Fracture behavior and damage mechanisms of lightweight C_f/ZrB₂-SiC composites in the thermo-mechanical-oxygen coupling environment

Continuous carbon fiber-toughened ZrB₂-SiC ceramics matrix composites (C_f/ZrB₂-SiC), which combine the high strength of carbon fiber needled preforms with the ultra-high-temperature ablation resistance of ZrB₂-SiC ceramics, exhibit complex responses in the extreme thermo-mechanical-oxygen coupling environments. The fracture behavior and damage mechanisms of the lightweight C_f/ZrB₂-SiC composites were investigated by the thermo-mechanical-oxygen coupling tensile tests. The residual strength after oxidation was found to be synergistically reduced by temperature and pre-tensile load, with a linear negative correlation between pre-tensile stress and residual strength. The needled fibers improve the interlaminar toughness but introduce the localized porosity that accelerates oxygen diffusion and oxidative damage. Under air oxidation at 1100 °C, pre-tensile stress reopens self-healing microcracks, transforming the oxidation kinetics from diffusion-controlled to reaction-controlled regimes. This study can provide an experimental basis and practical guidance for the design of needled fiber preforms to balance oxidation resistance and mechanical properties.