First-principles calculations were reported which demonstrated that vacancies could combine with H impurities in bulk Al and play a crucial role in the embrittlement of this prototypical ductile solid. Studies of hydrogen-induced vacancy superabundant formation and vacancy clustering in Al led to the conclusion that a large number of H atoms (up to 12) could be trapped at a single vacancy, which overcompensated the energy cost in order to form the defect. In the presence of trapped H atoms, 3 nearest-neighbor single vacancies which would normally repel each other, aggregated to form a trivacancy on the slip-plane of Al, acting as embryos for micro-voids and cracks and resulting in ductile rupture along these planes.

Hydrogen Embrittlement of Aluminum - the Crucial Role of Vacancies. G.Lu, E.Kaxiras: Physical Review Letters, 2005, 94[15], 155501 (3pp)