In-situ integrated ultrasonic vibration-assisted grain refinement for suppressing anisotropic diamond cutting behavior of polycrystalline Cu

While inherent heterogeneous microstructures introduce significant anisotropic machining response of polycrystalline metals, reducing the anisotropy by grain refinement is crucial for achieving the ultrahigh surface integrity. In the present work, we propose an in-situ integrated grain refinement strategy of polycrystalline Cu by firstly ultrasonic vibration-assisted diamond cutting for suppressing the anisotropic cutting behavior in subsequent conventional diamond cutting, the two processes of which are carried out within one experimental setup. Specifically, the promoted propensity and underlying mechanisms of cutting-induced grain refinement within subsurface by vibration assistance are discovered by experiments and multiscale numerical simulations. A maximum decrease of average grain size in subsurface from initial 13.5 μm–5.3 μm accompanied by dislocation glide-dominated dynamic recrystallization is revealed. Subsequent in-situ conventional diamond cutting on the fine-grained Cu yields an ultrasmooth surface formation with significantly suppressed grain boundary surface steps, accompanied with a 71.1 % reduction of surface roughness from its coarse-grained counterpart. Subsequent instrumented nanoindentation tests on retaining refinement layer with a 4 μm thickness demonstrate the enhanced mechanical performance of machined surface of fine-grained Cu in terms of increased hardness and elastic modulus. This study demonstrates the feasibility and effectiveness of applying grain refinement by in-situ integrated vibration-assisted diamond cutting for improving the machining performance of polycrystalline metals.