Dresden 2009 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 9: Intermetallic Phases I
MM 9.4: Talk
Monday, March 23, 2009, 15:30–15:45, IFW B
Structural trends in topologically close-packed phases — •Bernhard Seiser1, Thomas Hammerschmidt2, Ralf Drautz2, and David Pettifor1 — 1Department of Materials, University of Oxford, Oxford, UK — 2ICAMS, Ruhr-University Bochum, Bochum, Germany
The creep properties of modern single-crystal Nickel-base superalloys are improved by adding refractory elements. This route of material design is limited by the precipitation of topologically close-packed (tcp) phases which can lead to failure during service. We have assessed the modelling techniques PHACOMP and CALPHAD which are commonly used to predict the tendency of tcp phase formation in austenitic alloys. Moreover, within a tight-binding framework, we have derived analytic bond-order potentials (BOP) that depend explicitly on the valence of the transition metal elements. In particular, we applied these BOPs to investigate the structural stability of tcp phases with respect to the filling of the d-band. From these BOP calculations, we find two groups of tcp phases that exhibit very similar dependence on the d-band filling: A15 and σ on one hand and µ and the Laves phases C14, C15, C36 on the other hand. Through the BOPs we have been able to unravel the link between structural stability and local topology and have identified the interactions that favour the formation of tcp phases.