Microstructures and characterisation ofSiCcomposites fabricated by liquid-phase sintering at relatively lower temperature

Silicon carbide (SiC) matrix composites have been obtained through liquid-phase sintering in air at temperature below 1600°C by adding three kinds of sintering additives, i.e. BaO–Al2O3, BaO–Al2O3–Y2O3 and BaO–Al2O3–CaO, respectively. Effects of type and content of the sintering additive on microstructures and mechanical properties of the composites were investigated. Among these three types of sintering additives, BaO–Al2O3–Y2O3system was determined to be the most effective. Densification occurs in the sintering process, during which a liquid-phase melt forms through reaction between the sintering additives and SiO2 (the oxidation product of SiC). The melt mostly transforms into crystalline oxides, which act as secondary phases and construct a strong bonding interface by connecting with the SiC particles tightly. By adding 30 wt-% BaO–Al2O3–Y2O3 sintering additives, bending strength and fracture toughness of the SiC composites sintered at 1550°C are up to 520 MPa and 6.7 MPa m1/2, respectively.