Models, software and databases, 3 pillars of the Calphad approach to Computational Thermodynamics

The development of the Calphad method to calculate equilibria and phase diagrams and to simulate phase transformations uses models describing how the thermodynamic properties depend on temperature, pressure and the constitution of the stable (and metastable) phases. These models must consider the crystalline structure of each phases as well as magnetic effects and similar physical features.

In order to be useful these models must be implemented in a software which can calculate equilibria for different types of conditions, not only temperature, pressure and the composition of the system but also how the equilibrium depend on the chemical potentials, the set of stable phases etc. The software must also be able to calculate phase diagrams and other types of diagrams for binary, ternary and higher order systems as well as metastable states needed for simulations of phase transitions together with kinetic data.

The databases are collection of assessments of model parameters assessed for binary and ternary systems. Such assessment must use the same descriptions of the pure elements (the unary database) and use similar models for the composition dependence of the phases. The assessment of a system is complex and typically takes 6-12 months. Parameters in higher order systems are rarely needed but experimental information from higher order systems are important to adjust the binary and ternary parameters.

Some experiences from the work on models, software, assessments and applications will be presented.