Radiation effects on the yield stress and dislocation channeling in neutron irradiated molybdenum
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Channeling in Neutron Irradiated Molybdenum D. F. HASSON, Y. H U A N G ,
E. PINK, A N D R. J. A R S E N A U L T
An i n v e s t i g a t i o n was u n d e r t a k e n to d e t e r m i n e the effect of n e u t r o n d a m a g e on the d e f o r m a tion c h a r a c t e r i s t i c s of m o l y b d e n u m s i n g l e c r y s t a l s . By a p r o c e s s of s o l i d s t a t e oxidation, followed by a high v a c u u m zone m e l t i n g p a s s , the t o t a l i n t e r s t i t i a l c o n c e n t r a t i o n was r e d u c e d to _< 10 w t - p p m in a l l s p e c i m e n s . Single c r y s t a l m o l y b d e n u m c o m p r e s s i o n s p e c i m e n s with o r i e n t a t i o n s of [100], [491], [110] and [111] w e r e p r o d u c e d f r o m e l e c t r o n b e a m zone m e l t e d r o d s . The [110] and [491] s p e c i m e n s e x h i b i t e d r a d i a t i o n h a r d e n i h g , while the [100] o r i e n t a t i o n s a m p l e s e x h i b i t e d s o m e r a d i a t i o n softening (i.e., a d e c r e a s e in the effective y i e l d s t r e s s ) . The e x i s t e n c e of a l o c a l m a x i m u m in the a c t i v a t i o n v o l u m e v e r s u s e f f e c t i v e s t r e s s , which ts p r e d i c t e d b y the d i s s o c i a t e d c o r e d i s l o c a t i o n m o d e l , was found. The o r i e n t a t i o n d e p e n d e n c e f o r a (10i) [111] s l i p s y s t e m showed the [100] to b e s t r o n g e r than the [110] c o m p r e s s i v e a x i s . D i s l o c a t i o n channeling in n e u t r o n i r r a d i a t e d and d e f o r m e d m o l y b denum was i n v e s t i g a t e d , and it was found that t e s t i n g t e m p e r a t u r e , s a m p l e o r i e n t a t i o n , and s t r a i n had no m a j o r e f f e c t on the channel c h a r a c t e r i s t i c s . However, the d i f f e r e n c e s in c h a n nel c h a r a c t e r i s t i c s b e t w e e n the c e n t r a l and end p o r t i o n s of the c o m p r e s s i o n s a m p l e s a r e significant.
DUEto the v e r y
low s o l u b i l i t y of i n t e r s t i t i a l s in m o l y b d e n u m , m o l y b d e n u m m a y be c o n s i d e r e d to be r e l a t i v e l y f r e e of i n t e r s t i t i a l s . T h e r e f o r e , the r a t e c o n t r o l l i n g b a r r i e r to d i s l o c a t i o n motion cannot d i r e c t l y be a t t r i b u t e d to i n t e r s t i t i a l s . This a l s o m e a n s that there cannot be a reduction of the thermal cornponent of the flow s t r e s s (~*) due to a r e d u c t i o n in the r a n d o m c o n c e n t r a t i o n of i m p u r i t y i n t e r s t i t i a l s , which can o c c u r a s a r e s u l t of n e u t r o n i r r a d i a t i o n . ~ It should be noted that in c o n s i d e r i n g the e f f e c t of neutron d a m age on 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 (or flow) s t r e s s , it is n e c e s s a r y to d i v i d e the flow s t r e s s (i.e., the r e s o l v e d s h e a r s t r e s s ) into i t s two p a r t s : the t h e r m a l c o m p o n e n t defin
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