Mechanical Response Curve of Duplex SiC f /SiC Cladding Tubes After Steam Corrosion

This study establishes a direct correlation between the mechanical response and oxidation‐induced damage of duplex silicon carbide fiber‐reinforced silicon carbide matrix composites (SiC f /SiC) cladding tubes by analyzing load‐displacement curves obtained from expanding plug tests after exposure to steam at 600°C, 900°C, and 1200°C. The load‐displacement curve of the unexposed duplex SiC f /SiC cladding tube consists of four stages: application of hoop stress to the cladding tube (Stage 1), crack initiation and propagation within the inner SiC f /SiC layers (Stage 2), fracture of the outer chemical vapor deposition SiC (CVD‐SiC) layer (Stage 3), and fiber pull‐out process (Stage 4). The shortening of Stage 2 in the 600°C steam environment indicates that steam reduces the crack tolerance of the specimen. The disappearance of Stages 2 and 4 in the 900°C steam environment indicates that steam causes the specimen to lose crack tolerance and inhibits fiber pull‐out. In the 1200°C steam environment, the reappearance of Stages 2 and 4 indicates that steam corrosion of the specimen is inhibited by the formation of a dense SiO 2 layer. These findings were further confirmed by microstructural observations of the interface between the SiC fiber and the SiC matrix, as well as the fracture surface of the SiC f /SiC composites.