Investigation of subsurface defects structural evolution in nano electro machining of copper

Abstract

In nano EM, a voltage is applied between workpiece and tool electrode, generating extremely high electric field (> 10 9 V/m). How the electric field influences the evolution of defect structures under the surface atoms during nano EM process has not been revealed, which is one of the most fundamental problems unsolved in nano EM. To investigate the subsurface defects structural evolution in nano EM, the monocrystalline and polycrystalline coppers were used in molecular dynamics (MD) simulation. The simulation results show that in nano EM of monocrystalline copper, a large number of subsurface defect structures were generated, in which the stacking faults occupied a dominant position. As the dislocation annihilated, the number of subsurface defect structures decreased. However, in nano EM of polycrystalline copper, the grain boundaries produced a significant influence on the evolution of defect structures and atoms removal process. The subsurface defect structures produced in polycrystalline copper were much more than these of monocrystalline copper, and the stacking faults generated in nano EM of polycrystalline copper were limited inside the grains due to the existence of grain boundaries. Furthermore, it is easier to generate a large number of removed atoms in nano EM of polycrystalline copper with a relatively low electric field strength. Sectional view of local atomic structure distribution of polycrystalline copper in nano EM