Interfacial optimization strategy of local point relax facilitates synergistic enhancement of strength and toughness in 2.5D SiC_f/SiC composites

Continuous SiC fiber reinforced silicon carbide matrix (SiC_f/SiC) composites have received considerable attention because of their high strength, low density and excellent high-temperature resistance. However, the mechanical performance potential of 2.5-dimensional (2.5D) SiC_f/SiC composites remains limited by interfacial property challenges. This study propose an interfacial optimization strategy that tunes local bonding and residual thermal stress (RTS). The spatial distribution of RTS and interfacial bonding behavior was examined using finite element model (FEM) simulations, scanning electron microscope (SEM), fiber push-in tests and Raman spectroscopy. The optimized interphase improved fracture toughness by 277% and flexural strength by 34%, demonstrating the effectiveness of the approach in achieving concurrent improvements in toughness and strength. The mechanisms responsible for these enhancements were clarified through signal analysis of acoustic emission (AE) monitoring and fracture morphology examination. Local point relaxation of the interface and RTS adjustment maintained efficient load transfer and promoted the development of complex three-dimensional stepped crack paths within the SiC matrix, accompanied by crack deflection at the pyrocarbon (PyC) interface. This design facilitates fibers to bear load from the early stages of deformation and resulted in a substantial increase in strength. This approach provides a simple and energy-efficient route to improve the mechanical performance of ceramic matrix composites.