Microstructure, mechanical properties and thermal expansion behavior of M55J C_f/SiC-SiBC composites with different interphase thicknesses

For space gravitational wave detectors, ultra-high-precision detection requires structural materials with excellent dimensional stability, and the development of near-zero expansion materials has emerged. In this work, M55J C_f/SiC-SiBC with different PyC thicknesses were fabricated, and the mechanical and expansion properties were studied. The compatibility between near-zero expansion and high load-bearing capacity was realized by regulating the interphase thickness. The results show that, as PyC thickness increases, both the intra-bundle matrix content and the proportion of fiber corrosion area decrease. As interphase thickness increases from 180 to 420 nm, the tensile strength increases from 159 ± 12–254 ± 18 MPa and then decreases to 229 ± 3 MPa. The CTE of M55J C_f/SiC-SiBC decreased from 0.09 × 10⁻⁶ to −0.31 × 10⁻⁶ K⁻¹. Through interphase thickness optimization, the macroscopic expansion is transformed to micro-zone deformation and the relative deformation between fiber and matrix can be coordinated, therefore the near-zero expansion property can be realized.