Lightweight C_f/HC–SiBCN composite for multifunctional applications

Carbon fiber composites hold significant promise as electromagnetic wave (EMW) absorbing materials, yet balancing lightweight with excellent mechanical properties, low thermal conductivity, and EMW absorption for multifunctional applications remains challenging. Herein, a novel hydrothermal carbon coated three-dimensional (3D) needled carbon fiber reinforced silicon-boron carbonitride (C_f/HC-SiBCN) composite was developed using an optimized precursor infiltration and pyrolysis (PIP) process combined with impregnation-filtration. By adjusting the precursor concentration and impregnation-filtration cycles, a hierarchical (C_f)/(HC)/(SiBCN) composite with a density of 0.32 g·cm⁻³ was achieved, exhibiting remarkable mechanical properties, including flexural strengths of 14.75 ± 0.43 MPa (xy-direction) and 14.45 ± 0.66 MPa (z-direction), along with a compressive strength of 9.36 ± 0.20 MPa (z-direction). It also demonstrated low thermal conductivity (0.145 W·m⁻¹·K⁻¹) and exceptional EMW absorption, with a minimum reflection loss (RL_min) of −58.13 dB and an effective absorption bandwidth (EAB) of 7.38 GHz. The combination of lightweight, enhanced mechanical properties, low thermal conductivity, and superior EMW absorption capabilities makes C_f/HC-SiBCN composites highly suitable for multifunctional applications.