Experimental study on the improvement of surface integrity of tungsten steel using acoustic levitation polishing

Abstract Surface integrity, including surface morphology, roughness, hardness and elastic modulus of tungsten steel, after the acoustic levitation polishing (ALP) process was investigated comprehensively. The mechanism of the ALP technology was first explored, and then numerical study revealed that a standing wave acoustic levitation can be formed in an in-house developed ALP system. Then experimental work was conducted to polish the tungsten steel using the mechanical polishing (MP) and further ALP processes, respectively. It is found that after the further ALP process the surface roughness decreases while some nano-dents can be found on the surface due to the cavitation bubbles induced by the ultrasonic vibration. The surface residual compressive stress is found to be decreased after the ALP process as compared with the MP process due to a cyclic loading of nano-particles on the target surface that reduces the energy stored in the deformed surface region and drives a residual stress relaxation. Similarly, the surface hardness and elastic modulus is found to be increased after the MP process with a work-hardening layer while after the further ALP process the cyclic loading of nano-particles could smooth the surface and refine the dislocation density, thereby reducing the surface hardness and elastic modulus.