High-temperature oxidation behavior of Ti_3AlC_2 in air

Not only the isothermal oxidation behaviors at 900-1 300℃for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-1 300℃for 30 cycles, were investigated by using TG, XRD, SEM. The isothermal and cyclic oxidation behaviors generally follow a parabolic rate law. The parabolic rate constants of the former increased from 1.39×10-10 kg2/(m4·s) at 900℃to 5.56×10-9 kg2/(m4·s) at 1 300℃. The calculated activation energy is 136.45 kJ/mol. The oxidation products areα-Al2O3 and little TiO2 at 900-1 000℃, however when the temperature is raised up to 1 200℃, TiO2 partially reacts to Al2TiO5, and the reaction is completed at 1 300℃. This demonstrates that Ti3AlC2 has excellent oxidation resistance and good thermal shock because the dense continuous oxide scale consists of massα- Al2O3 and little TiO2 and/or Al2TiO5. Generally, the oxide scale is grown by the inward diffusion of O2- and the outward diffusion of Ti4+ and Al3+.

Not only the isothermal oxidation behaviors at 900-1 300 ℃ for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-1 300 ℃ for 30 cycles, were investigated by using TG, XRD, SEM. The isothermal and cyclic oxidation behaviors generally follow a parabolic rate law. The parabolic rate constants of the former increased from 1.39×10^-10 kg^2/（m^4·s） at 900 ℃ to 5.56×10^-9 kg^2/（m^4·s） at 1 300 ℃. The calculated activation energy is 136.45 kJ/mol. The oxidation products are a-Al2O3 and little TiO2 at 900-1 000 ℃, however when the temperature is raised up to 1 200 ℃, TiO2 partially reacts to Al2TiO5, and the reaction is completed at 1 300 ℃. This demonstrates that Ti3AlC2 has excellent oxidation resistance and good thermal shock because the dense continuous oxide scale consists of mass a-Al2O3 and little TiO2 and/or Al2TiO5. Generally, the oxide scale is grown by the inward diffusion of O^2- and the outward diffusion of Ti^4＋ and Al^3＋.