The solid solubility of carbon in a Ni-Co alloy
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[9]
w h e r e N v = 3 f / 4 ~ r 3 and Sv, the b o u n d a r y a r e a p e r unit v o l u m e , is given by S v = 2 / L . In t h i s c a s e the c e l l s i z e L is n = Cr/f
Ua
[10]
w h e r e C = 2.71 as p r e d i c t e d by the Z e n e r m o d e l and C = [5.52 - 7 . 3 6 / Z ] V2 a c c o r d i n g to Gladman. A l l o w ing f o r the f a c t that the condition (S = 0, r = 0) is not p h y s i c a l l y r e a l i z a b l e , one obtains L = C,r/f
1/z + L o
[11]
w h e r e L 0 is the l o w e r l i m i t of a p p l i c a b i l i t y of the r e lation. That this r e l a t i o n is obeyed by the q u e n c h e d - a n d t e m p e r e d s t e e l s within the r a n g e of the a v a i l a b l e e x p e r i m e n t a l data is shown in Fig. 2. Also plotted in the f i g u r e a r e data f r o m the l i t e r a t u r e on q u e n c h e d - a n d t e m p e r e d s t e e l s 6 and on an i s o f o r m e d s t e e l 7 with s i m i l a r m i c r o s t r u c t u r e s . A l e a s t s q u a r e s fit g i v e s L o = 0.22/~m and C 1 = 1.63. If the c o n s t a n t C 1 m a y be a s s u m e d to be a p p r o x i m a t e l y the s a m e as C, then the o b s e r v e d v a l u e of C, is low c o m p a r e d to the v a l u e of 2.71 c a l c u l a t e d a c c o r d i n g to the Z e n e r r e l a t i o n . T h i s d i s -
The Solid Solubility of Carbon in a Ni-Co Alloy R. GIBALA AND P. MOSER T h e r e has b e e n g r e a t i n t e r e s t f o r many y e a r s in the t h e r m o d y n a m i c s of t e r n a r y s o l i d s o l u t i o n s in which one s o l u t e d i s s o l v e s i n t e r s t i t i a l l y . F r o m a p r a c t i c a l point of v i e w , m a n y such m a t e r i a l s a r e p r o t o t y p e s of c o m m e r c i a l l y i m p o r t a n t a l l o y s and m u s t be w e l l c h a r a c t e r i z e d f o r o p t i m u m use. F u n d a m e n t a l l y , the t h e o r e t i c a l d e v e l o p m e n t of the t h e r m o d y n a m i c s of so l i d s o l u t i o n s has b e e n a d v a n c e d c o n s i d e r a b l y in r e c e n t y e a r s , m a k i n g the a n a l y s i s of s o l u t e i n t e r a c t i o n s in sol i d s o l u t i o n s a s o m e w h a t e a s i e r ta s k . 1-3 In the c o u r s e of an i n v e s t i g a t i o n of the a n e l a s t i c and m a g n e t i c r e l a x a t i o n b e h a v i o r of t e r n a r y N i - C o - C s o l i d s o l u t i o n s , we found it n e c e s s a r y to know the d i f f e r e n c e in c a r b o n s o l u b i l i t y b e t w e e n the t e r n a r y a l l o y s and the
terminal Ni-C and Co-C binary alloys. The present paper gives carbon solubility data obtained from resistivity measurements on 50 pct Ni-50 pct Co-C alloys, which were the ones studied most extensively. The Ni-Co-C alloys were prepared by high frequency induction melting of appropriate amounts of the high purity constituents (Ni-99.95 pct, Co-99.95 pct, graphite-99.9 pct) in alumina crucibles in a purified hydroR. GIBALA was formerly Visiting Scientist, and P. MOSER is Project Director, Section de Physique du
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