Liquid film shearing polishing for high quality and low damage tungsten surface: Process optimization, removal mechanism, and processing defects

Surface quality can directly affect the hydrogen/helium retention behavior of tungsten, which will affect the safety and reliability of nuclear fusion reactors. At present, the polishing of polycrystalline tungsten for fusion reactors mainly has problems such as poor removal uniformity, preferential removal of grain boundaries, and processing defects. In this paper, a novel liquid film shearing polishing (LFSP) method was employed to process polycrystalline tungsten surfaces, which combines the shear rheological effect of non-Newtonian fluid with the strengthening effect of the surface-structured polishing plate. Systematic experiments were conducted to investigate the influence of various process parameters on surface quality, such as liquid film thickness, polishing speed, abrasive size, and abrasive concentration. The optimal polishing parameters were determined as a liquid film thickness of 2 mm, a polishing speed of 110 rpm, an abrasive size of 5 μm, and an abrasive concentration of 4 wt%. The surface morphology and roughness of samples were characterized by scanning electron microscopy and white light interferometry. Combined with surface force analysis, the material removal mechanism of LFSP was further revealed. Results show that the abrasive concentration was the critical factor affecting polishing quality, and the tungsten surface after LFSP was flatter than that after mechanical polishing (MP). Additionally, comparative analysis using transmission electron microscopy and positron annihilation spectroscopy revealed that tungsten polished by LFSP has fewer processing defects than MP. It seems that LFSP has a good application prospect in realizing high quality and low damage polishing of polycrystalline tungsten surface.