The microstructural evolution, mechanical and dielectric properties of BNW/SiO2 ceramics

Abstract

The boron nitride reinforced fused silica (BN/SiO2) ceramics are excellent high-temperature wave-transparent candidates, but encumbered by the unsatisfactory reliability and economy until now. Herein, promising BN whisker reinforced SiO2 (BNW/SiO2) ceramics are fabricated via hot-pressing, aiming to provide fundamental insight into their microstructural evolution, mechanical and dielectric properties. The densification behaviour and microstructural evolution are characterized by step-testing the sintering temperature and the BNW content, determining that SiO2 matrix undergoes crystal nucleus breeding (≤1300 °C), followed by nucleation and growth (＞1300 °C), and BNW presents a uniform and stable structure (≤1350 °C) and skin-core structure (1450 °C), respectively. The underlying strengthening and toughening mechanisms are elucidated through constructing a multilevel porosity dependence of mechanical behaviour associated with the BNW content. Compared with 5 wt. % BNW/SiO2 ceramic sintered at 1350 °C (S5-1350), the lightweight 20 wt. % BNW/SiO2 ceramic sintered at 1300 °C (S20-1300) exhibits 619.1% higher machinability parameter while maintaining the mechanical properties. Moreover, the lightweight S20-1300 possesses a low dielectric constant (ε) of 3.77, loss tangent (tan δ) of 1.25 × 10-3 and coefficient of thermal expansion (CTE) of 1.34 × 10-6 K-1. The insights obtained from this study would help to advance the application of BN/SiO2 ceramics in high-temperature radome.