Electroplating of chromium and Cr-carbide coating for carbon fiber

Carbon fibers have a poor wetting characteristics and high reactivity with molten metals. These drawbacks cause difficulties in fabricating metal matrix composites reinforced with carbon fibers, and deteriorate their physical and mechanical properties. One solution for these difficulties is to apply protective coating of a carbide layer on the carbon fiber surface. In the present work, carbon fiber of PAN type was electrolytically coated with chromium layer, which was transformed to chromium carbide using in-situ process. The influence of plating parameters such as current density and plating time on the coating thickness of chromium deposited layer was investigated. It was found that the coating thickness increases with increasing current density and plating time. The results reveal that 1 to 2 μm thickness of chromium coating on carbon fibers can be achieved at 0.27 A/cm2 and 15 min. The effect of time on the transformation of chromium layer to chromium carbide was studied. The results indicated that suitable time for complete transformation of the most stable carbide phase Cr3C2 was achieved by heating the chromium coated fiber for 6 h in vacuum at 900 °C. Surface morphology and structure of chromium and chromium carbide coatings were assessed by SEM, XRD and magnetic measurements. Wettability test of uncoated, Cr-coated, and chromium carbide coated carbon fibers were performed using the dipping method, in which, the fibers were immersed in molten aluminum for 5 s, decanted and then weighed. It was found that chromium carbide coated carbon fiber has better wettability than that of chromium coated fiber, but, the uncoated carbon fiber showed non-wetting characteristics.