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Reaction-bonded silicon carbide (RB-SiC) ceramic, one of the best candidates for large optical mirrors, is difficult to machine because of its high hardness and brittleness. A hybrid process called electrical discharge diamond grinding (EDDG) exhibits potential for improving the machinability of RB-SiC by combining electrical discharge machining (EDM) and diamond grinding. However, this hybrid process leads to damages that differ from those in conventional processes owing to the simultaneous actions of EDM and diamond grinding. In the present study, surface and subsurface damages induced by the interactions between EDM and diamond grinding during the EDDG of RB-SiC were examined. The effect of the discharge energy was considered.The surface and subsurface topographies and microstructures were characterized via scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. The EDM and grinding zones exhibited distinctive surface topographies and different dominant material removal mechanisms. An increase in the discharge energy facilitated ductile removal of the material and decomposition of SiC. Thus, a thinner subsurface damage layer was obtained compared with that in the less-thermally affected zone. The decomposed C and material migration tended to increase with the discharge energy. Owing to the interactions between EDM and diamond grinding, the subsurface was a mixture of amorphous/crystalline C, polycrystalline/nanocrystalline

Thermal-assistant is considered potentially as an effective approach to improve machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by the purposely introduced heat is crucial to obtain high quality machined surface. This paper aims to reveal material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. Material removal mode, scratching hardness, critical depth of ductile-brittle transition, scratching force and friction were discussed under different penetration depths. Size effect of scratching hardness was used to assess the plastic deformation at elevated temperature. A modified model was established to predict the critical depth at elevated temperatures by taking into account of the changes of mechanical properties. The results revealed that the material deformation and adhesive behaviour enhanced the material removal in ductile regime and the coefficient of friction at elevated temperatures.

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