Molecular Dynamics Simulation of Nanomechanics Behavior of SiC Layer of TRISO Particle
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摘要: 三元结构各向同性（TRISO）颗粒碳化硅（SiC）层在辐照和高温考验后会发生晶粒的相变、断裂和异常长大等现象，这些SiC层的力学行为对TRISO颗粒的安全性研究非常重要。本文采用分子动力学模拟研究SiC层的纳米力学行为和性能。根据实验现象构建了4种典型SiC层结构：服役前3C-SiC、辐照考验后3C-SiC、高温考验后6H-SiC、高温+辐照考验后6H/3C-SiC，并通过载荷-深度曲线、位错演化、应力应变、原子扩散等参量分析了SiC层的纳米力学行为和性能。结果表明，服役后的SiC层在纳米压痕加载过程中的位错间相互作用更少，使塑性变形减少，所以杨氏模量降低。辐照考验后和高温+辐照考验后的SiC层的应力应变在压头正下方的集中程度降低，且应力应变和原子扩散的横向分布程度提高，所以硬度降低；高温考验后的SiC层的应力应变在压头正下方集中程度提高，且应力应变和原子扩散的纵向分布程度提高，所以硬度提高。研究结果对各种类型的SiC层力学行为和性能给出了定量解释，有助于理解SiC层微观结构、力学行为和力学性能之间的关系。Abstract: The grain of the SiC layer of tristructural-isotropic (TRISO) particles will undergo phase transformation, fracture and abnormal growth after irradiation and high temperature test. The mechanical behavior of these SiC layers is very important for the safety study of TRISO particles. In this paper, molecular dynamics simulation is used to study the nanomechanical behavior and properties of SiC layer. Four typical SiC layer structures are constructed according to the experimental phenomena: 3C-SiC before service, 3C-SiC after irradiation test, 6H-SiC after high temperature test, and 6H/3C-SiC after high temperature & irradiation test. The nanomechanical behavior and mechanical properties of SiC layer are analyzed by load-depth curve, dislocation evolution, stress & strain, and atomic diffusion. The results show that the SiC layer after service has less interaction between dislocations during the nanoindentation loading process, which reduces the plastic deformation, resulting a decrease in Young's modulus. For the SiC layer after irradiation test and high temperature & irradiation test, the concentration degree of stress and strain directly below the indenter decreases, and the transverse distribution of stress, strain, and atomic diffusion increases, resulting in a decrease in hardness. For the SiC layer after high temperature test, the concentration degree of stress and strain directly below the indenter increases, and the vertical distribution of stress, strain, and atomic diffusion increases, resulting in an increase in hardness. The research results give a quantitative explanation for the mechanical behavior and properties of various types of SiC layers, which is helpful to understand the relationship among the microstructure, mechanical behavior and mechanical properties of SiC layers.
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Key words:
- SiC /
- Nanoindentation /
- Mechanical behavior /
- Molecular dynamics
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图 1 TRISO颗粒SiC层分子动力学模拟材料模型构建过程
Figure 1. Material Model Construction Process of Molecular Dynamics Simulation of the SiC Layer of TRISO Particles
图 4 模型Ⅱ~Ⅴ的载荷-深度曲线与力学性能理论值和模型Ⅱ~Ⅴ的硬度理论/实验值对比
Figure 4. Load-depth Curves and Theoretical Value of Mechanical Properties of Model Ⅱ~Ⅴ, and Comparison of Theoretical/Experimental Hardness Values of Model Ⅱ~Ⅴ
图 5 模型Ⅱ~Ⅴ在加载过程中的位错演化
Figure 5. Dislocation Evolution of Model Ⅱ~Ⅴ During Loading Process
图 6 模型Ⅱ~Ⅴ的应力应变分布与晶粒分布
Figure 6. Stress-strain Distribution and Grain Distribution of Models Ⅱ~Ⅴ
图 7 模型Ⅱ~Ⅴ在加载过程中的均方位移
Figure 7. Mean Square Displacement of Model Ⅱ~Ⅴ During Loading Process
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