Formation mechanism of ductile surface in ultrasonic elliptical vibration cutting of tungsten alloys basing on cemented carbide tools

Tungsten alloys are widely employed in the fields of optics, medicine, and high-energy physics due to their exceptional physical properties. However, their inherent hardness, brittleness, and significant phase disparity present substantial challenges for precision & ultra-precision machining, including severe tool wear and surface defects. This research introduces ultrasonic elliptical vibration cutting (UEVC) with cemented carbide tools. It draws from the experience of UEVC of tungsten alloys with natural diamond tools in successfully achieving nanoscale surface. Comparative experiments involving cutting processes with and without the application of ultrasonic elliptical vibration were conducted to evaluate tool wear, chip formation, surface integrity, and the evolution of subsurface microstructures. The findings reveal that UEVC significantly suppresses tool wear and enables the formation of defect-free surfaces (Sa = 115 nm) compared to conventional cutting. The subsurface features a uniform, nanocrystalline layer (similar to 1000 nm in depth, with grain sizes ranging from 50 to 100 nm) and a broader dislocation distribution. This research corroborates the beneficial effects of ultrasonic vibrations in UEVC. It attributes the suppression of surface defects during the material removal process to the continuous ultrasonic impacts exerted by the tool. These impacts promote the proliferation, long-range motion, and interaction of dislocations, leading to a transition from brittle fracture to ductile removal modes, thereby supporting the prevailing "ultrasonic theory."