Creep of precipitation-hardened nickel-base alloy single crystals at high temperatures
- PDF / 3,538,132 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 225 Views
B. H. KEAR,
AND
J. M. OBLAK
Single c r y s t a l s of a y ' p r e c i p i t a t i o n - h a r d e n e d n i c k e l - b a s e s u p e r a l l o y , M a r - M 2 0 0 , w e r e t e s t e d in c o n s t a n t load c r e e p at 1575~ It was found that s h e a r of the y ' p r e c i p i t a t e by p a i r s of a/2 (110) d i s l o c a t i o n s c o n t r o l l e d d e f o r m a t i o n in both p r i m a r y and s t e a d y - s t a t e c r e e p . This c o n t r a s t s with 1400~ c r e e p b e h a v i o r w h e r e s h e a r of y' i s d o m i n a t e d by a/3 (112) d i s l o c a t i o n s in p r i m a r y c r e e p , but by p a i r s of a/2 (110) d i s l o c a t i o n s in s t e a d y s t a t e c r e e p . The o r i e n t a t i o n d e p e n d e n c e of the s t e a d y - s t a t e c r e e p r a t e at 1575~ i s e x p l a i n e d b y the n a t u r e of d i s l o c a t i o n junction r e a c t i o n s for the d i f f e r e n t o r i e n t a t i o n s . C r y s t a l s along the [ 0 0 1 ] - [ l h ] b o u n d a r y have the g r e a t e s t c r e e p r e s i s t a n c e b e c a u s e of the f o r m a t i o n of s t a b l e d i s l o c a t i o n n e t w o r k s at the m a t r i x - p a r t i c l e (y') i n t e r f a c e s , w h e r e a s the l o w e r c r e e p r e s i s t a n c e of c r y s t a l s o r i e n t e d along the [001]-[011] b o u n d a r y is a c o n s e q u e n c e of the low p r o b a b i l i t y f o r the f o r m a t i o n of s t a b l e j u n c t i o n r e a c t i o n s . F i n a l l y , e v i d e n c e , in the f o r m of r e s o l v a b l e a/2 (110) d i s l o c a t i o n p a i r s within the y' p r e c i p i t a t e , is p r e s e n t e d for a r e d u c t i o n in the l o c a l a n t i p h a s e b o u n d a r y e n e r g y of y' at high t e m p e r ,xtures.
IN a p r e v i o u s
study of the c r e e p at 1400~ of single c r y s t a l s of a y' p r e c i p i t a t i o n - h a r d e n e d n i c k e l - b a s e a l l o y , M a r - M 2 0 0 , it was shown that p r i m a r y c r e e p d e f o r m a t i o n took p l a c e by a {111} (112) m o d e of s h e a r . 1'2 Although d i s l o c a t i o n s with a/2 s h e a r of the 7' is about 60 k c a l / m o l e . In c o n t r a s t , at 1575~ the a v e r a g e a c t i v a t i o n e n e r g y ( ~ / ) for s t e a d y - s t a t e c r e e p , where it is obvious that a / 2 (110> d i s l o c a t i o n p a i r s a r e d o m i n a n t , is 147 k c a l / m o l e . Since s t e a d y - s t a t e c r e e p at 1400~ has an a c t i v a t i o n e n e r g y of 150 k c a l / m o l e , z it m u s t t h e r e f o r e be concluded that s t e a d y - s t a t e c r e e p at 1400~ is s i m i l a r l y c o n t r o l l e d by the motion of a / 2 (110> d i s l o c a t i o n p a i r s and that (112) s h e a r is p r e d o m i n a n t only d u r i n g p r i m a r y c r e e p . B) O r i e n t a t i o n Dependence of C r e e p Behavior The r e a s o n for the s t r o n g o r i e n t a t i o n dependence of the s t e a d y - s t a t e c r e e p r a t e was d i s c u s s e d in Section IIC. B r
Data Loading...
