Study on the fiber/matrix interface modification of Si3N4 f/SiO2 composites with polymer derived double-layer coatings

Strong fiber/matrix interface combination is a tricky problem for Si3N4 f/SiO2 composites to be applied as antenna windows in harsh thermal conditions. In this study, perhydropolysilazane derived silicon oxynitride coating was prepared on the surface of Si3N4 fiber pre-coated with BN coating to generate a BNc/SiONc doublelayer interface. The optimized SiON coating thickness is -140 nm, while the corresponding tensile strength of the Si3N4 f/BNc/SiONc fiber is 1.21 GPa. The composites with optimised BNc/SiONc coatings possess improved bending strength (-20% up) and fracture toughness. The double-layer coatings benefit to crack propagation and reduced the penetration crack along the fibers. In addition, good thermal stability and dielectric performance (epsilon = 3.24-3.28 at 12-18 GHz) are indicated.