Influence of interphase boundary structure upon the mechanism of eutectoid decomposition in a Ti-Ni alloy
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Influence of Interphase Boundary Structure Upon the Mechanism of Eutectoid Decomposition in a Ti-Ni Alloy T. P. DIEBOLD, G. W. FRANTI
H. I. AARONSON,
AND
A r e c e n t s u r v e y of e u t e c t o i d 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 a l l o y s d e m o n s t r a t e d that in hypoe u t e c t o i d a l l o y s r e a c t e d b e t w e e n the e u t e c t o i d t e m p e r a t u r e and e i t h e r the M s o r the lowest t e m p e r a t u r e at which t r a n s f o r m a t i o n s t i l l o c c u r s at a r e a s o n a b l e r a t e , the only e u t e c t o i d d e c o m p o s i t i o n p r o d u c t is bainite* when X is Bi, Co, F e , Mn, Ni, lab and P d . ~ *The generalized microstructural definition of bainite 2 is employed. In the context of Ti-X alloys, bainite so defined is a non-lamellar dispersion of intermetallic compound particles amongst proeutectoid a. Other, quite different definitions of bainite are also used. 2,3 No confusion should result, however, if one bears in mind that this Communication is solely concerned with the occurrence of two different modes of eutectoid decomposition: the non-lamellar (bainite) and the lamellar (peadite) modes.
The s a m e r e s u l t was p r e v i o u s l y r e p o r t e d for hypoe u t e c t o i d T i - C r a l l o y s . 4,5 Hypoeutectoid T i - C u r e p r e s e n t s the one e x c e p t i o n found. 1 Only a s m a l l p r o p o r t i o n of the e u t e c t o i d s t r u c t u r e is p e a r l i t e n e a r the e u t e c t o i d t e m p e r a t u r e but at lower t e m p e r a t u r e s n e a r l y a l l eut e c t o i d d e c o m p o s i t i o n t a k e s p l a c e b y the p e a r l i t i c m e c h a n i s m . T h e s e r e s u l t s a r e quite d i f f e r e n t f r o m t h o s e found in h y p o e u t e c t o i d F e - C a l l o y s , w h e r e p e a r lite i s n o r m a l l y the only e u t e c t o i d s t r u c t u r e at low T. P. DIEBOLD, f o r m e r l y U n d e r g r a d u a t e Student, D e p a r t m e n t o f Metallurgical Engineering, Michigan Technological University, H o u g h t o n , Mich., is n o w G r a d u a t e Student, D e p a r t m e n t of Materials Science, N o r t h w e s t e r n University, Evanston, Ill. 60201. G. W. F R A N T I and H. I. A A R O N S O N are P o s t d o c t o r a l Research Associate and Professor, respectively, D e p a r t m e n t o f Metallurgical Engineering, Michigan Technological University, H o u g h t o n , MI 4 9 9 3 1 . Manuscript s u b m i t t e d March 17, 1978. METALLURGICAL TRANSACTIONS A
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