Measurement of stacking fault energy from dislocation interactions
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The t h e o r i e s and m e t h o d s applied to the d e t e r m i n a t i o n of the s t a c k i n g fault e n e r g y (y) u s i n g t e c h niques of d i r e c t o b s e r v a t i o n of d i s l o c a t i o n c o n f i g u r a t i o n s a r e r e v i e w e d . The four p r i n c i p a l m e t h ods, utilizing d i s l o c a t i o n nodes, m u l t i p l e r i b b o n s , s t a c k i n g fault t e t r a h e d r a , and faulted dipoles, a r e d i s c u s s e d in d e t a i l . Different t h e o r e t i c a l t r e a t m e n t s a r e c o m p a r e d w h e r e v e r p o s s i b l e . Exp e r i m e n t a l p r o c e d u r e s and q u a n t i t a t i v e m e a s u r e m e n t methods a r e r e v i e w e d , c o n c e n t r a t i n g on 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 t e c h n i q u e s . Detailed e x a m p l e s of the application of each m e t h o d a r e given. F o r y/l~b in the r a n g e of 2 x 10 -4 to 5 • 10 -3 (~ the s h e a r modulus, b the B u r g e r s vector), m e a s u r e m e n t s on d i s l o c a t i o n nodes o r m u l t i p l e r i b b o n s in favorable e a s e s should p e r m i t d e t e r m i n a t i o n s of the s t a c k i n g fault e n e r g y to a p r e c i s i o n of 5 pet. For l a r g e r v a l u e s of y/t~b (up to 12 • 10-s), m e a s u r e m e n t s can be made on t e t r a h e d r a o r faulted dipoles with l e s s p r e c i s i o n . L a r g e r v a l u e s of the s t a c k i n g fault e n e r g y r e q u i r e high r e s o l u t i o n s t u d i e s of d i s l o c a t i o n s ; t h e s e t e c h n i q u e s a r e not yet well e s t a b l i s h e d . P o s s i b l e s o u r c e s of s y s t e m a t i c b i a s a r e d i s c u s s e d . Two s i g n i f i c a n t t h e o r e t i c a l p r o b l e m s r e m a i n c o n c e r n i n g the t r e a t m e n t of the d i s l o c a t i o n core and the use of a n i s o t r o p i e e l a s t i c i t y . It is of p r i m e i m p o r t a n c e to c h a r a c t e r i z e as c a r e f u l l y as p o s s i b l e the m a t e r i a l s Studied if a c c u r a t e r e s u l t s a r e d e s i r e d . J.HE f i r s t d i r e c t d e t e r m i n a t i o n of the s t a c k i n g fault e n e r g y (SFE) was r e p o r t e d b y Whelan x f r o m m e a s u r e m e n t s on a magnified i m a g e of an extended d i s l o c a t i o n c o n f i g u r a t i o n . He o b s e r v e d extended d i s l o c a t i o n nodes in thin s t a i n l e s s s t e e l foils u s i n g the 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 e . A s i m p l e a n a l y s i s of the force b a l ance in the node b e t w e e n the c u r v e d d i s l o c a t i o n a r m s and the s t a c k i n g fault showed that the SFE in this m a t e r i a l was about 13 e r g p e r sq c m (m joule p e r sq m). The t h e o r e t i c a l solution of the node p r o b l e m has b e e n r e f i n e d c o n s i d e r a b l y in s e v e r a l d i f f e r e n t t r e a t m e n t s s i n c e then. O_her faulted d i s l o c a t i o n s t r u c t u r e s have b e e n o b s e r v e d
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