Diffusion-phenomenon in Ti-Ti 5 Ge 3 eutectic
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Diffusion-Phenomenon in Ti-Ti sGe3 Eutectic A. S. YUE AND F. W. CROSSMAN
F I B E R - r e i n f o r c e d metal matrix composites produced by the e u t e c t i c s o l i d i f i c a t i o n technique a r e s u p e r i o r to those p r o d u c e d by p h y s i c a l l y m i x i n g the c o m p o n e n t s b e c a u s e 1) the f o r m e r have high i n t e r f a c i a l bond s t r e n g t h b e t w e e n m a t r i x and f i b e r p h a s e s under load; I'2 2) they a r e stable at e l e v a t e d t e m p e r a t u r e s ; 3 3) d a m a g e to the f i b e r s d u r i n g handling can be a v o i d e d b e c a u s e in e u t e c t i c s o l i d i f i c a t i o n , both m a t r i x and f i b e r p h a s e s a r e grown s i m u l t a n e o u s l y f r o m a e u t e c t i c liquid; 4 and 4) the f i b e r phase is e v e n l y d i s t r i b u t e d in the m e t a l m a t r i x , s,6 The only d i s a d v a n t a g e of the e u t e c t i c c o m p o s i t e is that one cannot i n c r e a s e the v o l u m e f r a c t i o n of the f i b e r phase which is fixed by the phase d i a g r a m of the s y s t e m . C o n s e q u e n t l y , m o s t e u t e c t i c s y s t e m s studied to date have f i b e r v o l u m e f r a c t i o n s l e s s than the c r i t i c a l f i b e r v o l u m e f r a c t i o n s n e e d e d to have r e i n f o r c e m e n t . T h i s note will outline an idea which would i n c r e a s e the v o l u m e f r a c t i o n of the f i b e r phase during cont r o l l e d e u t e c t i c s o l i d i f i c a t i o n . An explanation to a c count f o r the i n c r e a s e of the f i b e r phase i s a l s o given. C o n s i d e r a portion of a h y p o t h e t i c a l b i n a r y phase d i a g r a m a s shown in F i g . 1 which shows the e x i s t e n c e of a e u t e c t i c r e a c t i o n at t e m p e r a t u r e T E and a e u t e c told r e a c t i o n at a l o w e r t e m p e r a t u r e T ~ . When a c y l i n d e r of a e u t e c t i c liquid of c o m p o s i t i o n C E i s s o l i d i f i e d u n i d i r e c t i o n a l l y , a e u t e c t i c solid c o n s i s t i n g of a solid solution and AxBy i n t e r m e t a l l i c compound of the s a m e o v e r a l l c o m p o s i t i o n is n u c l e a t e d and grown f r o m the e u t e c t i c liquid at a l o w e r t e m p e r a t u r e T1. The amount of u n d e r - c o o l i n g n e e d e d to n u c l e a t e and g r o w the e u t e c t i c s o l i d is T E - T1. At t e m p e r a t u r e TI, the wt pct of AxBy i n t e r m e t a l l i c phase is a/(a + b) which f a v o r s the f o r m a t i o n of f i b e r - l i k e e u t e c t i c a c c o r d i n g to s t a t i s t i c a l data r e p o r t e d e l s e w h e r e , v If the c r y s t a l s t r u c t u r e of AxBy is known, then its density and thus its v o l u m e f r a c t i o n can be c a l c u l a t e d . As the s o l i d i f i e d e u t e c t i c solid continues to cool slowly to a l o w e r t e m p e r a t u r e T2, as i n d i c a t e d in Fig. 1, the c~ s o l i d solution phase will have a c
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