TRISO颗粒SiC层辐照行为与力学性能的分子动力学模拟

Molecular Dynamics Simulation of Irradiation Behaviors and Mechanical Properties of SiC Layer of TRISO Particles

碳化硅(SiC)材料对TRISO颗粒的安全性能有重要影响,因此有必要对SiC层的辐照行为和力学性能进行研究。本文采用分子动力学模拟对等轴状多晶和长轴状多晶两类SiC层进行辐照行为模拟,计算发现,SiC层的辐照肿胀程度和力学性能的理论值与实验值吻合较好。通过肿胀程度、密度、原子结构类型、点缺陷演化等参量详细考察了SiC层的辐照行为。结果表明,辐照过程中的非晶化存在晶体结构转化为中间态结构,再转化为非晶结构的过程。在辐照早期,点缺陷以C空位、Si间隙原子和C反位原子为主,但在辐照剂量趋于饱和后差异逐渐消失。非晶化和点缺陷演化倾向于从晶界附近开始发展。辐照会导致SiC层力学性能的降低,但在辐照剂量趋于饱和后不再有显著影响。微观分析表明,SiC层力学性能的降低与其在外力作用下的承受能力和塑性变形程度减小、应力应变分布紊乱密切相关。研究结果有助于理解TRISO颗粒SiC层的辐照行为演化和力学性能变化的关系。

Silicon carbide(SiC)is an important material for shielding nuclear fission products in tri-structural isotropic(TRISO)particles for high-temperature gas-cooled reactors.It has an important influence on the safety performance of TRISO particles.Therefore,it is necessary to study the irradiation behaviors and mechanical properties of the SiC layer of TRISO particles.The irradiation process and nanoindentation process can be described accurately by molecular dynamics simulations.It is helpful to analyze the irradiation behavior and mechanical properties of materials.In this paper,molecular dynamics simulations were used to study the irradiation behavior of equiaxed polycrystalline and long-axis polycrystalline SiC layers obtained from experiments.The calculated theoretical values of the irradiation swelling degree and mechanical properties of the SiC layer are in good agreement with the experimental values.It shows the strong applicability of the potential functions and other simulation system parameters used in this paper.The irradiation behavior of the SiC layer was studied in detail by swelling degree,density,atomic structure type,and point defect evolution.The results show that the grain structure of the SiC layer has no significant effect on its irradiation swelling and amorphization.The amorphization is not directly converted from the crystal structure to the amorphous structure during the irradiation process.The crystal structure is converted into an intermediate state structure and then converted into an amorphous structure.The point defects are mainly C vacancies,Si interstitial atoms,and C antisite atoms in the early stage of irradiation.The difference between the ratio of C point defects and Si point defects gradually disappears after the irradiation dose tends to be saturated.The evolution of amorphization and point defects tends to start nearby the grain boundaries.Irradiation reduces the mechanical properties of SiC layers.It no longer has a significant effect on the mechanical properties of the SiC layer after the irradiation dose tends to be saturated.The changes in the mechanical properties of the SiC layer before and after irradiation were analyzed by load-depth curve and stress&strain.The results show that the decrease in mechanical properties of the SiC layer is closely related to the mechanical behaviors under external force.For example,the bearing capacity and plastic deformation degree decrease,and the stress&strain distribution are disordered.The results provide a quantitative explanation for the irradiation behavior of the SiC layer of TRISO particles and the change of mechanical properties under irradiation.It is helpful to understand the irradiation behavior and relationship between the irradiation behavior and mechanical properties of the SiC layer.