Role of grain boundary and dislocation loop in H blistering in W: A density functional theory assessment

We report a first-principles density functional theory study on the role of grain boundary and dislocation loop in H blistering in W. At low temperature, the {\Sugma}3(111) tilt grain boundary, when combined with a vacancy of vanishing formation energy, can trap up to nine H atoms per (1x1) unit in (111) plane. This amount of H weakens the cohesion across the boundary to an extent that a cleavage along the GB is already exothermic. At high temperature, this effect can be still significant. For an infinitely large dislocation loop in (100) plane, four H can be trapped per (1x1) unit even above room temperature, incurring a decohesion strong enough to break the crystal. Our numerical results demonstrate unambiguously the grain boundaries and dislocation loops can serve as precursors of H blistering. In addition, no H2 molecules can be formed in either environment before fracture of W bonds starts, well explaining the H blistering in the absence of voids during non-damaging irradiation.