The influence of segregation on grain boundary cohesion
- PDF / 699,902 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 256 Views
AND H. L. MARCUS
B a s e d upon a d e t a i l e d t h e r m o d y n a m i c a n a l y s i s where a g r a i n gives up one or s e v e r a l dilute s o l u t e s to the g r a i n boundary, we have d e v i s e d two models which adequately des c r i b e the e n e r g e t i c s of g r a i n b o u n d a r y s e g r e g a t i o n induced i n t e r g r a n u l a r f r a c t u r e . In the f i r s t m o d e l the cohesive e n e r g y of the p r e c i p i t a t e is much s m a l l e r than the o r i g i n a l m a t e r i a l giving r i s e to easy s e p a r a t i o n of the b o u n d a r y r e g i o n . In the second model a highly cohesive d i r e c t i o n a l l y bonded g l a s s y s e g r e g a t e f o r m s at the b o u n d a r y . The t e r n a r y g l a s s y s e g r e g a t e bonds well with i t s e l f but not with the s u r r o u n d i n g lattice giving r i s e to a weak i n t e r f a c e between the g r a i n b o u n d a r y s e g r e g a t e and the lattice,
I N a r e c e n t r e v i e w a r t i c l e , McMahon 1 has d i s c u s s e d the r e s u l t s of i m p u r i t i e s on t e m p e r e m b r i t t l e m e n t of i r o n b a s e a l l o y s . He p r o v i d e s e v i d e n c e that Group VI e l e m e n t s in the p e r i o d i c t a b l e a r e the m o s t potent e l e m e n t s i n i n d u c i n g i n t e r g r a n u l a r f r a c t u r e . Of Groups IV and V, the d i s c u s s i o n he gives s u g g e s t s that t e r n a r y s o l u t e s m u s t b e p r e s e n t and s e g r e g a t e to the g r a i n b o u n d a r y to a s s i s t in the e m b r i t t l e m e n t . T h u s , we may a s s u m e that b i n a r y i r o n alloys cont a i n i n g S, Se, and Te will be s u s c e p t i b l e to t e m p e r e m b r i t t l e m e n t ; w h e r e a s , alloys c o n t a i n i n g t h e s e e l e m e n t s or Sn, Sb, P, and As could c a u s e e m b r i t t l e m e n t when the t e r n a r y s o l u t e s Ni, Cr, or Mn a r e p r e s e n t . A t h e r m o d y n a m i c model is c o n s t r u c t e d , which exp l a i n s the changes which take place in the cohesive e n e r g y of g r a i n b o u n d a r i e s with solute s e g r e g a t i o n . The model is c o m p a r e d to p r e v i o u s l y published exp e r i m e n t a l r e s u l t s and is used to p r e d i c t other s y s t e m s which would suffer i n t e r g r a n u l a r w e a k n e s s through solute s e g r e g a t i o n . In the model, no a s s u m p t i o n s a r e made r e g a r d i n g the t h e r m o d y n a m i c m o d e l of the g r a i n boundary; however, it will be c o n v e n i e n t to a s s u m e thai the s o l u t e s s e g r e g a t i n g f r o m the l a t t i c e to the b o u n d a r y a r e s u f f i e i e n t l y dilute to follow H e n r y ' s law. B R I E F DEFINITION OF MODEL The g r a i n b o u n d a r y will be viewed as composed of a " b o u n d a r y " r e g i o n of homogeneous m a t t e r subjected to a s u r f a c e t e n s i o n 02 . Between the b o u n d a r y and the lattice a r e two r e g i o n s each called a m a t
Data Loading...
