CALPHAD Models and their Application to Phase-based Properties

The CALPHAD method is currently the only available method in computational thermodynamics for the calculation of multi-component, multi-phase equilibria and properties. The CALPHAD method was originally developed for the calculation of phase diagrams and thermochemical properties but its approach has been shown to be suitable for the modeling of all kinds of phase-based properties. For modeling these phase-based properties it is generally agreed upon to use the same formalisms for their compositional dependence as that for the description of the Gibbs energy. Alternatives to the traditional modeling of the composition dependence in the description of ordered phases are being explored. The performance of a new model formalism is traditionally evaluated on the basis of how well it describes the thermodynamic properties and phase equilibria but rarely on how well it will be suited to describe diffusion and other phase-based properties. An overview of model requirements will be presented.