A thick-interface model for diffusive and massive phase transformation in substitutional alloys

Based on the application of the thermodynamic extremal principle, a new model for the diffusive and massive phase transformation in multicomponent substitutional alloys is developed. Interfacial reactions such as the rearrangement of the lattice, solute drag and transinterface diffusion are automatically considered by assigning a finite thickness and a finite mobility to the interface region. As an application of the steady-state solution of the derived evolution equations, the kinetics of the massive gamma -> alpha transformation in the Fe-rich Fe-Cr-Ni system is simulated. The thermodynamic properties of the interface may influence significantly the contact conditions at the interface as well as the conditions for the occurrence of the massive transformation and its kinetics. The model is also used for the simulation of the diffusion-induced grain boundary migration in the same system. By application of the model a realistic value for the Gibbs energy per unit interface area is obtained. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.