Revealing the influence of composition and interface on the mechanical and dielectric properties of Si3N4 fiber-reinforced ceramic composites

• • Si3N4f/SiO2–BN achieves interfacial shear strength 1.86× and 2.35× that of Si3N4f/BN and Si3N4f/SiO2, respectively, due to a thicker interfacial diffusion region. This over-strong bonding suppresses fiber pull-out and causes brittle fracture, reducing flexural and compressive strengths—critical for load-bearing radome applications where damage tolerance is paramount. • • Si3N4f/BN exhibits the highest flexural strength among the three composites, while Si3N4f/SiO2 demonstrates superior damage tolerance via long single-fiber pull-out enabled by higher porosity. This trade-off between strength and toughness dictates material selection for hypersonic vehicle antenna windows, where both mechanical integrity and thermal shock resistance are required. • • All three composites maintain dielectric constants < 4.5 and dielectric loss tangents < 0.005 up to 1100 °C, confirming excellent high-temperature wave transparency. The use of BN and SiO2 matrices effectively reduces dielectric constant and loss tangent, with fiber-matrix interface having minimal influence on dielectric properties—validating their use in extreme-environment communication systems. • • Thermal expansion mismatch between Si3N4 fiber and matrix induces residual stress that, combined with excessive interfacial bonding, degrades mechanical performance in Si3N4f/SiO2–BN. This highlights the necessity of tailoring interfacial chemistry to balance bonding strength and residual stress for optimized composite performance.