Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 19: Computational Materials Modelling IV - Finite Temperature
MM 19.6: Vortrag
Dienstag, 27. März 2012, 11:30–11:45, TC 006
The solubility of oxygen in HCP-Ti revisited on the basis of first-principles calculations — •Paul Erhart1 and Mark Asta2 — 1Department of Applied Physics, Chalmers University of Technology, Gothenburg, Sweden — 2Department of Materials Science and Engineering, University of California, Berkeley
Most experimental and computed phase diagrams for the Ti–O system indicate a very large solubility of O of up to 30% in hexagonal closed packed (HCP) Ti at low temperatures. Yet already much smaller amou nts of oxygen on the order of just fractions of a percent are known to cause rather dramatic changes of the mechanical properties, most notably the ductility. Using a combination of first-principles calculations and Monte Carlo simulations based on lattice Hamiltonians, we have systematically investigated the Ti-rich end of the Ti–O phase diagram. The simulations predict three distinct Ti–O phases that are based on the HCP lattice: Ti6O, Ti3O, and Ti2O. The structures of these phases are in exact agreement with the results of neutron diffraction experiments that hitherto have been integrated incompletely or not at all into available phase diagrams. Using our approach we obtain a revised equilibrium phase diagram in the concentration range up to 33% oxygen. Our results show that the effectice equilibrium solubility of O in Ti is fact less than 1% at room temperature. Beyond this concentration excess oxygen precipitates in the form of Ti6O. We suggest that the Ti6O regions effectively lead to a form of precipitation hardening (as opposed to solution hardening) and thus have an important effect on dislocation motion and plasticity.