Tensile-tensile fatigue behavior of plain-woven SiCf/SiC ceramic matrix composites with differently spaced film cooling holes and environmental barrier coatings in high-temperature water-oxygen environments

Abstract

Monotonic tensile behavior of plain-woven SiCf/SiC ceramic matrix composites is investigated at 1200 °C and 1350 °C in water–oxygen environments. In addition, tensile–tensile fatigue behavior at 1200 °C in water–oxygen environments is discussed. Specimens are prepared using chemical vapor infiltration (CVI) process. To enhance their resistance to oxidation in high-temperature water–oxygen environments, environmental barrier coatings (EBCs) are deposited on their surface. Two rows of film cooling holes (FCHs) with 0.5 mm diameter, each row consisting of five FCHs, are designed to compare the effects of two different hole spacings on specimen fatigue and tensile performance. The evolution of strain and normalized modulus during fatigue cycling is investigated in detail. Microstructures of specimens that failed under tensile and fatigue conditions are observed using scanning electron microscopy (SEM), and elemental analyses of specimens after fatigue test failure are performed using energy-dispersive spectroscopy (EDS). The results reveal that tensile strength of specimens with large FCH spacing is greater than that of specimens with small FCH spacing. However, fatigue performance of specimens with small FCH spacing was better than that of specimens with large FCH spacing. This phenomenon is caused by a reduction in strength due to stress concentration effect near holes with small FCH spacing. Holes with large FCH spacing are closer to the specimen edge during fatigue test, leading to high failure rate. The oxidation and embrittlement that surround holes caused by FCHs compromised structural integrity of the specimen and allowed water–oxygen environment to penetrate the specimen interior. This has significant impact on mechanical performance of the material.