The effect of elastic anisotropy on dislocations in Ni 3 Fe
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C. S. HARTLEY
The s i n g l e c r y s t a l e l a s t i c c o n s t a n t s of Ni3Fe w e r e m e a s u r e d by an u l t r a s o n i c i n t e r f e r o m e t r i c technique in the t e m p e r a t u r e r a n g e -196 ~ to 300~ Both C n and C~4 d e c r e a s e with i n c r e a s i n g t e m p e r a t u r e , while C~2 r e m a i n s a l m o s t constant below room t e m p e r a t u r e , then i n c r e a s e s with t e m p e r a t u r e up to 100~ and s u b s e q u e n t l y d e c r e a s e s a s t e m p e r a t u r e i n c r e a s e s f u r t h e r . The c o n s t a n t s have been u s e d to c a l c u l a t e 1) the i n t e r a c t i o n force between p a r a l l e l Shockley p a r t i a l d i s l o c a t i o n s and 2) the e n e r g y f a c t o r of a s t r a i g h t p e r f e c t d i s l o cation a s a function of d i s l o c a t i o n o r i e n t a t i o n . While d i s s o c i a t i o n of a s c r e w d i s l o c a t i o n s e e m s quite n o r m a l , the f o r c e s between p a r t i a l s in a d i s s o c i a t e d edge d i s l o c a t i o n a r e a t t r a c t i v e at -196 ~ and 100~ In g e n e r a l , the m a x i m u m stacking fault e n e r g y for which d i s sociation is e n e r g e t i c a l l y f a v o r a b l e , Ym, d e c r e a s e s a s t e m p e r a t u r e i n c r e a s e s . I n v e r s e Wulff plots i n d i c a t e that the a/2 (110> total d i s l o c a t i o n in Ni3Fe is stable for all o r i e n t a t i o n s and t e m p e r a t u r e s .
ELASTIC
a n i s o t r o p y can have c o n s i d e r a b l e i n f l u e n c e on d i s l o c a t i o n m o b i l i t y , 1'~ the ease of c r o s s - s l i p of s c r e w dislocations,3'4 the p r e f e r r e d d i r e c t i o n along which d i s l o c a t i o n s lie, 5 and the a c t i v e slip s y s t e m . 2 Since no r e a l c r y s t a l s a r e e l a s t i c a l l y i s o t r o p i c , e l a s t i c a n i s o t r o p y m u s t be e m p l o y e d to conduct a c o m p l e t e a n a l y s i s of d i s l o c a t i o n b e h a v i o r in c r y s t a l s . The s t r o n g l y d i r e c t i o n a l n a t u r e of bonding in o r d e r e d a l l o y s and i n t e r m e t a l l i c compounds s u g g e s t s that the effects of e l a s t i c a n i s o t r o p y may be m o s t p r o n o u n c e d in t h e s e materials. The d e p a r t u r e f r o m i s o t r o p i c e l a s t i c i t y in c r y s t a l s having cubic s y m m e t r y can be c h a r a c t e r i z e d by Z e n e r ' s a n i s o t r o p y f a c t o r , A, defined as A = 2C44/(Cu - C~2). F o r e m a n 6 showed that an i n c r e a s e in A can c a u s e a d e c r e a s e in the d i s l o c a t i o n self e n e r g y . Teutonico v found that a l a r g e v a l u e of A h a s a g r e a t i n f l u e n c e on the t e n t e n d e n c y for d i s s o c i a t i o n of g l i s s i l e d i s l o c a t i o n s on {111} p l a n e s of fcc c r y s t a l s and on {112} p l a n e s of bcc c r y s t a l s . F r a n c e , H a r t l e y , and Reid 5 studied a n i s o t r o p i c effects on d i s l o c a t i o n s o
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