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Abstract

The contribution of vacancies to the hydrogen-induced degradation of materials properties (hydrogen embrittlement [1]) is of both scientific interest and technological relevance, especially for Fe-based alloys such as steels. The strong interaction of hydrogen interstitials with other point defects might be one of the key issues in explaining the observed effects.

In our study we employ an adaptive kinetic Monte Carlo [2] approach to investigate the diffusion of hydrogen in the presence of vacancies in bcc-iron. To ensure a reliable description of the underlying potential energy surface we use density functional theory to determine energies and forces.

Within the adaptive kinetic Monte Carlo method possible diffusion mechanisms do not have to be assumed a priori, but are discovered during the simulation by the system itself. This flexibility in identifying mechanisms is of importance since hydrogen interstitials are trapped by vacancies and the formed hydrogen-vacancy clusters might exhibit a diffusion behaviour that differs significantly from that of a single vacancy. Within our simulations the diffusion of hydrogen interstitials, vacancies and hydrogen-vacancy clusters is treated simultaneously and various mechanisms are discussed.

[1] J. P. Hirth, Metall. Trans. A 11A, 861 (1980).

[2] G. Henkelman and H. Jonsson, J. Chem. Phys. 115, 9657 (2001).