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

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 degrees C presents optimal mechanical properties with bending strength of 124.8 +/- 3.4 MPa and fracture toughness of 1.76 +/- 0.32 MPa m(1/2). The improved bending strength is mainly ascribed to the strengthening effects of BNw and crystallized nanosized alpha-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 x 10(-3)), the tiny mean thermal expansion coefficient (1.40 x 10(-6) K-1) and thermal diffusivity (1.16 mm(2 )s) suggest that the BNw/SiO2 composite is definitely a promising high temperature electromagnetic wave transparent material.