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for t h r e e s y s t e m s Cu-Ni, C u - A g and Cu-Sb will be p r e s e n t e d and d i s c u s s e d as they r e l a t e to 1) the p r i m a r y d e n d r i t e s in b i n a r y a l l o y s , 2) the p r i m a r y dend r i t e s in a t e r n a r y alloy, and 3) s e c o n d a r y d e n d r i t e s . M e a s u r e m e n t s of p r i m a r y and s e c o n d a r y d e n d r i t e a r m spacings, as a function of d i s t a n c e f r o m the chill, will be c o n s i d e r e d and r e l a t e d to the p o u r i n g t e m p e r a t u r e , f r e e z i n g r a t e , and cooling r a t e . F i n a l l y , from the s o l ute d i s t r i b u t i o n a s s o c i a t e d with i n d i v i d u a l p r i m a r y d e n d r i t e s , the extent of i n t e r d e n d r i t i c fluid m i x i n g d u r i n g s o l i d i f i c a t i o n will be evaluated. EXPE RIME NTAL The alloys i n v e s t i g a t e d were c o p p e r - b a s e b i n a r y a l loys c o n t a i n i n g 1 to 8 pct Ni, 1 to 8 pct Ag and 1 to 8 pct Sb. To e x a m i n e the effect of two solute additions a 4.5 pct Ni 4.5 pct Ag t e r n a r y alloy was also e x a m ined. To p r o d u c e the ingots, the c o n s t i t u e n t s of 99.99 pct p u r i t y were m e l t e d in vacuum, by induction, irl a g r a p h ite c r u c i b l e for the Cu-Ag and Cu-Sb a l l o y s and an a l u m i n a c r u c i b l e for the Cu-Ni a l l o y s , u s i n g the app a r a t u s shown in Fig. 1. The m e l t was allowed to hom o g e n i z e for 30 m i n and then c a s t t h r o u g h a hole in the bottom of the c r u c i b l e into a c a s t i n g c h a m b e r , by lifting a t h e r m o c o u p l e n o r m a l l y b l o c k i n g the hole. The c a s t i n g c h a m b e r c o n s i s t e d of a heated quartz s l e e v e for the C u - N i alloys, or graphite for the other alloys. Solidification o c c u r r e d p r o g r e s s i v e l y f r o m a w a t e r cooled copper chill, positioned in the bottom of the sleeve j u s t p r i o r to casting, r e s u l t i n g in a c o l u m n a r d e n d r i t i c s t r u c t u r e which was o b s e r v e d to be q u a l i t a tively the s a m e for all the a l l o y s e x a m i n e d . The c a s t ing p r o d u c e d was 3 cm in d i a m e t e r and a p p r o x i m a t e l y 7 cm in height. VOLUME 3, JANUARY 1972-93

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Fig. 1--Apparatus for directionally casting copper alloys in vacuum. Melt t e m p e r a t u r e s w e r e d e t e r m i n e d by c h r o m e l a l u m e l or p l a t i n u m - p l a t i n u m 10 pct r h o d i u m t h e r m o couples i m m e r s e d in the m e l t . P o u r i n g t e m p e r a t u r e s w e r e in the r a n g e of 1150 ~ to 1350~ T e m p e r a t u r e s in the c a s t i n g were m e a s u r e d with fine c h r