Preparation and mechanical properties of unidirectional boron nitride fibre reinforced silica matrix composites

The unidirectional BNf/SiO2 composites were prepared via sol-gel method, and the structure, composition and mechanical properties were studied. The results show that the composites consist of BN fibres and alpha-cristobalite matrix probably as well as the interface phases of Si3N4 and B2O3. The composites have a density of 1.70 g cm(-3) and an open porosity of 20.8%. The average flexural strength, elastic modulus and fracture toughness at room temperature are 51.2 MPa, 23.2 GPa and 1.46 MPa M-1/2, respectively. The composites show a very plane fracture surface with practically no pulled-out fibres. The mechanical properties of BNf/SiO2 composites at 300-1000 degrees C are desirable, with the maximum flexural strength and residual ratio being 80.2 MPa and 156.8% at 500 degrees C, respectively, while it is a sharply reduced trend as for SiO2f/SiO2 composites. The high thermal stability of BN fibres and self-healing properties caused by the fused SiO2 and B2O3 enable the composites fine high-temperature mechanical properties. (C) 2011 Elsevier Ltd. All rights reserved.