Oxidation behavior of melt-infiltrated SiC-TiB2 ceramic composites at 500-1300 °C in air

The oxidation behavior of melt-infiltrated SiC-TiB2 ceramic composites at 500-1300 degrees C in air for 32 h was investigated by the isothermal oxidation test. The phase composition and microstructure evolution were studied through examining the surficial and cross-sectional oxide layer by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The oxidized surfaces were covered by scattered TiO2 particles, a continuous B2O3 layer, a B2O3-Al2O3 layer or a mullite layer depending on the oxidation temperature. The thickness of the oxide layer increased from 10 to 30 mu m as the oxidation temperature increased from 900 to 1300 degrees C. The analysis of the weight gain data revealed that the parabolic rate constant of melt-infiltrated SiC-TiB2 ceramic composites generally increased from 4.05 x 10(-3) to 3.16 x 10(-1) mg(2)/cm(4)/s, accompanied with a changed oxidation nature from parabolic to cubic, as oxidation temperature increased from 500 to 1300 degrees C. Formation of continuous B2O3 or Al2O3-based (Al2O3-B2O3 or Al2O3-SiO2) layer were identified on the surface of SiC-TiB2 ceramic composites after being oxidized at 700-1300 degrees C, which was responsible for the excellent oxidation resistance of such composites. The oxidation rate of the melt-infiltrated SiC-TiB2 ceramic composites was controlled by reaction rate of the composites at 500 degrees C and diffusion rate of oxygen through continuous B2O3 or Al2O3-based layer to the unaffected composites at 700-1300 degrees C.