Diffusion in Bcc iron base alloys
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v a n a d i u m . It was expected that this would lead to diff e r e n t diffusion b e h a v i o r when alloyed to i r o n . EXPERIMENTAL PROCEDURE Alloys used in this investigation were supplied by the British Iron and Steel Research Association in the form of rods 9.50 m m in diam. Compositions and analyses are given in Table I. The alloys were m a d e from high purity iron, the composition of which is given elsewhere. Iz Specimens were prepared and Cr 51 and V 48 deposited in exactly the same way as described in Ref. 12. Fe 59 was supplied as a carrier free chloride solution by United Kingdom Atomic Energy Authority A m e r s h a m . (The characteristics of Fe 5~ are: half life of 45 days; fl and y rays are emitted with the energy levels of fl-0.13, 0.27, and 0.46 m e v and y--0.19, I.i, and 1.29 mev.) The iron tracer was deposited from the chloride, the time required for sufficient deposition being about 30 min; resulting in an isotope thickness of _~4~/-4~-, the following equation can be used for this method of a n a l y s i s ~3
\
-9
-ioi
T R E A T M E N T O F RESULTS
~
Fe-17pctCr
D=0.46ex (- 52500) RT [18]
C o n s i s t e n c y of t r e n d s indicated by Eqs. [2] to [6], [15], [17], and [18] is e x t r e m e l y good. R e s u l t s on h i g h e r c h r o m i u m content a l l o y s , by other workers, are:-
1
4Dt
The s p e c i f i c a c t i v i t y (flAx) of a s e c t i o n of a c t i v i t y I and t h i c k n e s s Ax is d i r e c t l y p r o p o r t i o n a l to its c o n c e n t r a t i o n . Thus, a s t r a i g h t line d r a w n through the e x p e r i m e n t a l points on a in f l a x v s x z graph will have a s l o p e equal to - 1/4Dt. Plotting l n D vS 1 / T will then give the v a l u e s of the a c t i v a t i o n e n e r g y , Q, and the f r e q u e n c y f a c t o r , Do. 2768-VOLUME 1, OCTOBER 1970
C h r o m i u m in F e - 2 5 pct Cr xe D = 0.156 exp (\
48400
RT
)
[19]
F e - 4 9 pet Cr t6 D = 40 exp ( -
70000 R-T/
[20] METALLURGICALTRANSACTIONS
75500 ) RT
Fe-67 pct Cr ~ D = 24.6 exp
[21] 64200 RT /
F e - 8 3 p c t Cr ~ D = 0 . 3 7 6 e x p (
[22] 73200
pure Cr ~ D = 0.28 exp ( -
) [23]
Values of Q and Do f r o m Eqs. [17] to [23] a r e plotted t o g e t h e r with those of Eqs. [2] to [6] in Figs. 2 and 3. F o r p u r e cubic m e t a l s , Q and D Oobey the r e l a t i o n ships~a, ~s Q ~ 38T m
ii) F e - V System
[24]
Do = faa Tvo exp XflQ Tm
and
follow the t r e n d shown by the solidus o r liquidus, with b e t t e r c o r r e l a t i o n between Q and T s. This p a r a l l e l i s m is shown in Figs. 2 and 3, w h e r e the p r e s e n t r e s u l t s for 0 to 20 pct Cr follow the smooth c u r v e of the solidus r e a s o n a b l y c l o s e l y . The data for 50 and 70 pct Cr a r e the only r e s u l t s which do not follow this trend. In view of the a g r e e m e n t between the p r e s e n t r e s u l t s and those of Wolfe and Paxton, 15 Hag, l, 9 Askill and Tomlin, a and Paxton and Kunitake ~ (only for F e - 2 5 pct Cr) the region between 25 and 90 pct Cr
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