The effect of low melting point phases on the elevated temperature microstructural stability of hot pressed beryllium
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T H E w o r k is p a r t of a p r o g r a m d e s i g n e d to i m p r o v e the c r e e p p r o p e r t i e s of h o t - p r e s s e d b e r y l l i u m . One f a c t o r that is e x p e c t e d to be i m p o r t a n t in t h i s r e g a r d is b e r y l l i u m ' s a b i l i t y to m a i n t a i n a s t a b l e high t e m p e r a t u r e d i s l o c a t i o n s u b s t r u c t u r e . The h i g h e s t t e m p e r a t u r e at which this s u b s t r u c t u r e can be m a i n t a i n e d is o b v i o u s l y the r e c r y s t a l l i z a t i o n t e m p e r a t u r e which in t u r n is c o n t r o l l e d by the BeO p a r t i c l e s i z e . In this w o r k t h e r e f o r e the f a c t o r s c o n t r o l l i n g BeO p a r t i c l e s i z e in h o t - p r e s s e d b e r y l l i u m b l o c k a r e e x a m i n e d . 1.0 M A T E R I A L S The b e r y l l i u m used in this i n v e s t i g a t i o n was in the f o r m of h o t - p r e s s e d b l o c k s with the e x c e p t i o n of the high p u r i t y ingot s h e e t . The B r u s h - W e l l m a n (B-W) b l o c k s w e r e c o n v e n t i o n a l l y h o t - p r e s s e d , although in m a n y c a s e s p r e s s u r e was a p p l i e d b e f o r e r e a c h i n g m a x i m u m t e m p e r a t u r e and i n c r e m e n t a l l y i n c r e a s e d to full p r e s s u r e a p p l i e d at the m a x i m u m p r e s s i n g t e m p e r a t u r e . The KBI m a t e r i a l s with the e x c e p t i o n of RR242 w e r e p r o d u c e d by hot i s o s t a t i c p r e s s i n g (HIP). The HIP p r o c e s s u s e s p r e s s u r e s much h i g h e r than n o r m a l , allowing the p r e s s i n g t e m p e r a t u r e to be l o w e r . It a l s o p e r m i t s the use of v e r y p u r e b e r y l l i u m p o w d e r s , which in n o r m a l h o t - p r e s s i n g do not a c h i e v e full d e n s i t y without the addition of s i n t e r i n g aids such a s s i l i c o n . The c o m p o s i t i o n of the d i f f e r e n t m a t e r i a l s is given in Table I. 2.0 E X P E R I M E N T A L TECHNIQUES BeO p a r t i c l e s i z e was m e a s u r e d in both a s - p r e s s e d and h e a t - t r e a t e d b e r y l l i u m by 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 . Counts w e r e m a d e s e p a r a t e l y for p a r t i c l e s in the g r a i n b o u n d a r y and p a r t i c l e s within the g r a i n s . Counting was a c c o m p l i s h e d b y using a C a r l DONALD WEBSTER is Research Scientist at the Metallurgy and Composites Laboratory of Lockheed Missiles& Space Company, Inc., Palo Alto, Calif. 94304. Manuscript submitted March 27, 1974. METALLURGICAL TRANSACTIONS A
Z e i s s p a r t i c l e s i z e a n a l y z e r on p r i n t s f r o m 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 g r a p h at m a g n i f i c a t i o n s of 8000 o r 40,000. Two h u n d r e d p a r t i c l e s w e r e counted for e a c h d a t a point. The s t a b i l i t y of the oxide d i s p e r s i o n at high t e m p e r a t u r e s was d e t e r m i n e d by p a r
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