The diffusivity of H in polycrystalline material was simulated by using a Monte Carlo method which was based upon the random walk theory. Simulations were made of a sample with anisotropic grain boundaries were performed. The anisotropy of the grains corresponded well with columnar grains in real specimens, where diffusivity peaks were measured. For samples with anisotropic grain-shapes, the H diffusivity was enhanced on the longer side of the grain boundaries, for larger grains, and was increasingly suppressed by trapping at grain-boundary junctions in the case of smaller grains. This resulted in a complicated or disordered peak at some intermediate grain sizes.

Monte Carlo Simulation of Hydrogen Diffusivity in Aluminum with Anisotropic Grain Boundaries. M.Ichimura, Y.Sasajima: Japanese Journal of Applied Physics - 1, 1998, 37[11], 6107-10