The stacking fault energy dependence of the mechanisms of deformation in Fcc metals
- PDF / 884,299 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 221 Views
The influence of s t a c k i n g fault e n e r g y on the choice of d e f o r m a t i o n m e c h a n i s m s is c o n s i d e r e d . E x p e r i m e n t a l evidence is r e v i e w e d to d i s t i n g u i s h between the p o s s i b l e m e c h a n i s m s and a l i m ited a n a l y s i s of c r y s t a l r o t a t i o n s is p e r f o r m e d . It is shown that twinning, p e n c i l glide, and the m o r e u s u a l o c t a h e d r a l slip a r e all m e c h a n i s m s which could be o p e r a t i v e u n d e r different cond i t i o n s of stacking fault e n e r g y or t e m p e r a t u r e but that even if only o c t a h e d r a l slip o c c u r s stacking fault e n e r g y may affect slip r o t a t i o n s by influencing the choice of operative slip s y s t e m s . Using the s i m p l i f y i n g a s s u m p t i o n that d e f o r m a t i o n i s h o m o g e n e o u s , and applying Bishop and H i l l ' s m a x i m u m work p r i n c i p l e to d e r i v e p o s s i b l e c o m b i n a t i o n s of slip s y s t e m s , a s e t of c r i t e r i a a r e developed to indicate the influence of stacking fault e n e r g y on the choice f r o m among the available slip s y s t e m s , and hence on slip r o t a t i o n s . An e m p i r i c a l method of r e l a t i n g stacking fault e n e r g y to t e x t u r e is outlined and the e x p e r i m e n t a l r e s u l t s obtained by this method a r e c o m p a r e d with r e s u l t s obtained by other methods. D E F O R M A T I O N t e x t u r e s a r i s e b e c a u s e of the r o t a t i o n a s s o c i a t e d with d e f o r m a t i o n by s h e a r p r o c e s s e s , which is so f a m i l i a r in the case of s i n g l e and duplex slip obs e r v e d in single c r y s t a l p l a s t i c i t y . If a s h e a r s y s t e m is defined by s h e a r plane n o r m a l h and s h e a r d i r e c t i o n u the r o t a t i o n axis h • u. The r o t a t i o n thus depends on the choice of s h e a r s y s t e m s which in t u r n depends on m a t e r i a l and o r i e n t a t i o n v a r i a b l e s . When d e f o r m a t i o n twinning is an a v a i l a b l e s h e a r mode t h e r e is, of c o u r s e , an a d d i t i o n a l r e o r i e n t a t i o n , c o r r e s p o n d i n g to m i r r o r i m a g i n g with r e s p e c t to the twin plane. E x a c t t h e o r i e s of d e f o r m a t i o n t e x t u r e d e v e l o p m e n t cannot be f o r m u l a t e d b e c a u s e of the complexity in p o l y c r y s t a l l i n e p l a s t i c i t y , but r e a s o n a b l e a p p r o x i m a t i o n s c o r r e s p o n d i n g to the upper and lower bound t h e o r i e s of p o l y c r y s t a l l i n e p l a s t i c i t y , due to T a y l o r I and Sachs, 2 r e s p e c t i v e l y , can be obtained. E a r l y t h e o r i e s of the l a t t e r type will not be d i s c u s s e d h e r e , s i n c e it is cons i d e r e d that the upper bound t h e o r y of T a y l o r is c l o s e r to r e a l i t y . In the u p p e r bound theory it is a s s u m e d that each c r y s t a l u
Data Loading...
