High-temperature oxidation behavior and oxidation mechanism of C/SiBCN composites in static air

On account of the excellent oxidation resistance of precursor-derived SiBCN ceramics, carbon-fiber-reinforced SiBCN (C/SiBCN) composites are increasingly being used in high-temperature aerospace applications. However, very few studies have investigated the high-temperature oxidation behavior of C/SiBCN composites for their application to high-heat engines. Herein, C/SiBCN composites prepared by precursor infiltration and pyrolysis were tested in static air up to an oxidation temperature of 1700 degrees C. The composites' structural evolution after oxidation and their potential oxidation mechanisms were investigated in detail. The carbon fibers were preferentially oxidized at temperatures in the range of 1200-1500 degrees C and completely oxidized at 1500 degrees C. The oxidation of the fibers at 1500 degrees C resulted in the formation of abundant oxygen channels and consequently a high oxide scale growth rate of 5-7 mu m(2) h(-1) and a large mass loss of 54.6 wt%. At elevated temperatures in the range of 1600-1700 degrees C, a dense SiO2 oxide layer was formed by the sacrificial oxidation of the SiBCN matrix. The oxidation rate of the composites was therefore controlled by the diffusion rate of oxygen through the protective SiO2 oxide layer and the weight loss of the composites decreased to 28.6% after oxidation at 1600 degrees C for 60 min. The structural integrity of the composites was maintained after long-term oxidation at 1600 degrees C.