At high temperatures diffusion of components and migration of interfaces are activated in solid state systems. The microstructure evolves due to these processes, and both the volume fraction and chemical composition of the individual phases change. In this paper we formulate a boundary value problem for the microstructural evolution during a diffusional transformation in a binary alloy. We clarify the chemical and mechanical contributions to the thermodynamic driving force on the interface and derive the boundary condition that is implied by interface kinetics for solute diffusion in the bulk. By applying this framework, the consequences of (non-equilibrium) interface kinetics on the microstructure evolution during the ferrite transformation in low-carbon steels is predicted using both a novel analytical technique and finite difference numerical method.
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