(合肥工业大学 材料科学与工程学院，合肥 230009)
摘 要: 为了研究孪晶间距的大小对纳米钨力学性能及变形机理的影响，利用分子动力学对不同孪晶间距的孪晶钨进行了单轴拉伸模拟。使用近邻列表技术(CNA)和位错分析方法(DXA)对拉伸过程中纳米钨的变形失效过程和微结构演化进行了表征分析，从而揭示孪晶间距对纳米钨力学性能影响微观机理。结果表明：孪晶钨变形过程中出现的相变、孪晶界的变形以及去孪晶化的现象会改变孪晶钨中裂纹的扩展方式，提高孪晶界的变形能力；而随着孪晶间距的减小即孪晶密度的增加，可变形的孪晶界增多，导致纳米孪晶钨的断裂应变增加。由于孪晶界中存在能量较高的相互作用的特殊三原子结构使纳米钨中更容易出现晶体缺陷，缺陷会在拉伸载荷作用下快速形成裂纹，导致晶体断裂失效，严重降低了纳米钨的屈服强度。此外，孪晶界的存在显著降低了几何必须位错的数量同时阻碍了位错的滑移运动，位错难以发射和运动，从而导致塑性变差。
关键字: 钨；纳米孪晶界；孪晶距；位错；分子动力学
（School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China）
Abstract:In order to study the effect of twin boundaries spacing on the mechanical properties and deformation mechanism of nano-tungsten, uniaxial tensile simulation of twin tungsten with different twin boundaries spacing was carried out by molecular dynamics. The deformation failure process and microstructure evolution of nano-tungsten during tension were characterized and analyzed by using common neighbor analysis(CNA) and dislocation analysis method (DXA).The micro mechanism of the influence of twin boundaries spacing on the mechanical properties of nano tungsten was revealed. The results show that the phase transformation, the deformation of twin boundary and the phenomenon of de-twinning in the process of twin tungsten deformation will change the mode of crack propagation in twin tungsten and improve the deformation ability of twin boundary. With the decrease of twin boundaries spacing, that is, the increase of twin density, the number of deformable twin boundaries increases, resulting in the increase of fracture strain of nano-twin tungsten. Due to the existence of a special triatomic structure with high energy interaction in the twin boundaries, crystal defects are more likely to appear in the nano tungsten. The defects will form cracks quickly under the tensile load, resulting in the crystal fracture failure and seriously reducing the yield strength of the nano tungsten. Additionly, the existence of twin boundaries significantly reduces the number of geometric necessary dislocations and hinders the slip movement of dislocations, which makes it difficult for dislocations to emit and move, resulting in poor plasticity.
Key words: tungsten; nano twin boundary; twin distance; dislocation; molecular dynamics
