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

2.5D KD-1 SiC fabrics were employed to fabricate SiCf/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 SiCf/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 186 MPa is obtained when the Al2O3 content is 10 wt%, which is 75% higher than that of composites without filler (106 MPa). Both εʹ and ε″ of complex permittivity for the composites decrease as Al2O3 content increases from 0 to 20 wt%. With the incorporation of PyC interphase, the flexural strength of composites with 10 wt% Al2O3 filler is improved from 186 to 234 MPa, and its complex permittivity increases from 20.5-i15.5 to 43-i37.