Chapter eight - Application of computational thermodynamics to rapidly determine multicomponent phase diagrams

Abstract

This chapter describes a novel approach in accelerated phase diagram determination/assessment by coupling CALPHAD modeling with selected experiments. Taking advantage of available thermodynamic assessments of many binary (and some ternary) systems, one can perform a preliminary assessment of a ternary (or a higher order) system by assuming that there are no ternary (or higher order) compounds and that the solubilities of the elements in the binary (or the higher order) compounds are negligible. Such an approximate assessment is used to predict a phase diagram of interest that guides the selection of key alloy compositions to maximize the significance of the input data points. The phase equilibrium information obtained from the selected alloys is then used to improve the thermodynamic model parameters for better description of the ternary (or the higher order) system. The chapter presents examples, such as Mg–Al–Sc and Mo–Si–B–Ti systems to illustrate how the process works. Some systems may need multiple iterations to develop a reliable thermodynamic description. This methodology has the advantage of higher efficiency in obtaining a thermodynamic description of a multicomponent system with limited alloys.