Hydrogen effect on shearing and cleavage of Al: A first-principles study

We report on first-principles calculations of the effect of a (111) hydrogen layer embedded in Al on generalized stacking fault energies and cleavage energy for different choices of the slip and cleavage planes. It is shown that the H layer softens Al against shear by reducing the stable and unstable stacking fault energies relative to pure Al. This finding points to a possible enhancement of plasticity of Al by H. The H layer also reduces the cleavage energy on the (111) plane. The reductions in the cleavage energy and unstable stacking fault energy compensate each other and produce only a moderate change in the Rice criterion of ductile versus brittle fracture.