Tensile properties of a microduplex 15 pct nickel silver
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e x p e r i m e n t s on a v a r i e t y of c o p p e r - b a s e a l l o y s have d e m o n s t r a t e d that e x c e p t i o n a l l y high m e c h a n i c a l p r o p e r t i e s can be d e v e l o p e d t h r o u g h the c o m b i n a t i o n of s e v e r e cold r e d u c t i o n (> 95 pct) and low t e m p e r a t u r e aging. ~-4 Such t r e a t m e n t s have b e e n a p p l i e d to p h o s p h o r b r o n z e (CA-510),~-3 t i n - c o n t a i n i n g c u p r o n i c k e l s (CA-725), ~ C u - B e a l l o y s (CA-172), ~ and 60-12 n i c k e l s i l v e r s (CA-762). 1-4 The s t r e n g t h e n i n g a c h i e v e d by this technique i s the r e s u l t of a c o m b i n a tion of c r y s t a l l o g r a p h i c t e x t u r e s t r e n g t h e n i n g , s t r a i n h a r d e n i n g and c o l d - w o r k - a c c e l e r a t e d p r e c i p i t a t i o n . 1-4 The s e v e r e l y r o i l e d 60-12 n i c k e l s i l v e r w a s found to p r e c i p i t a t e the N i Z n i n t e r m e t a U i c , with p r e c i p i t a tion o c c u r r i n g p r e f e r e n t i a l l y at s u b g r a i n b o u n d a r i e s . 4 T e n s i l e s t r e n g t h s up to 170,000 p s i w e r e obtained but t e n s i l e e l o n g a t i o n was found to be quite low for the h i g h e s t s t r e n g t h a l l o y s . ~ In a d d i t i o n , a high d e g r e e of preferred orientation remained after heat treatment f o r the h i g h e s t s t r e n g t h aUoys.~'4 T h e p r e s e n t w o r k w a s i n i t i a t e d to e x a m i n e the e f f e c t of cold r o i l i n g and aging on an e x p e r i m e n t a l n i c k e l s i l v e r having a " m i c r o d u p l e x " s t r u c t u r e ( n o m i n a l c o m p o s i t i o n in wt pct: C u - 1 5 N i - 3 8 Z n ) . s The fine t w o p h a s e s t r u c t u r e ( i n t e r p h a s e s p a c i n g a p p r o x 0.001 mm) w a s e x p e c t e d to p r o v i d e a r a p i d b u i l d - u p of d i s l o c a tion s u b s t r u c t u r e d u r i n g cold r o i l i n g , p e r m i t t i n g a c c e l e r a t e d p r e c i p i t a t i o n a f t e r s m a l l e r cold r e d u c t i o n s . T h i s should r e s u l t in high s t r e n g t h s t r i p with a l e s s e r d e g r e e of a n i s o t r o p y of t e n s i l e p r o p e r t i e s than is p r e s e n t in n o m i n a n y s i n g l e p h a s e n i c k e l s i l v e r s that have been c o l d r o i l e d in e x c e s s of 95 p e t . ~'4 In a d d i tion, the e x t r e m e l y fine g r a i n s i z e of the m i c r o d u p l e x a l l o y should p r o v i d e i m p r o v e d t e n s i l e e l o n g a t i o n at the highest strength levels.
croduplex structure through simultaneous recrystall i z a t i o n and p r e c i p i t a t i o n 5 with i n t e r p h a s e s p a c i n g s of a p p r o x 1 ~ . T h e p r i m a r y p h a s e i s fee a and the p r e c i p i t a t e d p h a s e is bee ~.5,6 An o p t i c a l m i c r o g r a p h of the a n n e a l e d m i c r o d u p l e x s t r i p is shown in F i g . 1. P o r t i o n s of the a n n e a l e d m i c r o
