Heat-Treatment-Regulated X-band Microwave Absorption Performance of SiCf/SiCN Ceramic Matrix Composites

High-performance structural-functional materials are essential to address electromagnetic interference in aerospace and 5G/6G telecommunications.In this work, SiCf/SiCN ceramic matrix composites were fabricated by combining chemical vapor deposition (CVD) of a BN interphase with the polymer impregnation and pyrolysis (PIP) process. The effects of heat-treatment temperature (1300-1500 °C) on the microstructural evolution, dielectric response, and microwave absorption performance in the X-band (8.2–12.4 GHz) were systematically investigated. The results demonstrate that heat treatment promoted the transition of the SiCN matrix from an amorphous-dominated state to a crystalline-enhanced structure (SiC and Si3N4), while also increasing the porosity and the number of defect structures and heterogeneous interfaces. Benefiting from a better balance between impedance matching and dielectric loss, S1400 exhibited the best overall microwave absorption performance. At a thickness of 2.0 mm, the minimum reflection loss reached −26 dB. At a thickness of 2.4 mm, the minimum reflection loss was −24 dB, with an effective absorption bandwidth of 2.5 GHz. Its excellent microwave absorption performance is mainly attributed to the synergistic effects of moderate conduction loss, enhanced interfacial polarization, and multiple scattering induced by pores and microcracks. Furthermore, a periodic truncated-cone structure constructed based on the electromagnetic parameters of S1400 achieved a remarkable reflection loss of −48.9 dB across the 4–40 GHz range, indicating that structural design can further improve the broadband microwave absorption potential. This study provides experimental and theoretical framework for the design of integrated high-temperature structural microwave-absorbing ceramic matrix composites.