Silicon carbide micro-reaction-sintering using micromachined silicon molds

This paper describes a novel process,"silicon carbide micro-reaction-sintering," to reaction-sinter three-dimensional silicon carbide microstructures using micromachined silicon molds. This process consists of micromachining of silicon molds, filling the molds with material powders (cr-silicon carbide, graphite and phenol resin), bonding of the molds with adhesive, reaction-sintering by hot isostatic pressing (HIP) and release of a reaction-sintered workpiece from the mold by wet etching. Using this process, we have successfully fabricated silicon carbide microrotors with a diameter of 5 and 10 mm for a micromachined gas turbine. The shape of the silicon molds could be well transferred to the reaction-sintered samples within 3% shrinkage of the size. We used scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis to evaluate the reaction-sintered samples. They revealed the generation of beta -silicon carbide by the reaction between silicon and graphite in reaction-sintering process. They also revealed the presence of residual free silicon in the reaction-sintered samples due to low concentration of graphite in the material powders. We measured mechanical properties such as bending strength and Vickers hardness, The reaction-sintered samples had approximately 70% bending strength and 70-80% Vickers hardness compared with those of a commercially-available reaction-sintered silicon carbide.