Correlation of tensile strength with isostatic compaction pressure for metal powders
- PDF / 278,377 Bytes
- 2 Pages / 612 x 783.28 pts Page_size
- 50 Downloads / 211 Views
Fig. 5--Typical wedge type cracks at triple points and w e l l defined striations appearances of specimen 1. t e n s i l e f o r c e s . C h a n g . a n d G r a n t 17 h a v e a p p l i e d t h i s m e c h a n i s m to c r e e p r u p t u r e . C e l l , L e v e r a n t and W e l l s Is h a v e d i s c u s s e d the p o s s i b i l i t y of t h e f o r m a t i o n of c a v i t i e s at the i n t e r f a c e of t h e m a t r i x and c a r b i d e s o r o t h e r h a r d p a r t i c l e s . T h e y a l s o d i s c u s s e d c r a c k i n i t i a t i o n at g r a i n b o u n d a r i e s in e l e v a t e d t e m p e r a t u r e f a t i g u e t e s t s . U n d e r t h e high t e m p e r a t u r e f a t i g u e t e s t w i t h f r e q u e n c i e s of t h e o r d e r of 100 c y c l e s p e r s e c o n d , t h e p r o c e s s of f a t i g u e m a y b e a k i n to t h a t of c r e e p in w h i c h c a v i t i e s a r e n u c l e a t e d at s t r e s s c o n c e n t r a t i o n s i t e s b y g r a i n b o u n d a r y s l i d i n g , a~ W e s t w o o d and T a p l i n z~ h a v e also suggested that a pronounced grain boundary mig r a t i o n , w h i c h is a d o m i n a n t p h e n o m e n o n d u r i n g h i g h t e m p e r a t u r e c r e e p , o c c u r s in l o w - c y c l e high t e m p e r a t u r e f a t i g u e of a l p h a - i r o n , and h a v e m e n t i o n e d t h a t the c a v i t a t i o n m e c h a n i s m of f a t i g u e d i f f e r s s o m e w h a t f r o m t h a t found in c r e e p . As is s h o w n in F i g . 3 and 4, i n t e r g r a n u l a r c r a c k p r o p a g a t i o n at t r i p l e p o i n t s h a s b e e n b l o c k e d b y c r y s t a l a c c o m m o d a t i o n in the g r a i n at the c r a c k tip in t h i s r e g i o n . T h i s m a y i m p l y t h a t t h e m o v e m e n t of d i s l o c a t i o n s in t h e g r a i n c a n p r e v e n t t h e s u c c e s s i v e l i n k - u p of c r a c k s at g r a i n b o u n d a r i e s b y r e l i e v i n g the s t r e s s c o n c e n t r a t i o n at t h e c r a c k tip b e f o r e l i n k - u p of c r a c k s b e g i n s . T h e r i v e r l i n e s in t h e g r a i n m a y a l s o s u g g e s t crystal accommodation. It is i n t e r e s t i n g to n o t e t h a t t h e w e d g e t y p e c r a c k s a r e o b s e r v e d in t h e r e g i o n In t h e v i c i n i t y of the o v e r loaded intergranular failure zone together with welld e f i n e d s t r i a t i o n s , F i g . 5. F r o m t h e s e o b s e r v a t i o n s , it is a s s u m e d t h a t the w e d g e t y p e c r a c k at t r i p l e p o i n t s i n i t i a t e s d u r i n g h i g h t e m p e r a t u r e f a t i g u e and the m e c h a n i s m f o r t h e i r f o r m a t i o n is s i m i l a r to t h a t found in high temperature creep ruptured materials. 1. D. J. Duquette and M. Gell:Met. Trans., 1971, vol. 2, pp. 1325-31. 2. M. Gell and G. R. Leverant:Acta Met., 1968, vol. 16, pp. 553-61. 3. M. Cell and G. R. Leverant: Trans. TMS-AIME, 1968, vol. 242, pp. 1869-79. 4. D. J. Duquette, M. G
Data Loading...
