Effect of sintering temperature on microstructure and mechanical properties of boron nitride whisker reinforced fused silica composites

Abstract

Novel BN whisker reinforced SiO2 matrix composites were achieved via hot-pressing at various temperatures, oriented to an enhanced mechanical properties of fused silica. Near full dense BNW/SiO2 composite sintered at 1350 °C presents optimal mechanical properties with bending strength of 124.8 ± 3.4 MPa and fracture toughness of 1.76 ± 0.32 MPa m1/2. The improved bending strength is mainly ascribed to the strengthening effects of BNW and crystallized nanosized α-cristobalite. Indentation crack paths indicate that the crack deflection and interface debonding are the main toughening mechanisms when BNW/SiO2 composite is dense. The desirable dielectric properties (dielectric constant of 3.93 and loss tangent of 0.46 × 10−3), the tiny mean thermal expansion coefficient (1.40 × 10−6 K−1) and thermal diffusivity (1.16 mm2/s) suggest that the BNW/SiO2 composite is definitely a promising high temperature electromagnetic wave transparent material.