Interface modification of carbon fibers with TiC/Ti2AlC coating and its effect on the tensile strength

A uniform TiC/Ti2AlC gradient coating was obtained on carbon fibers via an in-situ reaction in molten salts. The results indicated that in-situ growth of TiC/Ti2AlC coating caused strong interfacial bonding and surface defects. In this case, evident stress concentration was induced and cracks penetrated the fiber easily during tensile loading. Thus the tensile strength of carbon fibers was dramatically decreased to 78 +/- 13 MPa. In order to improve the performance of the as-prepared TiC/Ti2AlC-coated carbon fibers, a pyrolytic carbon layer was pre-fabricated on carbon fibers. By introducing pyrolytic carbon layer, the interfacial bonding strength and surface defects were reduced accordingly. These improvements lead to a decrease of stress concentration and cracks propagation, and facilitate the interfacial debonding during tensile loading. As a result, the tensile strength of the fiber was significantly increased to 550 +/- 72 MPa. This fact indicates that pre-fabricating a pyrolytic carbon layer on carbon fibers is an effective method to improve the reliability of the TiC/Ti2AlC-coated carbon fibers. The present work also provides a feasible way to fabricate TiC/Ti2AlC interphase for high-performance Cf/SiC composites.