Carbon fibers coated with chromium carbide using the liquid metal transfer agent technique

Abstract

Protective coatings of chromium carbide were applied to PAN type carbon fibers by a liquid metal transfer agent (LMTA) technique using copper and tin as transfer agents, and the effect of the coating on the strength of the fibers was evaluated by performing single fiber tensile tests. The coatings were examined metallographically, by X-ray diffractometry, and by scanning electron microscopy. It was found that a tin transfer medium produced a smoother and more uniform coating than a copper transfer medium. The smallest carbide coating obtained using a copper transfer medium was approximately 1 μm, while coatings as thin as approximately 0.14 μm were obtained using a tin transfer medium. It was found that wetting of the fibers by the tin and copper alloys is associated with the spontaneous formation of a carbide layer of significant thickness, after which the carbide layer was found to grow parabolically with time and with an apparent activation energy of 139 kJ/mol. The strength of the carbon fibers decreased with increasing coating thickness.