钨中晶界、辐照缺陷和氢协同演化机制的理论模拟研究

One of the requirements of the plasma-facing material (PFM) is low hydrogen retention, which is one of the advantages of tungsten, a promising potential PFM candidate. The main problem of the use of tungsten is its high ductile-to-brittle transition temperature and therefore high brittleness at the operation temperature. In order to improve the ductility of tungsten, grain refinement was proposed. However, the introduction of a large number of grain boundary is bound to affect the hydrogen retention behavior in tungsten. Experiments show that the effect of grain refinement on hydrogen retention is very complicated, which is closely related to grain size, grain boundary type and irradiation condition. At the same time, the presence of hydrogen will affect the anti-radiation properties of fine-grained materials. Therefore, it is necessary to comprehensively understand the hydrogen retention behavior in fine-grained tungsten under irradiation and its effect on the anti-radiation properties of fine-grained materials. Consequently, we will investigate the long time co-evolution of the grain boundary, irradiation defect, and hydrogen in large system by the combination of the first-principles calculations, molecular dynamics, and object kinetic Monte Carlo. We will explore the dependence of hydrogen retention in tungsten on the grain size, grain boundary type, temperature, and the implantation flux and fluence of hydrogen ion. A window in these parameters space will be sketched, in which materials show a low hydrogen retention and a higher radiation resistance. The work will be served as a guide to the development of fine-grained tungsten-based materials as the PFM.

低氢滞留是聚变堆面向等离子体材料（PFM）的必要条件之一。钨具有低氢滞留、高熔点和高溅射阈值等优点，是最有前景的候选PFM。而钨也存在韧脆转变温度高、高温强度差和辐照脆化等问题，限制了其在聚变堆中的应用。晶粒细化可有效改善钨上述问题，但大量晶界的引入会改变钨低氢滞留性能。实验表明晶粒细化对氢滞留影响十分复杂，与晶粒尺寸、晶界类型、辐照条件等因素密切相关。同时，氢的存在也会影响晶界抗辐照性能。因此，需要全面认识辐照环境下细晶钨中氢滞留行为及其对晶界抗辐照性能的影响，才能扬长避短，进一步提升细晶钨基材料综合性能。为此，我们采用基于第一性原理和分子动力学的面向对象动力学蒙特卡洛方法模拟晶界、辐照缺陷和氢在大体系中长时间协同演化行为，揭示其微观机制，探寻兼有低氢滞留和高抗辐照性能的参数区间（晶粒尺寸、晶界类型、温度、氢离子辐照剂量等），为实验研发兼有抗辐照和低氢滞留性能的细晶钨基材料提供理论指导。

低氢滞留是聚变堆面向等离子体材料（PFM）的必要条件之一。钨因具有低氢滞留、高熔点和高溅射阈值等优点，是最有前景的候选PFM。而钨也存在韧脆转变温度高、高温强度差和辐照脆化等问题，限制了其在聚变堆中的应用。晶粒细化可有效改善钨上述问题，但大量晶界的引入会改变钨低氢滞留性能。本项目利用第一性原理、从头计算分子动力学、经典分子动力学详细研究了细晶钨中间隙氢聚集行为、氢主要滞留点-空位型缺陷的能量学和动力学行为以及空位型缺陷处的氢聚集行为、晶界的结构和能量学行为、晶界处空位/间隙型缺陷和氢的能量学和动力学行，计算获得了一系列<100>轴、<110轴>和<111>轴倾侧对称晶界的稳定结构和界面能，空位/间隙型缺陷和氢在该系列晶界处的形成能、偏聚能，间隙氢团簇结合能以及间隙氢团簇在不同应力条件下的形成能，纳米孔洞稳定结构及其形成能和结合能，纳米孔洞对氢的捕获能和捕获半径等性质参数。基于计算结果，进一步理论分析构建了用于描述间隙氢团簇结合行为的物理模型，结合弹性理论预测了应力条件下的间隙团簇形成能；发现了稳定纳米孔洞的形成能与其Wigner-Seitz表面积之间呈线性关系，进而推导出了纳米孔洞-空位结合能的模型公式；获得了氢原子在纳米孔洞的Wigner-Seitz正方形内表面上的吸附规律，进而构建了预测氢原子在纳米孔洞内的结构与能量的物理模型。在上述基础上，开发了一套面用于模拟氢同位素等离子体辐照下多晶钨中氢同位素滞留和热脱附的模拟软件，并利用该软件模拟了氢同位素辐照后钨中氢滞留和热脱附行为的典型实验，澄清了氢主要滞留点，揭示了相应的氢滞留机理。共发表论文13篇（包括1篇Nature Materials上，2篇Acta Materialia，1篇Nuclear Fusion，1篇Journal of Nuclear Materials），授权专利1项。培养博士研究生和硕士研究生各1名。