The thermodynamic models with optimized parameters for low-order (binary and ternary) subsystems can be used to provide good estimates for unexplored phase diagram and thermodynamic properties in low-order or high-order systems. In the thermodynamic optimization (modeling) based on the CALPHAD method, all available thermodynamic and phase equilibrium data for the system are critically and simultaneously evaluated in order to obtain one self-consistent set of model equations for the Gibbs energies which best reproduce the data for all phases as functions of temperature and composition. The CALPHAD methodology was introduced in the 1960s by Larry Kaufman and the essence is the optimization of the Gibbs energy functions to reproduce the known phase diagrams, and utilize it to make the prediction of unknown phase equilibria. All thermodynamic software packages include thermodynamic databases, which are developed based on the so-called CALculation of PHAse Diagram (CALPHAD) methodology. Nowadays, thermodynamic calculations using various commercial software are very popular in materials science and engineering fields.
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