Unveiling the underlying mechanism of ultrasonic vibration assisted machining: Tip-based single asperity nanoscratching experiments and insights from molecular dynamics simulations

To elucidate the underlying material removal mechanism in ultrasonic vibration-assisted manufacturing, ultrasonic vibration-assisted singe asperity nanoscratching (UVANS) was performed on a single crystal 4H-SiC using a diamond tip with a nanometer-scale curvature radius, integrated with an atomic force macroscope and an ultrasonic vibration platform. The singe asperity experimental results indicated that ultrasonic vibration significantly increases the removal rate while reducing the friction force compared to conventional nanoscratching (CNS) under the same loading conditions. Through carefully designed equivalent experiments, interfacial contact dynamics analysis, and molecular dynamics simulations, it was revealed that the improvement in material removal efficiency by UVANS is primarily contributed to increased contact frequency/velocity, improved processing energy, and intensified frictional flash heating. High-resolution transmission electron microscopy was employed to characterize the atomic structures beneath the machined surface for both CNS and UVANS cases, revealing that introducing ultrasonic vibration at the processing interface effectively mitigates surface and subsurface damage and leads to improved surface quality. The synergistic effects of ultra-high speed/ultra-short contact time, significant reduction in frictional force/contact area at the processing interface, along with a more homogeneous stress distribution in the contact micro-regions, collectively lead to substantial enhancements in both surface and subsurface quality in UVANS case. This study not only provides valuable insights for optimizing ultrasonic vibration-assisted tip-based nanofabrication but also has implications for improving ultrasonic-assisted ultra-precision surface manufacturing.