Mechanical properties of diffusion bonded beryllium ingot sheet
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A t e c h n i q u e f o r p r o d u c i n g t h i c k b e r y l l i u m p l a t e f r o m ingot s o u r c e m a t e r i a l by d i f f u s i o n bonding t o g e t h e r thin s h e e t s i s d e s c r i b e d . The bonds p r o d u c e d a r e a t l e a s t a s s t r o n g a s the m a t r i x , and a r e p r o d u c e d u n d e r c o n d i t i o n s w h e r e no s i g n i f i c a n t g r a i n growth o c c u r s . The l a m i n a t e d p l a t e h a s b e t t e r m e c h a n i c a l p r o p e r t i e s than t h e s h e e t f r o m which it w a s m a d e , and p r o p e r t i e s s u b s t a n t i a l l y s u p e r i o r to s h e e t of s i m i l a r t h i c k n e s s r o l l e d d i r e c t l y f r o m the ingot. Room t e m p e r a t u r e t e n s i l e e l o n g a t i o n s of a p p r o x i m a t e l y 18 pct w e r e o b s e r v e d in the l a m i n a t e d p l a t e . D i r e c t l y r o l l e d p l a t e of s i m i l a r t h i c k n e s s n o r m a l l y e x h i b i t s 2 to 4 pct e l o n g a t i o n , and t h e s h e e t f r o m which the l a m i n a t e w a s m a d e f a i l e d a f t e r about 12 pct e l o n g a t i o n . The i n c r e a s e d d u c t i l i t y of the l a m i n a t e i s a c o n s e q u e n c e of the c o m p r e s s i v e c r e e p d e f o r m a t i o n a c c o m p a n y i n g bonding and m o s t l i k e l y r e s u l t s f r o m a d i s l o c a t i o n s u b s t r u c t u r e , p r o d u c e d by the d e f o r m a t i o n , which d i f f e r s f r o m the s u b s t r u c t u r e d e v e l o p e d by a n n e a l i n g .
T H E b r i t t l e n e s s of b e r y l l i u m r e s t r i c t s i t s u s e in s t r u c t u r a l a p p l i c a t i o n s . T h e m a i n c a u s e of t h e low d u c t i l i t y of p o l y c r y s t a l l i n e b e r y l l i u m at r o o m t e m p e r a t u r e i s thought to b e t h e l a c k of a v a i l a b l e s l i p s y s t e m s a l o n g the c a x i s d i r e c t i o n . D e f o r m a t i o n r e s u l t s in the buildup of s t r e s s c o n c e n t r a t i o n s at the g r a i n b o u n d a r i e s and r e s u l t s in the f o r m a t i o n of bend p l a n e s , due to b a s a l s l i p , 1-s which l e a d s to c l e a v a g e and b r i t t l e f r a c t u r e s at s m a l l s t r a i n s , often only 1 to 3 p c t . T h e d u c t i l i t y i s g e n e r a l l y i n c r e a s e d by r e d u c i n g t h e g r a i n s i z e . z-s In a d d i t i o n , i n c r e a s e d d u c t i l i t y in the p l a n e of t h e s h e e t i s o b s e r v e d with i n c r e a s e d b a s a l t e x t u r e . The increased basal t~xture, however, simultaneously r e d u c e s f o r m a b i t i t y . 5'6 G r a i n s i z e r e d u c t i o n i s p r i m a r i l y a c h i e v e d in c a s t and w a r m - r o l l e d b e r y l l i u m by i n c r e a s i n g the t o t a l r e duction in t h i c k n e s s f r o m t h e o r i g i n a l ingot. B e r y l l i u m s h e e t s with a t h i c k n e s s of 0.025 in. (0.64 ram) a n d l e s s , and a g r a i n s i z e * of a b o u t 16 p m have b e e n p
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