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Abstract

Topological closed packed phases (TCP) are stable in Ni- and Co-based Superalloys, in the so-called High Entropy Alloys as well as in Steels and Aluminum alloys. Their thermodynamic modeling is important for phase stability, process control as well as alloy design. It passed already 15 years since the density functional theory (DFT) showed its usefulness to calculate enthalpies of formation for configurations related to TCP as Sigma, Mu and Laves phases that can be used together with experiments and other phases in the making of the Gibbs energies sets using the CALPHAD method. But contrary to the disorder solid solutions models, the sub-lattices models used together with the first-principles data do not extrapolate well to higher order systems. That demands, usually, auxiliary ternary values or the whole set of ternaries enthalpies from DFT what needs 3^5 values as the case, for example, of Sigma phase which has 5 nonequivalent sites.

In this lecture a review of the modelling of these phases will be presented including the very recently one by Dupin et all [1] , where F-P binary information can be re-arranged and used in multicomponent without the necessity of doing the expensive ternary calculations.

[1] N. J. Dupin, U. R. Kattner, B. Sundman, et al. Implementation of an effective bond energy formalism in the multicomponent Calphad approach Journal of Research of National Institute of Standards and Technology 123 123020 (2018)