Effect of gamma-gamma prime mismatch, volume fraction gamma prime, and gamma prime morphology on elevated temperature pr
- PDF / 2,119,590 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 65 Downloads / 253 Views
N O R D H E I M a n d G r a n tx c o r r e l a t e d the m i s m a t c h b e t w e e n the l a t t i c e s of a u s t e n i t e (~) a n d a g e - h a r d e n i n g g a m m a - p r i m e ( 7 ' ) p r e c i p i t a t e s w i t h c r e e p s t r e n g t h in 8 0 N i - 2 0 C r c o n t a i n i n g titanium a n d aluminum as h a r d e n e r s . B i g e l o w e t a l . ~ a n d M i h a l i s i n a n d D e c k e r3 SUEgested that the 7 - ~ ' mismatch and resultant coherency s t r a i n s c o n t r i b u t e d t o the a g e - h a r d e n i n g i n c o m m e r c i a l nickel-base superaIloys and experimental Ni-Ti-A1 alloys, respectively. Very recently, however, A n s e l l and h i s c o l l e a g u e s 4-6 q u e s t i o n e d the i m p o r t a n c e of c o h e r e n c y s t r a i n s i n Y ' s t r e n g t h e n e d a l l o y s . In a s y s t e m a t i c s t u d y d e s i g n e d t o p r o v i d e a c r i t i c a l t e s t f o r the b e n e f i c i a l r o l e of c o h e r e n c y s t r a i n s , D e c k e r a n d M i h a l i s i n 7 s h o w e d that by m a n i p u l a t i n g 7 - Y ' m i s m a t c h , a n d t h u s the c o h e r e n c y s t r a i n s , a g e d h a r d n e s s of N i - A 1 a l l o y s c o u l d i n d e e d be c o n t r o l l e d . In a s i m i l a r i n v e s t i g a t i o n , M a n i a r et a l l c o r r e l a t e d 7 - V ' m i s m a t c h w i t h s t r e s s r u p t u r e l i f e in a s e r i e s of N i - C r / F e - N i - C r e x p e r i m e n t a l a l l o y s c o n t a i n i n g t i t a n i u m , a l u m i n u m m~d, i n a f e w c a s e s , molybdenum. Although t r e n d s were developed t o e s t a b l i s h the c r i t i c a l i n f l u e n c e of m i s m a t c h , e f f e c t of o t h e r equally i m p o r t a n t v a r i a b l e s , such a s v o l u m e f r a c tion y ' a n d 7 ' m o r p h o l o g y w e r e not c o n t r o l l e d . T h i s s t u d y w a s d e s i g n e d t o d i s c e r n the e f f e c t of m i s m a t c h f r o m s o m e of t h e s e v a r i a b l e s .
T h e c h e m i c a l a n a l y s e s of the a l l o y s s t u d i e d a r e g i v e n i n T a b l e I. A t r a c e q u a n t i t y of b o r o n w a s a d d e d t o all t h r e e h e a t s f o r e a s e in h o t w o r k i n g . T h e h e a t s were c a s t into 2 by 2-~ in. i n g o t s a n d h o m o g e n i z e d a t 2 1 0 0 ° F f o r 6 h r . T h e h o m o g e n i z e d i n g o t s w e r e f o r g e d t o -~ i n . sq b a r s a t 2 0 5 0 ° F . T h e p r o c e s s i n g of the t h r e e h e a t s w a s m a i n t a i n e d as uniform a s possible. X - r a y Diffraction Analysis T h e Y - 7 ' m i s m a t c h d e t e r m i n a t i o n s w e r e m a d e in a c cordance with the procedure d e s c r i b e d e a r l i e r f A few s a m p l e s f r o m h e a t V 0 0 2 4 7 were o v e r a g e d to p r e c i p i t a t e 7 ' of f a i r l y c o a r s e s i z e . T h e a 0 m e a s u r e m e n t s m a d e o n the o v e r a g e d s o l i d s a m p l e s w e r e c o m p a r e d w i t h the s i m i l a r d a t a o b t a i n e d f r o m the e x t r a c
Data Loading...
