采用7 MeV的Xe²⁶⁺和1 MeV的Xe²⁰⁺在室温和600 ℃下分别对316SS块体和TEM试样进行了辐照实验. 利用纳米压痕仪测试材料辐照损伤前后的显微硬度, 利用TEM观察辐照损伤前后的微观结构演变, 并将室温和600 ℃的实验结果进行了比对. 结果表明, 室温离子辐照造成316SS中形成大量尺寸在3~8 nm之间的位错环缺陷, 它们会阻碍材料内位错线的自由移动, 进而导致材料的硬化. 在600 ℃辐照下, 316SS内形成了尺寸介于4~12 nm之间的溶质原子团簇缺陷. 尽管其尺寸较室温辐照下形成的位错环有轻微的增大, 但是其体积密度较前者显著地降低, 辐照硬化现象发生了明显的回复, 材料辐照损伤行为存在温度效应.

Molten Salt Reactors (MSR) is one of the six most promising Generation IV fission reactors. In the ultimate goals, MSR should run at temperatures over 1000 K, and its neutron irradiation damage doses could reach 100 dpa or more for the core components. Hence, the evaluation of irradiation damage under high temperature for structural materials is of particular importance for ensuring the safe operation of MSR. It is generally accepted the structural materials used for MSR should be Ni-based alloys, especially the Hastelloy N alloy. Recently, the 316 austenitic stainless steel (316SS) was considered as a candidate structural material for MSR. In this study, bulk and TEM specimens of 316SS have been characterized by nanoindentation and TEM to determine the change of micro-hardness and microstructural evolution after 7 MeV Xe²⁶⁺ and 1 MeV Xe²⁰⁺ iron irradiation, respectively. The irradiation experiments were carried out at room temperature (about 22 ℃) and 600 ℃, and the ion fluences correspond to calculated peak damge dose of 0.62 and 3.7 dpa. The nanoindentation results for bulk specimens showed the irradiation induced hardening of 316SS irradiated at room temperature, and the hardenability increases with increasing ion damage dose. However, in the case of the irradiation at 600 ℃, the hardness of 316SS keep the same level with that of the unirradiated specimen. The recovery of irradiation induced hardening occurred at 600 ℃ compared with the room temperature irradiation. The TEM results showed that the presence of high number density of nanoscale dislocation loops, with the diameter of 3~8 nm, in 316SS irradiated at room temperature. The number density of these dislocation loops increase with the increase of ion damage dose. As far as the irradiated 316SS under 600 ℃, several solute clusters were observed with the size range from 4 to 12 nm, which a little larger than the dislocation loops. It should be noted that the number density is far smaller than that of the dislocation loops in former case. The radiation induced defects (dislocation loops, solute clusters) were believed to be responsible for the hardening in 316SS. The temperature effect of Xe ion irradiation to 316SS was discussed using the Orowan mechanism. The stronger diffusion of point defects caused by ion implantation at 600 ℃ was considered to be the main reason for the recovery of irradiation induced hardening, in which the vacancies and interstitials have greater probability for recombination and then disappear, resulting in the exiguous nucleation sites for the formation of solute clusters.