Anodic polarization accelerated titanium carbide coating formation in molten salt

Salt-thermo-carburizing (STC) by simply soaking transition metals in molten CaCl 2 -CaC 2 is an effective method to prepare carbide coatings on metallic substrates. Herein, more efficient anodic carburizing (AC) is demonstrated in the same molten salt via electrochemical oxidation of C 2 2− , which greatly accelerating the growing rate of the carbide coating. Typically, TiC coating was successfully prepared on titanium anode coupled with a graphite cathode. The effect of current density, reaction temperature, and reaction time on the composition, morphology, and structure of the carbide coating was systematically investigated. The results demonstrate that anodic carburizing enables a dense, uniform TiC coating formation with a relatively high rate. The growing kinetics of TiC follows parabolic law for both of AC and STC process, but the rate constant of AC (17.61 μm h -0.5 ) is much higher than that of STC (5.17 μm h -0.5 ). It only takes ~0.7 h for the AC process to get a TiC coating with a thickness of 15 μm at 875 °C, but takes >8 h for the STC process. The applied anodic polarization improves the interfacial carbon potential gradient by promoting the C 2 2− oxidation, thereby accelerating the growth rate of TiC coatings.