Stacking fault energy and mechanical properties
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S e v e r a l d e f o r m a t i o n m e c h a n i s m s a r e d i s c u s s e d which m a y be i n f l u e n c e d by the stacking fault e n e r g y : f o r e s t cutting at the b e g i n n i n g of p l a s t i c d e f o r m a t i o n in fcc and hex m e t a l s , c r o s s slip in fcc m e t a l s , p r i s m a t i c slip in hexagonal m e t a l s , and slip in bcc m e t a l s . Existing e x p e r i m e n t a l data for the t e m p e r a t u r e and s t r a i n r a t e d e p e n d e n c e of the s h e a r s t r e s s at which the r e l e v a n t d e f o r m a t i o n m e c h a n i s m b e g i n s a r e a n a l y z e d . It is shown that the data for c r o s s slip in fcc m e t a l s , for p r i s m a t i c slip, and for slip in bcc m e t a l s can be d e s c r i b e d by an A r r h e n i u s e q u a t i o n with a n a c t i v a t i o n e n e r g y that is p r o p o r t i o n a l to the l o g a r i t h m of the s t r e s s . Stacking fault e n e r g i e s a r e d e t e r m i n e d f r o m the s t r a i n rate s e n s i t i v i t y of the s h e a r s t r e s s . J . H E s t a c k i n g fault e n e r g y (SFE) is an i m p o r t a n t p a r a m e t e r in the evaluation of p l a s t i c p r o p e r t i e s of s o l ids. S F E ' s m a i n l y d e t e r m i n e the amount of s p l i t t i n g of d i s l o c a t i o n s into p a r t i a l s and c o n s e q u e n t l y affect the m o b i l i t y of d i s l o c a t i o n s if for t h e i r m o v e m e n t a change in d i s l o c a t i o n splitting is r e q u i r e d . T h e r e f o r e , i n f o r m a t i o n about the amount of s p l i t t i n g and of the SFE can be o b t a i n e d by m e a s u r i n g d i s l o c a t i o n m o b i l i t i e s . Cons t r i c t i o n or s e p a r a t i o n of p a r t i a l s d u r i n g d i s l o c a t i o n m o v e m e n t can o c c u r in s e v e r a l d i f f e r e n t ways. The following p o s s i b i l i t i e s have b e e n d i s c u s s e d p r e v i o u s l y : a) The l o c a l c o n s t r i c t i o n of a n extended d i s l o c a t i o n when c u t t i n g i n c l i n e d f o r e s t d i s l o c a t i o n s , b) C o n s t r i c tion of s c r e w d i s l o c a t i o n s along a c e r t a i n length. This c o n s t r i c t i o n o c c u r s 1) if the d i s l o c a t i o n changes the glide p l a n e d u r i n g c r o s s l i p i n fcc m e t a l s , 2) if the fault is e x t e n d e d in a p l a n e d i f f e r e n t f r o m the glide plane as p r o p o s e d for p r i s m a t i c glide in hexagonal m a t e r i a l s , or 3) if the d i s l o c a t i o n s a r e s p l i t in m o r e than one glide p l a n e , as p r e s u m a b l y in bcc m e t a l s , c) Movem e n t of one d i s s o c i a t e d p a r t i a l d i s l o c a t i o n only, p r o ducing e i t h e r twins or a m a r t e n s i t i c phase. S F E ' s a r e d e t e r m i n e d e x p e r i m e n t a l l y by m e a s u r i n g the s t r e s s at which the effect of the s p l i t t i n g can be o v e r c o m e and the d i s l o c a t i o n s b e g i n to move. This method is quite
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