Composition effects on mechanical properties of HFC-strengthened molybdenum alloys
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d e v e l o p m e n t of m o l y b d e n u m a l l o y s d u r i n g the l a s t d e c a d e has shown the u s e f u l n e s s of c a r b i d e s of t i t a n i u m and z i r c o n i u m in p r o v i d i n g high s t r e n g t h at high t e m p e r a t u r e s , l'e B e c a u s e of the p o t e n t i a l of g r e a t e r s t a b i l i t y with HfC a s a d i s p e r s e d p h a s e at high t e m p e r a t u r e , Raffo s t u d i e d the M o - H f - C a l l o y s and r e p o r t e d outstanding m e c h a n i c a l p r o p e r t i e s f o r v a r i o u s c o m p o s i t i o n s , p a r t i c u l a r l y for t h e r m o m e c h a n i c a l l y p r o c e s s e d m a t e r i a l s . ~S The p r e s e n t study extends this w o r k f o r the p u r p o s e of e x a m i n i n g the effects of e x c e s s Hf on the m e c h a n i c a l p r o p e r t i e s of t t f C - s t r e n g t h e n e d Mo a l l o y s . An a d d i t i o n a l a i m was to d e t e r m i n e if any d u c t i l i z i n g effect would r e s u l t f r o m the a d d i t i o n of 2 at. p c t Re to M o - H f - C a l l o y s . T h e e f f e c t i v e n e s s of d i l u t e c o n c e n t r a t i o n s of Re in l o w e r i n g the d u c t i l e - b r i t t l e t r a n s i t i o n t e m p e r a t u r e of u n a l l o y e d Mo h a s been d e m o n s t r a t e d . 6 In this i n v e s t i g a t i o n the e f f e c t s of HfC and of e x c e s s Hf on both the low t e m p e r a t u r e d u c t i l i t y and high t e m p e r a t u r e s t r e n g t h of Mo a l l o y s w e r e e x a m i n e d . Swaged Mo-2Re-Hf-C alloys were evaluated by tensile tests at low temperatures (-185 to 425~ and at high temperatures (980, 1315, and 1650~ and by creep tests at 1315 and 1650~ The annealing behavior of these alloys was examined, and the tensile and 'creep properties of recrystallized Mo-2Re-HI-C alloys were determined. The relations between alloy strength and extracted carbide particle composition are discussed. E X P E R I M E N T A L PROCEDURE M a t e r i a l s and P r o c e s s i n g The s e v e n t e e n M o - 2 R e - H f - C a l l o y s in this study contained f r o m 1.6 to 2.4 at. p c t Re, 0.2 to 1.1 at. p c t Hf, and 0.1 to 1.9 at. p e t C. Oxygen and n i t r o g e n i m p u r i t i e s in the f a b r i c a t e d a l l o y s r a n g e d f r o m 31 to 143 ppm and 2 to 18 p p m by weight, r e s p e c t i v e l y . T h e c o n tent of HfC in m o l e p e r c e n t was a s s u m e d to b e e q u a l to the content of e i t h e r Hf o r C in a t o m i c p e r c e n t w h i c h e v e r w a s lower. Hafnium c o n t e n t s w e r e d e t e r m i n e d by a s p e c t r o p h o t o m e t r i c method. 7 C a r b o n d e t e r m i n a t i o n s w e r e m a d e by a c o m b u s t i o n c h r o m a t o WALTER R, WITZKE is Research Metallurgist, NASA Lewis Research Center, Cleveland, OH 44135, Manuscript submitted June 9, t975. METALLURGICAL TRANSACTIONS A
g r a p h i c p r o c e d u r e (Leco) and a r e c o n s i d e r e d to have a p r e c i s i o n of about a:5 pct. M a t e r i a l
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