Dresden 2020 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 28: Computational Materials Modelling - Hydrogen in metals
MM 28.3: Talk
Tuesday, March 17, 2020, 14:45–15:00, IFW B
A grand canonical approach for modelling hydrogen trapping at vacancies in α-Fe — •Michael W. Finnis1, Erlend R. M. Davidson1, Thomas Daff2, and Gábor Csanyi2 — 1Thomas Young Centre, Imperial College London, UK — 2Engineering Laboratory, University of Cambridge, UK
Vacancies in iron are a potential trap for hydrogen, of importance in the understanding of hydrogen embrittlement of steel. We present a grand canonical approach to computing the trap occupancy, which deals with the entire range of hydrogen concentration, from practically zero to super-saturation. Our method is demonstrated here for hydrogen in α-Fe as a function of both temperature and bulk concentration, using a machine-learned H-Fe potential that we develop for the purpose, which enables rapid sampling with near density-functional theory accuracy. The statistical mechanical calculation of the trap occupancy is enabled by the technique of nested sampling. The almost universally used conventional assumption based on Oriani theory is that at industrially relevant concentrations and ambient conditions vacancy traps are fully occupied. In contrast we find that vacancy traps are less than fully occupied under these conditions, necessitating a reevaluation of how we think about *mobile hydrogen* in iron and steel.