Improved oxidation resistance of SPS sintered Si₂BC₃N ceramics with disilicides (MoSi₂, HfSi₂, TaSi₂) addition

Although Si₂BC₃N ceramics have excellent oxidation resistance under high temperature (1000–1400 °C) in both dry and moist air, the oxidation resistance under higher temperatures (above 1400 °C) are still challenged due to the quick escape of volatile CO, B₂O₃ and SiO. Generally, the formation of stable and continuous protective layer is critical for improving the oxidation resistance under high temperature. Given the chemical compatibility and the formation of nonvolatile oxides after oxidation, the present work mainly investigated the influences of disilicides addition, including MoSi₂, HfSi₂ and TaSi₂, on the phase composition and oxidation resistance of Si₂BC₃N ceramics sintered by SPS. The results showed that nano sized disilicides would transform into carbides (MoC, Mo₅Si₃, and TaC) and oxides (TaO, HfO₂) during sintering process. The preferential oxidation of Mo and Hf related phases and the formation of much stable oxidation layer could improve the oxidation resistance significantly, where the oxidation layer thickness was less than 10 μm after testing at 1600 °C for 3 h.