Enhanced mechanical and microwave absorption properties of SiC_f/SiC composite using aluminum powder as active filler

SiC_f/SiC composites have been recognized as an ideal structural and microwave absorbing materials, however the use of SiC_f/SiC composites still restricted at the stage of laboratory research due to their poor mechanical and microwave absorbing properties. In this study, both the bending strength and the complex permittivity for microwave absorbing purpose were successfully improved with the addition of aluminum fillers during the Precursor Infiltration and Pyrolysis (PIP) process of SiC_f/SiC composites. The effects of aluminum powder content on the microstructural evolutions of polycarbosilane (PCS) derived SiC matrix, mechanical and dielectric properties of composites were investigated. The results confirm that the flexural strength of composite reaches the maximum value of 317 MPa when the aluminum content is 10 wt% owing to the higher densification and the generation of β-SiC and Al₄C₃. The values of ε′ and ε′′ can be reduced to suitable levels with good impedance matching and dielectric loss when the aluminum content is 5 wt% attributed to the reduction of free carbon in the matrix. Furthermore, the reflection loss values of composites can be as low as −56 dB and the optimal bandwidth below −10 dB is 3.4 GHz when incorporating 5 wt% aluminum powders.