材料期刊网

采用多尺度准连续介质法分别模拟无缺陷和具有初始缺陷两种状态下, 单晶Al薄膜纳米压痕初始塑性变形过程, 得到载荷--位移响应曲线和应变能--位移变化曲线. 研究了初始缺陷对纳米压痕过程中位错形核与发射、Peierls应力以及位错发射临界载荷的影响. 结果表明, 在整个纳米压痕过程中出现了多次位错形核与发射现象, 初始缺陷对第1和第3对位错的形核与发射影响较小, 而对第2对位错的形核与发射具有明显的推迟作用, 并伴随有裂纹扩展现象; 由于初始缺陷引起薄膜材料内部严重的晶格畸变, 导致系统应变能和位错运动的Peierls应力增加; 裂纹扩展前, 发射第2对位错需要的临界载荷增加, 裂纹失稳后, 位错发射需要的临界载荷下降. 模拟获得的纳米硬度和Peierls应力与实验结果吻合.

In order to study the early stages of plastic deformation with initial defect under the action of an indenter, the nanoindentation processes of the single crystal aluminum thin film were simulated using the quasicontinuum method. The load vs displacement response curves and strain energy vs displacement curves of the single crystal aluminum thin film with initial defect and defect--free were presented, respectively. The nanoindentation processes under influences of the initial defect were investigated about dislocation nucleation, dislocation emission, Peierls stress and load necessary for dislocation emission. The results demonstrate that the load vs displacement response curves experience many times abrupt drops with the emission of dislocations beneath the indenter. The initial defect is found to be insignificant on nucleation and emission of the 1^st and 3^rd dislocation dipoles, but has a distinct effect on the 2^nd dislocation dipole. The nucleation and emission of the 2^nd dislocation dipole is postponed obviously because of the effect of initial defect, and then crack propagation is accompanied. The strain energy of single crystal aluminum thin film and Peierls stress of dislocation dipole beneath the indenter increase with deformation processes due to the severe lattice distortion in the thin film. Before the cleavage occurs, the load necessary for the 2^nd dislocation dipole nucleation and emission increases in nanoindentation with initial defect, on the contrary, it decreases after the cleavage occurred. The nanohardness and Peierls stress in this simulation show a good agreement with relevant theoretical and experimental results.