Formation of metastable low temperature allotropie solid solutions in rare earth-zirconium systems
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the p r i m a r y solid s o l u t i o n s f o r m e d by r a r e e a r t h m e t a l s , both the r a r e e a r t h - m a g n e s i u m and r a r e e a r t h - z i r c o n i u m s y s t e m s a r e a t t r a c t i v e for the i n v e s t i gation of t h e i r t e r m i n a l solid solutions s i n c e l a r g e m u t u a l solid s o l u b i l i t i e s w e r e found in these s y s t e m s . In the p a s t y e a r s , s t u d i e s of the t e r m i n a l s o l u b i l i t y of these s y s t e m s at e q u i l i b r i u m conditions have yielded v a l u a b l e i n f o r m a t i o n r e g a r d i n g the atomic size effect of the r a r e e a r t h s in the f o r m a t i o n of solid s o l u t i o n s . In the p r e s e n t i n v e s t i g a t i o n , we will be c o n c e r n e d p r i m a r i l y with the alloying b e h a v i o r s b e t w e e n the r a r e e a r t h s and z i r c o n i u m at n o n e q u i l i b r i u m state (rectas t a b l e ) , which exhibits m a n y c h a r a c t e r i s t i c s quite diff e r e n t f r o m that o b s e r v e d at the e q u i l i b r i u m c o n d i t i o n s . The e q u i l i b r i u m phase d i a g r a m s of m o s t of the r a r e e a r t h - z i r c o n i u m s y s t e m s have a l r e a d y been i n v e s t i gated d u r i n g the p a s t decade. ~-s In g e n e r a l , r a r e e a r t h f o r m s a s i m p l e eutectic s y s t e m with z i r c o n i u m and no i n t e r m e d i a t e phase is found. Z i r c o n i u m d i s s o l v e s in both the high and low t e m p e r a t u r e allotropic f o r m s of r a r e e a r t h s (bee and hop r e s p e c t i v e l y ) with v a r y i n g s o l u b i l i t i e s . No m e a s u r a b l e s o l u b i l i t i e s of z i r c o n i u m a r e found in the f i r s t few r a r e e a r t h e l e m e n t s such as l a n t h a n u m and c e r i u m . 1 Only s m a l l a m o u n t s of s o l u bility a r e o b s e r v e d in n e o d y m i u mz and s a m a r i u m J F r o m g a d o l i n i u m to e r b i u m the s o l u b i l i t y i n c r e a s e s s u b s t a n t i a l l y , but it d e c r e a s e s again in l u t e t i u m . 2 The m a x i m u m s o l u b i l i t y of z i r c o n i u m among r a r e e a r t h m e t a l s has b e e n r e p o r t e d in the E r - Z r s y s t e m . A c c o r d ing to Copeland and Kato, 4 at eutectic t e m p e r a t u r e , up to 20.0 at. pct Z r d i s s o l v e s in a - e r b i u m , w h e r e a s Love ~ r e p o r t s a d i f f e r e n t value of 27.3 at. pet Z r . The c o n s i s t e n c y among d i f f e r e n t w o r k e r s on the z i r c o n i u m - r i c h side is r a t h e r p o o r , as shown in F i g . 1. R a r e e a r t h s have b e e n o b s e r v e d to d i s s o l v e m o s t l y in R. WANGis Assistant Professor, Department of Materials Science, University of Southern California, Los Angeles,Calif. Manuscript submitted July 21, 1971. METALLURGICALTRANSACTIONS
the high t e m p e r a t u r e a l l o t r o p i c f o r m (bcc)of z i r c o n i u m . S m a l l s o l u b i l i t i e s a r e o b s e r
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