Shear Thickening Polishing of Black Lithium Tantalite Substrate

Abstract

To achieve high efficiency in the polishing process to obtain a high surface quality of black LT substrate (a kind of soft brittle material), shear thickening polishing (STP),which is a “gentle” finishing process developed in recent years, was employed in this study. The influence of three key parameters in the STP process including polishing speed, diamond abrasive size and diamond abrasive concentration were analyzed. To investigate the potential mechanical effect of the nanometre abrasive, nano-SiO2 abrasive particles were added in the slurry, and the concentration of SiO2 abrasive was also taken as a factor. Taguchi method was utilized to evaluate the influence of the four factors and optimize the polishing conditions. The surface roughness (Ra/Rz) was used as the evaluation index, and the optimized polishing conditions were verified through experiments. Diamond abrasive size has the most significant effect on Ra/Rz, followed by diamond abrasive concentration and then SiO2 concentration, as the polishing speed has been selected and limited in a small variation rang according to the previous study. Based on the S/N average response analysis, the surface quality is the best under the conditions with 8000# diamond abrasive, 5 wt% diamond abrasive concentration, 90 rpm polishing speed and 10 wt% SiO2 concentration. After 4 min polishing, the surface roughness Ra/Rz is reduced rapidly from 200.5/1374.6 to 4.2/22.1 nm without embedded abrasive particles on the surface of the black LT substrate. It also shows that the mechanical effect plays a dominant role in the material removal. A certain amount (10 wt% in this study) of nano-SiO2 can reduce friction between solid colloidal and workpiece, and helps to improve surface quality.