Simple and efficient densification of SiCf/SiC composites by gradated concentration polymer infiltration and pyrolysis

Silicon carbide fibre reinforced/SiC matrix (SiCf/SiC) composites are promising materials for aerospace applications, due to their excellent high-temperature stability and mechanical properties. Here we have developed a novel Gradated Concentration Polymer Infiltration and Pyrolysis (GC-PIP) method whereby repeated increasingly concentrated polycarbosilane/xylene solutions were used every PIP cycle to fabricate SiCf/SiC composites with low porosity (<6% according to X-ray μ-CT). The resulting SiC matrix in composites was highly nano-crystalline, having a composition, crystallinity and Young's modulus similar to the 2nd Generation SiC fibres. No damage to the fibres or the interphase was observed after processing of pressure-free pyrolysis at 1300 °C. The resulting composite displayed enhanced mechanical properties under three-point bending, giving a tough fracture behaviour with extensive crack deflection and fibre pull-out. This novel method can be easily applied to other precursors and fibres, and is a promising approach to fabricating low porosity SiCf/SiC composites displaying excellent mechanical properties.