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Abstract

The formation of topologically close-packed (TCP) phases in Ni-based superalloys may lead to the degradation of the mechanical properties of the turbine blades. For the development of new superalloys that do not show the formation of TCP phases only some guidance is provided by the semi-empirical PHACOMP and NewPHACOMP schemes. In this talk we develop a microscopic understanding of the factors that control TCP phase stability by coarse-graining the electronic structure from density functional theory to tight-binding to bond-order potentials (BOPs). The BOPs depend explicitly on the electron per atom (e/a) ratio, so that they predict the structural sequence from bcc to sigma to chi to hcp that is found, for example, across the W-Re system. The observed stability of the mu and Laves phases may be explained by the additional contribution of size and electronegativity differences. Remaining challenges in modelling TCP phase formation will be briefly discussed.