Age hardening in Cu-15Ni-8Sn alloy
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addition of n i c k e l to c o p p e r - t i n b r o n z e s i m p r o v e s the quality of c a s t i n g s and p r o v i d e s a d d i t i o n a l h a r d n e s s J '2 Age h a r d e n i n g of these alloys was noted as e a r l y as 19283,4 and was e x p l o r e d s h o r t l y t h e r e a f t e r as a m e a n s of s t r e n g t h e n i n g both cast and wrought a l l o y s of up to 12.5 Sn and 15 Nt. 1. Age h a r d e n i n g *Compositions are in wt pct.
r e s u l t s f r o m the d e c o m p o s i t i o n of the C u - r i c h solid solution ot phase. The l i m i t s of the ~ phase b o u n d a r y w e r e i n v e s t i g a t e d by E a s h and Upthegrove ~ and by P r i c e , G r a n t and P h i l l i p s 3 and was found to d e c r e a s e with d e c r e a s i n g t e m p e r a t u r e . The effect of Ni is to d e c r e a s e the solubility of Sn in Cu and open up a two phase (or + 7) field. 5,~ More r e c e n t work by Bastow and Kirkwood 7 suggested that, for c o m p o s i t i o n s >~5 Ni, high t e m p e r a t u r e d e c o m p o s i t i o n of ~ c o n s i s t s p r i m a r i l y of Sn s e g r e g a t i o n along tie l i n e s of n e a r l y constant C u / N i r a t i o to produce a m i x t u r e of ~ + ~. T h e s e a u t h o r s concluded that the y phase is d e r i v e d f r o m the C u - S n b i n a r y with Ni s u b s t i t u t i n g on the Cu s u b l a t t i c e to p r o duce (Cu,Ni)sSn with e i t h e r the DO3 or the r e l a t e d L21 structure.8 Badia ~ p r o p o s e d that p r e c i p i t a t i o n of the e q u i l i b r i u m y phase is r e s p o n s i b l e for age h a r d e n i n g in C u - h N i 5Sn. L a t e r work on age h a r d e n i n g t r a n s f o r m a t i o n s in this s y s t e m was c a r r i e d out by Leo 9 on the alloy Cu6Ni-6Sn with the aid of high r e s o l u t i o n 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 (TEM) and d i f f r a c t i o n t e c h n i q u e s . He d e t e r m i n e d that, within the ~ + ~ r e g i o n , the m a j o r h a r d n e s s changes o c c u r below 400~ with the c o n t i n u ous f o r m a t i o n of a m e t a s t a b l e f i n e - s c a l e s t r u c t u r e (not v i s i b l e by optical m e t a l l o g r a p h y ) t e n t a t i v e l y identified as the 5 phase. Aging at l o n g e r t i m e s or higher t e m p e r a t u r e s r e s u l t e d in the d i s c o n t i n u o u s p r e c i p i t a t i o n of a W i d m a n s t / i t t e n s t r u c t u r e identified as the V p h a s e . M o r e r e c e n t work in this s y s t e m has been c a r r i e d out by Schwartz, Mahajan and P l e w e s 1~ on the alloy C u - 9 N i - 6 S n . They d e t e r m i n e d that age h a r d e n i n g at 400~ and below is a c c o m p a n i e d by spinodal d e c o m p o s i t i o n of the c~ phase. They also found that s u b s e q u e n t B. G. L E F E V R E , A. T. D ' A N N E S S A are Members Technical Staff, and D. K A L I S H is Supervisor, Metallurgical Engineering, Bell Laboratories, 2 0 0 0 N.E. E x p r e s s w a y , Norcross, G A 30071, Manuscript s u b m
