College of Mechanical Science & Engineering, Jilin University, Renmin Street 5988, Changchun, Jilin 130025, China.
Nanoscale Res Lett. 2013 May 4;8(1):211. doi: 10.1186/1556-276X-8-211.
The physical properties of the machining-induced new surface depend on the performance of the initial defect surface and deformed layer in the subsurface of the bulk material. In this paper, three-dimensional molecular dynamics simulations of nanoindentation are preformed on the single-point diamond turning surface of single-crystal copper comparing with that of pristine single-crystal face-centered cubic copper. The simulation results indicate that the nucleation of dislocations in the nanoindentation test on the machining-induced surface and pristine single-crystal copper is different. The dislocation embryos are gradually developed from the sites of homogeneous random nucleation around the indenter in the pristine single-crystal specimen, while the dislocation embryos derived from the vacancy-related defects are distributed in the damage layer of the subsurface beneath the machining-induced surface. The results show that the hardness of the machining-induced surface is softer than that of pristine single-crystal copper. Then, the nanocutting simulations are performed along different crystal orientations on the same crystal surface. It is shown that the crystal orientation directly influences the dislocation formation and distribution of the machining-induced surface. The crystal orientation of nanocutting is further verified to affect both residual defect generations and their propagation directions which are important in assessing the change of mechanical properties, such as hardness and Young's modulus, after nanocutting process.
机械加工诱导新表面的物理性能取决于基体材料内部初始缺陷表面和变形层的性能。本文对单晶铜的单点金刚石车削表面与原始单晶面心立方铜进行了纳米压痕的三维分子动力学模拟。模拟结果表明，在加工诱导表面和原始单晶铜上进行纳米压痕试验时，位错的形核方式不同。位错胚体在原始单晶试样中从压头周围的均匀随机形核位置逐渐发展，而位错胚体则来源于亚表面损伤层中的空位相关缺陷。结果表明，加工诱导表面的硬度比原始单晶铜的硬度软。然后，在同一晶面上沿着不同的晶体取向进行了纳米切削模拟。结果表明，晶体取向直接影响加工诱导表面的位错形成和分布。进一步验证了纳米切削的晶体取向会影响残余缺陷的产生及其扩展方向，这对于评估纳米切削后机械性能（如硬度和杨氏模量）的变化非常重要。
