Molecular dynamics simulation on formation mechanism of grain boundary steps in micro-cutting of polycrystalline copper

[Display omitted] •Molecular Dynamics model was built to investigate the formation of grain boundary steps in micro-cutting of polycrystalline copper.•Sub-grains with transitional crystal orientations formed at the grain boundary due to plowing of the cutting edge and crystal rotation.•The misalignment in the slip directions between sub-grains and original grain resulted in the grain boundary step.•A peak of cutting force appeared at the grain boundary because of the geometrical hardening effect. Three-dimensional molecular dynamics (MD) simulations were performed to investigate the formation mechanism of grain boundary (GB) steps in the micro-cutting of polycrystalline copper. The effects of the GB and misorientation angle on the surface quality were studied. Based on the simulation results, the surface maximum peak-to-valley height of polycrystalline copper was greater than that of single crystal copper owing to the formation of grain boundary steps. The dislocations continuously nucleated on the tool-workpiece interface were stopped and piled up at the GB. As the dislocations piled up at the GB, the dislocations became aligned and formed the sub-grain boundary to minimize the total system energy. Sub-grains with transitional crystal orientations formed at the GB during the micro-cutting of polycrystalline copper for the plowing of the cutting edge and crystal rotation. The misalignment in the slip directions between sub-grains and original grain resulted in the grain boundary step. A peak cutting force appeared at the GB in the cutting of polycrystalline owing to the geometrical hardening effects. It is revealed that the GB has a strong effect on the surface quality of a workpiece during the micro-cutting process.