Tensile strength, oxidation resistance and wettability of carbon fibers coated with a TiC layer using a molten salt method

Abstract

Titanium carbide (TiC) coating were synthesized on Polyacrylonitrile (PAN)-based carbon fibers by a molten salt method using the molten salt mixture composed of LiCl, KCl and KF as a reaction medium. The surface morphology, tensile strength and oxidation resistance of the uncoated and TiC-coated carbon fibers were investigated. The wettability of these fibers by molten magnesium (Mg) and aluminum (Al) was also examined. TiC coatings obtained have a thickness of approximately 0.05–0.6μm and are found to be uniform and adherent to the carbon fibers. After being coated with a uniform and continuous TiC layer, the tensile strength of the carbon fibers decreases and their oxidation resistance is improved significantly. An increase in the TiC coating thickness leads to the reduction in the tensile strength of the carbon fibers and the improvement of their oxidation resistance. The oxidation activation energy of the carbon fibers increases from 127 to 170kJ/mol after being coated with a 124nm thick layer of TiC. Coating of carbon fibers with TiC also induces an increase in the total surface free energy of the carbon fibers, and as a result the wettability of carbon fibers with molten Mg and Al is improved remarkably. TiC coating is found to be stable at 1000°C in molten Mg. However it is readily decomposed by the molten Al at high temperature, which brings about carbon fibers being attacked by the molten Al and the consequent severe damage of carbon fibers.