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 promising candidates for high-temperature wave-transparent applications, yet the relationships among composition, interface characteristics, and mechanical performance remain inadequately understood. This study designs three kinds of composites: Si₃N_4f/BN, Si₃N_4f/SiO₂, and Si₃N_4f/SiO₂-BN and systematically investigates their performances. Results reveal that reaction between BN precursors and silanol groups in the SiO₂ matrix during the fabrication of Si₃N_4f/SiO₂-BN enhance the chemical compatibility between fiber and matrix, promoting elemental interdiffusion and forming a thicker interfacial diffusion region. Consequently, the interfacial shear strength of Si₃N_4f/SiO₂-BN is 1.86 and 3.73 times that of Si₃N_4f/BN and Si₃N_4f/SiO₂, respectively. The stronger fiber-matrix bonding in Si₃N_4f/SiO₂-BN suppresses fiber pull-out, whereas the weaker bonding in the other two composites permits it. Si₃N_4f/BN primarily exhibits fiber bundle pull-out, whereas Si₃N_4f/SiO₂ shows long single-fiber pull-out, indicating improved damage tolerance. In contrast, Si₃N_4f/SiO₂-BN displays a typical brittle fracture behavior with minimal fiber pull-out and degraded mechanical properties. The excessive interfacial bonding, together with the thermal residual stress arising from the thermal expansion mismatch between the Si₃N₄ fiber and the matrix, degrades the 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 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.