聚变环境下钨中合金原子偏聚行为计算模拟研究

Tungsten-based alloys are considered as most promising candidates for plasma facing materials (PFM) in future fusion reactor due to their good properties of high melting point, low sputtering yield and high thermal conductivity. The precipitate formation in tungsten-based alloy irradiated by high-energy neutron in nuclear fusion environment usually changes the physical and chemical properties of the material. The precipitate formation may seriously degrade the service performance of the materials, and affect the safe and stable operation of future fusion reactors. Therefore, it is of great importance to investigate the nucleation, evolution and distribution mechanisms of precipitate in tungsten-based alloys under irradiation. In the present proposal, tungsten-rhenium, tungsten-osmium, tungsten-tantalum and so on models are used as the objects of the study. Density functional theory method and statistical mechanics methods, i.e., cluster expansion method and Monte Carlo method will be used to systematically investigate the diffusion kinetics and aggregation nucleation of rhenium, osmium, and tantalum in tungsten-based alloys. The nucleation and growth of precipitate, the structure character and atom configuration in precipitate with various size under various temperature, alloying solute and solute concentration will be investigated. The evolution and distribution laws of precipitate with the changes of alloying solute concentration, vacancy concentration and temperature will be obtained to guide tungsten alloys design and predict the service performance of tungsten-based alloys as plasma facing materials in nuclear fusion reactor.

钨基合金以其高熔点、低溅射产额和高热导率等优良特性而被视为未来核聚变反应堆中最有前景的面向等离子体材料（PFM）。聚变服役环境下中子辐照易导致钨中合金原子偏聚形成偏聚物从而改变材料的物理和化学性质，严重影响材料的服役性能及未来核聚变反应堆的安全稳定运行。因此，开展辐照条件下钨合金偏聚物的成核、演化和分布机理研究具有十分重要的意义。本项目将以钨-铼、钨-锇和钨-钽等合金为研究对象，以密度泛函理论方法结合统计力学中的集团展开方法和蒙特卡罗方法为研究手段。系统研究钨材料中铼、锇和钽等合金原子以及空位的扩散动力学特性和偏聚成核行为。通过改变温度、合金组分和空位浓度等条件，研究合金原子聚集成核和演化生长过程以及不同尺寸偏聚物的原子构型特征。最终获得合金原子偏聚物随合金组分浓度、空位浓度和温度等条件的演化和分布规律，从而为聚变堆面向等离子体钨合金的设计及其服役性能预测提供理论指导。

钨被视为未来核聚变堆中最有前景的面向等离子体材料。聚变环境下高能中子辐照诱导材料发生嬗变反应生成铼、锇和钽等嬗变元素。嬗变元素在材料中聚集形成偏聚物从而导致材料脆化、硬化和断裂并影响聚变堆的安全稳定运行。因此，开展中子辐照下钨中嬗变元素偏聚物的成核、演化和分布机理研究具有重要意义。本项目以钨-铼、钨-锇和钨-钽等为研究对象，编写了钨合金的集团展开程序及蒙特卡罗程序。基于密度泛函理论及集团展开方法系统研究了钨中铼、锇和钽等的溶解及其与辐照缺陷和缺陷团簇的相互作用，嬗变元素聚集成核，嬗变元素对彼此偏聚成核行为的影响以及偏聚物随合金浓度、缺陷浓度及温度的演化和分布行为。研究发现，仅嬗变元素锇可在完美的钨中形成偏聚物，辐照缺陷可促进铼和锇在钨中偏聚。然而，存在辐照缺陷时钽仍然无法在钨中偏聚。锇可促进铼偏聚物形成，且在钨-铼-锇三元体系中锇在偏聚物形成中起主导作用。钽可抑制钨中铼和锇偏聚物的形成，该研究结果被实验所证实。此外，铼和锇在辐照空位处的偏聚降低了空位的迁移速率，从而降低空位的密度并抑制空洞的形成。该研究结果很好地解释了钨中嬗变元素铼和锇偏聚成核的微观机制，并解释铼抑制空洞密度的微观原因。为聚变堆面向等离子体材料的合金设计及服役性能评估提供有用建议。