Dislocation configurations developed during carburization of nickel
- PDF / 3,016,030 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 217 Views
K. BOAH
AND
P. G. WINCHELL
D i s l o c a t i o n c o n f i g u r a t i o n s a r e shown to develop in nickel single c r y s t a l s as a r e s u l t of diffusion of c a r b o n f r o m a vapor s o u r c e . Since c a r b o n is d i s s o l v e d i n t e r s t i t i a l l y in nickel, the p r e s e n c e of such d i s l o c a t i o n c o n f i g u r a t i o n s d e m o n s t r a t e s that l a t t i c e p a r a m e t e r changes suffice for g e n e r a t i n g d i s l o c a t i o n a r r a y s and that the v a c a n c y r e q u i r e m e n t s involved in diffusion of s u b s t i t u t i o n a l l y d i s s o l v e d a t o m s a r e n o n e s s e n t i a l . In p a r t i c u l a r , c a r b o n was diffused for 30 m i n at 1000~ into the (111) s u r f a c e s of thick n i c k e l c r y s t a l s , and the r e s u l t i n g d i s l o c a t i o n a r r a n g e m e n t s in the diffusion zone were e x a m i n e d by etch pitting (111) s e c t i o n s . The d i s l o c a t i o n d e n s i t y i n c r e a s e s f r o m the " g r o w n - i n " 1.5 x 106 p e r cm z so that in some r e g i o n s n e a r that s u r f a c e it is about 107 per cm 2. At l e a s t half of all the d i s l o c a t i o n s a p p e a r to be a r r a y e d in s u b g r a i n b o u n d a r i e s in t h e s e s e c t i o n s . The d i s l o c a t i o n d e n s i t y d e c r e a s e s t o w a r d s the i n t e r i o r until at about 3.5 D4~e ( D~-~e = 2 1 0 / l m ) it a p p r o x i m a t e s the " g r o w n - i n " d i s l o c a t i o n density, but even at d i s t a n c e s exceeding 0 . 7 ( D t e t h e r e s t i l l exist l o c a l l y high d e n s i t y r e g i o n s . T h e s e have a r e g u l a r g e o m e t r y in which d i s l o c a t i o n s appear to be on ( i l l ) , (1[1) or ( l l i ) slip p l a n e s . The s u b g r a i n size is 3 6 / l m n e a r the a s - d i f f u s e d s u r f a c e and i n c r e a s e s , until at 3.5~Dt e , it is 160/~m, which is the a v e r a g e s u b g r a i n s i z e in the undiffused crystal.
T H E d e n s i t y and a r r a n g e m e n t of d i s l o c a t i o n s in conc e n t r a t i o n g r a d i e n t s d u r i n g the p r o g r e s s of c h e m i c a l diffusion have b e e n the s u b j e c t s of s e v e r a l e x p e r i m e n tal and t h e o r e t i c a l i n v e s t i g a t i o n s . ~'2'3 Such d i s l o c a tions a r e of i n t e r e s t b e c a u s e they m a y affect the e l e c t r i c a l p r o p e r t i e s of s e m i c o n d u c t o r device j u n c t i o n s and b e c a u s e by pipe diffusion they m a y modify the c o n c e n t r a t i o n g r a d i e n t in which they exist. T h e s e s t u d i e s did not c l e a r l y d i s t i n g u i s h whether the d i s l o cations a r i s e to supply v a c a n c i e s for diffusion or to a c c o m m o d a t e l a t t i c e p a r a m e t e r g r a d i e n t s or whether both w e r e i m p o r t a n t . T h e o r e t i c a l c a l c u l a t i o n s of the v a r i o u s a r r a n g e m e n t s of d i s l o c a t i o n s that a c c o m m o d a t e loca
Data Loading...
