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t wO o-phase m S La t e r i a l s Iwith r e gDu l a r s t r u c t u r e s can S o m e t i m e s be p r e p a r e d by a o n e - s t e p p r o c e s s . To e n s u r e p e r f e c t s t r u c t u r e s , the f o r m a t i o n of d e n d r i t e s and c e l l u l a r s t r u c t u r e s m u s t be avoided. The m o s t w i d e l y i n v e s t i g a t e d s i n g l e - s t e p p r o c e s s is the u n i d i r e c t i o n a l s o l i d i f i c a t i o n of a b i n a r y e u t e c t i c m e l t . The s i m p l e s t way to a v o i d d e n d r i t e s is to s o l i d i f y a m e l t of e x a c t e u t e c t i c c o m p o s i t i o n , as the a v e r a g e c o m p o s i t i o n of the two s o l i d p h a s e s is then e x a c t l y the s a m e a s file c o m p o s i t i o n of the e u t e c t i c liquid. This is g e n e r a l l y not t r u e , h o w e v e r , for the s o l i d i f i c a t i o n of a t e r n a r y liquid whose c o m p o s i t i o n l i e s in a e u t e c t i c t rou g h . In a p r e v i o u s p a p e r I we r e p o r t e d the e x i s t e n c e of a c u r v e of c o m p o s i t i o n s in the F e - C r - C s y s t e m c o r r e s p o n d i n g to m o r e o r l e s s r e g u l a r s t r u c t u r e s of (Cr, Fe)TC s r o d s in a m e t a l m a t r i x , a f t e r u n i d i r e c t i o n a l s o l i d i f i c a t i o n under s t e a d y - s t a t e c o n d it io n s , i.e., w i t h out m e t a l d e n d r i t e s o r thick p r i m a r y c a r b i d e n e e d l e s . This c u r v e was c o m p a r e d with the p r o j e c t i o n of the e u t e c t i c trough on the c o m p o s i t i o n plane as d e t e r m i n e d by s e v e r a l a u t h o r s . 2-s Though t h e r e a r e r a t h e r l a r g e d i s c r e p a n c i e s b e t w e e n the r e s u R s of t h e s e a u t h o r s , the p r o j e c t i o n s w e r e a ll s i t u a t e d on the s a m e side of the c o m p o s i t i o n c u r v e that had b e e n d e t e r m i n e d by us. This e x p e r i m e n t a l r e s u l t r e f l e c t s a g e n e r a l f e a t u r e . R will be shown that the e u t e c t i c t r o u g h in a t e r n a r y s y s t e m g e n e r a l l y does not c o i n c i d e with the c u r v e of m e a n c o m p o s i t i o n s of the two s o l i d p h a s e s , which we c a l l the e f f e c t i v e t e r n a r y s o l i d u s c u r v e (ETS c u r v e ) ( s e c t i o n 1).*

1) SOLIDIFICATION O F A LIQUID IN A T E R N A R Y E U T E C T I C TROUGH; TH E E F F E C T I V E T E R N A R Y SOLIDUS CURVE A s y s t e m A - B - C at a c o n s t a n t p r e s s u r e is c o n s i d e r e d . F o r the s a k e of s i m p l i c i t y it is a s s u m e d that the b i n a r y s y s t e m s A - B and B - C f o r m s i m p l e e u t e c t i c s w h e r e a s A and C a r e m i s c i b l e in the s o l i d s t a t e . The e x i s t e n c e r e g i o n s of the B p h a s e and of the m i x e d A - C p h a s e in the d i r e c t i o n of B a r e a s s u m e d to be i n f i n i t e s i m a l . It is f u r t h e r a s s u m e d that the c o m p o n e n t s a r