通过分子动力学模拟、黏塑性本构模型和纳米压痕试验验证相结合的研究方法,系统研究了双峰结构(晶粒尺寸服从统计学中双峰分布)纳米晶铜的变形机理与力学性能。结果表明:在塑性变形过程中位错首先在纳米晶铜的细晶区形核和扩展,且方向互相平行;而粗晶区的位错滑移方向相互交叉,且粗晶尺寸越大,越容易发生位错缠绕和交滑移。双峰结构纳米晶铜的流变应力随着粗晶尺寸的增大而增大,硬度随着粗晶体积分数的增大而减小。由黏塑性本构方程计算得到的应力变化规律与由经验公式和分子动力学模拟得到的结果一致,且本构方程计算得到的流变应力和经验公式所得结果的相对误差小于5%。

The deformation mechanism and mechanical properties of nanocrystalline copper with a bimodal structure (grain size obeying bimodal distribution in statistics) were systematically investigated by combination of molecular dynamics simulation, visco-plastic constitutive model and nanoindentation test verification. The results show that during the plastic deformation, dislocations were first nucleated and expanded in the fine grain zone of the nanocrystalline copper, and the directions were parallel to each other; while the dislocation slip directions in the coarse grain zone crossed each other, and the larger the size of coarse grains, the more likely dislocation entanglement and cross-slip occurred. The flow stresses of the nanocrystalline copper with a bimodal structure increased with increasing coarse grain size, and the hardness decreased with increasing volume fraction of coarse grains. The stress variation law calculated by the visco-plastic constitutive equation was consistent with that by the empirical formula and molecular dynamics simulation, and the relative error between the flow stresses calculated by the constitutive equation and the empirical formula was less than 5%.