Effect of fiber surface state on mechanical properties of Cf/Si–O–C composites

Three-dimensional braided carbon fiber reinforced silicon oxycarbide composites (3D-B Cf/Si–O–C) were fabricated via a polysiloxane infiltration and pyrolysis route. The effects of fiber surface state on microstructure and mechanical properties of Cf/Si–O–C composites were investigated. The change of carbon fiber surface state was achieved via heat treatment in vacuum. The results showed that heat treatment decreased carbon fiber surface activity due to the decrease of the amount of oxygen and nitrogen atoms. The Cf/Si–O–C composites fabricated from the carbon fiber with low surface activity had excellent mechanical properties, which resulted from perfect interfacial bonding and good in situ fiber strength. The flexural strength and fracture toughness of the Cf/Si–O–C composites from the treated fiber were 534 MPa and 23.4 MPa m1/2, respectively, which were about 7 and 11 times more than those of the composites from the as-received carbon fiber, respectively.