Regensburg 2010 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 20: Topical Session Designing Innovative Structural Materials and Steels VI
MM 20.4: Talk
Tuesday, March 23, 2010, 12:15–12:30, H4
New structure maps for topologically close-packed phases in Ni-based superalloys — Bernhard Seiser1, Thomas Hammerschmidt2, •Ralf Drautz2, and David G. Pettifor1 — 1Department of Materials, University of Oxford, Oxford, United Kingdom — 2ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Refractory elements like Re and W are added to Ni-based superalloys to improve the creep resistance. It is observed that too large concentrations induce the formation of topologically close-packed phases (TCPs) that destroy the single-crystal lattice of the Ni-based superalloys and are detrimental to the mechanical properties. In this talk we will present analytic bond-order potentials that are suitable for the prediction of TCP phase stability. By using the moments theorem that relates the crystal structure to the electronic density of states, the analytic interatomic bond-order potentials are obtained by expanding the tight-binding electronic structure in terms of response functions that depend on the Fermi energy and moments of the density of states that are given as functions of the local atomic environment. With the help of the analytic bond-order potentials the structural stability of TCP phases is then characterized as a function of valence-electron count and lattice structure. For example, at the fourth moment level we observe a distinct separation of the TCP phases in two groups. Based on the analysis of the stability of the TCP phases as a function of size difference and valence-electron count, we propose a new structure map that separates the TCP phases in different regions of stability. We compare the predictions of the structure map to DFT calculations.