Sandwich structured SiC_f/Si₃N₄-SiC-Si₃N₄ composites for tunable microwave absorption, mechanical strength and high-temperature tolerance

This work fabricates a high-performance SiC_f/Si₃N₄-SiC-Si₃N₄ composites by architecting a sandwich-structured matrix, where continuous SiC fibers serve dual roles as structural reinforcement and electromagnetic loss medium. In this composites, the outer Si₃N₄ layer promotes impedance matching, while the integrated contributions from SiC fibers, multi-heterogeneous interfaces, and free carbon significantly enhance dielectric loss. Specifically, the low-density (1.33 g/cm³) composites exhibit strong, broad-band absorption in the X and Ku bands, with a minimum reflection loss (RLmin) of −68.55 dB, an effective absorption bandwidth (EAB) of 6.89 GHz, and a flexural strength of 25.76 MPa. As the porosity decreases from 45.6% in S1 to 13.8% in S4, the RLmin and EAB of the composites decrease to −44.13 dB and 5.30 GHz, respectively. The flexural strength significantly increases to 380.53 MPa, achieving a good balance between absorption and mechanical properties. Notably, after oxidation at 1000 °C for 2 h, S4 achieves −70.19 dB (>99.99999% absorption rate) of RLmin and 5.06 GHz of EAB. Simultaneously, the flexural strength is maintained at 227.45 MPa. The SiC_f/Si₃N₄-SiC-Si₃N₄ composites developed in this work combines low density, high-temperature tolerance, high strength and broad-band strong absorption, providing a new strategy for achieving multifunctional applications of ceramic matrix composites.