Monte Carlo Simulation of Grain Boundary Cross Effect on Hydrogen Diffusivity in Aluminum

Assuming the jumping of interstitial impurities to neighboring sites, the diffusivity is simulated by the Monte Carlo method based on the random walk theory. The jumping probability along a grain boundary is greater than that in the lattice of an inside grain. The crossing point of grain boundaries has a smaller jummping probability to neighboring sites on the grain boundary than that in the lattice. The results of simulation support the grain boundary cross effect, proposed experimentally by us, on the grain size dependence of hydrogen diffusivity in an aluminum polycrystal. The diffusivity shows a peak at some critical grain size. The peak includes two conflicting effects of grain boundaries: enhancement of diffusion along grain boundaries and suppression of diffusion by trapping at grain boundary junctions.