Interface Energy and Phase Transformations: A Comparative Analysis of Cahn-Hilliard and CALPHAD-based Models in Ternary Substitutional Alloys

There are various methods for modeling phase transformations in materials science, including general classes of phase-field methods and reactive diffusion methodologies, which most importantly differ in their treatment of interface energy. These methodologies appear mutually exclusive since the respective numerical schemes only allow for their primary use case. To address this issue, a novel methodology for modeling phase transformations in multi-phase, multi-component systems, with particular emphasis on applications in materials science and the study of substitutional alloys is introduced. The fundamental role of interface energy in the evolution of a material's morphology will be studied by example of binary and ternary systems. Allowing full control over the interface energy quantity enables more detailed investigations and bridges the gaps between known methods. We prove the thermodynamic consistency of the derived method and discuss several use cases, such as vacancy-mediated diffusion. Furthermore a scheme for relating Onsager and Diffusion coefficients is proposed, which allows us to study the intricate coupling that is observed in multicomponent systems. We hope to contribute to the development of new mathematical tools for modeling complex phase transformations in materials science.