Determination of eutectic compositions in complex metal systems
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S I N C E the publication of a paper by Yue and C l a r k ' on the d e t e r m i n a t i o n of eutectic c o m p o s i t i o n s in m e t a l lic s y s t e m s by the z o n e - m e l t i n g technique, m a n y i n v e s t i g a t o r s have used this approach to r e d e t e r m i n e e u t e c t i c c o m p o s i t i o n s of m a n y b i n a r y s y s t e m s for m e c h a n i c a l p r o p e r t y studies. L e m k e y , B a y l e s , and Salkind 2 used this technique to r e d e t e r m i n e the e u t e c tic c o m p o s i t i o n s in Ni-NiBe and T i - T i B b i n a r y s y s t e m s and found that t h e i r c o r r e c t eutectic c o m p o s i t i o n s a r e 4.6 wt pct Be and 2.0 wt pct B a s c o m p a r e d with c u r r e n t l y used v a l u e s 3 of 5.7 wt pct Be and 3.6 wt pct B. L a t e r , L e m k e y , H e r t z b e r g , and F o r d 4 r e d e t e r m i n e d the eutectic c o m p o s i t i o n of the A1-AlsNi s y s tem to be 6.2 wt pct a g a i n s t 5.7 wt pct p r e v i o u s l y r e ported by Wiley 5 and in a g r e e m e n t with the l a t e s t r e p o r t e d value.6 Shapiro and F o r d ~ have used the s a m e technique to r e d e t e r m i n e the eutectic c o m p o s i t i o n of the Ni-B s y s t e m and found that the e u t e c t i c c o m p o s i tion of 3.11 + 0.05 wt pct B a g a i n s t the value of 4.0 wt pct r e p o r t e d by K o l o m y t s e v f In t h e i r r e c e n t s t u d i e s on the m e c h a n i c a l p r o p e r t i e s of t i t a n i u m - b a s e e u t e c t i c s , Yue and C r o s s m a n ~ have r e d e t e r m i n e d the eutectic c o m p o s i t i o n of the t i t a n i u m - r i c h end of the T e - G e b i n a r y s y s t e m and found that the c o r r e c t eutectic composition is T i - 2 1 wt pct Ge. Recent i n t e r e s t in r e d e t e r m i n i n g e u t e c t i c c o m p o s i tions in b i n a r y eutectic s y s t e m s s t e m s f r o m the fact that in o r d e r to obtain a l i g n e d m i c r o s t r u c t u r e s in eutectic c o m p o s i t e s for m e c h a n i c a l p r o p e r t y s t u d i e s , a c o r r e c t eutectic c o m p o s i t i o n m u s t be known. If a eutectic composite of an i n c o r r e c t c o m p o s i t i o n was used d u r i n g the solidification p r o c e s s , p r o e u t e c t i c compounds o r p r o e u t e c t i c p r i m a r y d e n d r i t e s a r e p r o duced c o e x i s t i n g with the a l i g n e d eutectic s t r u c t u r e . The e x i s t e n c e of p r o e u t e c t i c d e n d r i t e s in s p e c i m e n s under load p r o m o t e s t h e i r p r e m a t u r e f a i l u r e , thus d e c r e a s i n g the s t r e n g t h of the a l i g n e d eutectic. F u r t h e r m o r e , Salkind e t a l . I~ have r e p o r t e d that the a l i g n m e n t of d e n d r i t e - f r e e A13Ni r o d s e m b e d d e d in the a l u m i n u m m a t r i x has r e s u l t e d in a t h r e e f o l d i n c r e a s e in s t r e n g t h over that exhibited by a s - c a s t m a t e r i a l s . F o r this r e a s o n , m e t a l l i c c o m p o s i t
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