Grain boundary effect on diffusion of hydrogen in pure aluminum

Abstract

Hydrogen diffusivity and solubility in pure solid aluminum were measured in a high temperature range from 573 to 923 K, by means of a desorption technique, which was an outgassing study from thermally hydrogen-charged cylindrical samples with various grain sizes. The diffusion coefficient depended linearly upon an inverse of temperature in the Arrhenius plot. There were two characteristics in the plot; one of them was a change of apparent activation energy for diffusion being a fixed diffusivity at about 900 K, while another was a correlation between the increase of activation energy and the decrease of grain size. We proposed a simple model for grain size dependence of the hydrogen diffusivity. The decrease in diffusivity at a lower temperature for the smaller grain size was explained by trapping of hydrogen at nodes of grain boundaries. In a very large grain size, there was a possibility of a fast diffusion along the grain boundary. The increase in solubility usually expected from a trapping process was not found in this study.