Oxidation behavior and subsequent mechanical properties of SiC/BN/ SiBCN composite after exposure to steam at high temperature

Despite its importance when considering jet engine environments, the behavior of ceramic matrix composites following high temperature exposure in steam has received much less attention than in air. The present study investigates the oxidation behavior and the corresponding mechanical properties of a SiC/BN/SiBCN composite after exposure to steam at 950 degrees C, 1050 degrees C, 1200 degrees C and 1350 degrees C for 30 h. The SiBCN matrix shows crack-filling behavior, whereby microcracks are filled with oxide hindering internal oxidation of the composite. The oxide layers formed on both the SiC fiber and the SiBCN matrix exhibit a double layer structure, with the outer layer being more porous. With increasing temperature, the BN interphase is consumed and replaced by borosilicate glass that bonds the fiber and matrix. This alters the debonding location from the fiber/BN interface to the BN/ SiBCN matrix interface. Three-point bending test shows the composite retains good flexural strength and a tough failure response even after exposure to steam at 1350 degrees C. Single fibre push-out test shows a slight increase in interfacial shear strength with increasing thermal exposure.