SiCN-based composite ceramics fabricated by chemical vapor infiltration with excellent mechanical and electromagnetic properties

A novel SiCN ternary phase was introduced into porous Si₃N ₄ preform by chemical vapor infiltration from SiCl₄-C ₃H₆-NH₃-H₂-Ar, which was used to fabricate Si₃N₄-SiCN composite ceramics. SiCN was composed of amorphous Si₃N₄ matrix and crystalline SiC nano-particles (with a homogeneous size of ~5 nm) uniformly distributed in amorphous matrix. This distinctive microstructure made the Si₃N ₄-SiCN ceramics not only maintain a high flexural strength of 227 MPa but realize a low dielectric constant and a high dielectric loss, which led to a minimal electromagnetic wave reflection coefficient of -42.6 dB, ranking the best level in the already-reported structural and wave-absorbing ceramic materials for high-temperature applications.