Intersecting martensite plates in an Fe-27Ni-0.5C alloy
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s t r e s s , without solute pinning or i n t e r a c t i o n with o t h e r d i s l o c a t i o n s , has i m p o r t a n t c o n s e q u e n c e s . It will be i m portant for the b e h a v i o r of d i s l o c a t i o n s in the c r y s t a l l a t t i c e of m o s t m e t a l s , s i n c e it has b e e n s u g g e s t e d 7 that, e v e n for high SFE m e t a l s like A1, the e q u i l i b r i u m c o n f i g u r a t i o n of p e r f e c t d i s l o c a t i o n s is one of s l i g h t d i s s o ciation. Taken t o g e t h e r with the SFE v a r i a t i o n found by G l e i t e r and Klein, it will be i m p o r t a n t f o r the b e h a v i o r of d i s l o c a t i o n s in and n e a r g r a i n and twin b o u n d a r i e s , p a r t i c u l a r l y in the e a r l y s t a g e s of y i e l d i n g and in the p r o c e s s of g r a i n b o u n d a r y sliding. 1. H. Gleiter and 1~.P. Klein:Phil. Mag., 1973,vol.27, pp. 1009-26. 2. T. Malis,D. J. Lloyd, and K. Tangri:Phys. Status SolidiA, 1972, vot. 11, pp. 275-86. 3. T. Malis,D. J. Lloyd, and K. Tangri:Phil. Mag., 1972, vol. 26, pp. 1081-87. 4. J. Weertman and J. R. Weertman:Elementary Dislocation Theory,p. 102, MacMillanCo., London, 1964. 5. J. Friedel:Dislocations, p. 176, PergamonPress, London, 1964. 6. J. P. Hirth:Met. Trans., 1970,vol. 1, pp. 2367-74. 7. E. A. Harrison:ActaMet., 1973,vol. 21, pp. 1111-16.
Intersecting Martensite Plates in an Fe-27Ni-0. 5C Alloy D. S. SARMA AND S. R. KEOWN
It is now well e s t a b l i s h e d that four d i f f e r e n t m o r p h o l o g i e s of m a r t e n s i t e can o c c u r in F e - 0 . 5 wt pct C - N i a l loys depending on the n i c k e l content. 1-3 At low n i c k e l l e v e l s (up to about 10 wt pct) lath m a r t e n s i t e s a r e f o r m e d but with.16 to 19 wt pct n i c k e l , m a r t e n s i t e t a k e s the shape of c h e v r o n p l a t e s . 24 wt pct n i c k e l g i v e s c h a r a c t e r i s t i c b u r s t m a r t e n s i t e of l e n t i c u l a r p l a t e s c o n t a i n ing m i d r i b s and the t r a n s f o r m a t i o n of 27 wt pct to 30 wt pct Ni a l l o y s p r o d u c e s m a r t e n s i t e p l a t e s with s m o o t h and p a r a l l e l i n t e r f a c e s and with no m i d r i b . When plate m a r t e n s i t e s a r e f o r m e d the f i r s t f o r m e d p l a t e s act as e f f e c t i v e b a r r i e r s to s u b s e q u e n t p l a t e s so that it is unc o m m o n f o r p l a t e s to i n t e r s e c t ( i . e . c r o s s ) one another. It has, h o w e v e r , b e e n found in the p r e s e n t i n v e s t i g a tions on m a r t e n s i t e f o r m a t i o n in an F e - 2 7 pct N i - 0 . 5 C pct alloy that the p l a t e s f r e q u e n t l y i n t e r s e c t . A h o t - r o l l e d F e - 2 7 . 2 wt pct N i - 0 . 4 8 wt pct C alloy (which has an M s t e m p e r a t u r e of - 130~ was h o m o g e n i z e d at 1175~ for 50 h and s m a l l r o d s of 50 m m length and 3 m m d i a m w e r e p r o d u c e d by cold swaging and m a c h i n i n g . The r o d s w e r e a u s t e n i t i
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