Solute diffusion in alpha- and gamma-iron
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a-Fe
y-Fe
(-59,900 RT /
Chromium
D = 8.52 exp k
/-69,700 \ D = 10.80 e x p k ~ ]
Vanadium
(-57,600~ D = 3.92 exp k ~ /
/-63,100h D = 0.25 exp k ~ R - T - - J
Hafnium
D = 1.31 exp (-69,300~
[-97,300\ D = 3600 ex p k ~ j
k
RT
/
The d i f f e r e n c e s in diffusion r a t e s a r e d i s c u s s e d in t e r m s of the c o m p r e s s i b i l i t y of the diffusing at o m . Diffusion of c h r o m i u m in y - F e w as a l s o m e a s u r e d by a m i c r o p r o b e a n a l y s i s t e c h n i q u e . The result is:
(-68,500~
D = 4.08 exp \ ~ ]
C o m p a r i s o n is m a d e b e t w e e n diffusion a n a l y s i s by t r a c e r t e c h n i q u e s and by e l e c t r o n p r o b e mieroanalysis.
BECAUSEof its
t e c h n o l o g i c a l i m p o r t a n c e , it is n e c e s s a r y that the diffusion r a t e s of a ll p o s s i b l e a l l o y i n g e l e m e n t s in i r o n be known. T h i s p a p e r is a r e p o r t on the diffusion r a t e s of c h r o m i u m , v a n a d i u m , and h a f nium in c~- and v - F e . T h e study was p a r t of a l a r g e r p r o g r a m , involving the i n v e s t i g a t i o n of diffusion in b c c i r o n al l o y s . ~ In o r d e r to study diffusion in a - F e o v e r as l a r g e a t e m p e r a t u r e r a n g e a s p o s s i b l e , r e s u l t s w e r e a l s o obtained on an a l l o y , F e - 2 pct V; L a i and B o r g 2 have a l r e a d y shown that t h e r e is no s y s t e m a t i c d i f f e r e n c e b e t w e e n diffusion in pure i r o n and in an al loy of s i m i l a r c o m p o s i t i o n to the one u s e d in the p r e s e n t i n v e s t i g a t i o n . T h e r e f o r e , the r e s u l t s for i m p u r i t y diffusion in F e - 2 pct V should be s y n o n y m o u s with diffusion in pure a - F e , within e x p e r i m e n t a l e r r o r . Most measurements were made using tracer techn i q u e s ; additional m e a s u r e m e n t s u s e d the e l e c t r o n p r o b e m i c r o a n a l y z e r for c h r o m i u m diffusion.
n e a l e d (at 1000~ for a - F e s t u d i e s and at 890~ for v - F e s t u d i e s ) for 7 days in flowing d r y h y d r o g e n in o r d e r to e l i m i n a t e m a c h i n i n g s t r a i n s and to give a g r a i n s i z e of b e t w e e n 2 and 3 r a m . P r i o r to the d e p o s i tion of the i s o t o p e each s p e c i m e n w a s given a final polish on a 1 ~m d i am o n d w h e e l . I m m e d i a t e l y p r i o r to p l a t i n g each s p e c i m e n was e t c h e d in 2 pet ni t a l to r e m o v e any d e f o r m e d l a y e r which m a y have b e e n int r o d u c e d d u r i n g f i n al p o l i s h i n g . The c h a r a c t e r i s t i c s of the i s o t o p e s C r 51, V 48, and Hf 181 a r e g i v en in T a b l e II. Th e i s o t o p e s w e r e s u p p l i e d by U n i t e d Kingdom A t o m i c E n e r g y A u t h o r i t y , A m e r s h a m . C r 51 was supplied as s o d i u m c h r o m a t e ; V 4s and Hf 1B1 a s the c h l o r i d e in HC1. All s o l u t i o n s w e r e c a r r i e r f r e e .
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