氦离子辐照下金属表面损伤机制的高分辨透射电镜研究

Refractory metals, such as tungsten and molybdenum, are known by their excellent performance. They receive intensive research interests as plasma facing materials for nuclear fusion reactors. However, under the irradiation of low energy helium ions, micro- and nanoscale damage will be generated on the surface and this will cause the degradation of their performance. In general, SEM and conventional TEM are used to investigate the irradiation damage, but the defects caused by helium ions irradiation, such as interstitial atoms, vacancies, and nanoscale helium bubbles, are all in atomic-scale. The evolution of these defects are also closely associated with the crystallographic orientations, crystal grain boundaries, and dislocations. In this research, helium implantation will be used to create the irradiation damage on the surface and the defects in the damage structure will be investigated by aberration-corrected TEM. The microstructure of the irradiation damage and the evolution of the defects will be characterized in the sub-angstrom scale. The mechanism of the irradiation damage will be revealed, which may find a path to improve the irradiation resistance of metal materials.

钨、钼等高熔点金属材料由于其性能优异，作为核聚变装置的面向等离子体材料受到广泛地关注，但在聚变反应产生的低能氦离子冲刷下，其表面会产生微、纳米尺度的损伤结构，直接影响其使用性能。目前实验上主要还是通过扫描电镜与常规透射电镜等分析手段对损伤结构进行表征。但氦离子进入后产生的间隙原子、空位、纳米级氦泡等缺陷都是原子尺度的微观结构，这些缺陷的演化发展与金属自身的晶粒取向、晶界、位错结构等都密切相关。本项目拟通过氦离子注入方法模拟聚变堆内等离子体辐照条件，运用高分辨球差矫正透射电镜，在亚埃尺度研究辐照损伤层的微观结构，精确表征氦离子注入所产生的缺陷在金属表面损伤层内的形成与演化状态，从原子尺度上揭示金属表面辐照损伤的微观机制，进而对提高金属材料抗辐照损伤能力提出可行性建议。

钨、钼等高熔点金属材料由于性能优异，作为核聚变装置的面向等离子体材料受到广泛地关注；但在聚变反应产生的氦离子辐照与热冲击下，其表面会产生微、纳米尺度的损伤结构，直接影响其使用性能。本项目通过氦离子注入方法模拟聚变堆内等离子体辐照条件，结合原位透射电镜加热技术，运用高分辨像差矫正透射电镜，精确表征了钨、钼及锆-铌多层膜表面损伤层内的辐照缺陷，获得了金属表面微观结构及以氦泡为主的缺陷随温度的演化规律。氦离子辐照后在金属表层形成了大量的纳米级氦泡，氦泡在0.3倍金属熔点温度以下基本保持稳定；当温度超过0.3倍熔点温度后，氦的扩散能力显著提升，导致氦泡发生迁移、合并与长大。金属内部的界面、晶面及表面缺陷都是氦的主要扩散通道，金属的本征结构决定了氦缺陷的最终形态。氦泡在高温下的演化最终会导致金属表层的损伤、破坏，甚至污染聚变等离子体。本项目揭示了该体系材料在辐照条件下随温度演化的表面损伤机制，进而对金属材料抗辐照损伤能力的提高具有普遍指导意义。