Berlin 2008 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 43: Phase Transitions IV
MM 43.2: Vortrag
Donnerstag, 28. Februar 2008, 16:15–16:30, H 0107
First-principles study of hexagonal to cubic phase transformations in Laves phases NbCr2 and TaCr2 — •Olena Vedmedenko1, Frohmut Rösch1, and Christian Elsässer2 — 1Institut für Theoretische und Angewandte Physik, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart — 2Fraunhofer-Institut für Werkstoffmechanik, Wöhlerstr. 11, 79108 Freiburg
The Laves phases NbCr2 and TaCr2 are two technically attractive intermetallic compounds with high melting temperature, high oxidation resistance, and low density. The thermodynamically most stable phases of both are hexagonal (C14) at high temperatures and cubic (C15) at low temperatures. However, the kinetics of the phase transformations leads to significantly different microstructures. To get a deeper scientific understanding of their evolution from the atomic scale, we have systematically studied the hexagonal to cubic phase transformations with respect to a synchroshear deformation mechanism. Total energies of structurally optimised atomistic supercell models have been calculated from first principles, by means of density functional theory with the local density approximation and a mixed-basis pseudopotential method. We obtain a quantitative description of activation energy profiles for deformation paths from hexagonal (high-temperature) to cubic or twinned cubic (low-temperature) phases. Based on these activation energy profiles we discuss differences in the transformation behaviour and interpret recently reported experimental observations of microstructural features for the two compounds.