An observation of vacancy sources during substitutional diffusion in thoriated nickel alloys
- PDF / 5,167,544 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 95 Downloads / 225 Views
D. WHITTENBERGER
V a r i o u s s o l i d - s o l i d diffusion couples w e r e a s s e m b l e d f r o m t h o r i a t e d and n o n t h o r i a t e d a l l o y s , welded, and diffusion a n n e a l e d at 1530 K. C o n c e n t r a t i o n p r o f i l e s of the diffused couples i n d i c a t e d that a t h o r i a d i s p e r s i o n does not affect diffusion in Cr(alloy) :Ni and N i 4.8A1 :Ni types of couples u n l e s s a fine g r a i n s t r u c t u r e is r e t a i n e d by the t h o r i a p a r t i c l e s . M e t a l l o g r a p h y r e v e a l e d the p r e s e n c e of ThO2-free bands in the t h o r i a t e d nickel side of the diffusion zone. The bands f o r m e d at g r a i n b o u n d a r i e s p e r p e n d i c u l a r to the d i r e c t i o n of diffusion and, in some c a s e s , contained n o n - K i r k e n d a l l p o r o s i t y . A m e c h a n i s m b a s e d on the o p e r a t i o n of v a c a n c y s o u r c e s is p r o p o s e d to explain the ThOz-free bands. T H E d i s p e r s i o n - s t r e n g t h e n e d alloy Ni-20Cr-2ThO2* is
annealing. Metallography revealed light-colored bands n e a r the c h r o m i z e d s u r f a c e . T h e s e w e r e a p p r o x i m a t e l y p a r a l l e l to the s u r f a c e and existed only in the c h r o m i u m of c u r r e n t i n t e r e s t for use in v a r i o u s high t e m p e r a t u r e diffusion zone. The b a n d s could be o b s e r v e d both in the a p p l i c a t i o n s that r e q u i r e high c r e e p s t r e n g t h and good etched and unetched c o n d i t i o n s . The bands o c c u r r e d r e oxidation r e s i s t a n c e . Such a l l o y s a r e c u r r e n t l y being g a r d l e s s of the c h r o m i z i n g conditions o r lot of T D - N i . m a n u f a c t u r e d by two d i s t i n c t p r o c e s s e s . F a n s t e e l , Inc., Also, the width of the r e g i o n c o n t a i n i n g these bands and p r o d u c e s sheet, c o m m e r c i a l l y n a m e d T D - N i C r , through a c o m b i n a t i o n of powder m e t a l l u r g y t e c h n i q u e s and t h e r - the width of individual b a n d s i n c r e a s e d as the c h r o m i z i n g m o m e c h a n i c a l processing.~ S h e r r i t t - G o r d o n M i n e s , Ltd., t i m e i n c r e a s e d . Through e l e c t r o n m i c r o p r o b e a n a l y s i s and e l e c t r o n r e p l i c a t i o n , it was e s t a b l i s h e d that the p r o d u c e s thin sheet, c o m m e r c i a l l y n a m e d D S - N i C r , b a n d s w e r e v i r t u a l l y f r e e of ThO2 p a r t i c l e s . F u r t h e r through the pack c h r o m i z i n g of Ni-2ThO2 sheet. 2 m o r e , the individual ThO2 p a r t i c l e size was the s a m e As a m a n u f a c t u r i n g p r o c e s s , the pack c h r o m i z i n g method is of i n t e r e s t b e c a u s e of its dependence on c h r o - before and a f t e r c h r o m i z i n g , and the t h o r i a - d i s p e r s e d m i u m diffusion into n i c k e l . The r a t e of c h r o m i u m diffu- population ( n u m b e r of p a r t i c l e s /
Data Loading...
