Oxidation behavior and kinetics of in situ (TiB2 + TiC)/Ti3SiC2 composites in air

The isothermal oxidation behavior of in situ (TiB₂ + TiC)/Ti₃SiC₂ composite ceramics with different TiB₂ content has been investigated at 900-1200 °C in air for exposure times up to 20 h by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. The oxidation of (TiB₂ + TiC)/Ti₃SiC₂ composites follows a parabolic rate law. With the increase in TiB₂ content, the oxidation weight gain, thickness of the oxidation scale, and parabolic rate constant decrease dramatically, which suggests that the incorporation of TiB₂ greatly improves the oxidation resistance of the composites. With the increase in oxidation temperature, the enhancement effect becomes more pronounced. Due to the incorporation of TiB₂, the oxidation scale of (TiB₂ + TiC)/Ti₃SiC₂ composites is generally composed of an outer layer of coarse-grained TiO₂ and an inner layer of amorphous boron silicate and fine-grained TiO₂. Only the dense inner layer formed on the surface acts as a diffusion barrier, retarding the inward diffusion of O, and consequently contributing to the improved oxidation resistance of the (TiB₂ + TiC)/Ti₃SiC₂ composites.