Effect of Sintering Temperature on Microstructure and Mechanical Properties of SiO_2f/SiO₂ Ceramic Matrix Composites

The effects of sintering temperature on density, porosity, micromorphology, tensile properties, bending properties and toughness of SiO_2f/SiO₂ ceramic matrix composites were systematically studied, resulting in samples with high strength and high toughness. With increasing sintering temperature, density of the composites is increased. However, the porosity first decreases and then rises, which is attributed to the increase in shrinkage of the matrix and the microcracks produced due to the serious shrinkage at 850 ℃. With increasing sintering temperature and shrinkage, the SiO₂ matrix becomes smoother and smoother. Microstructure of the matrix changed from bonded particles to melting ceramics. Meanwhile, the connection between fiber and matrix becomes stronger and stronger. With increasing sintering temperature, the tensile strength gradually decreased, which is mainly dependent on toughness of the composites. The bending strength first increased, then decreased and reached the highest value of 71 MPa at 700 ℃. Only when the matrix possesses sufficiently high strength, the toughness can fully play its role. At temperatures of 650–750 ℃, tensile properties, bending properties and toughness of the composites can be optimized.