A regular solution model for impurity drag on a migrating grain boundary

We analyze the effect of solution thermodynamics on the mobility of grain b oundaries in the presence of diffusing impurities within the framework of t he impurity drag theory originally proposed by Cahn and Lucke and Stuwe for an ideal solution. The new derivation is performed within the framework of the regular solution model. The effects of non-ideality are largest when t he impurities are attracted to the grain boundary and the deviation from id eality is positive. Positive deviations from ideality lead to enhanced impu rity drag on the boundary and negative deviations lead to higher boundary m obility. When the impurities are attracted to the boundary, positive (negat ive) deviations from ideality produces larger (smaller) activation enthalpi es for boundary migration (relative to the ideal solution). At large impuri ty concentrations, the activation enthalpy becomes impurity concentration i ndependent. Decreasing impurity concentrations in ideal solutions and regul ar solutions with a negative deviation from ideality leads to a decrease in the activation enthalpy for migration. (C) 2001 Acta Materialia Inc. Publi shed by Elsevier Science Ltd. AII rights reserved.