Explosive strengthening of a Cu-Be alloy
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R. W. ROHDE,
AND
D. J. MOTTERN
The effects of shock loading on the m e c h a n i c a l p r o p e r t i e s and m i c r o s t r u c t u r e of a p r e cipitation hardening copper 1.91 wt pct b e r y l l i u m alloy were studied. Sheet s a m p l e s suitable f o r t e n s i l e t e s t i n g w e r e explosively loaded to p r e s s u r e s of 10, 20, 30, 40, and 50 GPa. Subsequent t e n s i l e t e s t s w e r e p e r f o r m e d on s a m p l e s in the a s - s h o c k e d and shocked plus aged conditions. T h e i r p r o p e r t i e s a r e c o m p a r e d to those of m a t e r i a l d e f o r m e d by cold r o l l i n g and aged a f t e r cold rolling. The m e c h a n i c a l s t r e n g t h in the a s - s h o c k e d condition i n c r e a s e s l i n e a r l y with p r e s s u r e . The s t r e n g t h of the shocked plus aged m a t e r i a l also i n c r e a s e s with shock p r e s s u r e but at a s l o w e r r a t e . Unaged m a t e r i a l shocked to 50 GPa has a higher yield strength than m a t e r i a l cold r o l l e d 37 pct. However, the cold r o l l e d m a t e r i a l r e s p o n d s b e t t e r to aging. In the aged condition, 37 pct cold r o l l e d m a t e r i a l is s t r o n g e r than the m a t e r i a l shocked to 50 GPa. 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 r e v e a l s the onset of deformation twinning between 10 and 20 GPa. The volume fraction of twins and the dislocation density both i n c r e a s e with i n c r e a s i n g shock p r e s s u r e . The r e s u l t s indicate that deformation twinning has little significant strengthening effect in this s y s tem and that y i e l d s t r e n g t h i n c r e a s e s can be accounted for on the b a s i s of i n c r e a s i n g d i s location density.
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have been a number of studies to d e t e r m i n e the effects of shock loading on the m i c r o s t r u c t u r e and m e c h a n i c a l p r o p e r t i e s of m e t a l s . ~-9 It has been found that shock loading r e s u l t s in the f o r m a t i o n of a very high dislocation density and may also induce twinning o r a phase change. In general, shock loading will significantly strengthen a m e t a l even though v e r y little p l a s t i c deformation is introduced. This behavior is in c o n t r a s t with q u a s i s t a t i c cold working where l a r g e d i m e n s i o n a l changes a r e r e q u i r e d to produce much strengthening. S e v e r a l questions s t i l l r e m a i n unanswered r e l a t i v e to the p r o p e r t i e s introduced by shock loading. It is u n c l e a r to what extent deformation twinning from shock loading enhances the q u a s i s t a t i c t e n s i l e s t r e n g t h . ~~ Some i n v e s t i g a t o r s claim such twinning has no effect on r e s i d u a l mechanical strength; ~'3 o t h e r s r e p o r t significant strengthening e f f e c t s ? '~ While t h e r e has been l i t t l e work on d e t e r m i n i n g the aging behavior o r m e c h a n i c a l r e s p o n s e of p r e c i p i t a tion hardening alloys after s
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