Effect of Heat Treatment on the Shear Strength of SiC/PyC/SiC Composites

In this study, the influence of heat treatment on the shear strength of SiC/SiC composites at room temperature and its causes were investigated. After heat treatment, the shear strength decreased, and the higher the heat treatment temperature, the more the shear strength decreased. The reason for the decrease of shear strength was the change of PyC interphase, SiC fiber and SiC matrix after heat treatment. The PyC interphase changed from disordered graphite structure to ordered graphite structure after heat treatment. The size of carbon layer increased and the arrangement of carbon layer became more orderly, which reduced the shear resistance and shear strength of PyC interphase. Meanwhile, the growth of SiC fiber and matrix grains and graphitization of free carbon also could influence the shear strength. Moreover, the thermal decomposition of SiC fiber during the heat treatment led to the overflow of O atoms, which increased the defects and pores on the SiC fiber and reduced the bonding strength between the SiC fiber and PyC interphase.