Mechanical alloying of IN-738

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need to develop i m p r o v e d s u p e r a l l o y s h a s s t i m u l a t e d r e s e a r c h in p r o c e s s i n g techniques like d i r e c t i o n a l s o l i d i f i c a t i o n and d i s p e r s i o n - s t r e n g t h e n ing. The m a i n r e q u i r e m e n t is for m a t e r i a l s which c o m b i n e good c r e e p s t r e n g t h at i n t e r m e d i a t e and e l e v a t e d t e m p e r a t u r e with good high t e m p e r a t u r e c o r r o s i o n r e s i s t a n c e . In the p a s t few y e a r s the p r o c e s s of m e c h a n i c a l a l l o y i n g 1 h a s b e e n used to p r o d u c e a d i s persion-strengthened nickel alloy called initially IN-853, which a l s o has the c o m m e r c i a l d e s i g n a t i o n M A - 7 5 3 (Nimonic 80A + Y203 d i s p e r s i o n ) . M e c h a n i c a l a l l o y i n g 2 c o n s i s t s of blending e l e m e n t a l p o w d e r s with m a s t e r a l l o y p o w d e r s in an a t t r i t o r , and b a l l - m i l l i n g t h e s e p o w d e r s under a d r y , p r o tective atmosphere. The resulting composite powder i s highly c o l d - w o r k e d . C o n s o l i d a t i o n by e x t r u s i o n n e a r the r e c r y s t a l l i z a t i o n t e m p e r a t u r e y i e l d s a d e n s e , f i n e - g r a i n e d b a r . In o r d e r to get good high t e m p e r a t u r e m e c h a n i c a l p r o p e r t i e s , h e a t t r e a t m e n t s to p r o duce a c o a r s e , e l o n g a t e d g r a i n s t r u c t u r e a r e n e e d e d . 3 I N - 8 5 3 , although p o s s e s s i n g e x c e l l e n t high t e m p e r a t u r e m e c h a n i c a l p r o p e r t i e s , has an i n t e r m e d i a t e t e m p e r a t u r e s t r e n g t h which is low if c o m p a r e d to the higher alloyed cast nickel base alloys. T h i s p a p e r r e p o r t s an a p p l i c a t i o n of m e c h a n i c a l a l l o y i n g to a l l o y IN-738, which in i t s c a s t f o r m is a p o t e n t i a l c a n d i d a t e m a t e r i a l for gas t u r b i n e b l a d e s . A s c o m p a r e d to N i m o n i c 80A, IN-738 contains l a r g e r a m o u n t s of yP f o r m i n g e l e m e n t s (Ti, A1), plus a h i g h e r p r o p o r t i o n of s o l i d s o l u t i o n s t r e n g t h e n e r s and c a r bide forming elements. Since thermomechanical proc e s s i n g t a k e s p l a c e at a t e m p e r a t u r e between the V' s o l v u s and the s o l i d u s t e m p e r a t u r e , and s i n c e t h i s t e m p e r a t u r e i n t e r v a l d e c r e a s e s r a p i d l y for h i g h e r a l GERNOT H. GESSINGER is Head of Physical Metallurgy, Alloy Development Group, Brown Boveri Research Centre, CH-5401 Baden, Switzerland. Manuscript submitted October 21, 1975. METALLURGICAL TRANSACTIONS A

loying c o n t e n t s , it was to be e x p e c t e d that e x t r u s i o n and r e c r y s t a l l i z a t i o n conditions would be m o r e c r i t i c a l than in I N - 8 5 3 . EXPERIMENTAL

PROCEDURE

Table I lists the nominal composition of the major alloying additions which were used. F

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