Rare-earth element doped Si3N4/SiC micro/nano-composites—RT and HT mechanical properties

Dense Si3N4/SiC micro/nano-composites with varying grain boundary phase composition were fabricated by hot-pressing under the same conditions. Six different sintering aids (Lu2O3, Yb2O3, Y2O3, Sm2O3, Nd2O3 and La2O3) were used. The formation of SiC nano-inclusions was achieved by in situ carbothermal reduction of SiO2 by C during the sintering process. Room temperature, fracture toughness, hardness and strength tended to increase when the cation radius of the rare-earth element used in the oxide additive decreased (i.e. from La3+ to Lu3+). The composite material with Lu2O3 sintering additive showed the highest hardness and had reasonably high fracture toughness and strength. The same micro/nano-composite also possessed the highest creep resistance in the temperature range from 1250 °C to 1400 °C and with loads in the range 50–150 MPa.