Internal oxidation and mechanical properties of TZM-Mo alloy
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INTERNAL oxidation has been investigated extensively in fcc m a t e r i a l s , for e x a m p l e the c o p p e r - b a s e 1"4 a l l o y s c o n t a i n i n g m i n o r a l l o y i n g a d d i t i o n s of Be, A1, Mg, Si, and Z r . However, b e c a u s e of the r e l a t i v e l y high d e g r e e of r e a c t i v i t y of the b a s e m e t a l in r e f r a c t o r y a l l o y s a s well a s o t h e r b c c m a t e r i a l s , only l i m i t e d i n f o r m a t i o n ~-7 is a v a i l a b l e f o r t h e s e s y s t e m s r e g a r d i n g the p r e c i p i t a tion of v a r i o u s f o r m s of Oxide and i t s c o r r e l a t i o n with mechanical properties. B e c a u s e of the high m e l t i n g point, p r o v e n f a b r i c a b i l ity, good c o r r o s i o n r e s i s t a n c e to a l k a l i m e t a l s , and e x c e l l e n t s t r e n g t h at e l e v a t e d t e m p e r a t u r e s , the r e f r a c t o r y a l l o y s such a s T-111 ( T a - 8 p e t W-2 pet Hf) and T Z M (Mo-0.5 pet T i - 0 . 0 8 pct Z r - 0 . 0 2 pct C) a r e c a n d i d a t e s t r u c t u r a l m a t e r i a l s for r a d i o i s o t o p e - f u e l e d t h e r m o e l e c t r i c - g e n e r a t o r s for u s e in s p a c e and for l i q u i d - m e t a l Rankine o r B r a y t o n c y c l e t u r b o e l e c t r i c p o w e r s y s t e m s . In t h e s e a p p l i c a t i o n s , the r e f r a c t o r y m a t e r i a l s a r e e x p o s e d to e i t h e r a l o w - p r e s s u r e o x i d i z i n g a t m o s p h e r e o r liquid a l k a l i m e t a l ( g e n e r a l l y c o n t a i n i n g a s m a l l amount of oxygen), r e s u l t i n g in a continuous pickup of oxygen and, in s o m e c a s e s , s e v e r e d e g r a d a t i o n of t h e i r m e c h a n i c a l p r o p e r t i e s , s'8'g The s t u d y of i n t e r n a l o x i d a t i o n in t h e s e a l l o y s is thus of both t e c h n o l o g i c a l and f u n d a m e n t a l i n t e r e s t . This p a p e r d e s c r i b e s a study of i n t e r n a l o x i d a t i o n in a m o l y b d e n u m - b a s e a l l o y (TZM), which was a i m e d at i n v e s t i g a t i n g the g e n e r a l i t y of the r e s u l t s o b t a i n e d p r e v i o u s l y 5 f r o m a s i m i l a r s t u d y on a t a n t a l u m - b a s e a l l o y ( T - I l l ) . E x p o s u r e of T-111 to l o w - p r e s s u r e o x ygen at 1273 K r e s u l t s in the f o r m a t i o n of fine, c o h e r ent z o n e s (< 50A) t h a t a r e d i s t r i b u t e d h o m o g e n e o u s l y through the m a t r i x . T h e s e zones h a r d e n the m a t r i x of the i n t e r n a l l y o x i d i z e d T - I l l and r e s u l t in c o m p l e t e e m b r i t t l e m e n t at r o o m t e m p e r a t u r e at an oxygen l e v e l Of about 800 ppm. The d u c t i l i t y is not i m p r o v e d at t e s t t e m p e r a t u r e s to 1589 K. However, the d u c t i l i t y of e m b r i t t l e d T-111 i n c r e a s e s s i g n i f i c a n t l y with c o a r s e n i n g C. T. LIU and H. INOUYE are Metallurgists, Metals and Ceramic
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