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MM: Fachverband Metall- und Materialphysik

MM 15: Poster session I

MM 15.5: Poster

Monday, March 7, 2016, 18:00–20:00, Poster B3

Anharmonically stabilized temperature-dependent cluster-expansions applied to β-NiTi — •Sascha B. Maisel, Dominique Korbmacher, Blazej Grabowski, and Jörg Neugebauer — Max-Planck Institut für Eisenforschung, Max-Planck-Strasse 1, 40239 Düsseldorf, Germany

The high temperature state β-NiTi is unstable with respect to transformation to a low-symmetry state at lower temperatures and to different phases at off-stoichiometric compositions. This poses several methodological challenges when developing effective models for the Ni-Ti system, which are integral in order to understand its intrinsic shape memory effect. Using recently improved methods for the temperature-dependent cluster-expansion (CE) approach, we derive and compare a hierarchy of descriptions of varying sophistication for the β-Ni-Ti high-temperature state. These descriptions are all based exclusively on ab-initio data or an ab-initio-based thermodynamic upscaling method known as the TU-TILD method [1], but yield surprisingly different results. This high sensitivity to the DFT input parameters is a consequence of the strong relaxations and dynamical instabilities that are ultimately responsible for the material’s shape-memory properties. The various approaches are critically discussed regarding both their computational efficiency and their ability to reproduce CALPHAD free energies.
[1] A. I. Duff et al.: PRB 91, 214311 (2015)