Molecular dynamics simulations of collision cascades in polycrystalline tungsten

Using molecular dynamics methods, simulations of collision cascades in polycrystalline tungsten (W) have been conducted in this study, including different primary-knock-on atom (PKA) directions, grain sizes, and PKA energies between 1 keV and 150 keV. The results indicate that a smaller grain size leads to more defects forming in grain boundary regions during cascade processes. The impact of high-energy PKA may cause a certain degree of distortion of the grain boundaries, which has a higher probability in systems with smaller grain sizes and becomes more pronounced as the PKA energy increases. The direction of PKA can affect the formation and diffusion pathways of defects. When the PKA direction is perpendicular to the grain boundary, defects preferentially form near the grain boundary regions; by contrast, defects are more inclined to form in the interior of the grains. These results are of great significance for comprehending the changes in the performance of polycrystalline W under the high-energy fusion environments and can provide theoretical guidance for further optimization and application of W-based plasma materials.