The stress-dependence of high temperature creep of tungsten and a tungsten-2 Wt pct ThO 2 alloy

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~C = A '((yc/fff) n the p r e s e n t c r e e p data for t u n g s t e n and the t u n g s t e n alloy at v a r i o u s t e m p e r a t u r e s w e r e m u c h b e t t e r c o r r e l a t e d . H e r e , ~c i s the e x p e r i m e n t a l c r e e p r a t e , a c is the applied s t r e s s for c r e e p , af i s the flow s t r e s s of the m a t e r i a l at the s a m e t e m p e r a t u r e in a c o n s t a n t s t r a i n r a t e t e n s i l e t e s t , and A ' is function of t e m p e r a t u r e , s t r u c t u r e , and s t r a i n r a t e .

T H E s t r e s s d e p e n d e n c e of c r e e p at high t e m p e r a t u r e s i s often e x p r e s s e d by the following equation:

= B ( T , S)O~c

[1]

w h e r e ~c is the steady s t a t e c r e e p r a t e and % i s the applied c r e e p s t r e s s . The t e r m B ( T , S) is a f u n c t i o n of s t r u c t u r e (S) and t e m p e r a t u r e (T). Eq. [1] is obeyed by a n u m b e r of m e t a l s when t e s t e d at c o n s t a n t t e m p e r a t u r e and at s t r a i n r a t e s of about 10 -7 to 10-4see -1. In t h e s e c a s e s , the exponent n has u s u a l l y been found to v a r y f r o m 3 to 7.1'2 In o r d e r to c o r r e l a t e c r e e p data obtained at different ~ m p e r a t u r e s , the t e r m B ( T , S) m u s t be explicitly defined. R o b i n s o n and Sherby 3 and a l s o M u k l m r j e e , B i r d , a n d Dorn 4 have p r o p o s e d exp l i c i t r e l a t i o n s h i p s which c o m p e n s a t e for the effect of t e m p e r a t u r e and s t r e s s on the s t e a d y - s t a t e c r e e p r a t e of m a t e r i a l s at high t e m p e r a t u r e s . In the p r e s e n t i n v e s t i g a t i o n , c r e e p data on p u r e powd e r m e t a l l u r g y (PM) t u n g s t e n and a W-2 wt pet ThO2 a l l o y a r e r e p o r t e d . The c r e e p r e s u l t s w e r e found to be in poor a g r e e m e n t with the p r o p o s e d c o r r e l a t i o n s . 3'4 A new r e l a t i o n s h i p b a s e d on a power law of c r e e p y i e l d e d a s i g n i f i c a n t l y i m p r o v e d fit for the data. EXPERIMENTAL PROCEDURE AND RESULTS P u r e t u n g s t e n and a W-2 wt pct ThO~ a l l o y with a finely d i s p e r s e d s e c o n d phase w e r e p r o d u c e d by a powder m e t a l l u r g y t e c h n i q u e . The m e a n ThO2 p a r t i c l e s i z e in the alloy was about 750.~ with a n i n t e r p a r t i c l e s p a c i n g of about 0.3 g i n . The alloy was t e s t e d in both the r e c r y s t a l l i z e d ( a n n e a l e d 6 h r at 2850~ and the whereas r e c o v e r e d condition (annealed -~ 1 h r at 2400~ the p u r e t u n g s t e n was t e s t e d only in the r e c r y s t a l l i z e d condition (annealed -~ h r at 2400~ The g r a i n s in the alloy w e r e highly elongated p a r a l l e l to the rod a x i s , with a width of about 20 g m in the r e c o v e r e d condition a n d about 130 # m in the r e c r y s t a l l i z e d condition. The recovered~alloy a l s o had a stable s u b s t r u c t u r e with G. W. KING is Seni