Study On The Mechanism In Oxidation Assisted Polishing Of Reaction Bonded Silicon Carbide Optical Parts

Technology in machining of Reaction bonded silicon carbide(RB-Si C) has been one of the research focuses in the field of processing of optical mirrors. Since the hardness of RB-Si C is high and the components in RB-Si C are complex, the major problems in machining are low polishing removal rate and poor surface property. Oxidation assisted polishing is a new technology which has been developed for the machining of materials with ultrahigh hardness, such as sapphire, diamond, and so on. Through assisted chemical reaction, the material surface is transformed to oxide layer which has low hardness, and then the oxide is polished. By applying the technology of oxidation assisted polishing into the machining of RB-Si C, there will be a new method for the manufacturing of RB-Si C optical parts. On the basis of feasibility analysis of oxidation assisted polishing of RB-Si C, this thesis founds oxidation models for the three oxidation processes, and then designs and builds each oxidation assisted polishing experimental systems, respectively. Afterwards, the oxide characteristics of oxidized surface and machining specialties of oxidation assisted polishing are studied. The research supplies new technology for the development of machining of RB-Si C. The major research efforts in this thesis include the following points.1. The feasibility of oxidation assisted polishing of RB-Si C is analyzed. By using SEM-EDX to analyze the surface morphology and chemical components, the properties and characters of Si C phase and Si phase in RB-Si C are investigated. Through researches in the oxidative ability of RB-Si C and the polishing property of oxide layer, the feasibility of oxidation assisted polishing of RB-Si C is discussed. The research result indicates that oxidation assisted polishing can solve the problems in machining RB-Si C, such as low material removal rate and poor surface property.2. Oxidation models for RB-Si C are built. Models are built for the oxidation of single crystal Si and single crystal Si C based on inner single-direction diffusion theory in and inner-outer double-direction diffusion theory, respectively. These models are used in the modeling of oxidation processes in anodic oxidation, plasma oxidation, and thermal oxidation of RB-Si C. The thickness of oxide layer in macro lay and oxide morphology in micro lay in each oxidation methods are analyzed, and the machining effect of each oxidation assisted polishing method is forecasted, which will supply theoretical direction for the improvement of removal rate and the advance of surface property in machining of RB-Si C by using oxidation assisted polishing method.3. Experimental systems for oxidation assisted polishing of RB-Si C are founded. According to the requirements of each oxidation method, the suitable experimental systems for oxidation assisted polishing of RB-Si C are designed and built, and the structures of the systems are optimized by taking the adjustment of each process parameters into account. These systems supply hardware supports for the following researches in the morphology characteristics of oxidation surface and the machining speciality of oxidation assisted polishing.4. Morphology characteristics of oxidation surface on RB-Si C are analyzed. By using SEM-EDX, AFM, SWLI interferometer, and other observation and analysis equipment, the morphology characteristics of oxidation surface in the three oxidation methods are investigated by researches on difference of oxidation rate between the two phases, distribution of the oxide, surface roughness after oxidation, and so on. These investigations establish foundation for the following research in the surface property of the oxidation assisted polishing of RB-Si C.5. Machining specialities of the oxidation assisted polishing of RB-Si C are investigated. The thicknesses of oxide layers on RB-Si C are analyzed by using TEM and SWLI interferometer. The Machining specialities of oxidation assisted polishing of RB-Si C are inspected by the theoretical analysis and the experimental validation. These researches supply directive opinions for the applications of each oxidation assisted polishing method in machining process of RB-Si C.