Effects of microstructures on the material removal mechanisms in nanomachining of polycrystalline materials

Based on the new three-dimensional polycrystal models proposed by the authors [1- 3], atomistic simulations of machining polycrystalline copper by diamond cutting tool have been carried out to investigate the material removal mechanism at nanoscale. Microstructures, including grain cell, grain boundary, triple junction were indentified and the effect of microstructures on workpiece internal stress distribution, machined surface generation, defect structures nucleation and propagation and chip formation have been obtained by large-scale molecular dynamics simulation method. The internal stress at grain boundary and primary deformation zone is much higher than that at grain cell and results in a stress gradient. In particular, the stress field addresses the question whether internal stress responsible for defect structures propagation directions during nanomachining. Our results indicated that for polycrystalline materials the deformation is highly localized. For the large grains in the deformation zone, the material removal mechanism is dislocation-mediated, while for the small grains, grain interface sliding and diffusion tends to be dominated. The atomic analysis shows that the residual defect structures impose a major change on the workpiece physical properties and machined surface quality.