Oxide dispersed copper alloys by surface oxidation
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T H E d e v e l o p m e n t of oxide d i s p e r s e d (OD) o r oxide s t a b i l i z e d a l l o y s has b e e n r e l a t i v e l y slow s i n ce the d i s c o v e r y of SAP in 1946.1 One of the p r i m a r y r e a s o n s for the slow m a t u r a t i o n of OD a l l o y s h a s b e e n the difficult p r o b l e m of p r o d u c i n g and r e p r o d u c i n g l a r g e q u a n t i t i e s of m a t e r i a l p o s s e s s i n g p r o p e r t i e s e q u a l to o r e x c e e d i n g t h o s e shown by the s a m e m a t e r i a l p r o d u c e d on a s m a l l e r s c a l e in the l a b o r a t o r y . A s e c o n d r e a s o n r e s i d e s in the high c o s t of the a l l o y s , due in l a r g e p a r t to the e x p e n s i v e and i n t r i cate p r o c e s s i n g s t e p s c a l l e d for in m a n y i n s t a n c e s . The work r e p o r t e d h e r e i s the r e s u l t of an inv e s t i g a t i o n into a new m e t h o d of p r o c e s s i n g OD a l l o y s , a technique which is s u f f i c i e n t l y s i m p l e and i n e x p e n s i v e to o f f e r p r o m i s e of e a s i e r s c a l e - u p and c o m m e r c i a l i z a t i o n . The technique c o n s i s t s e s s e n t i a l l y of p r o d u c i n g a l l o y p o w d e r s with a v e r y l a r g e s p e c i f i c s u r f a c e a r e a . The a l l o y s a r e c h o s e n so that a highly o x i d i z a b l e solute a l l o y i n g e l e m e n t h a s a s o l i d s o l u b i l i t y of about 1 to 3 at. pet in the base m e t a l or alloy. If the solubility l i m i t is e x c e e d e d in the s t a r t i n g a l l o y , enough solute should be c o n v e r t e d to oxide to r e t u r n to a s o l i d solution. T h i s is a c c o m p l i s h e d by g e n e r a t i n g a l a r g e s p e c i f i c s u r f a c e a r e a in s u b m i c r o n t h i c k flake m a t e r i a l to g u a r a n t e e s i g n i f i c a n t c o n v e r s i o n of the oxidizable solute e l e m e n t to s t a b l e , r e f r a c t o r y oxide p a r t i c l e s and f i l m s . T h e a m o u n t of oxide f o r m e d depends on the solute c o n c e n t r a t i o n and the s u r f a c e a r e a g e n e r a t e d in c o m m i n u t i o n ; the oxide m u s t not flake off d u r i n g p r o c e s s i n g . The high f r e e e n e r g y of f o r m a t i o n of the oxide of the solute e l e m e n t p r o m o t e s r e a d y oxidation e v e n at r o o m t e m p e r a t u r e . D e p e n d i n g on the c o m p o s i t i o n , o t h e r m e t a l oxides will f o r m b e c a u s e of the high r e a c t i v i t y of the thin flake p o w d e r s . T h e s e n o n r e f r a c t o r y o x i d e s , which a r e m u c h l e s s s t a b l e , can e i t h e r be r e d u c e d or u t i l i z e d for i n t e r n a l o x id at i o n of additional solute in s u b s e q u e n t p r o c e s s i n g . T h u s , u n d e r the conditions of p r o p e r c o m p o s i t i o n , and s t a r t i n g al l o y p o w d e r , p a r t i c l e s i z e , and shape, one can p r o d u ce OD a l l o y s with r e a s o n a b l y
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