Defect clusters in neutron-irradiated vanadium containing oxygen
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AND
M. S. WECHSLER
Single c r y s t a l s a m p l e s of h i g h - p u r i t y v a n a d i u m c o n t a i n i n g 95, 300, and 500 wt ppm oxygen w e r e i r r a d i a t e d at 95~ in the A m e s L a b o r a t o r y R e s e a r c h R e a c t o r to a dose of 1.4 • 10 ~9 n e u t r o n s / c m 2 (E > I MeV). The d e n s i t y and s i z e d i s t r i b u t i o n of r a d i a t i o n - p r o d u c e d defect c l u s t e r s w e r e a n a l y z e d by t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y in a s - i r r a d i a t e d and p o s t i r r a d i a t i o n - a n n e a l e d m a t e r i a l . The defect c l u s t e r d e n s i t y was o b s e r v e d to i n c r e a s e with i n c r e a s i n g oxygen c o n c e n t r a t i o n and the a v e r a g e defect c l u s t e r s i z e to d e c r e a s e . Upon p o s t - i r r a d i a t i o n a n n e a l i n g the d e n s i t y d e c r e a s e d and the a v e r a g e s i z e i n c r e a s e d , but h i g h e r a n n e a l i n g t e m p e r a t u r e s w e r e r e q u i r e d for higher oxygen m a t e r i a l . The r e s u l t s a r e d i s cussed in t e r m s of the n u c l e a t i o n of defect c l u s t e r s at oxygen a t o m s and s m a l l o x y g e n - a t o m a g g r e g a t e s . The i n c r e a s e d s t a b i l i t y a g a i n s t a n n e a l i n g of higher oxygen v a n a d i u m is b e lieved to be due to the g r e a t e r s e g r e g a t i o n of oxygen at the defect c l u s t e r s . D E F E C T c l u s t e r s (black spots and d i s l o c a t i o n loops) have now been widely o b s e r v e d in i r r a d i a t e d m e t a l s of a l l t h r e e c r y s t a l s t r u c t u r e types (fee, bee, and hop) a s a r e s u l t of b o m b a r d m e n t with n e u t r o n s , ions, e l e c t r o n s , and f i s s i o n f r a g m e n t s . T h e s e o b s e r v a t i o n s have b e e n d e s c r i b e d i n a n u m b e r of r e v i e w s . ~-4 Although m o s t of the e a r l i e r work was done on fcc m e t a l s , bcc m e t a l s have r e c e i v e d i n c r e a s i n g a t t e n t i o n i n r e c e n t y e a r s . ~-6 The i n f l u e n c e of i m p u r i t y c o n c e n t r a t i o n s on r a d i a t i o n produced defect c l u s t e r s has, however, not b e e n g r e a t l y i n v e s t i g a t e d . In this p a p e r , we r e p o r t on the effect of v a r i a t i o n s of oxygen i m p u r i t y c o n c e n t r a t i o n s on the d e n s i t y and s i z e d i s t r i b u t i o n of defect c l u s t e r s in n e u t r o n - i r r a d i a t e d v a n a d i u m . V a n a d i u m was chosen for this study b e c a u s e it i s a v a i l a b l e in f a i r l y high p u r i t y and has a reasonably- high solid s o l u b i l i t y for i n t e r s t i t i a l i m p u r i t i e s , p a r t i c u l a r l y oxygen. 7 F u r t h e r m o r e , v a n a d i u m is c o n s i d e r e d to be an a t t r a c t i v e m e t a l for advanced r e a c t o r s y s t e m s , e s p e c i a l l y for fusion r e a c t o r s , 8 w h e r e r a d i a t i o n effects a r e p a r t i c u l
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