The character of dislocations in copper single crystals after creep at high temperatures
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al. x have r e c e n t l y concluded that the motion of jogged s c r e w d i s l o c a t i o n i s not r a t e - c o n t r o l l i n g in high t e m p e r a t u r e c r e e p . One of the m a i n r e a s o n s to d i s c a r d the s c r e w d i s l o c a t i o n model c o m e s f r o m the e x p e r i m e n t a l r e s u l t s by C l a u e r 2'3 who found, by t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y , that m o s t of the d i s l o c a t i o n s both within s u b g r a i n s and in subbounda r i e s a r e edge d i s l o c a t i o n s in c r e p t m o l y b d e n u m single c r y s t a l s . In c r e p t copper single c r y s t a l s , howe v e r , it was found that t h e r e were m a n y s c r e w d i s l o c a t i o n s within s u b g r a i n s . The r e s u l t s a r e p r e s e n t e d here briefly. A s e r i e s of e x p e r i m e n t s by m e a n s of B e r g - B a r r e t t t e c h n i q u e , 4 e t c h - p i t technique, s a n d t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y 6 have b e e n c a r r i e d out by the p r e s e n t a u t h o r s to r e v e a l the s u b s t r u c t u r e developed i n copper single c r y s t a l s d u r i n g high t e m p e r a t u r e c r e e p . The t e n s i l e axis of single c r y s t a l s p e c i m e n s were in the c e n t e r of the s t e r e o g r a p h i c t r i a n g l e . C r e e p t e s t s were p e r f o r m e d in a r g o n a t m o s p h e r e at 0.65 T m = 610~ and 0.75 Trn = 745~ (Tin: the m e l t i n g t e m p e r a t u r e in deg Kelvin). Thin foil s p e c i m e n s with the p r i m a r y slip plane (111) p a r a l l e l to the plane of the foil were p r e p a r e d f r o m the c r e p t c r y s t a l s a n d exa m i n e d with a 500 kv e l e c t r o n m i c r o s c o p e . The a v e r -
age t h i c k n e s s of the thin foil s p e c i m e n s was about 1.5~2~. Some e x a m p l e s of the d i s l o c a t i o n a r r a n g e m e n t s a r e shown in F i g s . 1 and 2. Most of the s u b b o u n d a r i e s f o r m e d d u r i n g c r e e p d e f o r m a t i o n were g e n e r a l l y p a r a l l e l to the [19.1] d i r e c t i o n as shown in Fig. 1. The s u b b o u n d a r i e s a r e thought to be tilt b o u n d a r i e s cons i s t i n g m a i n l y of edge d i s l o c a t i o n s . However, within s u b g r a i n s d i s l o c a t i o n l i n e s r u n n i n g in v a r i o u s d i r e c t i o n s were o b s e r v e d . A s s u m i n g that the i s o l a t e d long d i s l o c a t i o n s belong to the p r i m a r y slip s y s t e m , the a n g l e s between d i s l o c a t i o n s e g m e n t s and the B u r g e r s v e c t o r were m e a s u r e d on photographs. The total length of d i s l o c a t i o n l i n e s and the total a r e a of the photographs e x a m i n e d were about 280 ~ and 6400 ~tz, r e s p e c t i v e l y . The r e s u l t s a r e given in Fig. 3, which c l e a r l y shows that d i s l o c a t i o n s with l a r g e s c r e w c o m ponent a r e m o r e f r e q u e n t l y o b s e r v e d than
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