The effect of uniaxial stress on the periodic morphology of coherent gamma prime precipitates in nickel-base superalloy
- PDF / 1,329,403 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 115 Downloads / 182 Views
T H E m a j o r s t r e n g t h e n i n g p r e c i p i t a t e in most n i c k e l b a s e s u p e r a l l o y s is y', a n i n t e r m e t a l l i c c o m p o u n d , w h i c h s h a r e s a c o m m o n c r y s t a l s t r u c t u r e and o r i e n t a t i o n with the f c c y s o l i d s o l u t i o n m a t r i x , y a n d y' p h a s e s are normally completely coherent even a f t e r e x t e n s i v e a g i n g , any l a t t i c e m i s f i t b e i n g a c c o m m o d a t e d e n t i r e l y by e l a s t i c c o h e r e n c y s t r a i n , bz In a l l o y s w h e r e l a t t i c e m i s f i t is a b s e n t , the y' p a r t i c l e s a r e o b s e r v e d to b e s m a l l s p h e r o i d s that a r e a l w a y s r a n d o m l y d i s t r i b u t e d in the m a t r i x .3 In c o n t r a s t , when the l a t t i c e m i s f i t is e i t h e r p o s i t i v e o r n e g a t i v e , r a n d o m l y d i s t r i b u t e d s p h e r o i d s a r e e v i d e n t only in the e a r l y s t a g e s of p r e c i p i t a t i o n ; s u b s e q u e n t c o a r s e n i n g r e s u l t s in a s t a b l e p e r i o d i c a r r a y of ( 1 0 0 ) a l i g n e d c u b o i d s of f a i r l y u n i f o r m s i z e .4'5 The r e s u l t s of p r e v i o u s i n v e s t i g a t i o n s s u g g e s t that a p p l i e d s t r e s s c a n h a v e a p r o n o u n c e d e f f e c t on the p e r i o d i c m o r p h o l o g y of y ' . W e b s t e r and Sullivan, 6 and W e b s t e r , P i e a r c e y , a n d Sullivan, 7 o b s e r v e d this e f f e c t in t h e i r i n v e s t i g a t i o n s of the high t e m p e r a t u r e c r e e p b e h a v i o r of f u l l y aged p o l y c r y s t a l l i n e U d i m e t - 7 0 0 . U n d e r t e n s i l e s t r e s s , they f o u n d that the y' m o r p h o l ogy in c e r t a i n g r a i n s h a d t r a n s f o r m e d to a c o n f i g u r a tion c o n s i s t i n g of p a r a l l e l s t r i n g e r s , w h i l e in o t h e r g r a i n s the ~' m o r p h o l o g y w a s a p p a r e n t l y not a f f e c t e d b y the a p p l i e d s t r e s s . T h e r e is e v i d e n c e that t h e s e o b s e r v a t i o n s a r e c o m m o n to o t h e r n i c k e l - b a s e s u p e r a l l o y s s u c h a s M a r - M 2 0 0 8 a n d B - 1 9 0 0 .9 It a p p e a r s that c h a n g e s in the p e r i o d i c m o r p h o l o g y of c u b o i d a l Y' c a n b e i n d u c e d b y the a p p l i c a t i o n of u n i a x i a l s t r e s s ; h o w e v e r , the e x a c t y' s h a p e c h a n g e a n d its d e p e n d e n c e o n s t r e s s o r i e n t a t i o n a n d s e n s e of s t r e s s h a v e not b e e n
J . K. TIEN is SeniorResearch Associate, Advanced Materials Research and Development Laboratory, Pratt & Whitney Aircraft, Middletown, Conn. S. M. COPLEY, formerly Section Supervisor, Advanced Materials Research and Development Laboratory,Pratt & Whitney Aircraft, is Associate Professor of Materials Science and Mechanical Engineering, University of Southern California, Los Angeles, Calif. Manuscript submitted May 28, 1970.
Data Loading...
