The thermal stability of the fibrous copper-chromium eutectic
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i s o t h e r m a l s t a b i l i t y of e u t e c t i c m i c r o s t r u c t u r e s h a s b e e n of r e c e n t i n t e r e s t . 1-1~ M o s t s y s t e m s that h a v e b e e n s t u d i e d e x h i b i t e x c e l l e n t m i c r o s t r u c t u r a l s t a b i l i t y in c o m p a r i s o n to c o n v e n t i o n a l high t e m p e r a t u r e a l l o y s . B e c a u s e of the g e n e r a l l y u n i f o r m m i c r o s t r u c t u r e of t h e s e m a t e r i a l s , c o a r s e n i n g t h a t d o e s o c c u r i s f r e q u e n t l y r e l a t e d to, o r i n i t i a t e d by~ s t r u c t u r a l d e ! e a t s such2as p h a s e t e r m i n a t i o n s , l, 7 , b r a n c h e s , , b a n d i n g o r i n t e r f a c i a l l e d g e s , 9 a l l of which a r e f o r m e d d u r i n g the s o l i d i f i c a t i o n p r o cess. T h e C u - C r e u t e c t i c was one of the f i r s t f i b r o u s eutecties investigated insofar as mechanical propert i e s w e r e c o n c e r n e d , x~'12 H o w e v e r , no s t u d i e s on i t s i s o t h e r m a l s t a b i l i t y have y e t b e e n r e p o r t e d . It i s of a d d i t i o n a l i n t e r e s t b e c a u s e it i s a s y s t e m c o m p o s e d of two m e t a l l i c p h a s e s and, t h e r e f o r e , a study of the e x t e n t of c o a r s e n i n g in a s y s t e m s u c h a s t h i s would be u s e f u l f o r c o m p a r i s o n to c o a r s e n i n g r a t e s in the more widely studied metal-intermetallic systems. T h e w o r k h e r e i n r e p o r t e d i s a d e s c r i p t i o n of a s t u d y of the i s o t h e r m a l s t a b i l i t y of the C u - C r s y s t e m . I. E X P E R I M E N T A L PROCEDURE M a s t e r a l l o y s (99.999 p c t p u r i t y of Cu and C r ) of the e u t e c t i c c o m p o s i t i o n (1.5 wt p c t Cr) w e r e p r e p a r e d by a r c m e l t i n g under an a r g o n a t m o s p h e r e . The m a s t e r a l l o y i n g o t s w e r e p l a c e d in an a l u m i n a c r u c i b l e and s u b s e q u e n t l y d i r e c t i o n a l l y s o l i d i f i e d u n d e r a r g o n , u t i l i z i n g induction h e a t i n g f o r m e l t i n g . A m a x i m u m t e m p e r a t u r e of 1300~ ( e u t e c t i c t e m p e r a t u r e --- 1075~
L. Y. LIN is Postdoctoral Research Associate, Department of Materials Engineering, Drexel University, Philadelphia, PA. T. H. COURTNEY is Professor, Department of Metallurgical Engineering, Michigan Technological University, Houghton, MI 49931. J. P. STARK and K. M. RALLS are both Professors, Department of Mechanical Engineering, Materials Science Laboratory, The University of Texas at Austin, Austin, TX. Manuscript submitted January 9, 1976. METALLURGICAL TRANSACTIONS A
w a s u s e d in t h i s w o r k . S o l i d i f i c a t i o n r a t e s of a p p r o x i m a t e l y 2.5 and 1.2 cm//h w e r e u s e d . S p e c i m e n s f o r c o a r s e n i n g s t u d i e s w e r e r e m o v e d f r o m the c e n t e r p o r t i o n s of the ingot to i n s u r e u n i f o r m f i b e r d e
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