Effects of carbothermal reduction on microstructure and mechanical properties of PIP-based Cf/SiOC composites

Abstract Two-dimensional carbon fiber reinforced silicon oxycarbide (2D C f /SiOC) composites were fabricated by preceramic-polymer-based prepreg and multiple polysiloxane impregnation and pyrolysis cycles. The structural and property evolution of SiOC matrices and C f /SiOC composites pyrolyzed at various temperatures were examined. Below 1100 °C, the SiOC matrix remained amorphous with an incompletely developed network, but exhibited good thermal stability. Phase separation and carbothermal reduction above 1300 °C generated abundant amorphous SiC 4 structure units presumably with minor β-SiC formation, leading to optimal thermal stability. At 1500 °C, carbothermal reduction and SiC-SiO 2 reactions produced a SiC-dominated matrix with only scarce SiO₂. In C f /SiOC composites, pyrolysis at 1300 °C (C1300) resulted in the highest flexural strength (83.59 MPa), attributed to controlled fiber–matrix interfacial weakening (interphase and/or pre-existing interfacial cracks) that activates the crack deflection and fiber pull-out. Pyrolysis at 1500 °C (C1500) enhanced oxidation resistance through the formation of a dense β-SiC interphase surrounding the fibers, despite increased porosity. Overall, 1300 °C is identified as the optimal pyrolysis temperature for maximizing mechanical performance, whereas 1500 °C is preferable for achieving superior oxidation resistance, underscoring the importance of temperature-specific optimization in PIP-derived C f /SiOC composites for targeted applications.