Material removal and micro-roughness in fluid-assisted smoothing of reaction-bonded silicon carbide surfaces

The magnetic fluid-assisted polishing for fuse silica and other optical materials with a high degree of success, and a super-smooth surface (Ra < 1 nm) and subsurface-damage-free layer can be produced. However, the fundamental mechanisms of the process for polishing reaction-bonded silicon carbide (RB-SiC) have not yet been studied in detail. This paper is concerned with the fabrication processability aspect of the RB-SiC components, and investigates results obtained by magnetorheological finishing (MRF) of RB-SiC mirror. It details experimentally the features of different polishing fluids and the characteristics of relative removal rates, analyses the processing limitations of the normal processing techniques and studies the effects of certain processing parameters on surface accuracy. The final surface roughness with an initial value of Ra = 17.58 nm reached 4.03 nm after 15 h of polishing, and then convergent to 1.03 nm after another 7 h fine polishing. Experimental results based on the magnetorheological (MR) fluids show that, a MR fluid containing diamond particles helps to accelerate removal rates. Additionally, by adding a small amount of CeO₂ into the diamond-based MR fluid, it is possible to finish RB-SiC material to a higher level of surface quality.