Enhanced machinability of Ni-based single crystal superalloy by vibration-assisted diamond cutting

The machined surface integrity of Ni-based single crystal superalloy is one major factor that affects the performance of its component. It is extremely difficult to achieve a nanometric surface quality by only using ordinary cutting (OC) technology due to the rapid tool wear. Hence, in this work ultrasonic vibration cutting (UVC) with single crystal diamond tool is applied to investigate the machinability of Ni-based single crystal superalloy, including a series of comprehensive investigations on the surface integrity machined in OC and UVC, such as surface roughness, surface morphology, chip formation, tool wear, sub-surface damage, and so on. The experimental results indicated that as compared to OC where finished surface deteriorates seriously due to rapid tool wear, the surface roughness by applying UVC is decreased from Sa 60 nm in OC to Sa 4.815 nm in UVC due to the efficient suppression of tool wear. And the maximum profile error of 1.314 μm achieved in OC is significantly reduced to 0.038 μm with eliminated anisotropic machining effect in UVC. It is also clarified that there are obvious grain refinements and severe plastic deformation near the sub-surface in OC, which is mainly caused by the huge thermo-mechanical loading driven by the tool wear. Moreover, due to the grains are significantly refined in OC, the workpiece material is seriously work hardened. In contrast, the thickness of sub-surface damage is decreased from 2.27 μm in OC to 0.1902 μm in UVC due to the small loading forces, accompanied with more uniform evolution of microstructures.