Effect of fiber heat treatment on microstructure and mechanical properties of 2.5D T700 carbon fiber reinforced SiC composites

T700 carbon fibers were heat treated at 1300 °C and 1600 °C to investigate the effect on microstructure of pyrolytic carbon (PyC) interphase and mechanical properties of 2.5D T700 carbon fiber reinforced SiC (2.5D C_f/SiC) composites, and the untreated carbon fiber acts as a comparison. The flexural strength was measured using three-point bending test and the fracture toughness was evaluated by a single-edge notched beam test. Results show that heat treatment at 1300 °C leads to highest mechanical properties of 2.5D C_f/SiC composites, with the flexural strength in warp direction of 248.6 ±12.3 MPa, the flexural strength in weft direction of 421.6 ±15.1 MPa, and the fracture toughness of 18.7 ±1.7 MPa • m^1/2. Nevertheless, both the unheated and heat treatment at 1600 °C result in a decrease in mechanical properties. The microstructural investigations revealed that the bonding strength between the carbon fiber and PyC is best when the heat treatment of carbon fiber at 1300 °C.