Effect of fiber argon heat treatment on microstructure and properties of SiC/SiC composites prepared by CVI+RMI

The state of the silicon carbide (SiC) fibers in SiC/SiC composites is the key to the properties of these composites. In this study, the effects of Ar treatment of Cansas-III SiC fibers at 1400 °C, 1500 °C, and 1550 °C on the mechanical properties of the composites prepared from them were investigated. The composites were prepared using chemical vapour infiltration combined with reactive melting infiltration. The bending strength of the composites obtained from the untreated fibers was approximately 634.67 MPa. Compared with the untreated samples, the strength of the composites prepared with fiber heat treatment was decreased significantly, and the flexural strength of the composites after fiber treatment at 1400 °C was only approximately 287.02 MPa. Additionally, line scan and transmission electron microscopy results suggested that the surface of the heat-treated fibers could react with the boron nitride interface, forming a brittle reaction layer that was strongly bonded to the fibers. This reaction layer was the main cause of brittle fracture in the composites prepared after heat treatment of the fibers.