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MM: Fachverband Metall- und Materialphysik

MM 36: Topical Session Electron Theory V

MM 36.4: Talk

Thursday, March 17, 2011, 15:15–15:30, IFW A

Ab initio prediction of thermodynamic data for selected phases of the Al-Mg-Si-Cu system — •Albert Glensk, Blazej Grabowski, Tilmann Hickel, and Joerg Neugebauer — Max-Planck Institut fuer Eisenforschung GmbH, Max-Planck-Strasse 1, D-40237 Duesseldorf, Germany

Al-Mg-Si-Cu alloys are widely used in engineering applications due to their excellent mechanical properties: low density, high hardness and melting temperature. To tailor these properties, quantitative simulations (like CALPHAD) rely on exact thermodynamic potentials which are nowadays mostly derived from calorimetric experiments. First principles calculations emerge as an alternative for reliable thermodynamic functions in cases of non-existent experimental data or in regions of phase boundaries where the reliability of experiments is limited due to the transient nature of metastable phases. We have, therefore, calculated highly accurate ab initio free energies as a function of temperature and molar volume for selected binary, ternary and quaternary phases of the Al-Mg-Si-Cu system with focus on hcp Mg, diamond Si and Mg2Si. Various quantities are derived from the thermodynamic potentials: Gibbs free energies of formation, enthalpies, entropies, heat capacities, thermal expansions, vacancy concentrations etc. We compare our results to a variety of experiments and put special emphasis on temperature effects due to lattice vibrations. We find the Debye model not to be sufficient at high temperatures and demonstrate that our consistent ab initio approach can improve previous CALPHAD parameterizations of Mg2Si with respect to current experiments.