Dynamic strain aging in carbide-strengthened molybdenum alloys
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L. R A F F O
A study was made of the d y n a m i c s t r a i n aging p r o c e s s e s in c a r b i d e s t r e n g t h e n e d m o l y b d e n u m a l l o y s . S tr e n g th e n in g due to d y n a m i c s t r a i n aging was o b s e r v e d in the t e m p e r a t u r e range 1500 ~ to 2400~ The s t r e n g t h e n i n g i s b e l i e v e d to a r i s e f r o m the pinning of m o b i l e d i s l o c a t i o n s by m e t a l - c a r b o n p a i r s or c l u s t e r s a n d / o r c a r b i d e p r e c i p i t a t e s . T h i s i m m o b i l i z a t i o n of the d i s l o c a tions led to a high work h a r d e n i n g r a t e and the o b s e r v e d s t r e n g t h e n i n g .
AN i m p o r t a n t
c l a s s of high s t r e n g t h m o l y b d e n u m a l loys a r e those s t r e n g t h e n e d by the addition of a group IVA c a r b i d e f o r m e r (titanium, z i r c o n i u m , o r hafnium) and carb o n . D e t e r m i n a t i o n s of the p r o p e r t i e s of t h ese a l l o y s in the wrought condition have led to the c o n c l u sion that t h e i r s t r e n g t h is d e r i v e d f r o m a fine d i s p e r sion of the c a r b i d e s of t i t a n i u m , z i r c o n i u m , o r hafnium. 1- 4 Chang ~ and the p r e s e n t a u t h o r 4 have m e a s u r e d the t e n s i l e p r o p e r t i e s of s o m e M o - T i - Z r - C and M o - H f - C a l l o y s a f t e r a high t e m p e r a t u r e solution t r e a t m e n t . T h i s t r e a t m e n t was found to i n t r o d u c e a peak in the s t r e n g t h - t e m p e r a t u r e c u r v e in the t e m p e r a t u r e range 1500 ~ to 2400~ a c c o m p a n i e d by s e r r a t e d p l a s t i c flow and a high w o r k h a r d e n i n g r a t e . In c o n t r a s t the s t r e n g t h of the wrought a l l o y s d e c r e a s e s s m o o t h l y with i n c r e a s i n g t e m p e r a t u r e . Chang i n t e r p r e t e d the peak 1 a s b e i n g due to the p r e c i p i t a t i o n of c a r b i d e s d u r i n g p l a s t i c d e f o r m a t i o n , a f o r m of d y n a m i c s t r a i n aging. The e v i d e n c e f o r t h i s was m a i n l y d e r i v e d f r o m h a r d n e s s m e a s u r e m e n t s made on the d e f o r m e d and u n d e f o r m e d p o r t i o n s of t e s t e d t e n s i l e s p e c i m e n s . It was shown that age h a r d e n i n g o c c u r r e d m o r e r a p i d l y in the s t r a i n e d p o r t io n of the t e n s i l e s p e c i m e n . The o b j e c t i v e of the p r e s e n t p r o g r a m was to obtain data which would aid in d e t e r m i n i n g a d e t a i l e d m e c h a n i s m of d y n am i c s t r a i n aging in this c l a s s of m o l y b denum a l l o y s . T h i s was a c c o m p l i s h e d by studying the t e m p e r a t u r e and s t r a i n r a t e d e p e n d e n c e of the t e n s i l e s t r e s s - s t r a i n b e h a v i o r of a solution t r e a t e d c o m m e r c i a l M o - T i - Z r - C a l lo y ( M o - T Z C ) and two e x p e r i m e n t a l M o - Z r - C a l l o y s . The d e f o r m e d a l l o y
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