Most experimental work on radiation damage is performed to fairly high doses, where cascade overlap effects come into play, yet atomistic simulations of the primary radiation damage have mainly been performed in initially perfect lattice. Here, we investigate the primary damage produced by energetic ion or neutron impacts in bcc Fe and W. We model irradiation effects at high fluence through atomistic simulations of cascades in pre-damaged systems. The effects of overlap provide new insights into the processes governing the formation under irradiation of extended defects. We find that cascade overlap leads to an increase in the numbers of large clusters in Fe, while in W such an effect is not seen. A significant shift in the morphology of the primary damage is also observed, including the formation of complex defect structures that have not been previously reported in the literature. These defects are highly self-immobilized, shifting the damage away from the predominance of mobile $1/2〈111〉$ loops towards more immobile initial configurations. In Fe, where cascade collapse is extremely rare in molecular dynamics simulations of individual cascades, we observe the formation of vacancy-type dislocation loops from cascade collapse as a result of cascade overlap.

大多数辐射损伤的实验工作都是在相当高的剂量下进行的，其中级联重叠效应起作用，而主要辐射损伤的原子模拟主要是在最初完美的晶格中进行的。在这里，我们研究了由高能离子或中子撞击bcc Fe和W中产生的主要破坏。我们通过在预损坏系统中级联的原子模拟对高能量通量下的辐照效应进行建模。重叠效应为扩展缺陷辐照下的形成过程提供了新的见解。我们发现级联重叠导致Fe中大簇的数量增加，而在W中则没有这种效果。还观察到主要损伤的形态发生了显着变化，包括以前没有文献报道的复杂缺陷结构的形成。这些缺陷是高度自我固定的，从而将损害从移动设备的优势转移到其他方面$\mathrm{1个}/\mathrm{2个}〈111〉$循环到更固定的初始配置。在Fe中，级联坍塌在单个级联的分子动力学模拟中极为罕见，我们观察到由于级联重叠而导致的级联坍塌形成空位型位错环。