Effect of core-diameters and shell-thicknesses of Fe3O4/SiO2 composite abrasives on the performance of ultrasound-assisted magnetorheological polishing for sapphire

Abstract

In this paper, the Fe 3 O 4 /SiO 2 (core/shell) composite abrasives with different core-diameters and shell-thicknesses were prepared successfully by adjusting the TEOS dosages in the hydrolysis reaction, and characterized on the aspects of surface morphology, internal structures, phase components and magnetic properties. Then, targeted experiments were conducted to explore the effects of core-diameters and shell-thicknesses of the composite abrasives on the performance of ultrasound assisted magnetorheological polishing (UAMP) for sapphire wafer. The experimental results show that when the shell-thickness of the composite abrasives is reduced from 30 nm to 10 nm, the surface roughness Ra of thus polished sapphire wafers decreases firstly and then increases afterward, which is opposite to the trend of material removal rate (MRR). And Ra and MRR reach the optimal values of 0.276 nm and 2.068 µm/h, respectively, when using the magnetorheological slurry of composite abrasive with 15 nm shell-thickness. It is believed that the formation rate of the softer chemical products on sapphire surface and their mechanical removal rate almost attain a balance in this case. For abrasives with constant shell-thickness of 10 nm, a lower Ra is achieved when using the composite abrasive with a core-diameter of 100 nm, compared to those abrasives with the core diameter of 200 nm or 20 nm. Although the utilization of composite abrasive with larger core-diameter achieves a higher MRR in UAMP, the surface quality of sapphire wafer deteriorates significantly, with many scratches existing on the wafer surface.