Interdiffusion in the α-Solid Solution of the Fe-Sn System

Abstract

For the purpose of studying interdiffusion in the α-solid solution of the Fe-Sn system, experiments were performed using the method of vapor-solid couple at temperatures between 1073 and 1373 K. As a vapor source, fine powder of a 40 mass%(23.9 at%)Sn-Fe alloy was used. The surface concentration of Sn in diffusion-annealed test pieces almost coincided with the solubility limits reported in the Fe-Sn phase diagram at 1173–1373 K, while significant deviations in the solubility limits were found at 1073 K and 1123 K. Fine alumina markers placed on the test pieces prior to diffusion remained on the surface after annealing. Each penetration curve at temperatures between 1073 and 1173 K was similar to the error function curve for a particular \Tilde{D} value.The value of \Tilde{D} showed a relatively small dependence upon the Sn concentration at each temperature. The activation energies for interdiffusion, \Tilde{Q}, decreased from 228 to 221 kJ/mol with increasing Sn concentration. The impurity diffusion coefficients of Sn in Fe, DSn*, between 1073 and 1173 K were obtained from extrapolation of \Tilde{D} to 0 at%Sn and its activation energy, QSn*, was evaluated to be 229 kJ/mol. The relationship between the entropy term, \Tilde{D}0, and \Tilde{Q} is represented by the following equation:(This article is not displayable. Please see full text pdf.)