Berlin 2015 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 30: Methods in Computational Materials Modelling III: Thermodynamics

MM 30.4: Talk

Wednesday, March 18, 2015, 11:00–11:15, H 0106

Ab initio description of unstable phases at finite temperatures: The Ti bcc to ω transition — •Dominique Korbmacher, Albert Glensk, Blazej Grabowski, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

Ti-based alloys are a technologically important class of structural materials. A detailed knowledge of their phase diagrams and transitions is important for optimizing the properties of these alloys. However, the occurrence of phases that become thermodynamically and dynamically stable only at high temperatures makes an ab initio computation of phase diagrams a challenging task.

We have therefore developed and applied an ab initio based methodology that allows to accurately compute free energies even of unstable phases. The method employs thermodynamic integration starting from a reference of optimized embedded atom potentials that were fitted to reproduce ab initio molecular dynamics data for a narrow volume and temperature range. We apply our technique to the bcc phase of pure Ti and compute its free energy up to the melting point. Our results show a second order phase transformation at around 1000 K upon lowering the temperature. A careful investigation of the molecular dynamics trajectories allows us to identify the low temperature phase as the technologically important hexagonal ω structure.