From binary assessments to thermodynamic databases

Abstract

Abstract The Calphad method is a very powerful method for dealing with phase equilibria and thermodynamic properties of multicomponent alloy systems. In fact, it is the only method that can do this. However, in order to do this it is necessary to construct multicomponent databases, and the requirements on thermodynamic evaluations, in particular of binary systems, are quite different compared to the case when they are only used as stand-alone evaluations. A number of these issues are discussed in this paper and in particular the influence of changes of the values of binary interaction parameters on the ternary systems Cr–Cu–Ni and Cr–Cu–Fe is investigated. In addition, the Cr–Mo–Ni system is chosen as an example of a system where pure extrapolations (thermodynamic) from its binary subsystems produce a completely incorrect phase diagram. As a conclusion it is found that a massive effort on experimental and computational (Calphad) investigations of ternary systems, supported by ab-initio calculations, is needed in order to make further progress in the field of alloy thermodynamics possible. The quality of a multicomponent database is strongly dependent on the fraction of ternary datasets included in the database.