The effects of heat treatment and deformation on the homogenization of compacts of blended powders
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HECKEL
AND
M.
BALASUBRAMANIAM
H o m o g e n i z a t i o n of c o m p a c t s of b l e n d e d p o w d e r s is r e v i e w e d in t e r m s of the i n f l u e n c e of v a r i a b l e s which a r e known to affect the p r o c e s s . M a t h e m a t i c a l m o d e l s which d e s c r i b e m a j o r p r o c e s s v a r i a b l e s a r e d i s c u s s e d and evaluated with e x p e r i m e n t a l data. C o n s i d e r a t i o n is g i v e n to the effects of both heat t r e a t m e n t and d e f o r m a t i o n on the r a t e s of h o m o g e n i z a t i o n in o n e - p h a s e and m u l t i p h a s e b i n a r y s y s t e m s . G u i d e l i n e s a r e p r e s e n t e d which w i l l a s s i s t o t h e r w o r k e r s in the u s e of the m a t h e m a t i c a l m o d e l s a s p r e d i c t i v e t o o l s .
/ H E f a b r i c a t i o n of a l l o y s by powder m e t a l l u r g y p r o c e s s i n g m a y be c a r r i e d out through the u s e of p r e a l l o y e d powders o r by d i f f u s i o n a l h o m o g e n i z a t i o n of c o m p a c t e d b l e n d s of p o w d e r s . The l a t t e r method m u s t involve a d d i t i o n a l p r o c e s s i n g to a c h i e v e a s u i t a b l y mixed b l e n d of p o w d e r s and to b r i n g about the r e q u i r e d i n t e r d i f f u sion of the e l e m e n t s in the c o m p a c t e d blend. H o w e v e r , the h o m o g e n i z a t i o n p r o c e s s i n g r o u t e often p r o v i d e s the a d v a n t a g e of m i n i m a l c o m p a c t i o n d i f f i c u l t i e s c o m p a r e d with the p r e a l l o y route~ s i n c e one o r m o r e of the powd e r s m a y be a soft, e l e m e n t a l powder. In addition, diffusion p r o c e s s i n g o f f e r s the p o t e n t i a l for p r o v i d i n g m i c r o s t r u c t u r e s with " t a i l o r e d " a m o u n t s of i n t e r diffusion. The e a r l y t r e a t m e n t of the p r o b l e m of h o m o g e n i z a tion in powder c o m p a c t s by Rhines and Colton 1 has p r o v i d e d c o n s i d e r a b l e insight into a) the a n a l y s i s of the a p p r o p r i a t e diffusion p r o b l e m for o n e - p h a s e s y s t e r n s , and b) the method of applying this a n a l y s i s to e x p e r i m e n t a l data. They pointed out that both the d e v i ation of p a r t i c l e c o m p o s i t i o n f r o m the m e a n c o m p o s i tion and the d i s t a n c e b e t w e e n a d j a c e n t c e n t e r s of m a x i m u m and m i n i m u m c o n c e n t r a t i o n a r e i m p o r t a u t p a r a m e t e r s in the h o m o g e n i z a t i o n p r o c e s s . T h e i r data obtained on C u - N i c o m p a c t s of v a r i o u s c o m p o s i t i o n s and p a r t i c l e s i z e s , u s i n g e l e c t r i c a l r e s i s t i v i t y m e a s u r e merits to a s s e s s the p r o g r e s s of h o m o g e n i z a t i o n , showed that the a m o u n t of i n t e r d i f f u s i o n v a r i e s a) as the s q u a r e of the d i s t a n c e b e t w e e n the m a x i m u m and m i n i m u m c o n c e n t
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