STRAIN-INDUCED BOUNDARY MIGRATION (SIBM) IN ALUMINUM BICRYSTALS EACH WITH A <211> TILT BOUNDARY

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STRAIN-INDUCED BOUNDARY MIGRATION (SIBM) IN ALUMINUM BICRYSTALS EACH WITH

A TILT BOUNDARY

F. Inoko, M. Kobayashi

To cite this version:

F. Inoko, M. Kobayashi. STRAIN-INDUCED BOUNDARY MIGRATION (SIBM) IN ALUMINUM

BICRYSTALS EACH WITH A TILT BOUNDARY. Journal de Physique Colloques, 1988, 49 (C5),

pp.C5-605-C5-610. �10.1051/jphyscol:1988576�. �jpa-00228073�

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JOURNAL DE PHYSIQUE

Colloque C5, supplement au nOIO, Tome 49, octobre 1988

STRAIN-INDUCED BOUNDARY MIGRATION (SIBM) IN ALUMINUM BICRYSTALS EACH WITH A

<211> TILT BOUNDARY

F. INOKO and M. KOBAYASHI*

Department of Production Mechanics, Technical College of Tokushima University, Minamijosanjima, Tokushima 770, Japan

" ~ e p a r t m e n t of Precision Mechanics, Graduate Student, Tokushima University, Minamijosanjima, Tokushima 770, Japan

ABSTRACT

In order to clarify the effect of edge dislocations on the occurrence of the strain-induced boundary migration (SIBM), aluminum bicrystals each with a <211> tilt grain boundary were prepared. The bicrystals were tensile-deformed to 0.3 and annealed under certain con- ditions. Consequently, in the grain boundary recrystallization in the bicrystals with the primary edge dislocations in the component crys- t a l ( ~ ) parallel to the <211> tilt boundaries of large tilt angles, the SIBM mechanism played an important role. It could be considered that the phenomena of the SIBM are strongly related to the motion and annihilation of edge dislocations or their array, and the migration of the tilt boundaries with large tilt angles.

INTRODUCTION

In the series of our works (1-3), we have mainly examined the grain boundary recrystallization in the tensile-deformed and annealed bicrystals with a I1111 or I2111 twist grain boundary. During tensile- deformation screw dislocations of the primary slip systems in both component crystals were piled-up and crossed at the pre-existing boundaries. As the result, after annealing many new grains occurred along the boundaries preferentially. Their orientations were obtained by the rotation of deformed matrix mainly about the axis normal to the slip plane I1111 most parallel to the boundaries and partially about the axes normal to the other I1111 planes. Unlike reference (4-7) re- crystallized new regions because of the SIBM were hardly observed.

When they were observed, the dislocations of the coplanar slip system- (s) with edge component were piled-up to the boundaries. Therefore, in order to clarify the effect of edge dislocations on the occurrence of the SIaN, aluminum bicrystals each with a <211> tilt grain boundary as

shown in Figs.1

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3 were prepared. 'These bicrystals are characterized by the following:

(1) In a symmetric bicrystal only primary edge dislocations in both crystals, A and B , are piled-up to the <211> s/2 radian symmetric tilt boundary.

(2) In crystal B of a non-symmetric bicrystal, primary edge dislocations are piled-up to the <211> 5 ~ / 9 radian non-symmetric tilt

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988576

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C5-606 JOURNAL DE PHYSIQUE

boundary, w h i l e i n c r y s t a l A primary d i s l o c a t i o n s w i t h screw and edge components a r e p i l e d - u p t o t h e boundary.

EXPERIMENTAL PROCEDURE

99.99wt% aluminum b i c r y s t a l s e a c h w i t h a <211> t i l t g r a i n boundary were p r e p a r e d by u s i n g a "soft-moldu Bridgman t e c h n i q u e ( 8 , 9 ) . A sym- m e t r i c b i c r y s t a l had a t i l t boundary w i t h a <211> "/2 t i l t a n g l e ( F i g . 2 ) , w h i l e a non-symmetric b i c r y s t a l s had a non-symmetric t i l t boundary w i t h a <211> 5*/9 t i l t a n g l e (Fig.3): I n F i g . 1 t h e two f a c e s of t h e b i c r y s t a l s normal t o t h e X-axis and X-one were c a l l e d " f r o n t f a c e " and

"back f a c e " , r e s p e c t i v e l y ( 1 - 3 ) . The <211> t i l t boundary p l a n e was nor- m a l t o t h e Y-axis. The t e n s i l e d i r e c t i o n was p a r a l l e l t o t h e Z-axis.

Specimens were t e n s i l e - d e f o r m e d t o 0 . 3 a t room t e m p e r a t u r e and a t f i r s t a n n e a l e d a t 753 K f o r 480 s , s e c o n d a l y a t 753 K f o r 960 s and f i n a l l v a t a h i g h e r t e m ~ e r a t u r e o f 793 K f o r 300 s . The deformed and a n n e a l e d b i c r y s t a l s were examined by t h e naked eye and a n o p t i c a l m l - c r o s c o p e . Scanning e l e c t r o n (SEM) and X-ray d i f f r a c t i o n were a l s o u s e d .

RESULTS AND DISCUSSION

I n t h e symmetric b i c r y s t a l s e v e r a l l a r g e new g r a i n s ( o r new r e - g i o n s ) were remarkably o b s e r v e d o v e r t h e wide range a l o n g t h e p r e - e x i s t i n g boundary a s shown i n F i g s . 4 and 5. The new r e g i o n s from b o t h component c r y s t a l s m u t u a l l y invaded i n t o t h e a d j o i n i n g c r y s t a l s . The o r i e n t a t i o n s o f t h e new r e g i o n s e x i s t e d w i t h i n a p p r o x i m a t e l y i a/18 of t h a t of p a r e n t c r y s t a l A o r 8 , e a c h o r i e n t a t i o n of e i g h t new r e g i o n s , Nos.1

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8 , b e i n g i d e n t i c a l i n t h e f r o n t and back f a c e s . Four new g r a i n s , Nos.1, 3 , 4 and 7 , were formed by t h e SIBM o f p a r e n t c r y s t a l A . No.1 l e f t b e h i n d a f a i r l y d i s t i n c t sub-boundary w i t h t h e m i s o r i e n - t a t i o n w i t h i n a / 3 6 between i t s p a r e n t c r y s t a l A and i t s e l f . P a r e n t c r y s t a l A o f Nos.3 and 4 was consumed by t h e SIBM new r e g i o n , No.5, o f p a r e n t c r y s t a l B . Although t h e s u f f i c i e n t d i f f e r e n c e i n t h e d i s l o c a - t i o n d e n s i t y between t h e new r e g i o n A ' and i t s p a r e n t c r y s t a l A would e x i s t , t h e sub-boundary between A ' and A d i d n o t move back i n t o A. The above e v i d e n c e r e c o n f i r m e d t h a t t h e movement o f s u b - b o u n d a r i e s i s v e r y d i f f i c u l t d u r i n g a n n e a l i n g . However, as t h e SIBN new r e g i o n B ' had a h i g h t i l t a n g l e boundary f o r A , i t g r e w ~ i n t o A and consumed A. These r e s u l t s show t h a t t h e SIBM p r o c e s s i s s t r o n g l y dependent on t h e t i l t a n g l e o f t h e boundary between t h e growing c r y s t a l and t h e consuming one. The SIBM new r e g i o n s grew preferentially a l o n g t h e d e f o r m a t i o n bands l y i n g n e a r l y normal t o t h e p r i m a r y s l i p bands. F i g . 6 shows o p t i - c a l m i c r o g r a p h s o f t h e s l i p and d e f o r m a t i o n bands i n t h e f r o n t and back f a c e s o f t h e as-deformed symmetric b i c r y s t a l . The p a t t e r n s o f t h e s l i p and d e f o r m a t i o n bands were s y m m e t r i c a l . However, n e a r t h e bound- a r y many d e f o r m a t i o n bands a l t e r n a t e l y s p r e a d i n t o many b r a n c h e s from t h e boundary. T h e r e f o r e , i t c o u l d be c o n s i d e r e d t h a t t h e phenomena o f t h e SIBM a r e s t r o n g l y r e l a t e d t o t h e motion and a n n i h i l a t i o n of edge d i s l o c a t i o n s o r t h e i r a r r a y and t h e m i g r a t i o n o f t h e t i l t b o u n d a r i e s w i t h l a r g e t i l t a n g l e s . E s p e c i a l l y , t h e new r e g i o n s formed by t h e SIBX mechanism grew v e r y e a s i l y a l o n g and p a r a l l e l t o t h e d e f o r m a t i o n bands which were composed o f t h e edge d i s l o c a t i o n s w i t h t h e p l u s and minus s i g n s . I t s s c h e m a t i c d i a g r a m s a r e shown i n F i g . 7 . These mean t h a t t h e arrangement o f t h e d i s l o c a t i o n s i n t h e consuming c r y s t a l a l s o a f f e c t s t h e growth and i t s d i r e c t i o n of t h e growing c r y s t a l .

Next, l e t u s examine t h e g r a i n boundary r e c r y s t a l l i z a t i o n of t h e non-symmetric b i c r y s t a l w i t h a 5 a / 9 <211> t i l t boundary a n n e a l e d a t 753 K f o r 480 s . The p r i m a r y s l i p system whose Schmid f a c t o r ( m ) i s 0 . 4 8 i n c r y s t a l A had edge and s c r e w components i n t h e d i s l o c a t i o n s p a r a l l e l t o t h e boundary p l a n e . B u t , t h e Schmid f a c t o r o f t h e second- a r y s l i p s y s t e m , which c o r r e s p o n d e d t o t h e primary one o f c r y s t a l A i n t h e above symmetric b i c r y s t a l , was s t i l l l a r g e ( m = 0 . 4 7 ) . I n t h i s k i n d

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of b i c r y s t a l s , i t c o u l d be e x p e c t e d t h a t t h e SIBM new r e g i o n s and t h e

r o t a t i o n new g r a i n s might be o b s e r v e d a t t h e p r e - e x i s t i n g bound- a r i e s . I n t h e non-symmetric b i c r y s t a l a n n e a l e d a t 753 K f o r 480 s , no new g r a i n c o u l d be o b s e r v e d i n t h e f r o n t and back f a c e s , b u t i n t e r - a c t e d r e g i o n s i n t h e d e f o r m a t i o n between two c r y s t a l s A and B c o u l d be o b s e r v e d a l o n g and p a r a l l e l t o t h e boundary i n t h e s i d e o f c r y s t a l A.

Even a f t e r a d d i t i o n a l a n n e a l i n g a t t h e same t e m p e r a t u r e f o r 960 s , no new g r a i n c o u l d be o b s e r v e d n e a r t h e p r e - e x i s t i n g boundary even by t h e SEM. A f t e r f u r t h e r - a n n e a l i n g a t a h i g h e r t e m p e r a t u r e o f 753 K f o r 300 s , many new g r a i n s o r new r e g i o n s o c c u r r e d b e c a u s e o f t h e SIBM, and because of t h e r o t a t i o n o f A o r B, a s shown i n F i g . 8 . The t o t a l a r e a covered by t h e SIBM new r e g i o n s , Nos.1, 5 , 11, 17 and 21, grew i n t o c r y s t a l A b e c a u s e o f t h e SIBM o f p a r e n t c r y s t a l B . Two new r e - g i o n s , Nos.19 and 23, grew i n v e r s e l y i n t o B because o f t h e SIBM o f A.

However, t h e t o t a l a r e a o f t h e new r e g i o n s formed by t h e SIBM of c r y s - t a l A i n t o B was o n l y one t h i r d o f t h a t formed by t h e SlBN o f B i n t o A . The o c c u r r e n c e s o f t h e SIBM new r e g i o n s were more f r e q u e n t i n c r y s - t a l B w i t h t h e l a r g e r Schmid f a c t o r o f t h e primary s l i p system t h a n i n c r y s t a l A w i t h t h e s m a l l e r one. The d i r e c t i o n s of t h e d e f o r m a t i o n bands i n c r y s t a l s A and B, and i n t h e i n t e r a c t e d zone were d i f f e r e n t e a c h o t h e r

.

T h e r e f o r e , t h e r e g i o n s b e c a u s e o f t h e SIBM grew a l o n g t h e c o r r e s p o n d i n g d e f o r m a t i o n bands i n t h e above t h r e e c r y s t a l zones as shown i n F i g . 9 .

The o r i e n t a t i o n s o f f i f t e e n new g r a i n s c o u l d be o b t a i n e d by t h e r o t a t i o n o f c r y s t a l A a b o u t t h e a x e s normal t o t h e f o u r s l i p p l a n e s

{ I l l } , t h o s e of two new g r a i n s c o u l d be done by t h a t o f c r y s t a l B . I t was s u g g e s t e d t h a t t h e s e r e s u l t s c o u l d come from t h e f o r m a t i o n of t h e i n t e r a c t e d r e g i o n s i n c r y s t a l A a l o n g and p a r a l l e l t o t h e p r e - e x i s t i n g t i l t boundary, s i n c e t h e Schmid f a c t o r o f t h e p r i m a r y s l i p system i n c r y s t a l B was l a r g e r (m=0.50) t h a n t h a t i n c r y s t a l A, and t h e N . . v a l u e ( 1 0 , l l ) between t h e p r i m a r y s l i p system i n c r y s t a l B and l J t h e secondary s l i p system i n c r y s t a l A was v e r y l a r g e . F u r t h e r m o r e , t h e primary s l i p system i n c r y s t a l A had screw components i n t h e d i s l o c a - t i o n s p a r a l l e l t o t h e boundary p l a n e . t h u s , i n t h e non-symmetric b i - c r y s t a l s , t h e t i l t boundary r e c r y s t a l l i z a t i o n o c c u r r e d mainly b e c a u s e o f t h e SIBN mechanism and p a r t i a l l y because o f t h e r o t a t i o n one.

C o n s e q u e n t l y , i n t h e g r a i n boundary r e c r y s t a l l i z a t i o n i n t h e p r e s - e n t u i c r y s t a l s w i t h t h e p r i m a r y edge d i s l o c a t i o n s i n c r y s t a l ( s ) B o r

( a n d ) A p a r a l l e l t o t h e <211> t i l t b o u n d a r i e s o f l a r g e t i l t a n g l e s , t h e SIBN mechanism p l a y e d an i m p o r t a n t r o l e .

On t h e o t h e r hand, i n t h e t w i s t boundary r e c r y s t a l l i z a t i o n i n t h e p r e v i o u s b i c r y s t a l s ( 1 - 3 ) w i t h t h e p r i m a r y screw d i s l o c a t i o n s i n c r y s - t a l s A and B p a r a l l e l t o t h e I1111 o r I2111 t w i s t boundary, t h e

r o t a t i o n mechanism p l a y e d an i m p o r t a n t r o l e .

T h e r e f o r e , i t c o u l d be c o n s i d e r e d t h a t t h e phenomena of t h e SIBM a r e s t r o n g l y r e l a t e d t o t h e motion and a n n i h i l a t i o n of edge d i s l o c a - t i o n s o r t h e i r a r r a y , and t h e m i g r a t i o n o f t h e t i l t b o u n d a r i e s w i t h l a r g e t i l t a n g l e s .

REFERENCES

1. F. Inoko and T . F u j i t a , P r o c . JIMIS-4, Minakami, T r a n s . JIM, S u p p l . p.435 ( 1 9 8 6 ) .

2. F . Inoko, P r o c . 7 t h RISO I n t e r . Symp., R o s k i l d e , p.373 ( 1 9 8 6 ) . 3 . F. Inoko and G. Mima, S c r i p t a M e t a l l . Aug. ( 1 9 8 7 ) t o be p u b l i s h e d . 4. P. A . Beck and P. R . S p e r r y , J . Appl. Phys. 21, 150 ( 1 9 5 0 ) .

5. S. P. B e l l i e r and R . D . Doherty, Acta M e t a l l . 25, 521 ( 1 9 7 7 ) . 6 . Y . Inokuchi and R . D . D o h e r t y , A c t a M e t a l l . 26, 61 ( 1 9 7 8 ) . 7. R . D . D o h e r t y , R e c r y s t a l l i z a t i o n o f M e t a l l i c M a t e r i a l s , e d . F.

H a e s s n e r , p . 2 3 , D r . Rieder-Verlag Gmbh, S t u t t g a r t ( 1 9 7 8 ) . 8 . F. Inoko, K . Akizono, H . Yamaji and G . Mima, P r o c . ICM-2, p . 1 3 ,

Boston ( 1 9 7 6 ) .

9. G . Nima, F. Inoko and K . A t a g i , T r a n s . JIM 21, 89 ( 1 9 8 0 ) . 1 0 . J . D . L i v i n g s t o n and B . Chalmers, Acta X e t a l l . 5 , 322 ( 1 9 5 7 ) . 11. K . G . 3 a v i s , E . Teghtsoonian and A. Lu, Acta M e t a l l . 1 4 , 1677

( 1 9 6 6 ) .

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Schematic diagram o f t h e bi- crystal with the < 2 1 1 > tilt boundary.

C-

t Pole - ^{R i m y}

*

Crystal 11 101 11 1 11 ^ume A 0 A --- *onday slip B . A ^trwe

COmporrnt Pde - Prlmny rbp Crystal 11101 I1111 trwe

A o A --- ^Sec- rlp 6 . A ^trme

Z (Tensile direaim )

Fig. 2

Orientations o f component crystals A and B i n the symmetric bicrystal.

Symmetric Bicrystd

New G r m s

Fig. 3 Fig. 4

Orientations o f component crys- Morphologies and schematic diagram o f tals A and B in t h e non-symmet- the recrystallization mainly because ric bicrystal. o f the SIBM i n the symmetric bicrystal.

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Symmetric Bicfystal From

G.0 Motrlx B

Front

Fig. 5

Orientations of the recrys- tallized new regions ( new grains ) in the front face of the symmetric bicrystal.

Fig. 6

Optical micrographs of the slip and deforma~ion band patterns in the front and back faces of the as-deformed symmetric bicrystal to the tensile strain of 0.3.

Dislocation Arrangement and SlBM Regiom

As-deformed As-anwaled

Crystal A GB. CrysMI 6 Crysld A G.B. Crystd 6

Fig. 7

Schematic diagram of the arrangement of edge dislocations in the as-deformed symmetric bicrystal, and that of the SIBM growth of new regions along the deformation bands accompanied with the annihilation of plus and minus edge dislocations at the migrating boundary.

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Fig. 8

Blorphologies and schematic diagram of the recrystallization because of the SIBM and the  rotation in the non-symmetric bicrystal.

Process of Recrystolli~otion

Fig. 9

Schematic diagrams on the process of the recrystallization because of the SIBM in the non-symmetric bicrystal.

(1) Schematic diagram of deformation bands in the as-deformed non-symmetric bicrystal.

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⁽⁴⁾Schematic diagrams on the progressive stages of the recrystallization because of the SIBM.

The SiBW new regions grew along the deformation bands in the adjoining crystals.