Ti-A-C (A=Si, Al) MAX相低能反冲原子行为的第一性原理分子动力学模拟

Ti-A-C (A=Si, Al) systems in MAX phases attract extensive attentions as candidates of cladding materials in GIV nuclear reactor due to their good radiation damage tolerance. Because of the existence of impurities and solid solution atoms, the radiation experiments can not truly characterize the radiation damage tolerance of Ti3SiC2 and Ti3AlC2. Furthermore, the previous theoretical studies focused on the formation and migration of intrinsic point defects in MAX phases under thermodynamic equilibrium state. The results can not reflect the formation and accumulation of defects during initial non-equilibrium stage under nuclear radiation. In the present work, the threshold displacement energies of the recoil atoms and the defect configurations related to the primary knock-on atoms will be calculated by the ab-initio molecular dynamics to explore the process of atomic collisions and formation of defects during the initial stage under nuclear radiation of Ti-A-C compounds. By comparing the results of Ti3AC2, Ti3(Si,Al)C2, (Ti,Zr/Hf)3AC2, and Ti2AlC, the influence of chemical composites on Ti and A sites, and the Ti-C unit structure on process of defects formation under radiation can be revealed. Based on the present investigations, we aim to construct the physical profile of atomic collision and defect formation during the initial stage of nuclear radiation, and to understand the mechanism of radiation damage tolerance of MAX phases. Finally, we will provide theoretical guideline to optimize the radiation damage tolerance of MAX phases by tailoring the chemical composites and the crystal structure, furthermore, to search new MAX phases with good radiation damage tolerance.

Ti-A-C（A=Si和Al）体系MAX相具有良好的抗辐照损伤性能，成为了第四代核反应堆包壳材料的热门候选。受到样品杂质和固溶元素的影响，现有的实验结果不能真实反映Ti3AC2的本征抗辐照性能。已有的理论工作局限于描述平衡态点缺陷产生和迁移机制，不能与辐照初期非平衡过程联系起来。本项目拟用第一性原理分子动力学方法计算反冲原子的离位阈值、原子离位产生的缺陷构型，探索Ti-A-C中辐照初期原子碰撞和缺陷产生的物理过程；通过对比Ti3AC2、Ti3(Si,Al)C2、(Ti,Zr/Hf)3AC2和Ti2AlC的结果，揭示Ti和A位置化学成分、Ti-C层结构对缺陷产生过程的影响。本项目的研究结果将用于建立MAX相辐照初期原子碰撞和缺陷产生的真实物理模型，为理解MAX相抗辐照损伤的机理，指导实验中通过结构和化学成分调控优化抗辐照损伤性能，并进一步寻找新的抗辐照损伤性能优异的MAX相提供理论基础。

Ti-A-C（A=Si和Al）体系MAX相具有良好的抗辐照损伤性能，成为了第四代核反应堆包壳材料的热门候选。对其辐照损伤机制的研究可以为调控优化抗辐照损伤性能以及进一步寻找新的抗辐照损伤性能优异的MAX相提供理论指导。本项目采用第一性原理及第一性原理分子动力学方法研究了Ti3AC2（A=Si,Al）体系本征点缺陷的产生和迁移机制以及原子的低能反冲行为，获得了本征点缺陷的形成能、迁移能垒、初级离位原子的最低阈能值，研究结果表明Ti3AC2中本征点缺陷倾向于聚集在A原子面附近，且富集的点缺陷沿A原子面可以快速扩散，动力学模拟的结果显示原子离位过程具有明显的各向异性，离位原子产生的缺陷大都聚集在A原子面附近。这些结果表明A原子面附近的空间可以作为缺陷阱容纳辐照缺陷，使得MAX相在辐照后具有高的结构稳定性，是MAX相良好抗辐照损伤性能的来源。这种本征缺陷阱机制是一种新型的抗辐照损伤机理，调控优化MAX相抗辐照损伤性能的关键是调整和剪裁晶体中的本征缺陷阱结构。