S042011 超高温域におけるZrB_2-SiC-ZrCの酸化メカニズムの解明

Abstract

ZrB_2-SiC-ZrC (ZSZ) ceramics with four different compositions containing 16 vol% SiC were sintered by hot press and spark plasma sintering. The relative density of all the ZSZ ceramics made by both methods reached around 95%. These ZSZs oxidized continuously up to 1500℃ using thermo gravimetric analysis. The ZSZ containing the highest ZrB_2 indicated the lowest weight gain, and that containing the highest ZrC indicated the highest weight gain. After the oxidization, the microstructure of the samples' surface and cross section were studied by X-ray diffraction analysis, optical microscope and field emission scanning electron microscope along with X-ray dispersive spectroscopy. Results of these analyses for the samples revealed that ZSZs have oxidation resistance due to formation of the oxide scale, which act as the barrier for oxygen diffusion into the unoxidized substrate. In the next study, ZSZ ceramics was heated continuously up to 1700℃ in air using zirconia ultra high temperature furnace. Oxidation test was earned out at 1700℃ by IR image furnace. The surface of the oxidized specimen had a number of bubbles and appeared to be covered with zirconia and glassy compounds. These results suggest that the active oxidation of SiC was occurred at the interface between the oxide scale and the substrate. In addition, because the spallation between the oxide scale and the substrate was not occurred, it was implied that ZSZs showed the resistance to the active oxidation of SiC.