Precipitation hardening in Cu-Zn-Be alloys
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THE
p r e c i p i t a t i o n h a r d e n i n g e f f e c t s e x h i b i t e d by b e r y l l i u m - b e a r i n g c o p p e r , t i n b r o n z e , n i c k e l and cup r o - n i c k e l have a l s o b e e n o b s e r v e d *-4 in C u - Z n - N i - B e and t e r n a r y C u - Z n - B e a l l o y s . The b r i e f p u b l i s h e d d e s c r i p t i o n 3 of the l a t t e r s y s t e m i s e x p a n d e d h e r e to e x a m i n e the p o s s i b i l i t y that b e r y l l i u m b r a s s e s m a y aff o r d a u s e f u l r a n g e of t e n s i l e p r o p e r t i e s b e t w e e n t h o s e of the t i n b r o n z e s on the one hand, and c o m m e r c i a l b e r y l l i u m - c o p p e r s on the o t h e r . In addition, an a t t e m p t has b e e n m a d e to identify the c h a r a c t e r i s t i c s of the p r e c i p i t a t i o n r e a c t i o n in the C u - Z n - B e s y s t e m . E X P E R I M E N T A L PROCEDURE A s e r i e s of t e r n a r y a l l o y s w e r e c a s t and f a b r i c a t e d to a p p r o x i m a t e l y 4 m m (3/16 in.) s h e e t , then p r o c e s s e d t h r o u g h a heat t r e a t m e n t and cold r o l l i n g p r o g r a m d e s i g n e d to y i e l d m e c h a n i c a l t e s t d a t a on the e f f e c t s of t h e following f a c t o r s : (a) (b) (c) (d) {e)
Zinc content Beryllium content Aging temperature Aging time Cold work
two levels six levels five levels six levels five levels
20 and 30 wt pct 0 to 1 wt pet 200 to 400~ 0 to 720 rain 0 to 50 pct reduction.
Solution h e a t t r e a t m e n t s on the a p p r o x i m a t e l y 4 m m (3/16 in.) s h e e t s t a r t i n g m a t e r i a l s w e r e c a r r i e d out at 800~ for 1 h in an i n e r t a t m o s p h e r e , followed by w a t e r quenching to a m b i e n t t e m p e r a t u r e . The r e s u l t ant g r a i n s i z e v a r i e d b e t w e e n 0.03 and 0.1 m m e q u i v a lent g r a i n d i a m e t e r . T h e c h a r a c t e r i s t i c s of the p r e c i p i t a t e p h a s e and the p r e c i p i t a t i o n p r o c e s s in the t e r n a r y s y s t e m w e r e d e t e r m i n e d by e l e c t r o n m i c r o s c o p y , s e l e c t e d a r e a e l e c t r o n d i f f r a c t i o n and X - r a y d i f f r a c t i o n a n a l y s i s of p r e c i p i t a t e s i s o l a t e d by e x t r a c t i o n r e p l i c a s . The c o m p o s i tion e x a m i n e d was Cu-20 p c t Z n - 0 . 8 p c t B e . S a m p l e s of t h i s m a t e r i a l w e r e s o l u t i o n t r e a t e d at 800~ in a r g o n f o r 2 h, c o l d - w a t e r quenched, then a g e d f o r v a r i o u s t i m e s at 300, 350 and 400~ D i s c s p r e p a r e d by s p a r k e r o s i o n m a c h i n i n g w e r e c h e m i c a l l y thinned in 10 p c t s u l f u r i c a c i d , then e l e c t r o p o l i s h e d in 15 p c t n i t r i c a c i d in m e t h a n o l a t - 60~ Extraction replicas were p r e p a r e d by c a r b o n d e p o s i t i o n , followed by e l e c t r o p o l i s h i n g in the n i t r i c a c i d in m e t h a n o l s o l u t i o n
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