Phase-transition assisted synthesis of high-strength, low-dielectric fused silica/hBN composite ceramics

Fused silica (SiO2) exhibits exceptional thermal stability and dielectric properties, making it an attractive material for aerospace and military applications. However, its relatively poor mechanical performance has limited its widespread practical utilization. This study proposed an innovative approach to fabricate SiO2-hexagonal boron nitride (hBN) composite ceramics via spark plasma sintering (SPS), leveraging the high-temperature phase transformation of cBN to introduce randomly oriented hBN as a reinforcing phase within the SiO2 matrix. The randomly oriented hBN nanoplates allow cracks to propagate along stronger grain boundaries, rather than along weaker interlayers of hBN, significantly improving the overall strength and fracture toughness of the composite. The maximum flexural strength and fracture toughness achieved are 183.4 MPa and 2.06 MPa m1/2 respectively, which are 3.6 times and 4 times that of fused SiO2. Concurrently, the composites exhibit low dielectric constants (ε = 3.58–3.69) and dielectric losses (tan δ 1 MHz. This work successfully enhanced the mechanical performance of fused SiO2 while preserving its excellent dielectric characteristics, opening new possibilities for its potential applications in advanced structural and functional fields.