Keizo Nishida1, Harumitsu Murohashi2 and Tsuyoshi Yamamoto3
1Metals Research Institute, Faculty of Engineering, Hokkaido University, Sapporo
Iron test pieces were diffusion-annealed in an evacuated silica capsule containing the powdered (100∼200 mesh) 50 wt%Sb-Fe alloy consisting of α and ε phases as an Sb vapor source for 9∼440 hr at 700∼950°C. The test pieces were then analysed with an EPMA and the penetration curves of them were obtained.
Each penetration curve was analysed by means of the Matano-Boltzmann method to obtain the chemical diffusion coefficients ( \tildeD). From these values the activation energies for diffusion ( \tildeQ) were calculated.
Surface concentration of the test pieces ( α max) at each annealing temperature coincided approximately with the solubility observed in the phase diagram of an Fe-Sb system at lower temperatures, while a significant deviation was found in solubility at higher temperatures. Fine alumina makers placed on the test pieces prior to diffusion were found always on the surfaces after annealing so that it is considered that Sb atoms diffuse predominantly in the α -phase of this system. Each penetration curve was similar to an error function curve and \tildeD at each temperature showed a relatively small dependence upon Sb concentration. There was a gap in the Arrhenius plot owing to magnetic transformation. The activation energies for diffusion ( \tildeQ) obtained from the data at higher temperatures varied from 59.5 kcal/mol for 1 at%Sb to 52.5 kcal/mol for 4 at%Sb and that for impurity diffusion of Sb in iron (QSb*) was evaluated to be about 63 kcal/mol.
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