Effect of cascade morphology on defect production in tungsten: A molecular dynamics study

The effect of cascade morphology on defect production in tungsten has been investigated through molecular dynamics cascade simulations. The distributions of point defects, clusters and dislocation loops have been quantitatively compared in both unfragmented cascades and subcascades. In general, the subcascades exhibit fewer Frenkel pairs (FPs) at the peak damage, more survival FPs, and lower defect recombination rates, which can be attributed to the discrete deposition of energy and a shorter lifetime of the thermally enhanced recovery stage. However, the number of defects produced varies non-monotonically with the sphericity of the cascade morphology. In the unfragmented cascades, the dislocation loop size negatively correlates with the spatial dispersion of survival defects. The dislocation loops preferentially nucleate near the sharp edges of the molten region formed during the supersonic phase, where both kinetic energy density and local atomic density are higher. In the subcascades, the variation of the average sandwiched loop size with the separation distance between cascade fragments can be approximated by an exponential function. Injection and wavefronts compression are the two mechanisms for the formation of large sandwiched dislocation loops. The findings enhance the understanding of subcascade behavior and help to elucidate the initial stage of dislocation loop formation. • The distribution of defects in both unfragmented cascades and subcascades has been examined quantitatively. • Compared with the unfragmented cascades, the shorter thermal-spike lifetime in the subcascades leads to lower defect recombination rates. • The dislocation loop size negatively correlates with the spatial dispersion of survival defects in the unfragmented cascades. • A relationship has been proposed between the sandwiched loop size and the separation distance of fragments in the subcascades.