Activities and phase boundaries in the Cr-Ni system using a solid electrolyte technique
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ALTHOUGH
t h e r e have b e e n many e x c e l l e n t i n v e s t i gations of the C r - N i phase d i a g r a m ~-~3 s o m e a r e a s of the s y s t e m a r e s t i l l in q u e s t i o n . Hansen ~ p u b l i s h e d two d i a g r a m s and the m o r e gene r a l l y a c c e p t e d of t h e s e is shown in Fig. 1. T h i s was c o m p i l e d f r o m a r e v i e w of the data p r e s e n t e d by n u m e r o u s i n v e s t i g a t o r s 2-7 who used t h e r m a l a n a l y s e s , X - r a y , and m e t a l l o g r a p h i c t e c h n i q u e s . As shown, the s y s t e m is an e u t e c t i c type with two a p p r e c i a b l e s o l i d s o l u t i o n s and an e x t e n s i v e two phase a r e a in the s o l i d s t a t e . As c i t e d by H a n s e n , ' v a r i o u s i n v e s t i g a t o r s d e t e r m i n e d the e u t e c t i c to e x i s t at 46 pct Ni and 1345~ T h i s study i n v o l v e s the d e t e r m i n a t i o n of the s h a p e s and l o cat i o n s of the s o l v u s l i n e s . T h e shape of the s o l v u s line on the c h r o m i u m - r i c h side of the s y s t e m , a s shown in F i g . 1, s u g g e s t s that c o n s i d e r a b l e h y s t e r e s i s m a y have o c c u r r e d in t h e r m a l a n a l y s e s and s l u g g i s h t r a n s f o r m a t i o n m a y also have been r e s p o n s i b l e for i n a c c u r a t e m e t a l l o g r a p h i c and X - r a y s t u d i e s . As a r e s u l t , the ex ac t l o c a t i o n s of the s o li d s t a t e boundaries are questionable. The solid e l e c t r o l y t e technique was s e l e c t e d in the c u r r e n t work b e c a u s e it i n v o l v e s e x p e r i m e n t s which a r e conducted u n d e r conditions of i s o t h e r m a l e q u i librium. The second d i a g r a m p u b li s h e d by Hansen r e s u l t e d f r o m the e x p e r i m e n t s by B lo o m and Grant 8 a s w e l l as by Stein and Grant. 9 T h e i r w o r k i n d i c a t e d an a l l o t r o p i c t r a n s f o r m a t i o n in c h r o m i u m and s u g g e s t e d the p o s s i b i l i t y of an e u t e c t o i d at 1215~ and 32 wt pct Ni. T h e s e t r a n s f o r m a t i o n s have not been i n d ic a t e d by o t h e r s , to date. P e r h a p s t h e i r a l l o y s w e r e c o n t a m i n a t e d with a g a s e o u s c o n s t i t u e n t such as n i t r o g e n . If so t h e i r work r e p r e s e n t s a s e c t i o n of the C r - N i - N t e r n a r y s y s t e m . Sufficient w o r k has been done s i n c e the r e v i v a l of s o l i d oxide e l e c t r o l y t e t e c h n i q u e s by Kiukkola and W a g n e r ~4 so that no e x t e n s i v e r e v i e w is n e e d e d h e r e . A l s o s e v e r a l r e c e n t s y m p o s i a such a s the 1967 Conf e r e n c e ~s at the U n i v e r s i t y of London on " E l e c t r o m o L. A. PUGLIESE,formerly Research Metallurgist, Latrobe Steel Co., Latrobe, Pa., is with Crucible Inc., Division of Colt Industries, G. R. FITTERER is Distinguished Professor, Metallurgical Engineering and Director, Center for The
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