Diffusion processes in a migrating interface: The thick-interface model

During a solid/solid diffusive phase transformation from a parent β-phase to a product α-phase, dissipative processes due to diffusion in the bulk phases as well as rearrangement of the crystal lattice and diffusion in the interfacial region occur. A model has been developed that accounts for all the above-mentioned dissipative processes. By means of this thick-interface model it is possible to assign a finite thickness and a finite mobility to the interface. The evolution of the mole fraction profiles of the components in the bulk phases and in the interface can be simulated from a given initial state until a steady state or equilibrium is attained. Based on this theoretical framework the kinetics of the γ/α phase transformation in the Fe-rich Fe–Cr–Ni system is simulated. Starting from a certain initial composition the transformation kinetics exhibits the features of a massive or a bulk diffusion controlled transformation depending on temperature.