Application of the thermodynamic extremal principle to the diffusional phase transformations

Based on the application of the thermodynamic extremal principle a new model for the diffusional phase transformation in substitutional multi-component systems has been derived. The model does not require the prescription of any contact conditions for the chemical potentials at the migrating interface, and it admits a finite value of the interface mobility. The derived evolution equations reproduce diffusion equations for the bulk and the standard equation for the interface migration. Moreover, the evolution equations ensure automatically the proper contact conditions for chemical potentials at the migrating interface enforcing the jumps in chemical potentials being the same for all components. The model is demonstrated on simulations of the diffusional and massive transformations in the Fe-Cr-Ni system