Comparison of irradiation-induced void formations in tungsten with equiaxed and columnar structures

Tungsten (W) has been received much attention, since it is regarded as one of the most promising plasma facing materials for fusion reactors. There are two typical morphologies of unirradiated polycrystalline W, which have the equiaxed and columnar grains, respectively. However, the role of arrangement of grain boundary (GB) in absorbing irradiation-generated point defects is still waiting to be identified. In current investigation, irradiation-induced void formations in W with equiaxed and columnar microstructures are predicted, respectively, using the developed phase-field model. The significant kinetic behavior, such as the generation and annihilation of point defects and the interaction between point defects and GB, is reasonably considered. The density, size and porosity of void formed in these two microstructures are examined and analyzed according to the effects of GB ratio, temperature and damage rate. Our analytical results show that higher GB ratio can effectively reduce void porosity, and the columnar-grained structure has better irradiation resistance than that of the equiaxed one in the case of small grain size. Most importantly, the predicted void sizes changed with temperature and damage rate agree well with the experimentally measured ones. Our work has a more beneficial contribution to the microstructural improvement of International Thermonuclear Experimental Reactor-grade W.