Microstructural and mechanical evolution of SiCf/SiC composites in wet oxygen atmosphere above 1000 degrees C

As thermal-structural materials used in gas turbine hot sections, continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites serve under high temperature gas steam corrosion. Therefore the long-term durability of the composites is strongly dependent on the microstructural and mechanical stability under the corrosion. Here, the microstructural and mechanical evolution of SiCf/SiC were investigated in a simulated steam environment (22 vol% H2O + 78 vol% O-2, 1100-1300 degrees C). The results indicate that the temperature plays a major role in the corrosion of the composites. As the temperature rises up to 1200 degrees C, the fiber/matrix interphase (boron nitride) is completely dissipated due to oxidation. Meanwhile, a dense SiO2 scale forms on the composite surface and cristobalite phase tends to precipitate with the increase of temperature. The dissipation of interphase can lead to significant mechanical degradation on the composites. Furthermore, the degradation mechanism was also proposed in terms of stress distribution and fracture morphology. This study can offer new insight for understanding the wet-oxygen corrosion of SiCf/SiC and thus constructing SiCf/SiC with high stability in gas steam.