Correlation of gamma-gamma prime mismatch and strengthening in Ni/Fe-Ni base alloys containing aluminum and titanium as
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V a r i o u s a u t h o r s h a v e i n v o k e d c o h e r e n c y s t r a i n s a n d d i s r e g i s t r y b e t w e e n t h e c r y s t a l l a t t i c e s of t h e m a t r i x a n d y ' p h a s e to a c c o u n t f o r c o n s i d e r a b l e h a r d e n i n g i n y ' - s t r e n g t h e n e d s u p e r a l l o y s . H a g e l a n d B e a t t i e c o r r e l a t e d t h e m o d e of p r e c i p i t a t i o n w i t h t h e d e g r e e of i t s l a t t i c e m i s m a t c h . H e y d t a n d W h i t n e y u s e d t h i s a p p r o a c h d u r i n g t h e d e v e l o p m e n t of a n F e - N i b a s e h i g h t e m p e r a t u r e a l l o y . T o u n d e r s t a n d t h e r o l e of s u c h a r e l a t i o n s h i p , a n i n v e s t i g a t i o n o f a f e w e x p e r i m e n tal Ni-base/Fe-Ni b a s e a l l o y s w a s c a r r i e d out. T h e s e a l l o y s w e r e s t r e n g t h e n e d by v a r i a b l e titanium, aluminum, and molybdenum additions and contained chromium. Lattice parameters of the s o l u t i o n t r e a t e d a n d a g e d s a m p l e s w e r e m e a s u r e d . T h e 7' p h a s e w a s e l e c t r o l y t i c a l l y e x tracted for lattice parameter determinations, and y-~' mismatch calculated. The y-y' mismatch was correlated with room temperature hardness and stress rupture properties at 1200~ T h e i n f l u e n c e of a l l o y i n g a d d i t i o n s , m a t r i x a n d y ' l a t t i c e p a r a m e t e r s w e r e i n t e r r e l a t e d .
t r a i n sR and E d i s r e gN istry C o r mY ismatch C O H sE b e t w e e n t h e c r y s t a l l a t t i c e s of t h e a u s t e n i t e m a t r i x (y) a n d t h e g a m m a p r i m e (y') p r e c i p i t a t e s h a v e b e e n u s e d t o e x p l a i n t h e h a r d e n i n g of y ' - s t r e n g t h e n e d s u p e r a l l o y s . 1'2 H a g e l a n d B e a t t i e a e x p l a i n e d t h e m o r p h o l o g y of 7' p r e c i p i t a t e s i n t e r m s of y - y ' l a t t i c e mismatch. Heydt and Whitney 4 used this approach d u r i n g d e v e l o p m e n t of P y r o m e t 8 6 0 , a n F e - N i b a s e heat resistant alloy. More recent work by Pitler and Ansell 5 and Hamm o n d a n d A n s e l l , 8 h o w e v e r , d e e m p h a s i z e d t h e r o l e of coherency hardening in high nickel maraging and Fe-Ni base high temperature alloys, respectively. Maniar and James 7 confirmed many random orientat i o n s i n a d d i t i o n t o p r e f e r r e d o r i e n t a t i o n of ~ ' p r e c i p i t a t e s i n t h i n f o i l s of P y r o m e t 8 6 0 , a n d s u g g e s t e d t h a t t h e s t r e n g t h e n i n g in P y r o m e t 8 6 0 m a y b e d u e to both coherency and dispersion hardening. T h i s i n v e s t i g a t i o n w a s c o n d u c t e d to s t u d y t h e e f f e c t of ~ - ~ ' m i s m a t c h on p r o p e r t i e s , s p e c i f i c a l l y t h e stress-rupture, of a few y ' - h a r d e n e d N i / F e - N i b a s e experimental alloys. These alloys were strengthened by variable titanium, aluminum, and molybdenum additions
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