Isothermal oxidation behavior of reactive hot-pressed TiN–TiB2 ceramics at elevated temperatures

Isothermal oxidation behavior of reactive hot-pressed TiN–TiB2 ceramics with various TiN/TiB2 molar ratios of 2/1, 1/1 and 1/2 was evaluated in the temperature range of 500–800 °C in air. TiN–TiB2 ceramics have a relative density of 97–98.6%. The oxidation weight gains of TiN–TiB2 ceramics depend upon the composition, oxidation temperature and exposure time. The structure and morphology of oxidized layers of TiN–TiB2 ceramics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). During isothermal oxidation of TiN–TiB2 ceramics, anatase and rutile-TiO2 form as the oxidized products at 500 °C. However, phase transformation from anatase to rutile occurs at temperatures between 500 and 600 °C, and therefore rutile-TiO2 becomes the only crystalline phase after oxidation at temperatures of 600–800 °C for 10 h. The oxidation mechanism was proposed with reference to thermodynamically feasible oxidation reactions. The influence of composition on oxidation behavior of TiN–TiB2 ceramics varies with temperature.