The effect of neutron irradiation damage on niobium oxygen alloys
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INTRODUCTION W HE combined effect of i n t e r s t i t i a l i m p u r i t y (oxygen) a t o m s and r a d i a t i o n produced defects on the changes in the yield s t r e s s at low t e m p e r a t u r e s of c e r t a i n bcc m e t a l s a p p e a r s to be a v e r y s e n s i t i v e function of the i m p u r i t y i n t e r s t i t i a l content.~'~ (In all c a s e s , the yield s t r e s s r e f e r s to the r e s o l v e d s h e a r s t r e s s . ) If the yield s t r e s s (Ty) c o n s i s t s of the s u m of two components, the effective s t r e s s (7-*) and the l o n g - r a n g e i n t e r n a l s t r e s s ( r i ) , then it is p o s s i b l e to e x a m i n e the effect of the n e u t r o n damage on both components of ry. The effective s t r e s s of y i e l d i n g of the n e u t r o n i r r a d i a t e d s a m p l e s is defined as ~ r r , and the effective s t r e s s of yielding for the n o n i r r a d i a t e d s a m p l e s is defined as 7-*. The d i f f e r e n c e between 7-~rr and 7-* is 47-*. It has b e e n o b s e r v e d exp e r i m e n t a l l y in v a n a d i u m - o x y g e n alloys that Lx7* at low t e m p e r a t u r e s i n c r e a s e s as the i n t e r s t i t i a l content d e c r e a s e s , in the i n t e r s t i t i a l content range of 0 to 200 at. ppm. 1,~ F o r an i n t e r m e d i a t e i n t e r s t i t i a l content r a n g e , 200 to ~1000 at. ppm, Lx7* is negative, and for s t i l l l a r g e r i n t e r s t i t i a l contents, z~7* is z e r o . 1 A t t e m p t s to c o r r e l a t e the n e u t r o n - p r o d u c e d defects o b s e r v e d by m e a n s of t r a n s m i s s i o n e l e c t r o n m i croscopy (TEM) and the changes in the yield s t r e s s or AT-* have b e e n only p a r t i a l l y s u c c e s s f u l . 5-9 The change in 7"i can be q u a l i t a t i v e l y c o r r e l a t e d with the o b s e r v e d i n c r e a s e in defect d e n s i t y , if l a r g e defects (700A in diam) a r e not counted. The d e n s i t y of defects i n c r e a s e s with i n c r e a s i n g oxygen content for the C. YIN and R. J. ARSENAULTare Post-Doctoral Fellow and Professor of EngineeringMaterials, respectively, EngineeringMaterials Group, University of Maryland, College Park, MD 20742. Manuscript submitted January 20, 1978. METALLURGICALTRANSACTIONSA
s a m e n e u t r o n fluence, and the m a x i m u m size of the defect i n c r e a s e s as the oxygen content d e c r e a s e s . T h e r e is no a p p a r e n t c o r r e l a t i o n b e t w e e n ~XT-*and the o b s e r v a b l e defects. In the case of niobium, t h e r e have b e e n a few p r e l i m i n a r y i n v e s t i g a t i o n s of the effect of n e u t r o n damage on the low t e m p e r a t u r e yield s t r e s s . 1~ The r e s u l t s in t e n s i o n showed that the i n c r e a s e in ry, upon i r r a d i a t i o n , is independent of t e s t i n g t e m p e r a t u r e , which r a n g e d f r o m room t e m p e r a t u r e to 93 K. The abs e n c e of any change in the t e m p e r a t u r e dependence of the y
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