Application of Holzapfel’s Analytic Expression for Approximating the Debye Heat Capacity Function in CALPHAD Databases

The Debye model for the heat capacity of solids is highly successful in modeling a wide variety of materials. Yet, it is not used in currently-developed CALPHAD (Calculation of Phase Diagrams) thermodynamic databases, just because it requires numerical integration and thus is inconvenient in implementation. Holzapfel et al. developed a simple closed-form approximation of the Debye model. The present work demonstrates the utility of Holzapfel’s expression for use in CALPHAD thermodynamic databases and software, with examples of modeling the Gibbs energy of the metallic elements Al and W. Advantages over previous work in CALPHAD modeling are pointed out.