中文摘要：

本文采用30keV的He离子辐照HastelloyN合金，辐照温度为500。C，剂量分别为：1×10^15、5×10^15、1×10^16He＋／cm2。利用扫描电子显微镜（SEM）研究了辐照后块体样品的表面形貌。结果表明，辐照后的块体样品均观察到了表面起泡现象。利用透射电子显微镜（TEM）研究了辐照后TEM样品微结构的变化。结果表明，低剂量（1×10^15He＋／cm2）辐照的样品中出现了黑斑缺陷；随着辐照剂量的增加，开始出现位错环及纳米级的氦泡，同时黑斑密度减少；当剂量增至1×10^16He＋cm2，位错环以及氦泡的尺寸和密度明显增大，晶界处氦泡更加密集。

英文摘要：

Background： Hastelloy N alloys are selected as the structural materials of molten salt reactor （MSR）. Few results have been reported about their microstructures after irradiation. Purpose： To investigate the microstructural evolution of Hastelloy N induced by irradiation. Methods： Samples were irradiated at 500℃ with 30 keV He ions to different doses. Then the microstructures were characterized by scanning electron microscope （SEM） and transmission electron microscopy （TEM）. Results： Surface blisters were observed in all bulk samples. Black dot defects emerged in TEM sample irradiated at low dose （0.124 dpa）. As the dose increased, dislocation loops and He bubbles were observed and the density of black dots decreased. When the dose got to 1.24 dpa, both the sizes and density of dislocation loops and He bubbles increased remarkably. Conclusions： Black dot defects, dislocation loops and He bubbles are induced by He＋ irradiation at high temperature, the densities and sizes of which are related to the irradiation doses. Accumulation of He bubbles will result in blisters of alloys.