Rapid fabrication of a silicon modification layer on silicon carbide substrate.

We develop a kind of magnetorheological (MR) polishing fluid for the fabrication of a silicon modification layer on a silicon carbide substrate based on chemical theory and actual polishing requirements. The effect of abrasive concentration in MR polishing fluid on material removal rate and removal function shape is investigated. We conclude that material removal rate will increase and tends to peak value as the abrasive concentration increases to 0.3 vol. %, and the removal function profile will become steep, which is a disadvantage to surface frequency error removal at the same time. The removal function stability is also studied and the results show that the prepared MR polishing fluid can satisfy actual fabrication requirements. An aspheric reflective mirror of silicon carbide modified by silicon is well polished by combining magnetorheological finishing (MRF) using two types of MR polishing fluid and computer controlled optical surfacing (CCOS) processes. The surface accuracy root mean square (RMS) is improved from 0.087λ(λ=632.8  nm) initially to 0.020λ(λ=632.8  nm) in 5.5 h total and the tool marks resulting from MRF are negligible. The PSD analysis results also shows that the final surface is uniformly polished.