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Abstract

The detrimental effect of hydrogen on materials properties poses problems for many applications. Hydrogen embrittlement of iron and steels has been studied extensively in experiments and theory, but due to the complexity of the problem it is still not fully understood. Two of the most discussed mechanisms for hydrogen embrittlement are the HEDE and HELP mechanisms. To address these mechanisms from a microscopic point of view it is important to obtain a detailed understanding of the stability and mobility of hydrogen in the vicinity of point and extended defects.

We have performed density-functional theory calculations to investigate the solubility and diffusion behaviour of hydrogen close to grain boundaries and vacancies in bcc-Fe. In bcc-Fe, hydrogen at a grain boundary is energetically favoured compared to the bulk region.

Together with the very low diffusion barriers of hydrogen in bcc-Fe this may lead to a local accumulation of hydrogen around the defect even for rather small H concentrations. Employing kinetic simulations we investigate the diffusion of hydrogen in the presence of a defect and analyse the time evolution of the local hydrogen distribution.