(1. 西安交通大学 机械工程学院，西安 710049；
2. 西安交通大学 机械制造系统工程国家重点实验室，西安 710049)
摘 要: 采用分子动力学方法模拟不同孪晶密度和不同温度下纳米孪晶钛单轴拉伸力学行为。模拟结果表明：室温下随着孪晶密度的降低，纳米孪晶钛的屈服强度出现先提升后降低的现象，材料存在临界孪晶密度。当孪晶密度小于临界孪晶密度时，孪晶界对晶粒的细化作用导致材料的强度提升。当孪晶密度大于临界孪晶密度时，孪晶界、晶界和两者交汇处的位错成核增殖成为材料变形的主导因素；且当孪晶密度远离临界值时，孪晶间隔变小、位错源增多，位错成核与增殖加剧，材料的强度降低。相同孪晶密度条件下，晶粒尺寸的减小会减少晶粒内孪晶界的数量，进而减少孪晶和晶界交汇处位错源的生成，增强了屈服强度。此外，温度的变化会影响原子的活跃程度和晶格的变形机制。随着温度的升高，原子间结合力下降，晶界附近原子结构无序化和HCP-BCC相变程度加剧引起材料的弹性模量、屈服强度下降，同时位错形核与运动的加剧影响了材料的塑性变形。
关键字: 纳米孪晶钛；孪晶密度；位错；温度；分子动力学
（1. School of Mechanical Engineering, Xi’an Jiaotong University, Xi’an 710049, China;
2. State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China）
Abstract:The mechanical behavior of nano-twinned titanium under uniaxial tension was simulated by molecular dynamics at different twin densities and temperatures. The simulation results show that with the decrease of twin density, the yield strength of nano-twinned titanium first increases and then decreases at room temperature, and there is a critical twin density in the material. When the twin density is less than the critical twin density, the grain refinement effect of twins leads to the increase of the strength of the material. When the twin density is larger than the critical twin density, the nucleation and increment of dislocations at twin boundary, grain boundary and their intersection become the dominant factors of material deformation, which affect the mechanical properties of nano-twinned titanium. When the twin density is far away from the critical value, the twin spacing becomes smaller, the nucleation and proliferation of dislocations become more intense, and the strength of the material decreases. The change of temperature can affect the activity of atoms and the deformation mechanism of lattice. With the increase of temperature, the bonding force between atoms decreases, the disorder of atomic structure near the grain boundary and the degree of HCP-BCC phase transformation increase, resulting in the decrease of elastic modulus and yield strength, and the increase of dislocation nucleation and movement affects the plastic deformation of the material.
Key words: nano-twinned titanium; twin density; dislocation; temperature; molecular dynamics
