Coupling CPFE-CA simulation for grain refinement in ultrasonic elliptical vibration diamond cutting of polycrystalline Cu

While microstructure evolution is commonly observed in severe plastic deformation of polycrystalline metals, modulating the cutting-induced grain refinement in subsurface of polycrystalline metals is promising for promoting the performance of machined surface. In this study, we demonstrate the effectiveness of applying ultrasonic vibration assistance (UVA) in effectively grain refinement of polycrystalline Cu in ultra-precision diamond cutting by experiments and multiscale coupling simulations. Specifically, ordinary cutting (OC) and ultrasonic elliptical vibration-assisted cutting (UEVC) experiments of polycrystalline Cu are carried out, and subsequent cross-sectional characterizations of microstructure evolution in subsurface by metallurgical microscope and electron backscatter diffraction, as well as instrumented nanoindentation tests, are performed, which jointly demonstrate significantly promoted grain refinement in subsurface and increased machined surface hardness by UVA, due to increased dislocation density that is beneficial for the nucleation and growth of dynamic recrystallization. In particular, the multi-scale coupling of Crystal Plasticity Finite Element (CPFE) simulation and Cellular Automata (CA) method is firstly established for exploring the microstructural evolution during UEVC and OC of polycrystalline Cu, which is capable of elucidating the underlying correlation of grain refinement behavior in subsurface with characteristics of stress and strain fields in cutting area. Furthermore, the influence of amplitude on the propensity of grain refinement is experimentally and theoretically evaluated, which suggests a critical amplitude of 4 μm that leads to a maximum reduction in grain size by 80.9 % and a maximum increase in machined surface hardness by 55.8 % in UEVC from that in OC, because of the mostly pronounced strain accumulation and dislocation activity. The findings reported in this study demonstrate the effectiveness of applying ultrasonic vibration assistance for modulating the grain refinement accompanying strengthening of machined surface in ultra-precision diamond cutting of polycrystalline metals.