The low-temperature embrittlement of niobium and vanadium by both dissolved and precipitated hydrogen
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E X P E R I M E N T A L PROCEDURE R e a c t o r - g r a d e n i o b i u m and v a n a d i u m , obtained as -~ in. (9.5 ram) diam v a c u u m - a n n e a l e d rod, was coldswaged in t h r e e s t a g e s to ~ in. (6.3 m m ) d i a m then m a c h i n e d into t e n s i l e s p e c i m e n s with a 1 in. (25.4 m m ) gage length of 0.1 in. (2.54 m m ) diam and t h r e a d e d ends. C h e m i c a l a n a l y s e s of the m a t e r i a l s a r e given in Table I. Equiaxed g r a i n s t r u c t u r e s were obtained by a n n e a l Ing the n i o b i u m at 1250~ and the v a n a d i u m at l l 0 0 ~ for 1 h under a v a c u u m of < 10 -8 t o r r , to yield g r a i n s i z e s of 39 and 26/~m, r e s p e c t i v e l y , while r e d u c i n g the hydrogen content to below 2 ppm. The h y d r o g e n a t i o n of s p e c i m e n s was by m e a n s of a c l o s e d = s y s t e m t h e r m a l e q u i l i b r a t i o n technique. The e q u i l i b r i u m data r e p o r t e d by Komjathy xs was used for n i o b i u m a l l o y s w h e r e a s the a p p r o p r i a t e conditions were d e t e r m i n e d e x p e r i m e n t a l l y for v a n a d i u m b e c a u s e of the s h o r t a g e of p u b l i s h e d data. After p r e e t c h i n g the s p e c i m e n s in a 1:9 HF-HNO 3 m i x t u r e , to e n h a n c e the r e a c t i o n r a t e with hydrogen, the s p e c i m e n s w e r e heated to 600~ in a v a c u u m of < i 0 -6 t o r r . The s y s t e m was then i s o l a t e d f r o m the vacuUm p u m p s and p u r i f i e d hydrogen, g e n e r a t e d by the t h e r m a l d e c o m p o s i t i o n of z i r c o n i u m h y d r i d e , was a d m i t t e d to the r e q u i r e d p r e s s u r e . After allowing 4 h at 600~ to a c h i e v e e q u i l i b r i u m and h o m o g e n i z a t i o n , the s y s t e m was r a p i d l y cooled to r o o m t e m p e r a t u r e . Hydrogen c o n t e n t s w e r e c o n f i r m e d by v a c u u m = f u s i o n gas a n a l y s i s which a l s o r e v e a l e d slight deoxidation (20 to 40 ppm). T e n s i l e t e s t s w e r e g e n e r a l l y conducted on a h a r d b e a m t e s t i n g m a c h i n e , of 5000 lb. (2270 kg) capacity, with a u t o g r a p h i c r e c o r d i n g of load and d i s p l a c e m e n t , but for the highest s t r a i n r a t e a s p e c i a l jig allowed the use of the s a m e s p e c i m e n g e o m e t r y in an Izod i m pact m a c h i n e . Initial t e s t s were c a r r i e d out at t h r e e t e m p e r a t u r e s at each of four s t r a i n r a t e s (3.4 • 10 -4, 9.65 • 10 -4, 3.5 • 10 -2, 10 -1 s -~) and the i n t e r p l a y of t h e s e two v a r i a b l e s is such that this was sufficient to d e t e r m i n e which r e g i o n s r e q u i r e d m o r e p r e c i s e defin i t i o n . No f u r t h e r t e s t s were found n e c e s s a r y for n i o b i u m or v a n a d i u m without added hydrogen. For the VOLUME 4, MAY 1973-1247
Table I. Chemical Analysis of As-Received Materials, ppm Wt
niobium vanadium
Ta
Si
W
Fe
C
0
N
Cr
Cu
Ti
Nb
Ni
Mn
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