Enhanced microwave absorbing properties of 2.5D SiC_f/SiC composites fabricated by a modified precursor infiltration and pyrolysis process

SiC_f/SiC composites with enhanced microwave absorbing properties were prepared using a modified precursor infiltration and pyrolysis (PIP) process by the appropriate thermal cross-linking of polycarbosilane (PCS) precursor and decarbonization of SiC fibers. The results reveal that the complex permittivity of both SiC fibers and SiC matrix decreases to a suitable level after the treatments, thus the final composites show an optimized complex permittivity that favors for the impedance matching and attenuation characteristic. The reduction of complex permittivity is mainly attributed to the consumption of excessive carbon in these components by the introduced oxygen during these processes, which also results in the decline of flexural strength of the composites from 266 MPa to 223 MPa. The composites without treatments exhibit a poor reflection loss (RL) value less than -5 dB in the frequency range of 8.2-18 GHz. However, the minimum RL value of the composites with a thickness of 3.1 mm after treatments reaches -23.5 dB and the bandwidth below -10 dB extends to 5.9 GHz.