Transmission electron microscopy study of face-centered orthorhombic martensite in Ti-12.6 pct V alloy
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S O f a r t h e r e have b e e n r e p o r t e d t h r e e k i n d s of m a r t e n s i t e s in t i t a n i u m - b a s e a l l o y s : hcp, o r t h o r h o m b i c (distorted hcp) and fcc. The f i r s t hcp m a r t e n s i t e (c~') has been w e l l - e s t a b l i s h e d in morphology and c r y s t a l lography, and the i n t e r n a l i n h o m o g e n e i t i e s have also been brought to light r e c e n t l y by m e a n s of t r a n s m i s sion e l e c t r o n m i c r o s c o p y ? -7 The second o r t h o r h o m b i c m a r t e n s i t e (c~") was found in T i - M o , -W, - T a , - R e , -Nb, and -V alloys by m e a n s of X - r a y d i f f r a c t i o n ~ and e l e c t r o n t n i c r o s c o p y . 9'1~ In addition to the c~' and ~" m a r t e n s i t e s , the fcc m a r t e n s i t e has been found in thin foil s p e c i m e n s of T i - A 1 - V - M o , 2 T i - F e , 4 _ C r , n -Mo, 7 and -Mn7 a l l o y s , and it is c o n s i d e r e d to be c h a r a c t e r i s t i c of thin s p e c i m e n s u and to be p r o d u c e d s p o n t a n e o u s l y d u r i n g e l e c t r o p o l i s h i n g .7 S e v e r a l r e p o r t s on m a r t e n s i t e s in the T i - V alloy s y s t e m will be r e v i e w e d in m o r e detail with r e s p e c t to the p r e s e n t study. M c M i l l a n e t a l . ~ i n v e s t i g a t e d the m a r t e n s i t e in a T i - 7 . 5 wt pct V alloy by m e a n s of t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y and found only a n a ' m a r t e n s i t e with { 1 0 i l } twins. On the o t h e r hand, B a g a r i a t s k i i et al.a e x t e n s i v e l y i n v e s t i g a t e d m a r t e n s i t e s in T i - V a l l o y s a s well a s other a l l o y s by X - r a y d i f f r a c t i o n and h a r d n e s s m e a s u r e m e n t s , a n d r e p o r t e d the e x i s t e n c e of an o r t h o r h o m b i c m a r t e n s i t e (a") and a m i n i m u m value of h a r d n e s s n e a r the 10 wt pct V c o m p o s i t i o n . F r o m t h e i r r e s u l t s , they s u g g e s t e d that the c r y s t a l s t r u c t u r e of the m a r t e n s i t e changes to a " f r o m a ' with i n c r e a s i n g v a n a d i u m content. The e x i s t ence of the a " was c o n f i r m e d f r o m the s p l i t t i n g of c e r tain hcp lines in the X - r a y D e b y e - S c h e r r e r p a t t e r n . The splitting was d i s t i n c t for other t i t a n i u m a l l o y s , but not for the T i - V alloy b e c a u s e of the d i f f u s e n e s s of M. OKA and K. SHIMIZUaxe Associate Professor and Professor, respectively, Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan. C. S. LEE is Graduate Student, Faculty of Engineering, Osaka University. Manuscript submitted April 14, 1971. METALLURGICALTRANSACTIONS
the D e b y e - S c h e r r e r r i n g s . J a m e s e t a l . 9 a l s o studied the m a r t e n s i t e in a T i - 1 2 wt pct V a l l o y by m e a n s of X - r a y d i f f r a c t i o n and t r a n s m i s s i o n e l e c t r o n m i c r o scopy, and could no
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