Temperature-driven damage transition in C/SiC composites up to 1800 °C via quantitative in-situ μCT

Carbon fiber-reinforced silicon carbide (C/SiC) composites are promising candidates for ultrahigh-temperature structural applications. However, their three-dimensional damage evolution under service-relevant thermo-mechanical conditions remains poorly understood, as existing in-situ X-ray microtomography (μCT) studies are largely confined to lower temperatures and qualitative or low-dimensional analyses. Here, we combine ultrahigh-temperature in-situ μCT, quantitative image analysis, and SEM fractography to elucidate the damage mechanisms of C/SiC composite tested in vacuum at room temperature (RT), 1600 °C, and 1800 °C. A custom-built laboratory μCT tensile stage, capable of stable operation above 1800 °C, enables 3D tracking of damage evolution under these extreme conditions. The reconstructed volumes are analyzed using a multi-parameter framework that integrates pore geometry statistics, grayscale-based phase partitioning, and ellipsoidal crack metrics, establishing quantitative correlations between internal damage states and macroscopic tensile responses. The results reveal a systematic temperature-dependent transition in the governing damage mode: from matrix-dominated quasi-brittle cracking around an intact fiber network at RT, to interface-assisted fiber-bridged cracking with localized matrix detachment and matrix rarefaction at 1600 °C, and finally to rapid crack-pore coalescence and extensive matrix fragmentation within a thermally pre-damaged microstructure at 1800 °C. The results reveal a non-monotonic temperature dependence of damage evolution and mechanical response, suggesting the existence of a potentially favorable high-temperature regime for the C/SiC composite.