Green-chemical-jump-thickening polishing for silicon carbide

An ultra-precision machining approach called green-chemical-jump-thickening polishing (GC-JTP) is explored to improve surface accuracy and to achieve high-efficiency polishing for silicon carbide (SiC) ceramics. A new concept of green-chemical-jump-thickening polishing slurry (GC-JTPS) is developed to be an environmentally-friendly fluid with including two essential capabilities: one is the chemistry-induced jump-thickening (JT) mechanism and the other is green-chemical-thickening to enhance removal efficiency. Based on Navier-Stokes's equation and flow continuity equation, the polishing pressure in the GC-JTP process is calculated. On the basis of the rheological dynamics and abrasive nano-indentation analysis, a predictive understanding model to assess material removal rate (MRR) is proposed for the machining controllability of GC-JTP. Under the GC-JTP verification experiments, the maximal proportional error between the testing results and the theoretical calculation stands at only zeta = 7.8%, which proves the accuracy and effectiveness of the new theory MRR in GC-JTP. Through the fitting error, the correction coefficient of alpha = 0.929 should be used in the MRR model in order to better guide the actual processing. The analysis of the maximal cutting depth and the threshold of ductile-brittle transition revealing subsurface damages might generate. Under the optimized polishing conditions of the shearing velocity v(I) = 2.0 m/s, the abrasive size D-a = 2.0 mu m, the gap depth delta(0) = 1.5 mm, the sodium bicarbonate W-P = 15 wt%, the sorbitol W-o = 20 wt% and the abrasive CeO2 W-a = 30 wt%, the SiC ceramics roughness is reduced from Ra 768 nm to Ra 32 nm and the subsurface damages depth can be controlled at the range of 2.5 mu m-4.5 mu m to achieve good surface integrity. The work demonstrates that the GC-JTP is a green and efficient processing method for the low-damage polishing of SiC ceramics.