The eutectoid region of the ti-pd system
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J. C. WILLIAMS, H. I. AARONSON, AND B. S. HICKMAN 700
1.2"
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DURINGthe
c o u r s e of an i n v e s t i g a t i o n of eutectoid d e c o m p o s i t i o n m e c h a n i s m s in T i - X eutectoid s y s t e m s , the a u t h o r s l e a r n e d of the r e m a r k a b l e confusion which e x i s t s with r e s p e c t to the d e t a i l e d c o n f i g u r a t i o n of the eutectoid r e g i o n (and other a r e a s ) of the T i - P d phase d i a g r a m . T h r e e v e r s i o n s of the eutectoid r e g i o n p r e v i o u s l y r e p o r t e d a r e shown by the light l i n e s in Fig. 1 ; the f i r s t t h r e e e n t r i e s in Table I s u m m a r i z e the p r i n cipal f e a t u r e s of each v e r s i o n . The Table shows that t h r e e d i f f e r e n t i n t e r m e t a l l i c compounds have b e e n p r o p o s e d as the s o l u t e - r i c h phase in e q u i l i b r i u m with a at t e m p e r a t u r e s below that of the eutectoid, and that eutectoid t e m p e r a t u r e s v a r y i n g over a r a n g e of 115~ and eutectoid c o m p o s i t i o n s r a n g i n g f r o m 25 to 41 wt pet have b e e n r e p o r t e d . An i n v e s t i g a t i o n of the T i - P d eutectoid r e g i o n was t h e r e f o r e u n d e r t a k e n in an effort not only to r e s o l v e these s e r i o u s conflicts but also to a s c e r t a i n why they m a y have o c c u r r e d . The c o m p o s i t i o n s of the alloys e m p l o y e d a r e l i s t e d in Table II. A p p r o x i m a t e l y 30 g of each alloy were a r c m e l t e d by the t u n g s t e n e l e c t r o d e - i n e r t gas p r o c e s s on a water cooled copper h e a r t h . Each alloy was m e l t e d twelve t i m e s , and both alloy and t u n g s t e n e l e c t r o d e w e r e weighed before and after m e l t i n g to e n s u r e that no t u n g s t e n c o n t a m i n a t i o n o c c u r r e d . M t e r m e l t i n g the a l l o y s w e r e wrapped in t a n t a l u m foil, s e a l e d in e v a c u ated s i l i c a c a p s u l e s , h o m o g e n i z e d for 5 d at 1000~ and water quenched. Individual s l i c e s , c a . 0.05 cm. thick, were cut f r o m the a l l o y s , r e w r a p p e d in t a n t a l u m foil, and s e a l e d again in e v a c u a t e d s i l i c a c a p s u l e s . T h e s e s a m p l e s were then heat t r e a t e d in the following s e q u e n c e to d e t e r m i n e the phase b o u n d a r i e s . M t e r s o l u t i o n a n n e a l i n g for 30 m i n at 950~ the s p e c i m e n s were r e a c t e d in a lead bath for c a . 16 h at 550~ in o r d e r to f o r m l a r g e a m o u n t s of finely divided a and compound. The s a m p l e s were then up quenched to a higher e q u i l i b r a t i o n t e m p e r a t u r e in a n o t h e r lead bath and f i n a l l y quenched into iced 10 pct b r i n e . The c a p s u l e s were s h a t t e r e d d u r i n g the quench. Annealing t i m e s of 8 h w e r e e m p l o y e d for d e t e r m i n a t i o n s of the eutectoid t e m p e r a t u r e . Depending upo
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