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Abstract

Topological closed packed phases (TCP) are stable in Ni-based as well as in Co-based Superalloys. Their thermodynamic modeiing in 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 sublattices models used together with the first-principles data dont 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. Very recently, Dupin et all [1] ,suggested a model which uses the binary Sigma information (A-B, B-C and A-C) and represent them by effective pairs for which the extrapolations describe striking well the Gibbs energy of the ternary phase. We want to apply this model to the Mu phase of the Co-Ti-W system for which the binaries and ternaries formation enthalpies are available in the Naujoks et all [2] [1] Calphad Conference 2018 book of abstracts. [2] Acta Materialia, 138 p 100-110 (2017)