Tracer diffusion of 63 Ni in Fe-17 wt pct Cr-12 wt pct Ni
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Table I. Volume Diffusion of Nickel
Solvent
Frequency Factor, cm2/s
Fe Fe Fe-9pet Ni Steal Fc-17Cr-t2 Ni Fe-20Cr-25Ni/Nbsteel
DO v 0.77 1.25 5.6 X 10"s 8.8 • 10-3 4.06
Activation Energy kcal/mole
Qv 67.0 67.7 46.7 60.O 67.5
Reference
1 2 3 this study 4
Table II. Grain Boundary Diffusion of Nickel
Solvent Fe Fe-9pct Ni steel Fe-17Cr-12Ni Fe-20Cr-25Ni/Nbsteel
Frequency Factor,cma/s 2.5 X 10-6 1.8 X 10.9 3.7 X 10-9 1.5 X 10- 7
Activation Energy kcal/mole 445 28.6 31.5 47.9
Reference 2 3 this study 4
The data a r e of v a l u e in d e t e r m i n i n g the effects of m a j o r and p o s s i b l y m i n o r c o n s t i t u e n t s upon the a t o m i c motion of n i c k e l in v a r i o u s a u s t e n i t i c s t e e l s . A method has been used which allows the d e t e r m i n a t i o n of t r u e v o l u m e s e l f - d i f f u s i o n coefficients down to 600~ w h e r e as, m o s t i n v e s t i g a t i o n s yield an upward deviation f r o m the A r r h e n i u s plot at low t e m p e r a t u r e s due to " e n h a n c e d d i f f u s i o n . " T h e s e low t e m p e r a t u r e s a r e in the r a n g e of m a n y p r a c t i c a l e n g i n e e r i n g a p p l i c a t i o n s and will aid in r e l a t i n g b a s i c t r a n s p o r t p h e n o m e n a to p r a c t i c a l p r o b lems. EXPERIMENTAL PROCEDURE The F e - 1 7 wt pet C r - 1 2 wt pct Ni a l l o y was p r e p a r e d f r o m h i g h - p u r i t y Fe, Cr, and Ni by a r c m e l t i n g under an a r g o n a t m o s p h e r e . The alloy button was i n v e r t e d and r e m e l t e d s e v e r a l t i m e s to obtain an even d i s t r i b u tion of the c o n s t i t u e n t s and swaged into a rod 1.27 c m in d i a m e t e r . The swaged r o d was cut into p i e c e s 7 c m in length which were w r a p p e d in t a n t a l u m foil and p r e a n n e a l e d at 1300~ for 96 h in a h i g h - p u r i t y a r g o n a t m o s p h e r e . The c o m p o s i t i o n of the alloy is given in Table III. Specimens f r o m the rod w e r e a n a l y z e d at t h r e e points along its length to check the h o m o g e n e i t y of the alloy. The g r a i n size was d e t e r m i n e d to be a p p r o x i m a t e l y ASTM No. 0, o r 8 g r a i n s / m m 2. C y l i n d r i c a l s p e c i m e n s 1.2 c m in d i a m and 0.3 c m i n length w e r e then cut f r o m the alloy r o d s . One face of each s p e c i m e n was p o l i s h e d through 4 / 0 e m e r y p a p e r . Those s p e c i m e n s used for the low t e m p e r a t u r e a n n e a l s (600 ~ to 7500C) were f u r t h e r polished through 0.05 ~ a l u m i n a powder and a l t e r n a t e l y etched and p o l i s h e d t h r e e t i m e s to r e m o v e s t r a i n e d m a t e r i a l . (A s p e c i m e n p r e p a r e d each way was r u n at 1000~ and no d i f f e r e n c e was obs e r v e d in e i t h e r the diffusion coefficient obtained o r the r e s o l u t i o n of the v o l u m e diffusion zone n e a r the s u r f a c e . ) The SaNi isotope was then e v a p o r a t e d onto the s p e c i m e n f r
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