Thermal and mechanical responses of porous C/SiC and SiC ceramics during phase-change transpiration cooling under non-uniform heat flux

Transpiration cooling is a critical thermal protection strategy for high-speed flight. The existing literature has explored the transpiration cooling with sintered metallic powder or ceramic composite. However, there are few articles exploring the cooling disparities and mechanical degradation mechanism under a wide range of thermal boundaries, especially the evaluation of transpiration performances between different ceramic composites. To bridge these gaps, this study experimentally investigates and compares the phase-change transpiration cooling and mechanical performances of porous woven C/SiC and particle-sintered SiC ceramics under non-uniform oxyacetylene flame at various oxygen/fuel (O/F) ratios. With sufficient coolant (ṁ _c = 4.0 g/min), porous SiC exhibits lower surface temperatures and more uniform cooling due to its higher thermal conductivity. Under lower coolant mass (ṁ _c = 1.5 g/min), their behaviors diverge sharply: C/SiC suffers irreversible local overheating, while SiC displays periodic temperature oscillations (period: 209 s-320 s). Moreover, when O/F = 1.2 and ṁ _c = 2.0 g/min, SiC shows a lower peak temperature and a larger high-temperature surface area, compared to C/SiC. In addition, intense pressure pulses (56.4 kPa) generate inside porous SiC due to vapor blockage, far exceeding the pressure changes inside the C/SiC. The SiC fractures from thermal fatigue due to periodic thermal stresses and pressure pulse (O/F = 1.0). In contrast, the woven porous C/SiC exhibits superior mechanical strength under high temperature, with the maximum strength (189 MPa) higher than that of the porous SiC (10.6 MPa), yet suffers from hydro-oxidative corrosion. These findings provide essential guidance for selecting materials for advanced thermal protection systems.