The low strain tensile behavior of U-7.5 wt pct Nb-2.5 wt pct Zr
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- 7 . 5 wt pct Nb-2.5 wt pet Z r i s a high s t r e n g t h , c o r r o s i o n r e s i s t a n t u r a n i u m alloy. At t e m p e r a t u r e s b e tween 640~ and the s o l i d u s , this alloy has a single phase bcc s t r u c t u r e r e f e r r e d to a s the y phase, t A s t r u c t u r e v e r y c l o s e to that of the high t e m p e r a t u r e 7 p h a s e s t r u c t u r e can be r e t a i n e d by quenching to r o o m temperature. P e t e r s o n and V a n d e r v o o t e s t a b l i s h e d a t i m e - t e m p e r a t u r e - t r a n s f o r m a t i o n c u r v e for U-7.5 wt pct Nb-2.5 wt pct Z r u s i n g r e s i s t i v i t y and h a r d n e s s techniques.2 Dean expanded t h e i r work u s i n g m e t a l l o g r a p h y , m i c r o h a r d n e s s , and X - r a y d i f f r a c t i o n , 3 Fig. 1. Dean l a b e l s t h r e e t r a n s i t i o n fields. The Y(Ys ?) p h a s e t r a n s f o r m s to a T3 + a p h a s e above 400~ This r e a c t i o n has a " n o s e " in the T - T - T c u r v e between 500 ~ and 600~ at about 20 m i n . The r e a c t i o n p r o duces s t r u c t u r e s which a r e a m a z i n g l y s t e e l - l i k e in s t r u c t u r e , with p e a r l i t e s t r u c t u r e s p r o d u c e d at higher t e m p e r a t u r e s , and b a i n i t e s t r u c t u r e s at lower t e m p e r a t u r e s . A n o s e o c c u r s b e t w e e n 300 ~ and 400~ T h i s line m a r k s the t r a n s i t i o n f r o m Ys s t r u c t u r e to a y0 s t r u c t u r e with a m i n i m u m t i m e of about 1 m i n . A second nose o c c u r s in the s a m e t e m p e r a t u r e r e g i o n at l o n g e r t i m e s which i n v o l v e s a t r a n s i t i o n f r o m yo to a " . Dean l a b e l s the high t e m p e r a t u r e o r i g i n a l p h a s e a s y and the p h a s e r e t a i n e d by quenching to lower t e m p e r a t u r e s a s Ys without any i n d i c a t i o n of any phase transformation. Yakel 4 e s t a b l i s h e d the c r y s t a l s t r u c t u r e s of 7s and ~o u s i n g s i n g l e c r y s t a l d i f f r a c t i o n t e c h n i q u e s . He r e p o r t e d the Ys s t r u c t u r e a s bcc with slight d i s p l a c e m e n t s of the b o d y - c e n t e r e d a t o m s c o r r e l a t e d along (100) d i r e c t i o n s . He a l s o o b s e r v e d b r o a d e n i n g which C. ALBRIGHT is Technical Staff Member, Sandia Laboratories, Albuquerque, N.M.C. STEIN is Professor of Metallurgy,New Mexico Institute of Miningand Technology, Socorro, N. M. and Chief Metallurgist, Air Force Weapons Laboratory, Kirtland AFB, Albuquerque, N.M. Manuscript submitted September 3, 1971. METALLURGICAL TRANSACTIONS
he i n t e r p r e t e d a s d o m a i n s in which all d i s p l a c e m e n t s a r e a l i g n e d in a p a r t i c u l a r (100) d i r e c t i o n . He c a l c u lated t h e s e d o m a i n s to be 40 to 50A in d i a m e t e r . The yo phase was r e p o r t e d to be bct. The l a t t i c e p a r a m e t e r s a r e r e p o r t e d as:4 Ys
ao = 3.466 • 0.001A o
Yo
{ao = 3.499 § co
3.371
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