单晶钨纳米线拉伸变形机理的分子动力学研究

利用分子动力学方法, 对本课题组率先采用金属催化的气相合成法制备出的高纯度单晶钨纳米线进行拉伸变形数值模拟, 通过分析拉伸应力-应变全曲线及其微观变形结构, 揭示出单晶钨纳米线的拉伸变形特征及微观破坏机理. 结果表明: 单晶钨纳米线的应力-应变全曲线可分为弹性阶段、损伤阶段、相变阶段、强化阶段、 破坏阶段等五个阶段, 其中相变是单晶钨纳米线材料强化的重要原因; 首次应力突降是由于局部原子产生了位错、孪生等不可逆变化所致; 第二次应力突降是发生相变的材料得到强化后, 当局部原子再次产生位错导致原子晶格结构彻底破坏而形成裂口、且裂口不断发展成颈缩区时, 材料最终失去承载能力而断裂. 计算模拟得到的单晶钨纳米线弹性模量值与实测值符合较好. 关键词： 分子动力学 应力应变曲线 微观机理 单晶钨纳米线

Molecular dynamics simulation of tensile deformation mechanism of the single crystal tungsten nanowire

Molecular dynamics method was used to simulate tensile deformation of the high-purity single-crystal tungsten nanowire prepared by the metal-catalyzed vapor-phase reaction method first proposed by our research group. Stress-strain curve and microscopic deformation structure were analyzed in order to reveal the tensile deformation characteristics and microscopic failure mechanism of the single-crystal tungsten nanowire. Results show that the whole stress-strain curve can be classified into five stages: elastic stage, damage stage, phase transition stage, hardening stage and failure stage, where the phase transition is the main reason for hardening of the single-crystal tungsten nanowire. The first stress drop is caused by irreversible change of the local atomic dislocation and twinning, and the second stress drop is due to lattice structure failure resulting from the local atomic dislocation of the strengthened material and the development of split-forming necking area leading to the fracture of single-crystal tungsten nanowires. Calculated result of the elastic modulus is in good agreement with the test results of elastic modulus of the single-crystal tungsten nanowire.
Keywords： molecular dynamics stress-strain curve microscopic mechanism single-crystal tungsten nanowire