孪晶界和温度对纳米多晶铁变形机制影响的模拟研究

Effect of Twin Boundary and Temperature on Deformation Mechanism of Nano-Polycrystal Iron by Molecular Dynamics

摘要: 本文采用分子动力学模拟方法研究了在拉伸载荷下，孪晶界和温度对纳米多晶铁力学性能的影响。研究结果表明：杨氏模量随着孪晶厚度的增大而增大；在温度为10 K或300 K下，当孪晶厚度小于临界尺寸时，峰值应力都随着孪晶厚度的增大而增大，表现出反常的Hall-Petch的现象，当孪晶厚度大于临界尺寸时，峰值应力随着孪晶厚度的增大而减小，表现出Hall-Petch的现象；温度为10 K时的临界值明显低于温度为300 K的临界值，这说明温度的变化影响着临界值；模型中的孪晶界上由于应力的集中，使得孪晶界成为萌生变形孪晶的源，促进了塑性变形，这是孪晶界对于纳米多晶铁弱化的主要原因。此外，也观察到裂纹的成核、孪晶界迁移和退孪晶的现象。

Abstract: The effects of twin boundary and temperature on the mechanical properties of nano-polycrystal iron under tensile loading were studied by molecular dynamics simulation. The results show that the Young’s modulus increases with the increase of twin thickness. At temperatures of 10 K and 300 K, when the twin thickness is smaller than the critical size, the peak stress increases with the in-crease of the twin thickness, showing abnormal Hall-Petch phenomenon. However, when the twin thickness is larger than the critical size, the peak stress decreases with the increase of twin thickness, indicating the Hall-Petch relationship. When the temperature is 10 K, the critical size is obviously lower than the critical size of 300 K, which indicates that the temperature affects the critical size. The twin boundary in the model becomes the initiation source of the deformation twin due to the stress concentration, promoting the plastic deformation, which is the main reason for the weakening of nano-polycrystal iron. In addition, the phenomena of crack nucleation, twin boundary migration and twin retreat are also observed.