Effects of oxygen addition on the void-swelling behavior of vanadium
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D. I. POTTER,
AND
A. TAYLOR
V a n a d i u m - i o n i r r a d i a t i o n of v a n a d i u m alloys c o n t a i n i n g 1 to 4 at. pct O in solid solution was used to i n v e s t i g a t e void s w e l l i n g at t e m p e r a t u r e s f r o m 550 to 905~ Voids were obs e r v e d at all t e m p e r a t u r e s for V-1 O, with peak s w e l l i n g of ~0.88 pct for 20 dpa o c c u r r i n g at ~680~ Void size at 20 dpa i n c r e a s e d f r o m ~30A at 550~ to ~700/~ at 905~ T h i s was a c c o m p a n i e d by a d e c r e a s e in void n u m b e r d e n s i t y f r o m 4 • 10~6/cm3 to 3 • 1012/cm 3 at 550 and 905~ r e s p e c t i v e l y . The dependence of void s w e l l i n g in V on dose and oxygen c o m p o s i t i o n was i n v e s t i g a t e d at 700~ Swelling i n c r e a s e d m o n o t o n i c a l l y with dose f r o m 0.02 pct at 3 dpa to ~1 pct at 35 dpa in V-1 O and f r o m 0.001 pct at 3 dpa to ~0.2 pct at 35 dpa in V-2 O. Voids were not o b s e r v e d at 3 dpa in V-3 O and V - 4 O, and also at 20 dpa in V-4 O. At a fixed dose and 700~ the s w e l l i n g d e c r e a s e d a p p r o x i m a t e l y exponentially with oxygen content, dropping f r o m ~2.5 pct in unalloyed V to ~0.02 pct at 20 dpa in V-3 O. The t e m p e r a t u r e dependence of void s w e l l i n g in V-1 O was calculated u s i n g c u r r e n t v o i d - g r o w t h models modified for v a c a n c y t r a p p i n g by i n t e r s t i t i a l s o l u t e s . The c a l c u l a t e d c u r v e is a r e a s o n a b l e fit to the e x p e r i m e n t a l l y d e t e r m i n e d points. It is shown that m e c h a n i s m s i n addition to v a c a n c y - t r a p p i n g effects on void growth a r e n e c e s s a r y to explain the magnitude of s u p p r e s s i o n in s w e l l i n g o b s e r v e d in the m o r e concentrated alloys. 1. INTRODUCTION V A N A D I U M a l l o y s a r e c a n d i d a t e s for use in the v a c u u m wall of fusion r e a c t o r s . The f i r s t - w a l l m a t e r i a l s will be exposed to h i g h - e n e r g y (including 14.1 MeV) n e u t r o n b o m b a r d m e n t at t e m p e r a t u r e s to 600~ S e v e r a l i n v e s t i g a t i o n s x-9 have shown that s w e l l i n g and void f o r m a t i o n o c c u r d u r i n g e l e v a t e d - t e m p e r a t u r e i r r a d i a t i o n of v a n a d i u m and some of its a l l o y s . It is des i r a b l e , t h e r e f o r e , to find ways to r e d u c e or e l i m i n a t e this s w e l l i n g in o r d e r to extend the l i f e t i m e of the first-wall components. F a c t o r s affecting s w e l l i n g in an alloy include the types and q u a n t i t i e s of a l l o y i n g e l e m e n t s , t r a c e i m p u r i t i e s , p r e c i p i t a t e s , and m i c r o s t r u c t u r a l f e a t u r e s such a s g r a i n s i z e and d i s l o c a t i o n d e n s i t y . 3,1~ Previous i n v e s t i g a t i o n s of b o d y - c e n t e r e d - c u b i c m e t a l s have d e m o n s t r a t e d a r a t h e r complex effect of s m a l l q u a n t i t i e s of
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