High-efficiency free-damage electrochemical shear-thickening polishing of single-crystal silicon carbide

A novel electrochemical shear-thickening polishing (ESTP) technique was proposed and successfully applied to polish a 4H-SiC (000-1) workpiece. An in-depth investigation of the anodization mechanism was undertaken and nanoindentation experiments and X-ray photoelectron spectroscopy were conducted to analyze the physical and chemical properties of oxidation product, confirming that the oxidation product was SiO₂ and that the hardness decreased significantly from 21.07 GPa to 0.96 GPa after oxidation. The surfaces of 4H-SiC (000-1) workpieces were processed by ESTP at different voltages to study the relationship between the growth and removal rates of the oxide using scanning electron microscopy and energy dispersive spectrometry. The ideal voltage balancing the growth and removal rates of the oxide was determined to be 6 V based on Faraday's electromagnetic law. After 30 min of ESTP at 6 V, the average surface roughness S_a decreased significantly from 20.5 nm to 1.4 nm and the calculated material removal rate (MRR) was as high as 255.5 nm/min. Finally, the superiority of ESTP was subsequently demonstrated through a comparison with conventional shear-thickening polishing (STP) showing that ESTP exhibited an excellent polishing effect and effectively overcame the limited MRR of STP. In addition, the removal of subsurface damage was observed during the polishing process and confirmed by transmission electron microscopy. The observed phenomena demonstrate the efficient and nondestructive nature of the proposed ESTP technique, which represents an ideal polishing technology for hardy and brittle materials such as SiC.