聚变环境中晶体取向对金属钨辐照行为的影响

Tungsten is considered to be one of the most promising candidates for plasma-facing materials in Tokamak/fusion reactors by utilizing its unique physical, chemical and mechanical properties. However, attributing to irradiation damages induced by high energy transmutation ions, emitting particles from plasma and the neutron irradiation during fusion reactions in these facilities, tungsten will suffer serious problems like surface bubbling, wrinkling and peeling, surface sputtering and irradiation-induced brittlement, hardening and swelling, which are brought about by ionization, displacement damages, defects formation, gathering and migration. The discovery of applicant reveals that tungsten with certain crystal orientation will maintain its surface smooth with low sputtering rate after ion-beam irradiation. Therefore, this project will deeply engage in studying the influence of crystal orientation on irradiation behaviors of tungsten on the base of former research, and obtain the experiment data of microstructure evolution in full time and space under low energetic ion irradition and high energetic H+, He+ and W+ ions irradition. The applicant will study the consistency of irradiation results in condition of different irradiation parameters and search the intrinsic factors that influence and control irradiation behaviors of tungsten with diverse crystal orientation under low energetic ion irradiation. The defects induced by H+, He+ and W+ ion irradiation will be charactered and measured in tungsten grains with diverse crystal orientation. Attribute to above, data obtained will be applied on solving some of the basic scientific problems and providing explanation on irradiation phenomena, and finally promoting the mechanism study of crystal orientation affecting on tungsten irradiation behaviors. This project research has great sighificance not only for assessing the irradiation behaviors of tungsten, but also for making great progress on scientific theory of irradiation damage.

金属钨具有独特的特性被认为是托卡马克/聚变堆中面向等离子体用材料的最佳候选者之一。但钨在各种带能粒子的辐照下将形成表面溅射、表面起泡/起皱/起皮、辐照脆化/硬化/肿胀等系列问题。本课题组已观察到具有特定晶体取向的金属钨经离子辐照后晶体表面始终保持光滑且表面溅射率非常低。因此，本项目拟在此基础上，深入系统研究金属钨在低能重离子辐照和高能氢、氦与钨离子作用下的辐照行为，以获得其微观结构在时间与空间上的详实实验数据。通过对低能重离子各种辐照参数下晶体取向对金属钨辐照行为影响的一致性问题的研究和各种晶体取向钨晶体表面响应差异的本质因素的探讨，以及氦氢钨离子辐照作用下缺陷在各种取向钨晶体中的表征与衡量，以探寻离子辐照下晶体取向对钨辐照行为影响的最基础问题和现象的科学解释，揭示晶体取向对金属钨辐照损伤行为影响的机理。本项目的立项不仅更加深入理解金属钨的辐照性能而且对辐照损伤科学理论的发展具有重要意义。

钨具有高熔点和导热率，低热膨胀系数、氚滞留和溅射产额，高自溅射阀值等优异性能，被认为是托卡马克/聚变堆中面向等离子体用材料的最佳候选者之一。但服役中会遭受各种带能粒子辐照，降低其性能。因此研究其辐照行为尤为重要。本项目采用扫描电镜与聚焦离子束耦合系统和美国阿贡国家实验室的离子加速器与透射电镜联机设施分别采用低能聚焦Ga+离子束和400keV Kr+离子束实时原位研究了钨的微观结构在时间与空间上详实的演化行为。针对单一能量离子辐照导致位移损伤与离子浓度沿深度呈高斯分布的不足，采用了阶梯能量He+离子辐照，获得了位移损伤和氦离子浓度从表面到特定深度的均匀分布。根据所获得的实验数据，采用分子动力学等初步计算模拟了辐照行为。研究表明，聚焦Ga+离子诱导形成了表面纳米针，其分布状态与晶体取向有关，尺寸与辐照参数成函数关系。而在经阶梯能量He+离子辐照和退火的钨表面观察到自生长的纳米锥结构。纳米锥的分布特性、密度和形态与晶体取向具有显著关系，(111)晶粒表面上的纳米锥密度最高，(001)晶粒表面纳米锥密度最小，而(101)晶粒则介于之间。纳米锥的尺寸与退火时间成幂函数关系。晶体取向显著影响表面显微硬度，在原始态和辐照态样品中，靠近(0 0 1)取向的晶粒具有最高的显微硬度。而退火处理使得辐照样品的显微硬度值在0~1h内急剧下降，而后1~3h内下降速率降低，最后趋于平稳。同时靠近(111)比靠近(001)取向晶粒的显微硬度下降更快。实时原位研究Kr+离子束辐照时的钨微观结构演化行为得知，当剂量达1.0×1014 ions/cm2，位错环开始形成，且网状位错密度随Kr+离子剂量增加而增大。继续增大剂量则观察到1.3nm平均尺寸气泡，但提高辐照剂量与温度，长大不明显，表明Kr气泡长大能垒较大。对已有理论公式修正得到了一个计算气泡尺寸的经验公式。在辐照实验基础上，初步模拟计算了钨的辐照行为，例如探讨了钨中平衡态和亚稳态[100]对称倾斜晶界的空位偏析能量。本项目研究不仅深入理解了钨的辐照行为而且对辐照损伤科学理论发展具有重要意义。