Energetics of hydrogen impurities in aluminum and their effect on mechanical properties

The effects of hydrogen impurities in the bulk and on the surface of aluminum are theoretically investigated. Within the framework of density-functional theory, we have obtained the dependence on 14 concentration of the stacking fault energy, the cleavage energy, the Al/H surface energy, and the Al/H/Al interface formation energy. The results indicate a strong dependence of the slip energy barrier in the [(2) over bar 11] direction, the cleavage energy in the [111] direction and the Al/H/Al interface formation energy, on H concentration and on tension. The dependence of the Al/H surface energy on H coverage is less pronounced, while the optimal H coverage is less than or equal to0.25 ML. The calculated activation energy for diffusion between high-symmetry sites in the bulk and on the surface is practically the same, 0.167 eV. From these results, we draw conclusions about the possible effect of H impurities on mechanical properties and, in particular, on their role in ernbrittlement of Al.