The microscopic vacancy trapping mechanism for H bubble formation in W based on first-principles calculations of the energetics of H-vacancy interaction and the kinetics of H segregation was revealed. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of H2 molecule and nucleation of H bubble inside the vacancy. The critical H density on the vacancy surface before the H2 formation was found to be 1019 to 1020H/m2. It was suggested that such a mechanism was generally applicable to H bubble formation in metals and metal alloys

Vacancy Trapping Mechanism for Hydrogen Bubble Formation in Metal. Y.L.Liu, Y.Zhang, H.B.Zhou, G.H.Lu, F.Liu, G.N.Luo: Physical Review B, 2009, 79[17], 172103