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D. D. CROOKS,

AND

A. E. VIDOZ

The r e c r y s t a l l t z a t i o n b e h a v i o r of b e r y l l i u m c o n t a i n i n g fine BeO d i s p e r s i o n s has b e e n s t u d ied by following the changes of h a r d n e s s d u r i n g a n n e a l i n g and the m o d i f i c a t i o n s of the m i c r o s t r u c t u r e by optical and 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 . It was found that for equal c o n c e n t r a t i o n s of BeO 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 was dependent upon the size of the d i s p e r s o i d , b e i n g higher the f i n e r the m e d i a n p a r t i c l e size of the oxide. In an alloy with a m e d i a n size of 600A a d i s l o c a t i o n s u b s t r u c t u r e was m a i n t a i n e d up to v e r y n e a r the m e l t i n g point of b e r y l l i u m .

IT

has b e e n shown that a l a r g e p a r t of the high t e m p e r a t u r e s t r e n g t h of d i s p e r s i o n - h a r d e n e d m a t e r i a l s r e s u l t s f r o m the p r e s e n c e of a stable d i s l o c a t i o n s u b s t r u c t u r e . 1-3 For TD N i c h r o m e it was d e m o n s t r a t e d b y W e b s t e r 4 that the s u b s t r u c t u r e developed by t h e r m o m e c h a n i c a l t r e a t m e n t s is the d o m i n a n t s t r e n g t h e n ing m e c h a n i s m at e l e v a t e d t e m p e r a t u r e s . The d i s p e r sold plays an i m p o r t a n t r o l e in the f o r m a t i o n of the d i s l o c a t i o n s u b s t r u c t u r e by r e t a r d i n g or s u p p r e s s i n g r e c r y s t a l l i z a t i o n d u r i n g heat t r e a t m e n t . The d i s p e r s e d p a r t i c l e s i n c r e a s e 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 of the alloy, t h e r e b y allowing the use of t h e r m o m e c h a n i c a l p r o c e s s i n g to develop the stable d i s l o c a t i o n n e t s . T h e i r effect upon 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 depends on the c h a r a c t e r i s t i c s of the d i s p e r s o i d ; i.e., the v o l ume f r a c t i o n and p a r t i c l e size. F o r equal c o n c e n t r a tion of the d i s p e r s e d phase the s m a l l e r p a r t i c l e size the m o r e effective the d i s p e r s i o n . The work d e s c r i b e d h e r e is p a r t of a p r o g r a m whose objective is to i m p r o v e the high t e m p e r a t u r e c r e e p s t r e n g t h of b e r y l l i u m without d e t r i m e n t to its r o o m t e m p e r a t u r e m e c h a n i c a l p r o p e r t i e s . In this work the effect of oxide d i s p e r s i o n s on the high t e m p e r a t u r e s t r u c t u r a l s t a b i l i t y of b e r y l l i u m a r e d e s c r i b e d . P a r t i c u l a r e m p h a s i s has b e e n placed on the s t a b i l i t y of d i s l o c a t i o n s u b s t r u c t u r e s p r o d u c e d by cold work. I. E X P E R I M E N T A L PROCEDURE All the m a t e r i a l s used in this i n v e s t i g a t i o n were p r o duced by K a w e c k i - B e r y l c o I n d u s t