Coercive force and structure in a Co-Fe-Au alloy
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r e q u i r e m e n t s 1 for a p e r m a n e n t m a g n e t m a t e r i a l which m a i n t a i n s its m a g n e t i c p r o p e r t i e s while being s t r e s s e d in a c o m p l e x m a n n e r have led to the d e v e l o p m e n t 2 of a low m a g n e t o s t r i c t i v e alloy of c o m p o s i tion 8 2 C o - 1 2 F e - 6 A u . N e s b i t t , Chin, and Jaffe 2 have i n v e s t i g a t e d the m a g n e t o s t r i c t i v e p r o p e r t i e s of this alloy and the effect of cold work and a n n e a l i n g t r e a t m e n t s upon its c o e r c i v e f o r c e . They have found that the c o e r c i v e force of d r a w n w i r e s a m p l e s can be v a r i e d f r o m 1 to 15 oe by c o n t r o l of the d e g r e e of cold work and s u b s e q u e n t a n n e a l i n g c o n d i t i o n s as s u m m a r i z e d in Fig. 1. The p u r p o s e of this p a p e r is to p r e s e n t the r e s u l t s of an i n v e s t i g a t i o n p e r f o r m e d to d e t e r m i n e the s t r u c t u r a l changes which c a u s e these o b s e r v e d changes in c o e r c i v e force. E X P E R I M E N T A L PROCEDURE Strip s a m p l e s of an 8 2 C o - 1 2 F e - 6 A u alloy w e r e s o l u tion a n n e a l e d at 1055~ i n f o r m i n g gas (90N2-10Hz) and cooled quickly in a s t r e a m of f o r m i n g gas to p r o d u c e a s u p e r s a t u r a t e d fcc T phase. The solution t r e a t e d m a t e r i a l was then r o l l e d 50, 75, and 90 pct to t h i c k n e s s e s of 0.010, 0.005, and 0.002 in., r e s p e c t i v e l y . The cold worked s t r u c t u r e s w e r e heat t r e a t e d in the f o r m i n g gas a t m o s p h e r e to p r o v i d e s a m p l e s for m a g n e t i c t e s t ing and for s t r u c t u r a l e x a m i n a t i o n by light and e l e c t r o n m i c r o s c o p y . The k i n e t i c s of the o b s e r v e d t r a n s f o r m a tion w e r e d e t e r m i n e d q u a n t i t a t i v e l y by point counting, z and 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 o p y and d i f f r a c t i o n m e t h o d s w e r e used to identify the p h a s e s which w e r e o b s e r v e d with the light m i c r o s c o p e . Magnetic m e a s u r e m e n t s w e r e made with a p r e c i s i o n c o e r c i v e f o r c e m e t e r 4 and an e l e c t r o n i c h y s t e r e s i s g r a p h , s M i c r o h a r d n e s s m e a s u r e m e n t s w e r e made with a d i a m o n d pyramid hardness tester.
a m o u n t s and s u b s e q u e n t l y a n n e a l e d for 2 h r at d i f f e r e n t t e m p e r a t u r e s i s shown in Fig. 2. C o m p a r i s o n of F i g s . 1 and 2 shows that although the r e s p o n s e of the c o e r cive f o r c e to a n n e a l i n g i s s i m i l a r for w i r e and s t r i p s a m p l e s , the r e s p o n s e of c o e r c i v e f o r c e to cold work is s i g n i f i c a n t l y different in the w i r e and s t r i p s a m p l e s . The s t r i p s a m p l e s have a c o e r c i v e f o r c e about 50 pct of that of the w i r e s a m p l e s in the cold worked cond
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