Carbide-binder interface ledges in (V, Ti) C+ (Ni, Mo) cermets
- PDF / 1,602,459 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 90 Downloads / 184 Views
T
HE m a j o r c o n s t i t u e n t in m o s t c e m e n t e d c a r b i d e s is a r e l a t i v e l y hard and b r i t t l e c a r b i d e d i s p e r s e d in a r e l a t i v e l y soft and ductile b i n d e r p h a s e . S t r u c t u r e p r o p e r t y c o r r e l a t i o n s in this t e c h n o l o g i c a l l y i m p o r t a n t c l a s s of m a t e r i a l s have been the s u b j e c t of n u m e r o u s i n v e s t i g a t i o n s , most of which have c e n t e r e d on the c l a s s i c s y s t e m , W C - C o . S e v e r a l a t t e m p t s have b e e n made to c o r r e l a t e the h a r d n e s s of W C - C o with s t r u c t u r a l p a r a m e t e r s , such as c a r b i d e and b i n d e r v o l u m e f r a c t i o n , c a r b i d e g r a i n size and d i s t r i b u t i o n , and so forth. R e c e n t l y , Lee and G u r l a n d ~,2 p r o p o s e d the following e m p i r i c a l r e l a t i o n s h i p for the h a r d n e s s of W C - C o a l l o y s , Hc: [1]
H c = H w c V w c C + H m (1 - CVwc )
w h e r e Hwc and Hm a r e the h a r d n e s s of the c a r b i d e and b i n d e r , C is the contiguity f a c t o r and is a m e a s u r e of the c a r b i d e - c a r b i d e contact, and Vwc i s the v o l u m e f r a c t i o n of the c a r b i d e . T h e s e a u t h o r s a l s o p r o p o s e d that the in situ h a r d n e s s of the b i n d e r can be r e p r e s e n t e d by the e m p i r i c a l re lation:
[2]
H m = 304 + 12.7 X-~/2 ( k g / m m 2)
w h e r e d is the a v e r a g e g r a i n size of the c a r b i d e and is the b i n d e r m e a n f r e e path. Since the b i n d e r h a r d n e s s is the d e t e r m i n i n g factor in c o n t r o l l i n g the h a r d n e s s of most c e r m e t s , it is of i n t e r e s t to e s t a b l i s h the p h y s i c a l b a s i s for the e m p i r i c a l equation r e l a t i n g b i n d e r h a r d n e s s and m e a n free path. The s i m i l a r i t y of the e m p i r i c a l r e l a t i o n for the b i n d e r h a r d n e s s and the c o n v e n t i o n a l H a l l - P e t c h r e l a tion in p o l y c r y s t a l l i n e m e t a l s and alloys is s t r i k i n g . However, the b i n d e r phase in c e m e n t e d c a r b i d e s has a g r a i n s i z e 100 to 10,000 t i m e s the m e a n f r e e path. It a p p e a r s that the b i n d e r b e h a v e s a s if it has an a p p a r ent g r a i n size ~, the m e a n f r e e path. P r e v i o u s l y , p h y s i c a l i n t e r p r e t a t i o n of the H a l l - P e r c h r e l a t i o n s h i p in m e t a l s and alloys has been provided through d i s l o c a t i o n - p i l e - u p m o d e l s . 3-7 However, lack of e x t e n s i v e e x p e r i m e n t a l o b s e r v a t i o n s on d i s l o c a t i o n p i l e - u p s and i n c r e a s e d u n d e r s t a n d i n g of g r a i n b o u n d a r y s t r u c t u r e s have led to a r e e v a l u a t i o n of the d i s l o c a tion p i l e - u p model in m e t a l s and a l l o y s . An a l t e r n a t i v e R. K. VISWANADHAM,formerly with Marti
Data Loading...
