Mechanical and dielectric properties of 2.5D SiC_f/SiC-Al₂O₃ composites prepared via precursor infiltration and pyrolysis

2.5D KD-1 SiC fabrics were employed to fabricate SiC_f/SiC composites by a modified polymer infiltration and pyrolysis (PIP) process, using Al₂O₃ as inert filler. The effects of Al₂O₃ content on the microstructure, mechanical and dielectric properties of SiC_f/SiC-Al₂O₃ composites were investigated. The results reveal that the infiltration efficiency is remarkably improved by incorporating the Al₂O₃ filler into the PIP process. The Al₂O₃ filler can effectively compensate for volume shrinkage to form dense matrix and act as strengthening phase to deflect microcracks, thus a maximum flexural strength of 186MPa is obtained when the Al₂O₃ content is 10wt%, which is 75% higher than that of composites without filler (106MPa). Both ε' and ε″ of complex permittivity for the composites decrease as Al₂O₃ content increases from 0 to 20wt%. With the incorporation of PyC interphase, the flexural strength of composites with 10wt% Al₂O₃ filler is improved from 186 to 234MPa, and its complex permittivity increases from 20.5-i15.5 to 43-i37.