The thermally activated dislocation motion in neutron irradiated iron-nickel alloys
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P o l y c r y s t a l l i n e s a m p l e s of i r o n - n i c k e l a l l o y s with v a r i o u s i n t e r s t i t i a l i m p u r i t y l e v e l s w e r e i r r a d i a t e d to a f l u e n c e of 1.6• n / c m z (E > 1 MeV). The t e m p e r a t u r e and s t r a i n r a t e d e p e n d e n c e of the y i e l d s t r e s s of the a l l o y s have b e e n i n v e s t i g a t e d in the t e m p e r a t u r e r a n g e of 77 to 580~ The a c t i v a t i o n p a r a m e t e r s have a l s o b e e n e v a l u a t e d and u s e d to identify the r a t e c o n t r o l l i n g m e c h a n i s m s of the d i s l o c a t i o n motion. It was o b s e r v e d that above 300~ the t h e r m a l l y a c t i v a t e d d i s l o c a t i o n m o t i o n o v e r the n e u t r o n - p r o d u c e d o b s t a c l e s is the r a t e c o n t r o l l i n g m e c h a n i s m for the i r r a d i a t e d s a m p l e s . This o b s e r v a t i o n is in a g r e e m e n t with a p r e d i c t i o n m a d e b y A r s e n a u l t . The effect of p o s t - i r r a d i a t i o n a n n e a l i n g on t h e t e m p e r a t u r e d e p e n d e n c e of the y i e l d s t r e s s b e c o m e s s i g n i f i c a n t above 400~ t h e r e f o r e , b y the s i n g l e s t r a i n r a t e change t e s t s t h e r e is no way to d e t e r m i n e the a t h e r m a l s t r e s s f o r the i r r a d i a t e d s a m p l e s . The m o t i o n of double k i n k s in d i s l o c a t i o n s o v e r the P e i e r l s ' s t r e s s h i l l is the l o w e r t e m p e r a t u r e r a t e c o n t r o l l i n g m e c h a n i s m b e f o r e and a f t e r neutron irradiation.
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h a s b e e n t h e o r e t i c a l l y p r e d i c t e d that n e u t r o n p r o d u c e d d e f e c t s in b c c m e t a l s and t h e i r a l l o y s would not have a m a j o r effect on the r a t e c o n t r o l l i n g m e c h a n i s m of d i s l o c a t i o n motion. 1 If a d i v i s i o n of the y i e l d o r flow s t r e s s i s m a d e , that i s , the y i e l d s t r e s s c o n s i s t s of two c o m p o n e n t s , the e f f e c t i v e s t r e s s (T*) which is d e pendent upon s t r a i n r a t e and t e m p e r a t u r e and an a t h e r m a l c o m p o n e n t (~-u) which to a f i r s t a p p r o x i m a t i o n is independent of t e m p e r a t u r e and s t r a i n r a t e , then the t h e o r e t i c a l p r e d i c t i o n can b e e x a m i n e d in g r e a t e r d e t a i l . S p e c i f i c a l l y , it was p r e d i c t e d t h a t the n e u t r o n d a m a g e would only i n c r e a s e r* in the high t e m p e r a t u r e r a n g e i.e., at s m a l l v a l u e s of ~*. The following o b s e r v a t i o n s might s u p p o r t this p r e d i c t i o n : 1) Above 300~ the t e m p e r a t u r e d e p e n d e n c e of the y i e l d s t r e s s f o r the u n i r r a d i a t e d s a m p l e s of i r o n and its a l l o y s is a l m o s t z e r o ; h o w e v e r , for the i r r a d i a t e d s a m p l e s the t e m p e r a t u r e d e p e n d e n c e of the y i e l d s t
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