Effects of silica/alumina on mechanical, dielectric and microwave absorption properties of the SiCf/mullite composites

Silica/alumina (Al₂O₃/SiO₂) can form mixed crystal phase in a wide range of composition ratio, which affects the properties of the mullite. Thus, the effects of mass ratio (m_SiO2/m_Al2O3) on microstructure, mechanical, dielectric and microwave absorption properties of SiC fiber reinforced mullite matrix (SiC_f/Mullite) composites are studied. With the variation of m_SiO2/m_Al2O3 from 3/1 to 1/3, the crystallinity of the product increases, and the porosity decreases first and then increases, while density increases first and then decreases. When m_SiO2/m_Al2O3 is 1/2.57, the porosity and density of the composite reach 13.1% and 2.11 g·cm⁻³ respectively, and the complex permittivity reaches the maximum of 5.48-j3.1 at 10 GHz. When m_SiO2/m_Al2O3 is 1/3, the flexural strength and failure diaplacement of the SiC_f/Mullite composite reaches 219 MPa and 0.36 mm respectively, and the dielectric constant of the composite decreases under the effect of matrix composition and porosity. When m_SiO2/m_Al2O3 is 1/2.57, the minimum reflection loss is -38 dB at a thickness of 2.9 mm at 12 GHz, the reflection loss is less than − 10 dB in the whole X-band at a thickness of 3.4 mm. The systematic consideration of mechanical and microwave absorption properties of the composites indicates that the SiC_f/Mullite composites prepared by m_SiO2/m_Al2O3= 1/2.57 and 1/3 could be used as effective microwave absorption materials.