Homogenization of compacted blends of nickel and tungsten powders
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P O W D E R m e t a l l u r g y t e c h n i q u e s a r e i n c r e a s i n g in i m portance as a means for producing nickel-base alloys. In m o s t c a s e s the a l l o y s a r e f a b r i c a t e d f r o m e i t h e r p r e a l l o y e d p o w d e r s o r m e c h a n i c a l m i x t u r e s of c o n s t i t uent p o w d e r s . Although the f o r m e r method has b e e n u s e d f r e q u e n t l y , the l a t t e r h a s the a d v a n t a g e s of p r o v i d i n g h i g h e r g r e e n s t r e n g t h s and d e n s i t i e s in c o m p a c t s while a l s o p r o v i d i n g g r e a t e r f l e x i b i l i t y in the s e l e c t i o n of a l l o y c o m p o s i t i o n , s i n c e a wide r a n g e of p r e a l l o y p o w d e r c o m p o s i t i o n s is u n a v a i l a b l e at t h i s t i m e . The d i s a d v a n t a g e of p r o c e s s i n g c o m p a c t s of b l e n d e d p o w d e r s i s often the n e e d to p r o v i d e a s o l i d s t a t e , diffusional h o m o g e n i z a t i o n s t e p in the p r o c e s s . H o m o g e n i z a t i o n s t e p s can involve u n e c o n o m i c a l , h i g h temperature, long-time treatments unless careful cont r o l of p o w d e r and p r o c e s s p a r a m e t e r s i s taken with t r e a t m e n t s d e s i g n e d to b e only e x t e n s i v e enough to p r o v i d e the r e q u i r e d d e g r e e of h o m o g e n i z a t i o n . F o r e x a m p l e , a r e c e n t study h a s shown that H a s t e l l o y B s h e e t can be p r o d u c e d f r o m b l e n d s of e l e m e n t a l p o w d e r s with r e l a t i v e l y s h o r t - t i m e h e a t t r e a t m e n t s . 1 With t h i s p r o p e r c o n t r o l of the h o m o g e n i z a t i o n p r o c e s s , the m e c h a n i c a l and c o r r o s i v e p r o p e r t i e s w e r e found to be e q u i v a l e n t to t h o s e of c o m m e r c i a l c a s t and wrought sheet. Studies of the h o m o g e n i z a t i o n b e h a v i o r of c o m p a c t e d b l e n d s of e l e m e n t a l p o w d e r s in b i n a r y i s o m o r p h o u s s y s t e m s (e.g., Cu-Ni) have shown m a t h e m a t i c a l m o d e l s to give meaningful p r e d i c t i o n s of the h o m o g e n i z a t i o n k i n e t i c s and the e f f e c t s of p o w d e r and p r o c e s s v a r i a b l e s , z-5 The c o n c e n t r i c - s p h e r e m o d e l has been m o s t u s e f u l in p r o v i d i n g the b a s i s for c a l c u l a t i n g h o m o g e n i z a t i o n k i n e t i c s . 3-5 In this model, one component of the b l e n d is r e p r e s e n t e d b y a s p h e r i c a l p a r t i c l e ; the o t h e r
METALLURGICAL TRANSACTIONS A
VOLUME 6A, FEBRUARY 1975-329
Table I. Description of Ni and W Powders
r
0
1400
I ZO,I1
,,.f~
ID
~" 1000 I,-
X'-"~
|
I
E/2 ~ t/2
0
~12 [/2
~
II
Powder
Source
W W W W Ni
Sylvania Electric Products, Inc. Allied Cherrucal Carp9 Linde Corp. Lmde Carp9 International Nickel Co.
Mesh Size Range
Type M-40 (irregular) Spherical Spherical Spherical 123 (irregular)
200/270 200/270 14
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