• Aucun résultat trouvé

REARRANGEMENTS IN THE SYSTEM OF GRAIN BOUNDARY DISLOCATIONS AND MIGRATION OF GRAIN BOUNDARIES

N/A
N/A
Protected

Academic year: 2021

Partager "REARRANGEMENTS IN THE SYSTEM OF GRAIN BOUNDARY DISLOCATIONS AND MIGRATION OF GRAIN BOUNDARIES"

Copied!
6
0
0

Texte intégral

(1)

HAL Id: jpa-00230348

https://hal.archives-ouvertes.fr/jpa-00230348

Submitted on 1 Jan 1990

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

REARRANGEMENTS IN THE SYSTEM OF GRAIN BOUNDARY DISLOCATIONS AND MIGRATION OF

GRAIN BOUNDARIES

M. Imayev, L. Fionova

To cite this version:

M. Imayev, L. Fionova. REARRANGEMENTS IN THE SYSTEM OF GRAIN BOUNDARY DIS-

LOCATIONS AND MIGRATION OF GRAIN BOUNDARIES. Journal de Physique Colloques, 1990,

51 (C1), pp.C1-513-C1-517. �10.1051/jphyscol:1990180�. �jpa-00230348�

(2)

REARRANGEMENTS IN THE SYSTEM OF GRAIN BOUNDARY DISLOCATIONS AND MIGRATION OF GRAIN BOUNDARIES

M.F. IMAYEV and L.K. FIONOVA'

Institute of Metals Superplasticity Problems, URSS Academy of Sciences, frfa 450001, U.R.S.S.

Institute for Microelectronics Technology, URSS Academy of Sciences, Moscow-Chernogolovka 142432, U.R.S.S.

A b s t r a c t

-

The d i s l o c a t i o n s t r u c t u r e and b e h a v i o u r o f g r a i n b o u n d a r i e s i n a low s t r a i n e d n i c k e l a l l o y u n d e r s l o w and f a s t c o n t i n u o u s h e a t i n g was s t u d i e d . It i s e s t a b l i s h e d t h a t t h e p r o c e s s e s o f g r a i n boundary m i g r a t i o n a n d d i s s o c i a t i o n o f g r a i n b o u n d a r i e s s t a r t ( o n a m a c r o s c a l e ) n o t w i t h t h e d i s a p p e a r a n c e o f e l e c t r o n c ~ i c r o - s c o p i c c o n t r a s t due t o e x t r i n s i c g r a i n boundary d i s l o c a t i o n s , b u t a t h i g h e r tempe- r a t u r e s c o r r e s p o n d i n g t o a c t i v e r e a r r a n g e m e n t s o f l a t t i c e d i s l o c a t i o n s w i t h i n t h s g r a i n volume. B o u n d a r i e s o f a n o m a l o u s l y c o a r s e g r a i n s a r e c h a r a c t e r i z e d by an i n t a n - s i v e t w i n n i n g d u r i n g t h e i r motion and t h e m o t i v e f o r s e o f boundary d i s s o c i a t i o n i s a s s o c i a t e d w i t h t h e p r e s e n c e o f t h e p r o d u c t s o f d i s s o c i a t i o n o f t h e e x t r i n s i c g r a i n boundary d i s l o c a t i o n s i n t h e boundary. kJith t h e growth o f t h e r a t e o f c o n t i n u o u s h e a t i n g t h e p r o c e s s e s o f d i s l o c a t i o n r e a r r a n g e m e n t s b o t h i n t h e g r a i n b o u n d a r i e s and w i t h i n t h e g r a i n s would s h i f t i n t h e h i g h - t e m p e r a t u r e a r e a and t h e anomalous g r a i n growLh i s s u p p r e s s e d .

1

-

INTRODUCTION

Mhen low s t r a i n e d p o l y c r y s t a l s a r e h e a t e d t h e y d e m o n s t r a t e an anomalous growth o f g r a i n s which a t t r i b u t e d i n l i t e r a t u r e w i t h t h e g r a d i e n t o f t h e volume d e n s i t y o f l a t t i c e d i s l o c n - t i o n s (LD) /l/, a s w e l l a s t o t h e h i g h m o b i l i t y o f g r a i n b o u n d a r i e s d u r i n g t h e a b s o r p t i m o f e x t r i n s i c g r a i n boundary d i s l o c a t i o n s (EGBO) / 2 / . The growth o f t h e r a t e o f c o n t i n u o u s h e a t i n g s t o p s t h e anomalous g r a i n growth a f t e r c r y t i c a l s t r a i n / 3 / . A t t h e same t i m e t h e s t r u c t u r a l r e a s o n s f o r - t h i s phenonlenon a r e n o t c l e a r . The i n v e s t i g a t i o n o f t h e e v o l u t i o n o f d i s l o c a t i o n s t r u c t u r e w i t h i n t h e g r a i n s and i n g r a i n b o u n d a r i e s would b e h e l p f u l i n t h e u n d e r s t a n d i n g o f p r o c e s s e s which a r e e f f e c t i v e u n d e r s u c h h e a t t r e a t m e n t s . T h a t is why t h i s p a p e r i s c o n c e r n e d w i t h t h e i n v e s t i g a t i o n o f t h e v a r i a t i o n s o f t h e d e n s i t y o f LD and EGBD a s w e l l a s b e h a v i o u r o f g r a i n b o u n d a r i e s d e p e n d i n g on t h e t e m p e r a t u r e - t i m e c o n d i t i o n s o f h e a t i n g .

2

-

EXPERIMENTAL PROCEDURE AND MATERIALS.

A n i c k e l a l l o y of t h e f o l l o w i n y ! c o n p o s i t i o n : 0.01% C , 0.10% Mn, 0,63% S i , 0.003% P ,

0.003% S, 21.53% C r , 0,3S% F e , 0,06% A l , 0,005% T i , b a l s n s e N i was u s o d . 100 mm l o n g s p e c i - mens were c u t o u t o f a w i r e deformed by d r a w i n g from t h e d i a m e t e r o f 6 . 2 mm t o t h e d i a m e t e r - o f 4.5 mm a t room t e m p e r a t u r e . The i n i t i a l r e c r y s t a l l i z e d s t r u c t u r ~ w i t h a mean g r a i n s i z e

d

o f 5 pm was o b t a i n e d by t h e 2 h o u r a n n e a l i n g a t 760°C and g u e n c h i n g i n w a t e r . To o b t a i n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990180

(3)

Cl-514 COLLOQUE DE PHYSIQUE

p r e l i m i n a r y cold-working, t h e specimens were 5% t e n s i x ? s t r a i n e d a t room temperature.

Then t h e specimens were subjected t o continuous heatings up t o a v a r i e t y o f temperatures a t two r a t e s . Slow h e a t i n g a t t h e r a t e o f 0.2 O/s was e f f e c t u a t e d w i t h t h e furnace, f a s t h e a t i n g a t t h e r a t e o f 500°/s was conducted on s p e c i a l u n i t w i t h passing c u r r e n t . A f t e r t h o r e q u i r e d temperature was achieved a t a c e r t a i n r a t e o f heating, t h e specimens were immedia- t e l y quenched i n t h e 10% water s o l u t i o n o f NaCl w i t h o u t any i s o t h e r m i c h o l d i n g .

M i c r o s t r u c t u r e was s t u d i e d a f t e r t h e e l e c t r o l y t i c e t c h i n g i n t h e 10% s o l u t i o n o f s u l p h u r i c a s i d i n e t h a n o l and a d d i t i o n a l chemical e t c h i n g i n t h e a s i d s o l u t i o n : 30 m1 n i t r i c asid, 28 m 1 h y d r o c h l o r i c a c i d , 8 m1 orthophosphoric a c i d and 40 m 1 a c e t i c a c i d . Chemical e t c h i n g was used f o r a more p r e c i s e determination o f t w i n boundaries s i n s e a f t e r t h e e l e c t r o l y t i c e t c h i n g they were almost i n v i s i b l e . While counting

d

using t h e method o f secants 200 o r more g r a i n were taken.

The d e n s i t y o f LD was assessed by means o f t h e method o f secants using e l e c t r o n microscopy and t h e d e n s i t y o f EGBD was determined by t h e r a t i o o f t h e number o f d i s l o c a t i o n s i n t h e boundary t o t h e , l e n g t h o f t h e g i v e n p o r t i o n o f t h e boundary.

3

-

RESULTS

M e t a m h y . The dependence o f

d

( b o t h w i t h and w i t h o u t t w i n boundaries) on t h e tempe- r a t u r e o f low h e a t i n g i s shown i n F i g . 1.

0 " m 900 Ilum IIW

t , O c

-

F i g . 1

-

Dependence o f t h e mean g r a i n s i z e

d

on t h e temperature

t

o f low continuous hea- t i n g : 1 , 2 - w i t h o u t t w i n boundaries; 3,4 - w i t h g r a i n boundaries; 1,3

-

5% pre- s t r a i n i n g ; 2,4 - nondeformed specimens.

I n t h e deformed and nondeformed s t a t e s t h e g r a i n growth becomes pronounced above 800°C. I n nondeformed specimens, no matter what i s t h e method o f counting used, a normal g r a i n growth i s observed, i . e . t h e r e a r e no g r a i n s w i t h p r e f e r e n c i a l growth c o n d i t i o n s . I n deformed spe- cimens when t w i n boundaries are taken i n t o account, no anomalous g r a i n growth takes p l a s e and

d

c o i n s i d e i n b o t h s t a t e s . At t h e same t i m e , when

d

i s counted w i t h o u t t h e considera- t i o n o f t w i n boundaries, p r e f e r e n t i a l growth o f c e r t a i n g r a i n s which w i t h t h e r i s e o f tem- p e r a t u r e grow t o anomalously l a r g e s i z e s becomes pronounced i n t h e deformed s t a t e above 830°C. At t h e 950°C t h e r e a r e p r a c t i c a l l y no f i n e g r a i n s l e f t i n t h e s t r u c t u r e o f deformed specimens. Note t h a t according t o p r e l i m i n a r y experiments t h e l a r g e s t g r a i n s a t slow

-

h e a t i n g w i l l grow a f t e r t h e 5% s t r a i n , i . e . t h i s s t r a i n l e v e l i s c r y t i c a l . At llOO°C

d

i n b o t h s t a t e s become equal.

The anomalous g r a i n growth i s accompanied by an abrupt growth o f t h e f r a c t i o n o f t w i n boun- d a r i e s ( g ) i n t h e o v e r - a l l l e n g t h o f boundaries ( F i g . 2 ) . T h i s parameter grows up t o 950 'C and t h e n decreases w i t h f u r t h e r heating. At llOO°C

-

8 i n b o t h s t a t e s a r e equal.

Under f a s t heating, k i n both s t a t e s s t a r t growing a t 920°C and c o i n c i d e throughout t h e temperature i n t e r v a l up t o t h e m e l t i n g p o i n t . I n t h e deformed specimens t h e anomalous g r a i n growth i s suppressed and g r a i n s grow normally.

E l e c t r o n microscopy. I n t h e i n i t i a l s t a t e , b e f o r e deformation, t h e r e are p r a c t i c a l l y no -daries. After t h e 5% p l a s t i c deformation EGBD a r e found p r a c t i c a l l y i n

a l l boundaries ( F i g . 3). Under slow h e a t i n g t h e density o f L0 i n t h e f i n e - g r a i n e d deformed m a t r i x s t a r t decreasing above 600°C, b u t i t s value drops most a b r u p t l y b e f o r e t h e s t a r t and

(4)

t h e d e n s i t y o f L0 i n t h e a l l o y d e c r e a s e s t o t h e i n i t i a l l e v e l which c o r r e s p o n d s t o t h e non- d e f o r ~ n s d s t a t e .

F i g . 2

-

The v a r i a t i o n o f t h e f r a c t i o n o f t w i n b o u n d a r i e s (

d

) i n t h e o v e r - a l l l e n g t h o f b o u n d a r i e s d e p e n d i n g on t h e t e m p e r a t u r e , t , o f t h e c o n t i n u o u s h e a t i n g : 1 , 2

-

s l o w h e a t i n g ; 3 , 4

-

f a s t h e a t i n g ; 1 , 3

-

5% p r e - s t r a i n i n g ; 2 , 4

-

nondeformed s p e c i m e n s .

F i g . 3

-

The s t r u c t u r e o f t h e a l l o y a f t e r t h e 5% s t r a i n i n g a t room t e m p e r a t u r e . Arrows p o i n t a t EGBD.

During t h e s t u d y o f t h e a b s o r p t i o n p r o p e r t i e s o f g r a i n b o u n d a r i e s it was e s t a b l i s h e d t h a t t h e r e a r e two c h a r a c t e r i s t i c c u s p s on t h e c u r v e o f t h e t e m p e r a t u r e dependence o f t h e f r a c - t i o n o f b o u n d a r i e s (

3

) w i t h o u t EGBD ( F i g . 4 ) .

F i g . 4

-

The d e p e n d e n c e of LD d e n s i t y ( 1 , 2 ) and f r a c t i o n o f g r a i n b o u n d a r i e s (

3

) w i t h o u t EGBD ( 3 , 4 ) on t h e t e m p e r a t u r e o f c o n t i n u o u s h e a t i n g : 1 , 3

-

s l o w h e a t i n g ; 2 , 4

-

f a s t h e a t i n g .

(5)

Cl-516 COLLOQUE DE PHYSIQUE

The d e t e r m i n a t i o n o f g r a i n m i s o r i e n t a t i o n s h a s i n d i c a t e d t h a t i n t h e a b o v e t e m p e r a t u r e i n t e r - v a l s t h e s p r e a d i n g o f t h e e l e c t r o n m i c r o s c o p i c images o f EGBO (EGBO r e l a x a t i o n ) i n t h e random and s p e c i a l g r a i n b o u n d a r i e s . Under low h e a t i n g t h e c u s p s on t h e

3

(T) c u r v e a r n o b s e r v e d i n t h e t e m p e r a t u r e i n t e r v a l s o f 250-300°C and 550-600°C. I n t w i n b o u n d a r i e s t h e EGBO images a r e p r e s e r v e d u n t i l t h o s e b o u n d a r i e s a r e a b s o r b e d by t h e f r o n t o f a n o m a l o u s l y growing g r a i n s . With t h e r i s e o f t h e t e m p e r a t u r e o f h e a t i n g , e s p e c i a l l y i n t h e i n t e r v a l o f 800-850°C, t h e EGBO s y s t e m i n some o f t h e t w i n b o u n d a r i e s becomes o r d e r e d w i t h t h e q u a s i p e r i o d i c a l r o w s and n e t w o r k s b e i n g formed.

F a s t h e a t i n g s h i f t s t h e p r o c e s s e s o f t h e r e a r r a n g e m e n t o f d i s l o c a t i o n s b o t h w i t h i n t h e g r a i n s and i n g r a i n b o u n d a r i e s t o t h e i n t e r v a l o f h i g h e r t e m p e r a t u r e s ( F i g . 4 ) . T h u s , t h e t e m p e r a - t u r e s o f EGBO r e l a x a t i o n s i n random b o u n d a r i e s s h i f t by 250°C on t h e a v e r a g e , w h i l e i n s p e - c i a l b o u n d a r i e s t h e s h i f t is 180-200°C. The t e m p e r a t u r e i n t e r v a l o f t h e o r d e r i n g o f t h e EGBO s y s t e m i n t w i n b o u n d a r i e s s h i f t s by 100-150°C. A t t h e same time t h e t e m p e r a t u r e i n t e r v a l o f t h e d r o p i n t h e d e n s i t y o f LD s h i f t s o n l y by 70-100°C.

4

-

OISCUSSION

The growth o f g r a i n s b o t h i n t h e deformed and nondeformed s t a t e s d o e s n o t s t a r t a t t h e tempe- r a t u r e s o f EGBD r e l a x a t i o n , no m a t t e r what t h e r a t e o f h e a t i n g i s ( s e e F i g . 1 , 2 , 4 )

.

A t b o t h r a t e s o f h e a t i n g t h e s t a r t o f g r a i n g r o w t h c o r r e l a t e s w i t h t h e t e m p e r a t u r e i n t e r v a l i n which a n a b r u p t d r o p o f t h e d e n s i t y o f LD w i t h i n t h e g r a i n s t a k e s p l a c e .

An i n c r e a s e o f d and

8

( F i g . 1 , 2 ) i s o b s e r v e d i n t h e same t e m p e r a t u r e i n t e r v a l where t h e a b r u p t d r o p of t h e d e n s i t y LD u n d e r s l o w h e a t i n g o c c u r s ( F i g . 4 ) . The r e l a x a t i o n o f EGBD i n t h e g r a i n b o u n d a r i e s s t a r t e d s e v e r a l h u n d r e d s o f d e g r e e s below t h e t e m p e r a t u r e a t which t h e r e a r r a n g e m e n t s of LD w i t h i n t h e g r a i n s was l a u n c h e d , no boundary m i g r a t i o n b e i n g o b s e r v e d . However, b a s i n g on t h e d i f f e r e n c e o f t h e t e m p e r a t u r e s o f t h e EGBD r e l a x a t i o n and boundary m i g r a t i o n , no c o n c l u s i o n c a n be drawn on t h e a b s e n c e o f any r e l a t i o n between t h e d i s l o c a t i o n r e a r r a n g e m e n t p r o c e s s e s i n g r a i n b o u n d a r i e s and m i g r a t i o n and t w i n n i n g . According t o / 4 , 5 / m i g r a t i o n and d i s s o c i a t i o n o f g r a i n b o u n d a r i e s c a n b e d e s c r i b e d by a u n i v e r s a l d i s l o c a t i o n mechanism. The f a c t t h a t n o g r a i n - b o u n d a r y d i s l o c a t i o n s r e s p o n s i b l e f o r t h e s e p r o c e s s e s were o b s e r v e d i n t h e e l e c t r o n m i c r o s c o p e may b e due t o t h e s m a l l v a l u e s o f t h e i r B u r g e r s v e c t o r s . The f o r c e s o f i n t e r a t o m i c i n t e r a c t i o n i n g r a i n b o u n d a r i e s a r e known t o b e weaker t h a n t h o s e w i t h i n t h e g r a i n / 6 , 7 / . S i n c e e v e r y s i n g l e a c t o f m i g r a t i o n must b e accompanied by a c o o p e r a - t i v e s h i f t o f a g r o u p o f a t o m s i n c l u d i n g t h e a t o m s . f r o m w i t h i n t h e g r a i n s / B / , it i s o b v i o u s t h a t a t t h e t e m p e r a t u r e s o f EGBD r e l a x a t i o n no a t o m s from w i t h i n t h e g r a i n s a r e i n v o l v e d i n t h e r e a r r a n g e m e n t o f g r a i n boundary d i s l o c a t i o n s and g r a i n boundary d i s l o c a t i o n s move t o r e - l a t i v e l y s h o r t d i s t a n c e s . The a c t u a l m i g r a t i o n i s o f a m i c r o s c o p i c c h a r a c t e r . With t h e r i s e o f t e m p e r a t u r e a t o m s w i t h i n t h e g r a i n s become more m o b i l e , which i s e x p r e s s e d i n t h e motion o f L0 ( F i g . 4 ) , and a p o s s i b i l i t y a r i s e s t o move them u s i n g t h e motion o f g r a i n boundary d i s - l o c a t i o n s . T h i s r e s u l t s i n t h e m a c r o s c o p i c development o f t h e p r o c e s s e s o f m i g r a t i o n and d i s - s o c i a t i o n o f g r a i n b o u n d a r i e s which a r e aimed a t t h e d e c r e a s e o f t h e s u r p l u s e n e r g y o f t h e b o u n d a r i e s .

The p r e s e n c e o f a peak on t h e

8

v s t e m p e r a t u r e c u r v e ( F i g . 2 ) i n d i c a t e s t h a t d u r i n g t h e ano- malous g r o w t h o f g r a i n s t h e p r o c e s s o f s p e c i a l g r a i n boundary d i s s o c i a t i o n accompanied w i t h t h e f o r m a t i o n o f t w i n s p r e v a i l s w h i l e a f t e r t h e g r o w t h is f i n i s h e d it i s t h e merging o f t w i n b o u n d a r i e s which p r e v a i l s .

The growth o f d u r i n g h e a t i n g i s due t o t h e d i s s o c i a t i o n o f t h e b o u n d a r i e s o f anomalously c o a r s e g r a i n s . The m o t i v e f o r s e o f t w i n n i n g i n t h i s c a s e i s a s s o c i a t e d w i t h t h e p r e s e n c e o f s u r p l u s g r a i n boundary d i s l o c a t i o n s i n t h e d i s s o c i a t i n g b o u n d a r i e s , t h o s e d i s l o c a t i o n s b e i n g t h e p r o d u c t o f t h e EGBO d i s s o c i a t i o n . When t h e f i n e g r a i n e d deformed m a t r i x d i s a p p e a r s n e a r 950°C, t h e s o u r c e o f EGBD d i s a p p e a r s t o o , h e n s e , t h e m o t i v e f o r c e o f g r a i n boundary d i s s o c i a - t i o n s t a r t s d e c r e a s i n g . T h i s i s o n e o f t h e r e a s o n s f o r t h e d e c r e a s e o f

8

d u r i n g h e a t i n g a b o v e 950°C ( F i g . 2 ) . The o t h e r r e a s o n is c o n c e r n e d w i t h t h e c o m p e t i t i v e g r a i n g r o w t h a n d a b s o r p t i o n o f some_ o f t h e g r a i n s t o g e t h e r w i t h t h e t w i n s w i t h i n t h e m . The e q u a l i t y o f t h e 8 v a l u e s and a l s o d o f t h e deformed and non-deformed s t a t e a t llOO°C i n d i c a t e s t h a t a t t h i s t e m p e r a t u r e a c e r t a i n " e q u i l i b r i u m " f r a c t i o n o f t w i n s i s a v a i l a b l e .

The s e n s i t i v i t y o f t h e anomalous g r a i n growth t o t h e r a t e o f h e a t i n g show t h a t d u r i n g t h e c o n t i n u o u s h e a t i n g t h e r e i s a c o m p e t i t i o n o f t w o p r o c e s s e s l e a d i n g t o t h e d e c r e a s e o f t h e s y s t e m e n e r g y : t h e m i g r a t i o n o f t h e b o u n d a r i e s o f anomalously c o a r s e g r a i n s and r e c o v e r y w i t h i n t h e g r a i n s . Under s l o w h e a t i n g t h e p r o c e s s o f thr? m i g r a t i o n o f s u c h b o u n d a r i e s i s k i - n e t i c a l l y more p r e f e r a b l e and t h e anomalous g r o w t h o f g r a i n s i s o v e r b e f o r e t h e r e c o v e r y w i t h i n t h e g r a i n s h a s been a c c o m p l i s h e d . Under f a s t h e a t i n g t h e r e c o v e r y w i t h i n t h e g r a i n s becomes more p r e f e r a b l e and it i s o v e r b e f o r e t h e anomalous g r a i n growth h a s d e v e l o p e d . S i n c e

(6)

growth o f g r a i n s i n d i c a t e s t h a t w i t h increase o f r a t e o f h e a t i n g t h e processes o f t h e r e a r - rangement o f d i s l o c a t i o n s i n g r a i n boundaries s h i f t t o -the h i h temperature i n t e r v a l more considerable t h a n those w i t h i n t h e g r a i n s . IHowever, t h i s conc?usion i s n o t d e r i v e d d i r e c t l y from Fig. 4 s i n c e t h e r e l a x a t i o n o f EG8D i n g r a i n boundaries and rearrangement o f LD w i t h i n t h e g r a i n s s t a r t s w i t h a t d i f f e r e n t temperatures and t h e motion o f g r a i n boundary d i s l o c a - t i o n s r e s p o n s i b l e f o r t h e m i g r a t i o n o f boundaries cannot be seen i n t h e e l e c t r o n microscope because o f t h e very s m a l l Burgers vectors.

5

-

CONCLUSIONS

1. The temperature i n t e r v a l s o f t h e EGBD r e l a x a t i o n depend on t h e t y p e o f g r a i n boundaries.

With t h e r i s e o f t h e r a t e o f continuous h e a t i n g processes o f d i s l o c a t i o n rearrangements both w i t h i n t h e g r a i n s and i n g r a i n boundaries s h i f t t o h i g h e r temperatures, i n g r a i n boundaries t h e s h i f t being more considerable t h a n w i t h i n t h e g r a i n s .

2. I n t h e Ni-20%Cr a l l o y t h e temperatures o f t h e s t a r t o f t h e processes o f m i g r a t i o n and g r a i n boundary d i s s o c i a t i o n are h i g h e r t h a n t h e temperatures o f t h e EGBO r e l a x a t i o n . These processes s t a r t a t t h e temperatures o f t h e i n t e n s i f i c a t i o n o f L0 rearrangement w i t h i n t h e g r a i n s .

3. The anomalous g r a i n growth d u r i n g t h e annealing o f Ni-2(%Cr a f t e r c r y t i c a l s t r a i n i s accompanied w i t h t h e growth of t h e f r a c t i o n o f t w i n s i n t h e p o l y c r y s t a l . I t i s e s t a b l i s h e d t h a t t h i s i s connected w i t h t h e v a r i a t i o n o f t h e s t r u c t u r e and p r o p e r t i e s o f g r a i n bounda- r i e s due t o t h e LD trapped by them.

REFERENCES

/l/ G o r e l i k , S. S., R e c r y s t a l l i z a t i o n o f Metals and A l l o v s . Moscow: M e t a l l u r g i a Publ. (1978) ( i n Russian).

/2/ V a l i e v , R. Z., Gertsman, V. Yu., and Kaibyshev, 0. A. S c r i p t a Met. 18 (1984) 639.

/3/ Bodiako, M. N., Astapchik, S. A., Jaroshevitch, G. \ I . , Thermokineti= o f R e c r y s t a l l i z a - t i o n . Minsk: Nauka i Tekhnika Publ. (1968) ( i n Russian).

/4/ Rae, C. M. F. and Smith, D. A., P h i l . Mag. 4 1 (1980) 477.

/ 5 / And~eeva, A . V., Perevezentsev, V. N.., F i o n G a , L. K., and Shcherban, M. Yu., Poverkhnost N S (1982) 116 ( i n Russian).

/ 6 / Hashimoto, M., I s h i d a , Y., Yamamoto, R., and Doyama, D., Acta M e t a l l . 29 (1981) 617.

/7/ Imayev, M, F.. F i z i k a M e t a l l o v i Metallovedenie (FMM) 64, N 4 (1987) 8 z ( i n Russian) /8/ Bishop, G. H., Harrison, R. J . , Kwok, T., and Yip, S., J. Appl. Phys. 53 (1982) 5609.

Références

Documents relatifs

Plate 3 represents a fully relaxed sample where the grain boundary made up of dislocation lines has been partially replaced by a network of focal conics.. This is a

By contrast, specimens which are squat compared with their cross-section, for example niost ionic conductivity specimens compressed along the squat axis, enter

Thus, if high angle boundaries consist of dislocation networks embedded in C S L interfaces, lattice dislocations should undergo reactions with them, similar t o

— Measurements in this laboratory of cation diffusion in bicrystals, of silver injection in the grain boundary region, and of light-scattering and electron microscope observations

operation of Bardeen-Herring sources but the most efficient way is by means of dissociation of the so-called trapped lattice dislocations (TLDs) which were

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des

A reversal i n the direction of migration would require change in the dominant set of grain boun- dary dislocations a t various positions of the same