低能氦离子辐照诱导的钨材料结构演化

Low-energy helium-ions irradiation induced morphology and crystalline evolution of tungsten

在温度为923 K、氦离子流强为7×10^(21) m^(-2)·s^(-1)的条件下,考察了低能氦离子辐照对钨材料表面结构的影响。采用扫描电子显微镜(Scanning Electron Microscope,SEM)、导电原子力显微镜(Conductive Atomic Force Microscope,CAFM)、称重法、X射线衍射(X-ray Diffraction,XRD)以及电子背散射衍射(Electron Back-Scattered Diffraction,EBSD)对辐照后钨材料的结构演化规律进行了分析。SEM和CAFM的研究表明,在辐照初期样品表面形成了纳米尺寸的氦泡,随着辐照剂量的增加,氦泡的尺寸和密度逐渐增加,最终引起钨表层的剥落。质量损失和溅射产额的分析结果表明,钨材料表层的剥落是钨损伤的主要形式。SEM、XRD和EBSD的分析证实了辐照后钨样品的表面形貌变化与晶体取向之间具有很强的关联性。研究结果表明,相对于(101),氦原子更容易在(111)和(001)等晶面上吸附、扩散和聚集,这些研究结果将为面向等离子体材料的优化设计提供有用的参考。

Background： Currently, tungsten has been selected as one of the best plasma-facing materials for international thermonuclear experimental reactor （ITER） due to its low hydrogen solubility, low sputtering yield, high melting point and high thermal conductivity. Purpose： In this paper, the responses of polycrystalline tungsten to low-energy helium-ions irradiation were investigated. Methods： Helium-ions irradiation was performed at 923 K with a He＋ flux of 7x1021 m 2.s 1. A strong correlation between the surface morphology change and the grain orientation was confirmed from scanning electron microscope （SEM）, conducive atomic force microscope （CAFM）, X-ray diffraction （XRD） and electron backscattered diffraction （EBSD） analysis. Results： SEM and CAFM measurement revel that nano-scale helium bubble formed on the surface of tungsten at earlier stage. The size and number of the formed helium bubbles increase with the increase of helium fluence until they break. Mass loss and sputtering yields analysis indicated that the surface spalling caused by the damage of helium bubble is the main format of tungsten damage. XRD and EBSD found that helium atom is shown to be not energetically favorable todissolve, self-trap and cluster at （101） surface in comparison to （111） and （001） surface. Conclusion： The results will provide a useful reference for optimization of the plasma facing materials.