Revealing the influence of composition and interface on the mechanical and dielectric properties of Si3N4 fiber-reinforced ceramic composites
Si3N4 fiber-reinforced ceramic composites are candidate materials for high-temperature wave-transparent applications, yet the relationships among composition, interfacial characteristics, and mechanical performance remain inadequately understood. This study designs three composites—Si3N4f/BN, Si3N4f/SiO2, and Si3N4f/SiO2–BN—and systematically investigates their performances. The reaction between BN precursors and silanol groups in the SiO2 matrix during fabrication of Si3N4f/SiO2–BN enhances chemical compatibility between fiber and matrix, promoting elemental interdiffusion and forming a thicker interfacial diffusion region. Consequently, the interfacial shear strength of Si3N4f/SiO2–BN is 1.86 and 2.35 times that of Si3N4f/BN and Si3N4f/SiO2, respectively. The stronger fiber-matrix bonding in Si3N4f/SiO2–BN suppresses fiber pull-out, whereas weaker bonding in the other two composites permits it. Si3N4f/BN primarily exhibits fiber bundle pull-out, whereas Si3N4f/SiO2 shows long single-fiber pull-out, indicating improved damage tolerance. In contrast, Si3N4f/SiO2–BN displays typical brittle fracture behavior with minimal fiber pull-out and degraded mechanical properties. Excessive interfacial bonding, together with thermal residual stress arising from thermal expansion mismatch between the Si3N4 fiber and the matrix, degrades flexural and compressive strengths. Moreover, this excessive bonding restricts interfacial debonding and fiber pull-out, leading to a brittle fracture mode. Despite differences in interfacial microstructure, all three composites exhibit good dielectric properties. The use of SiO2 and BN matrices effectively reduces both the dielectric constant and the dielectric loss tangent of Si3N4 fiber-reinforced ceramic composites. These findings provide valuable insights into the design of high-temperature wave-transparent composites operated in extreme environments.