分子动力学模拟层错对钛疲劳裂纹扩展行为的影响

Molecular dynamics simulation of the effect of stacking fault on the fatigue crack propagation behavior of titanium

关键词:  分子动力学  层错  疲劳裂纹扩展  变形孪晶  温度

Key words:  molecular dynamics  stacking fault  fatigue crack propagation  deformation twins  temperature

摘要:

利用分子动力学模拟方法研究了2种内禀型层错(Stacking Fault, SF)结构对钛疲劳裂纹扩展行为的影响。结果表明,I₁型SF界面在裂纹扩展中始终存在,对裂纹扩展起到显著的阻碍作用,疲劳裂纹扩展速率较低；I₂型SF界面随着循环加载逐渐消失,孪晶界面(Twin Boundary, TB)上形核的孔洞引导裂纹迅速扩展,疲劳裂纹扩展速率较高。不同SF界面模型塑性变形机制以变形孪晶为主。I₁与I₂型SF界面模型的平均疲劳裂纹扩展速率均随着温度增加而增加,与I₂模型相比,I₁模型的裂纹扩展行为对温度敏感性较高。不同温度下,不同SF界面模型的循环J积分参数(ΔJ)与疲劳裂纹扩展速率均呈现良好的相关性。研究结果不但揭示了层错界面相关的疲劳裂纹扩展机理,同时可为钛合金的微结构设计提供理论指导。

Abstract:

This paper investigates the influence of two intrinsic stacking fault (SF) structures on the fatigue crack propagation behavior in titanium using molecular dynamics simulation methods. The results demonstrate that the interface of I₁ SF is consistently present during crack propagation, significantly hindering crack growth and resulting in a lower fatigue crack propagation rate. In contrast, the interface of I₂ SF gradually disappears with cyclic loading, and the nucleation of voids on the twin boundary (TB) facilitates rapid crack propagation, leading to a higher fatigue crack propagation rate. The plastic deformation mechanism of different SF interface models is dominated by deformation twins. Both the average fatigue crack extension rates of I₁ and I₂ SF interface models increase with increasing temperature; however, the crack extension behavior of the I₁ model is more sensitive to temperature changes compared to the I₂ model. At different temperatures, the cyclic J-integral parameter (ΔJ) of different SF interface models shows a good correlation with the fatigue crack growth rate. The results not only reveal the fatigue crack extension mechanism associated with the SF interface, but also can provide theoretical guidance for the microstructure design of titanium alloys.