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MM: Fachverband Metall- und Materialphysik
MM 5: Hydrogen in Metals: Ab initio approaches
MM 5.3: Vortrag
Montag, 16. März 2015, 11:00–11:15, TC 006
Hydrogen trapping at vacancies and hydrogen impact on vacancy diffusion and self-diffusion in Ni. — Yu Wang1,2, Damien Connétable2, and •Döme Tanguy1 — 1Institut Lumière Matière, UMR 5306, Université Lyon 1-CNRS, Villeurbanne, France — 2CIRIMAT,UMR 5085, ENSIACET, Toulouse, France
We have performed EAM and DFT calculations of H segregation energies at vacancies in Ni. The maximum binding is 0.27eV and 0.4eV in the single and divacancy respectively, in good agreement with Fukai's Thermal Desorption Spectroscopy results. By a comprehensive calculation of the formation energy of VHn clusters (n=1 to 14), it was shown that segregation occurs mostly on the octahedral site (off-centered) in the vacancy (O1) with almost no O1-O1 interactions, strong O1-T1 (tetrahedral) repulsion and weak attractive O1-O2 interaction. Approximately constant effective pair interactions can be extracted from these formation energies. Together with the segregation energies in the dilute limit, they constitute a simple energetic model from which we can derive the equilibrium distributions and concentrations of VHn (analytical formulas are validated against Monte Carlo simulations). A good separation of timescales between H diffusion events and vacancy-metal exchanges enables a simple calculation of the diffusion coefficient of the clusters from the equilibium distribution and a limited set of barriers. H drastically slows down the vacancies, but this effect is overcompensated by the increase in equilibrium vacancies and finally Ni self-diffusion is markedly increased.
J. Alloys Comp. 614 (2014) 211, acta mater 78 (2014) 135