n g l e - c r y s t a l specimens. This leads t o t h e q u e s t i o n t h a t whether t h e s i n g l e - c r y s t a l specimens used by the authors are c r y s t a l s w i t h o u t 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 p r e c i s e assumption as r e ~ a r d s t h e elementary mechanism r e s p o n s i b l e f o r t h e motion o f t h e d i s l o c a t i o n s i n s i d e t h e
rains
because o f t h e l a c k o f s u f f i c i e n t l y p r e c i s e values o f t h e a c t i v a t i o n parameters. Furthermore, one should be very c a r e f u l i n t a k i n ~Q-
1measurements 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 t h e "ambiguous" Q - ~ peaks r e s u l t e d from the annealins e f f e c t . I t i s v e r y d i f f i c u l t t o a v o i d t h e cold-working e f f e c t i n t r o d u c e d i n mounting t h e h i g h l y softened s i n c l e - c r y s t a l specimens f o r
C-'
measurements. Such e f f e c t can o n l y be " e l i m i n a t e d " by a long-time annealing a t v e r y h i g h tenperatures.It i s c e r t a i n t h a t t h e cold-work s t a t e ano t h e d i s l o c a t i o n c o n f i g u r a t i o n i n t h e g r a i n proper would i n f l u e n c e
63
beahvior and t h e d i s l o c a t i o n c o n f i g u r a t i o n i n t h e Ga'S, b u t t h e 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 t h e same d i s l o c a t i o n group as t h a t r e s p o n s i b l e f o r t h e p o s s i b l e r e l a x a t i o n peaks ob- served 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 . The r e l a x a t i o n behavior o f t h e s l i p bands ( d i s l o c a t i o n p i l e u p s ) 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 t h e d i s l o c a - t i o n groups i n high-angle GB'S may be s i m i l a r and may g i v e 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 n o t n e c e s s a r i l y i d e n t i c a l as regards t h e l o c a t i o n and the behavior d u r i n g successive annealings. Thus i t seems premature t o consider t h a t t h e "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.w o r k i n g 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 c o n s i d e r a b l e i n f l u e n c e on t h e GB r e l a x a t i o n b e h a v i o r . A h i g h e r amount o f p r e v i o u s c o l d - w o r k i n g s h i f t s t h e GB peak t o a l o w e r t e m p e r a t u r e / 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 n e i g h b o u r i n g g r a i n s . I t 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 spe- cimen=0.04 mm) decreased w i t h an i n c r e a s e 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 a n n e a l i n g and d i s a p p e a r e d 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 l o w - a n g l e GB's i n s t e a d o f t h e h i g h - a n g l e GB's i j h i c h g i v e r i s e t o t h e " o r t h o d o x " 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 i g h 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 p o l y g o n i z e d
,
so as a w a l l o f d i s l o c a t i o n , must i n d u c e someQ - ~
and t h e Q-l a t v e r y h i g h temperatures above t h e t e m p e r a t u r e 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 c o n n e c t i o n , t h e o b s e r v a t i o n o f medium-temperatureQ-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 F a n t o z z i /13/ i s n o t e w o r t h y . I n commenting a p r e v i o u s paper b y Esnouf, Gabbay and F a n t o z z i / l 4 / c o n c e r n i n g 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 ( a b o u t 0.08) i s o r i g i n a t e d f r o m 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 p o l y g o n i z e d w a l l s . Now Esnouf and F a n t o z z 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 m o t i o n by c r o s s - s l i p i s v e r y h i g h f o r hexagonal m e t a 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 b y 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 l o n g d i s l o c a t i o n s . However, t h e q u e s t i o n s 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 B u r g e r s v e c t o r ) i n t h e r m a l 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 c o r r e s p o n d i n g l y l a r g e modulus d r o p .
As t h e a u t h o r s mentioned t h a t t h i s peak i s a b s e n t i n 5N aluminium, i t seems t h a t t h e s e 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 t e m p e r a t u r e some- what below t h e t e m p e r a t u r e s 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 p u r e 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 ima- g i n e d 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 a b o u t 1
mm
which i s comparable w i t h t h e s m a l l e s t dimension o f t h e specimen. I t was shown i n t h e case o f 99.991 A1 t h a t a n o t i c e a b l e 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 i a m e t e r o f t h e w i r e specimenl . T h i s g i v e s an a d d i t i o n a l s u p p o 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-tempera- t u r e peaks a r e s o l v e n t GB peaks.
C5-424 JOURNAL DE PHYSIQUE
9 - 1 and dynamic modulus measurements d u r i n g d e f o r m a t i o n 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 s u b m i t t e d t o t h i s conference /24/, t h i s group r e p o r t e d 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 d e f o r m a t i o n 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 b o t h o f m o b i l e and immobile 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 andTEN
d a t a . The c o n c l u s i o n was made t h a t t h e e x p e r i m e n t a l d a t a a r e e i t h e r c o n s i s t e n t w i t h r e s p e c 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 a u t h o r s as a c o n f i r m a t i o n o f t h e assurn- p t i o n made i n t h e i r p r e v i o u s 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 b e p o i n t e d o u t t h a t t h e peak observed b y 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 a u t h o r s ) . 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 b y Gendi
'
S group (1976) /25/ i n 99.6 m a c r o c r y s t a l l i n eA1 i s n o t i n correspondence t o t h e K6 peak observed b y K6 (1947) /16/ ( a t 285°C f o r f = 0 . 8
Hz).
T h i s K-peak s h o u l d be compared w i t h t h e peak observed i n 99.2 p o l y c r y s - 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 h e K-peak ( o f m a c r o c r y s t a 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 t h a n 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 h e same p u r i t y . The a u t h o r ' s creep d a t a 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-- n e c t e d w i t h d i s l o c a t i o n s , b u t t h i s c o n c l u s i o n cannot be extended t o t h e K6 peak ob- served 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 h e 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 a n n e a l i n g and p o l y g o n i z a t i o n .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 d e f o r - m a t i o n cannot be c o n s i d e r e d as a s u p p o r 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 r a i n s . The s t r u c t u r e change a t t h e GB d u r i n s p l a s t i c d e f o r m a t i o n n a y a l s o cause t h e disappearance o f t h e GB peak
/ll/.
3. G r a i n Boundary R e l a x a t i o n .
-
A c o n c r e t e 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 c o n t i n u o u s d i s l o c a t i o n i n t h e GB's sugges- t e d by Sun and K6/3/ seems t o be a b l e t o e x p l a i n many e x p e r i m e n t a l r e s u l t s . F o r h i g h - p u r i t y i s o t r o p i c m e t a l s , 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 l o n g GB, Db, by an e x p r e s s i o n s i m i l a r t o E i n s t e i n - S t o k e s f o r - mula. The optimum temperatures o f GB Q-l peaks f o r a number o f pure m e t a l s c a l c u l a t e d a c c o r d i n g 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 c o r r e s p o n d i n g e x p e r i m e n t a l l y observed v a l u e s . I t i s shown t h a t f o r impure m e t a l s , t h e v i s c o s i t y o f some GG'S i s c o n s i d e r a b l y i n c r e a s e d by t h e s e l e c t i v e s e g r e g r a t i o n o f i m p u r i t i e s a l o n g them, so t h a t a n o t h e r Q-l peak ( t h e s o l u t e peak) appears a t a temperature above t h et 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 p u r e m e t a 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 a n o t h e r h i g h - t e m p e r a t u r e ? - l peak o r a h i g h 3 - 1 back-ground i n a d d i - t i o n t o t h e GB peak a s s o c i a t e d 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 c o n t i n u n a s 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 y p e s 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 p u z z l e 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 / 3 0 / . 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 t e m p e r a t u r e 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 s m a l 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 .-
I t i s i n s p i r i n g t h a t t h e h i g h - t e m p e r a t u r e 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 i g h - t e m p e r a t u r e background) have been a p p l i e d t o many problems h a v i n g 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 n and t h e s t a t e o f s m a l 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 mechanism o f t h e improvement o f t h e h i g h - t e m p e r a t u r e p r o p e r t i e s of Fe-Cr-A1 a l l o y s /32/, t h e n 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 s e g r e g a t i o n o f Sb and t h e g r o w t h k i n e t i c s o f t h e secondary 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 t e a d y s t a t e c r e e p 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 c r e e p 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
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