Blister growth model in proton-irradiated metals - application to tungsten irradiated by MeV protons

Tungsten and tungsten alloys are utilized as structural materials in nuclear facilities due to their excellent mechanical and thermal properties. Blistering is a primary failure mechanism of proton-irradiated tungsten, as well as in other metals, that may shorten the erosion lifetime of components. Furthermore, mature blisters with high internal gas pressure are likely to burst, leading to exfoliation of the surface. Recent MeV proton irradiation studies have found significantly larger blisters formed deeper below the surface than blisters formed from keV irradiation. Understanding these differences and predicting blistering phenomena require a model of blister growth. We develop a model of blister growth under irradiation that combines the mechanisms of plate bending and crack propagation through strain energy release. The process is assumed to be quasi-static and proceeds between equilibrium states. Closed-form expressions were obtained for limiting cases. The model's validity for blister growth under hydrogen pressure is evaluated by comparison with experimental blister results formed during MeV proton irradiation on single-crystal and polycrystalline tungsten at various temperatures. A blister aspect ratio (height to the area) was found to be a characteristic feature of blistering mechanics and strongly dependent on the ratio between plate-bending strain energy and material fracture toughness. The effect of irradiation on material properties is discussed in the context of our model and the experimental results.