On the growth kinetics of grain boundary ferrite allotriomorphs |
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Authors: | C Atkinson H B Aaron K R Kinsman H I Aaronson |
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Affiliation: | (1) Department of Mathematics, Imperial College of Science and Technology, London, UK;(2) Automotive Assembly Division, Ford Motor Company, 48121 Dearborn, Mich.;(3) Ford Motor Company, USA;(4) De-partment of Metallurgical Engineering, Michigan Technological Uni-versity, 49931 Houghton, Mich. |
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Abstract: | Previous work has shown that the thickening kinetics of proeutectoid ferrite allotriomorphs in an Fe-0.11 pct C alloy are
often more rapid than the kinetics calculated for volume diffusion-control from the Dube-Zener equation for the migration
of a planar boundary of infinite extent, assuming the diffusivity of carbon in austenite,D, to be constant at that of the carbon content of the Ae3. Recalculating the thickening kinetics, using a numerical analysis
of the infinite planar boundary problem previously developed by Atkinson in which the variation ofD with composition is taken fully into account, was found to increase this discrepancy. Measurements were then made of the
lengthening as well as the thickening kinetics of grain boundary allotriomorphs in the same alloy. Application to these data
of Atkinson’s numerical analysis of the growth kinetics of an oblate ellipsoid, in which the composition-dependence ofD is similarly considered, produced an acceptable accounting for nearly all of the data. It was concluded that the growth of
ferrite allotriomorphs is primarily controlled by the volume diffusion of carbon in austenite; the presence of a small proportion
of dislocation facets along one of the broad faces of the allotriomorphs, however, usually results in growth kinetics which
are somewhat slower. An alternate treatment of the lengthening and thickening data upon the basis of the theory of interfacial
diffusion-aided growth of allotriomorphs indicated that, in the temperature range investigated (735° to 810°C),the diffusivities
of carbon along γ:γ and γ:α boundaries required for this mechanism to make a significant contribution to growth are too high
to be physically plausible.
Formerly with Scientific Research Staff
Formerly with Scientific Research Staff, Ford Motor Company |
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