Vacancy trapping mechanism for hydrogen bubble formation in metal

Abstract

We reveal 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. Vacancy provides an isosurface of optimal charge density that induces collective H binding on its internal surface, a prerequisite for the formation of ${\text{H}}_{2}$ molecule and nucleation of H bubble inside the vacancy. The critical H density on the vacancy surface before the ${\text{H}}_{2}$ formation is found to be ${10}^{19}--{10}^{20}\text{ }\text{H}$ atoms per ${\text{m}}^{2}$. We believe that such mechanism is generally applicable for H bubble formation in metals and metal alloys.