The yield stress and saturization magnetization of Ir 3 Cr
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R. DiMICCO
AND
D. P. POPE
Y i e l d s t r e s s m e a s u r e m e n t s w e r e p e r f o r m e d on p o l y c r y s t a l l i n e Ir3Cr at t e m p e r a t u r e s between 673 and 1673 K. It was found that the y i e l d s t r e s s m e a s u r e d at e l e v a t e d t e m p e r a t u r e was e s s e n t i a l l y t e m p e r a t u r e independent while the y i e l d s t r e s s m e a s u r e d at 773 K on s a m p l e s quenched f r o m t e m p e r a t u r e s up to 1973 K showed a y i e l d s t r e s s p e a k at a quench t e m p e r a t u r e of 1633 • 10 K. M a g n e t i c m e a s u r e m e n t s c o m b i n e d with D e b y e - S c h e r r e r X - r a y m e a s u r e m e n t s on quenched s a m p l e s showed that Ir3Cr d i s o r d e r s at e l e v a t e d t e m p e r a t u r e with a l l e v i d e n c e for o r d e r d i s a p p e a r i n g at 1633 + 10 K. The s a t u r i z a t i o n m a g n e t i z a t i o n of fully o r d e r e d Ir3Cr is 5.8 e m u / g and that of d i s o r d e r e d m a t e r i a l is a p p r o x i m a t e l y z e r o . B a s e d on the shape of the m a g n e t i z a t i o n v s a p p l i e d m a g n e t i c f i e l d b e h a v i o r of p a r t i a l l y o r d e r e d s a m p l e s , I r z C r a p p e a r s to o r d e r h o m o g e n e o u s l y f o r s m a l l d e p a r t u r e s f r o m e q u i l i b r i u m and h e t e r o g e n e o u s l y for l a r g e d e p a r tures.
THE
y i e l d s t r e n g t h of o r d e r e d a l l o y s with the L12 c r y s t a l s t r u c t u r e , and the Cu3Au type s t r u c t u r e , gene r a l l y i n c r e a s e s with i n c r e a s i n g t e m p e r a t u r e . T h i s unusual effect can be due to at l e a s t two d i f f e r e n t p h y s i c a l m e c h a n i s m s , a s p o i n t e d out by L i a n g and Pope; 1 for a l l o y s with T c > T i n , c a l l e d C l a s s H a l l o y s , ~ the y i e l d s t r e n g t h i n c r e a s e is b e l i e v e d to be c a u s e d by the i n c r e a s i n g p r o b a b i l i t y of [110](1110) s c r e w d i s l o c a t i o n s c r o s s - s l i p p i n g to (001) p l a n e s a s the t e m p e r a t u r e is i n c r e a s e d . Ni3A1 i s the p r o t o t y p e for this c l a s s . One L12 o r d e r e d a l l o y a p p e a r e d to be an e x c e p t i o n to the above r u l e . B a s e d on hot h a r d n e s s t e s t s , W e s t b r o o k s r e p o r t e d that Ir3Cr shows no s t r e n g t h a n o m a l y at e l e v a t e d t e m p e r a t u r e s , yet I r 3 C r r e m a i n s o r d e r e d up to T m %5 The i n i t i a l goal of t h i s w o r k was to p e r f o r m u n i a x i a l c o m p r e s s i o n t e s t s on I r 3 C r at e l e v a t e d t e m p e r a t u r e s to s e e if W e s t b r o o k ' s r e s u l t s could be c o n f i r m e d (as they w e r e f o r Ni3A16'7), and a s s u m i n g the r e s u l t s would be c o n f i r m e d , to i n v e s t i g a t e the d i s l o c a t i o n s t r u c t u r e s giving r i s e to t h i s b e h a v i o r u s i n g t r a n s m i s s i o n e l e c t r o n m i c r o s c
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