First-principles study of vacancy interaction with grain boundaries of tungsten under tensile strains

A large number of vacancies can form in tungsten (W) when subjected to high-energy plasma particle fluxes and greatly influence the mechanical properties. Based on comprehensive first-principle calculations, the present study investigates the effects of tensile strain on vacancy interaction with two different grain boundaries (GBs) in W. We find that as the applied tensile strain increases, the vacancy formation energies increase monotonically vacancies for the sites at Σ3(112)[110] GB, but increases and then decreases those at the Σ5(310)[100] GB. The strain-induced change of average bond length was found to be an important factor in determining the vacancy formation energies at GBs under tensile loading. We also find that the vacancy formation energy at GBs and fracture strengthen of GBs are greatly affected by vacancy positions at GBs. For both GBs, the vacancy formation energy first decreases and then increases to a plateau when the vacancy position moves away from the GB plane. The results show that the vacancy position with the lowest formation energy was on the first layer from the GB, rather than on the GB plane. The underlying mechanism for this phenomenon was shown to be closely correlated with the lengths and energies of the bonds surrounding the vacancy position.