On the steady state cyclic deformation of iron
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AGING TIME @ 7 5 0 ~ C-SEC
Fig. 1--The effect of aging the austenite at 750~ on the tetragonality of the martensite formed on subsequent r e f r i g e r ation. c l u s t e r s no l o n g e r t r a n s f o r m to a b o d y - c e n t e r e d s t r u c t u r e with t h e m a t r i x . F i g . 1 p r e s e n t s the r e s u l t s of the m e a s u r e m e n t s m a d e on an F e - 2 9 . 3 N i - 4 T i a l l o y a f t e r v a r i o u s aging t r e a t m e n t s at 750~ The tetragonality i n c r e a s e s m a r k e d l y a f t e r the aging t r e a t m e n t s . The m e c h a n i s m w h e r e b y t h e c l u s t e r s m i g h t p r o d u c e the m a r t e n s i t e t e t r a g o n a l i t y is not c l e a r . E v i d e n c e e x i s t s ~ that the c l u s t e r s exhibit the c l a s s i c a l y ' AuCua s t r u c t u r e in t h e p a r e n t fcc a u s t e a i t e . A s noted e a r l i e r , the s m a l l e r Ni3Ti c l u s t e r s t r a n s f o r m to the b o d y - c e n t e r e d s t r u c t u r e with the m a t r i x . A b r a h a m and P a s c o v e r h a v e a l r e a d y shown the e f f e c t of a B a i n s t r a i n on the AuCu3 s t r u c t u r e . 1 It t u r n s out that a unique c - a x i s is d e l i n e a t e d within the o r d e r e d c l u s t e r s that c o n t a i n s only t i t a n i u m a t o m s . Within a g i v e n m a r t e n s i t e p l a t e , this unique c - a x i s is along the s a m e d i r e c t i o n in e a c h of the c l u s t e r s . T h i s a l i g n m e n t would p r o d u c e a t e t r a g onal d i s t o r t i o n in the l a t t i c e and it is r e a s o n a b l e to e x pect the r e s u l t a n t s t r u c t u r e to be t e t r a g o n a l . S e v e r a l e x p l a n a t i o n s f o r t h e i n c r e a s e in c / a r a t i o d u r i n g a g i n g , F i g . 1, m i g h t b e s e t f o r t h . T h e m o s t i m m e d i a t e r a t i o n a l i z a t i o n would be art i n c r e a s e in the n u m b e r of c o n t r i b u t i n g Ni3Ti c l u s t e r s . H o w e v e r , it m u s t be noted that it i s not p o s s i b l e to t o t a l l y d i s r e g a r d e x p l a n a t i o n s b a s e d on an i n c r e a s i n g t i t a n i u m f r a c t i o n in the c l u s t e r s o r an i n c r e a s i n g d e g r e e of o r d e r in the c l u s t e r s . W i n c h e l l and Speich ~ i n d i c a t e that t h e o c c u r r e n c e of an i n t e r n a l f r i c t i o n peak in th e m a r t e n s i t e is p r e d i c t e d on the b a s i s of t h e i r m o d e l . T h e i r d i s c u s s i o n of this p r e d i c t i o n is v e r y b r i e f but the r e l a x a t i o n p r o c e s s they e n v i s i o n 6 i n v o l v e s r o t a t i o n of the t e t r a g o n a l s y m m e t r y a x i s a s the r e s u l t of a s h o r t - r a n g e r e a r r a n g e m e n t of a t o m s in and a r o u n d a t e t r a h e d r a l point d e f e c t . 5 T h e y c o n s e q u e n t l y p r e d i c t t h e peak to o c c u r " a t f r e q u e n c i e s much h i g h e r th
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