Fatigue deformation of silver single crystals

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fatigue d e f o r m a t i o n of s i n g l e c r y s t a l s of fcc m e t a l s h a s b e e n s t u d i e d by m a n y i n v e s t i g a t o r s in r e cent y e a r s . The h a r d e n i n g d u r i n g fatigue d e f o r m a tion h a s b e e n a t t r i b u t e d to f o r e s t d i s l o c a t i o n a c t i v i t y , 1'2 point d e f e c t c l u s t e r s 3-6 and the f r e e length of the s c r e w d i s l o c a t i o n s e g m e n t m o v i n g i n s i d e the c e l l s . 7 The a c c o m m o d a t i o n of p l a s t i c s t r a i n a m p l i t u d e by d i s l o c a tion m o t i o n h a s b e e n a t t r i b u t e d to e i t h e r c e l t - s h u t ting ~'9 o r d i s l o c a t i o n d i p o l e flipping. 1~ The p r o m i n e n t f e a t u r e s of the d e f e c t m i c r o s t r u c t u r e in the s a t u r a tion s t a g e a r e point d e f e c t c l u s t e r s , 6 a t h r e e - d i m e n s i o n a l c l o s e d - c e l l s t r u c t u r e 7 and p e r s i s t e n t s l i p bands. 2,u-12 A d e t a i l e d m i c r o s t r u c t u r a l a n a l y s i s of the s i l v e r s i n g l e c r y s t a l s s u b j e c t e d to c o n s t a n t p l a s t i c s t r a i n a m p l i t u d e fatigue d e f o r m a t i o n into the s a t u r a t i o n s t a g e h a s b e e n m a d e to a n s w e r the following q u e s tions: F i r s t , what is the q u a n t i t a t i v e r e l a t i o n s h i p be n tween the s t r u c t u r a l f e a t u r e s in the s a t u r a t i o n s t a g e of fatigue d e f o r m a t i o n and the s a t u r a t i o n s t r e s s ? Secondly, what i s the effect of s t a c k i n g fault e n e r g y on the d e f e c t m i c r o s t r u c t u r e in the s a t u r a t i o n s t a g e of p u r e fcc m e t a l s ? 1. E X P E R I M E N T A L PROCEDURE Single c r y s t a l s of 99.999+ p c t s i l v e r w e r e grown by the m o d i f i e d C h a l m e r s technique. The s i z e and s h a p e of the c r y s t a l s w e r e s i m i l a r to t h o s e d e s c r i b e d e l s e w h e r e . 13 T e n s i o n - c o m p r e s s i o n fatigue t e s t s w e r e p e r f o r m e d at c o n s t a n t p l a s t i c s h e a r s t r a i n a m p l i t u d e , 7p, in the r a n g e Tp = • to • Sections were cut p a r a l l e l to the p r i m a r y o r (111) p l a n e f r o m the gage length of the t e s t s p e c i m e n s in the S e r v o m e t s p a r k c u t ting m a c h i n e . The s e c t i o n s w e r e thinned c h e m i c a l l y and d i m p l e d by the e l e c t r o l y t i c j e t technique. The S. M. L. SASTRY is with the Metallurgy and Ceramics Division, Aerospace Research Laboratories, Wright-Patterson Air Force Base, DAYTON, OH 45433. B. RAMASWAMIand F. GOETZ are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto MSS 1A4, Canada. Manuscript submitted July 7, 1975. METALLURGICAL TRANSACTIONS A

d i s c s w e r e e l e c t r o p o l i s h e d until p e r f o r a t i o n and e x a m i n e d in b r i g h t field, d a r k field, and weak b e a m d a r k f i e l d m o d e s in a P h i l

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