Atomic insights into nano-cutting behavior of single-crystal CuZn alloy

Coupled effects of crystal orientation and cutting depth have an essential influence on the evolution of microscopic defects during nano-cutting process. However, few studies report the synergistic effect of these two factors on the material removal behavior at nano scales, and especially the formation mechanism of stacking fault tetrahedra is still unclear. In this paper, the material dynamic deformation and removal behavior, surface microstructural evolution, and stress distribution characteristics of single-crystal CuZn alloys are investigated with dislocation theory analysis and molecular dynamics simulation during nano-cutting. The work-hardening properties of the machined surface are characterized with nanoindentation tests to reveal the microscopic formation mechanism of stacking fault tetrahedra. The results indicate that the [111] crystal orientation is categorized as a cutting-hard orientation due to its small Schmid factor and difficult activation of the slip system, and its cutting force and cutting temperature are significantly higher than the other crystal orientations. On the contrary, the [100] crystal orientation exhibits as an easy-to-machine orientation. A cutting depth of 3 nm with relative tool sharpness of one is the critical depth at which the material removal mechanism is transformed. In addition, the [110] crystal orientation presents a higher depth of subsurface damage than the other crystal orientations, while the effect of machining hardening is increased by 31.3 %. The main causative factor for work hardening is the formation of stacking fault tetrahedral, which is formed by a different mechanism than conventional quenching or irradiation-induced supersaturated vacancies to form Frank dislocation rings. The cutting depth is more sensitive than crystal orientation to the variation of Von Mises stress and hydrostatic stress. This paper elucidates the key role of the synergistic effect of crystal orientation and cutting depth in reducing surface roughness, exploiting work-hardening effect, optimizing stress distribution, and improving machining quality. Moreover, the research can provide a new perspective for the study of microscopic cutting behavior and material deformation mechanism for nanoscale single-crystal CuZn alloy.