In the previous chapters it has been shown how to obtain the best possible agreement between thermodynamic models and experimental data using adjustable model parameters for binary and ternary systems. Even if each such assessment can be very important by itself, the main purpose of these assessments is to provide the building blocks of multicomponent thermodynamic databases. This objective must be considered when performing an assessment because it imposes some restrictions on the assessment of the individual system and on the possibilities of adjusting data and models to new experimental data. Such problems will be discussed in this chapter, together with the general concepts concerning thermodynamic databases.

Experience has shown that thermodynamic databases based on a limited number of ternary assessments, all centered around a “base” element like Fe or Al, can give reliable extrapolations to multicomponent alloys based on that element. This means that the database can be used to calculate the amounts of phases, their compositions, and transformation temperatures and that the calculated values have an accuracy close to that of an experimental measurement. Such databases are a very valuable tool for planning new experimental work in alloy development, since detailed experimental investigations of multicomponent systems are very expensive to perform. It is important that the databases are based on ternary assessments, not just binaries, because the mutual solubilities in binary phases must be described, otherwise the extrapolations are not reliable.