An Introduction to the Calphad Method – How to navigate the multicomponent alloy phase space

Seminar (in English):

Thermodynamic modelling using the Calphad method (computer coupling of phase diagrams and thermochemistry) has been successfully used for a large number of applications since the 1980s. The core application is alloy development, but beyond that, almost anything that involves thermodynamics or phase stability within the inorganic realm has been addressed. It is also used as basis for simulation of phase transformations and modelling of properties that depend the microstructure of a material. However, in order for this to work it is necessary to have access to a database with sufficient accuracy covering the relevant chemical elements. To reach sufficient accuracy (which strongly depends on the intended application) the database must contain good models of all binary and a sufficient number of ternary systems. Beyond that, the database relies mostly on extrapolation. Calphad modelling is an attempt to describe all knowledge about phase diagrams and thermochemistry of a specific system using simple models with a (relatively) small number of coefficients. The particular challenge is that phase equilibria depend on small differences in Gibbs energy, typically too small to be measured directly or calculated by atomistic methods, i.e. experimental measurements of phase equilibria are absolutely necessary to “calibrate” the models. In my talk I will try to describe how the Calphad method works, give some ideas why it works and why it is not probable that it can be replaced by either atomistic simulation or artificial intelligence. I will also give a couple of examples of the use of Calphad calculations for multicomponent alloys.