On the concept of the coefficient of liquid metal embrittlement
- PDF / 336,668 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 252 Views
On the Concept of the Coefficient of Liquid Metal Embrittlement M . H. KAMDAR N O R M A L L Y d u c t i l e s o l i d m e t a l s c a n be c a u s e d t o b e h a v e i n a b r i t t l e m a n n e r by e x p o s u r e t o c e r t a i n s u r face active l i q u i d m e t a l environments. For example, d u c t i l e z i n c m o n o c r y s t a l s a r e k n o w n t o f r a c t u r e by b a s a l (0001) c l e a v a g e w h e n t e s t e d i n l i q u i d m e r c u r y e n v i r o n m e n t s a t 2 9 8 ° K .1 S u c h a p h e n o m e n o n of l i q u i d m e t a l e m b r i t t l e m e n t o f a s o l i d is p r e s e n t l y c o n s i d e r e d t o r e s u l t f r o m a b s o r p t i o n of t h e l i q u i d m e t a l a t o m s a t r e g i o n s o f s t r e s s c o n c e n t r a t i o n s in t h e s o l i d m e t a l , e . g . , a t t h e t i p s o f c r a c k s ,2'3 o r d u r i n g c r a c k i n i t i a t i o n i n t h e v i c i n i t y o f p i l e d up g r o u p s o f d i s l o c a t i o n s n e a r a n o b s t a c l e , c a u s i n g r e d u c t i o n s i n the c o h e s i v e s t r e n g t h of a t o m i c b o n d s a c r o s s t h e f r a c t u r e p l a n e . 4 Q u a n t i t a t i v e e x p e r i m e n t a l e v i d e n c e in s u p p o r t o f t h i s m e c h a n i s m h a s b e e n o b t a i n e d by s t u d y i n g c r a c k p r o p a g a t i o n in z i n c in l i q u i d m e r c u r y e n v i r o n m e n t s u s i n g t h e d o u b l e c a n t i l e v e r c l e a v a g e t e c h n i q u e . 2 It w a s shown that t h e e n e r g y r e q u i r e d t o p r o p a g a t e c l e a v a g e c r a c k s on t h e b a s a l p l a n e (0001) i n z i n c m o n o c r y s t a l s i n t h e p r e s e n c e of l i q u i d m e r c u r y e n v i r o n m e n t s , (pp ( Z n - H g , 298°K) i s s i g n i f i c a n t l y l o w e r ( - 4 0 p c t ) t h a n t h a t in t h e a b s e n c e o f m e r c u r y in a n i n e r t e n v i r o n m e n t ( e . g . , l i q u i d n i t r o g e n ) , @p ( Z n , 7 7 ° K ) . T h e l a t t e r is c o n s i d e r e d e q u i v a l e n t to ~ ( Z n ) , t h e cleavage surf a c e e n e r g y o f (0001) p l a n e in z i n c . T h e r a t i o ~p = q~p ( Z n - H g , 298°K)Abp ( Z n , 7 7 ° K ) w a s f o u n d t o be 0.61 ± 0.12 a n d w a s d e f i n e d a s t h e c o e f f i c i e n t o f e m b r i t t l e m e n t f o r c r a c k p r o p a g a t i o n . ~?p i s c o n s i d e r e d an environmental variable. T h e s e observations and a c o n s i d e r a t i o n of t h e m e c h a n i s m o f c r a c k n u c l e a t i o n i n t h e p r e s e n c e a n d in t h e a b s e n c e o f a n a b s o r p t i o n a c t i v e l i q u i d m e t a l a t o m s at o r near t h e obstacle s u g g e s t e d that a c o e f f i c i e n t o f e m b r i t t l e m e n t f o r c r a c k i n i t i a t i o n , ~?I f o r a z i n c - m e r c u r y e m b r i t t l e m e n t c o u p l e m a y a l s o be d e f i n e d a s t h e r a t i o o f t h e e n e r g y t o b r e a k a t o m i c b o n d s a c r o s s t h e f r a c t u r e p l a n e
Data Loading...
