Strain-induced transformation in shock-deformed Fe-Mn alloys
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has b e e n shown z'2 that shock d e f o r m a t i o n of quenched F e - M n a l l o y s r e s u l t s in a s h o c k - i n d u c e d p h a s e t r a n s f o r m a t i o n with the high p r e s s u r e p h a s e r e t a i n e d upon r e l i e f . The s t a b i l i z a t i o n of the high p r e s s u r e p h a s e depends on the m a n g a n e s e content i n the bcc m a r t e n s i t e p r i o r to s h o c k - l o a d i n g . C h r i s t o u a n d B r o w n 2 have shown that 1) F e - M n a l l o y s quenched f r o m 900~ and containing m a n g a n e s e in the r a n g e of 3 to 16 wt pct t r a n s f o r m to a s t a b l e c l o s e - p a c k e d p h a s e u n d e r s h o c k - l o a d i n g , with the high p r e s s u r e p h a s e r e t a i n e d a f t e r p r e s s u r e r e l e a s e , and 2) F e - M n a l l o y s cont a i n i n g m a n g a n e s e in the r a n g e of 3 to 16 wt pct, but which w e r e s l o w - c o o l e d f r o m 900~ p r i o r to s h o c k loading did not r e t a i n tl~e c l o s e - p a c k e d high p r e s s u r e p h a s e at a t m o s p h e r e i c p r e s s u r e s . In the s a m e study of F e - M n a l l o x s , z it was concluded that the a d d i t i o n of m a n g a n e s e to i r o n d e c r e a s e s the t r a n s i t i o n p r e s s u r e f r o m 133 k b a r for p u r e i r o n to l e s s than 90 k b a r for F e - 1 4 wt pct Mn, which a g r e e s with p r e v i o u s work done on F e - M n a l l o y s . 3 X - r a y diffraction r e s u l t s 2 have i n d i c a t e d that for the F e - 7 wt pct Mn alloy, the ~ (fcc) p h a s e has b e e n s t a b i l i z e d at r o o m t e m p e r a t u r e a f t e r shock d e f o r m a t i o n , while the e (hcp) phase h a s b e e n s t a b i l i z e d in the F e - 1 4 wt pct Mn alloy. The s a m e a l l o y s w e r e u s e d in the p r e s e n t study of the t e n s i l e and s t r e s s r e l a x a t i o n p r o p e r t i e s of the p r e s s u r e f o r m e d phases. In t h i s p a p e r , the r e s u l t s of t e n s i l e d e f o r m a t i o n of the F e - M n a l l o y s with r e t a i n e d high p r e s s u r e p h a s e s a r e p r e s e n t e d . F o u r a l l o y s ( F e - 0 . 4 Mn, F e - 4 Mn, F e - 7 Mn, and F e - 1 4 Mn) have been h e a t - t r e a t e d and s h o c k - l o a d e d a c c o r d i n g to the method developed by C h r i s t o u and Brown, 2 so that p a r t i a l r e t e n t i o n of the high p r e s s u r e p h a s e s o c c u r s . P o s t - s h o c k s t r e s s data of the a l l o y s a r e p r e s e n t e d , and it i s shown that s e r r a t e d flow o c c u r s for a l l o y s which r e t a i n e d a c l o s e packed p h a s e a f t e r s h o c k - l o a d i n g . S t r e s s r e l a x a t i o n e x p e r i m e n t s w e r e p e r f o r m e d on quenched and shocked s p e c i m e n s and it was found that p l a s t i c s t r a i n s r e s u l t e d in p a r t f r o m a c l o s e - p a c k e d to bcc phase t r a n s f o r m a t i o n , if; s o m e c l o s e - p a c k e d phase had b e e n A. CHRISTOUis Research Metal
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