Changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites

The changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites were studied. The H, N and O atoms escaped and the carbon content in the carbon fiber increased when the heat treatment temperature exceeds 1200 °C. Meanwhile, the growth of graphite crystallite leaded to stress concentration and reduced the tensile strength of carbon fiber to 2.98 GPa by 1200 °C heat treatment. The active atoms on the surface of the carbon fiber were reduced, thus weakening the bonding force between the carbon fiber and the pyrolytic carbon interface layer and improving the pullout mechanism of the carbon fiber. This result was also observed by synchrotron radiation X-ray computed tomography. The flexural strength of the C/SiC composite increased from 300 MPa without treatment to 364 MPa after 1600 °C heat treatment. •The surface bonds and tensile strength of carbon fiber after heat treatment are analyzed.•The weak interface between carbon fiber and PyC improves the flexural strength of the C/SiC composites.•The pull-out mechanism of carbon fiber in C/SiC composites has been proved by SR-CT.