Regensburg 2013 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 22: Computational Materials Modelling - Phase Stability II

MM 22.1: Talk

Tuesday, March 12, 2013, 11:45–12:00, H24

Stability analysis of complex phases in transition-metal alloys with analytic bond-order potentials — •Thomas Hammerschmidt and Ralf Drautz — ICAMS, Ruhr-Universität Bochum, Germany

Topologically close-packed (TCP) phases play in important role for precipitate hardening in steels and as detrimental brittle phase in single-crystal superalloys. The structural stability of TCP phases can be attributed to an interplay of band-filling effects and differences in atomic size. In order to further understand this interplay, we apply a hierarchy of electronic-structure methods: On the level of density-functional theory (DFT), we determine the formation energies of the TCP phases A15, sigma, chi, mu, C14, C15 and C36 in the binary systems Ta-V/Nb, Re-V/Cr/Nb/Mo, and Co-V/Cr/Nb/Mo. The binary structures as obtained from relaxations by DFT are then analyzed on the basis of a simple canonical tight-binding (TB) model that provides a coarse-grained description of the electronic structure. The solution of the tight-binding problem is computed within the formalism of analytic bond-order potentials (BOPs) as a second coarse-graining step. This enables us to decompose the binding energy in contributions from different neighbor shells in terms of moments of the electronic density-of-states obtained from analytic BOP. We analyze the importance of internal relaxations in the DFT-relaxed structures across the transition metals series for elemental TCP phases. Furthermore we discuss the identification of size effects in binary TCP phases obtained from DFT calculations in terms of moments from analytic BOP.