Anodic carbidation of tantalum in molten CaCl2-CaC2

Making a tantalum carbide (TaC) coating on Ta substrates is an effective way to improve the mechanical and anti-corrosion properties of Ta. However, conventional methods for making a TaC coating require high-temperature conditions of over 1600 °C to get a TaC thickness of > 20 μm. Herein, a TaC coating of > 20 μm thickness was prepared on a Ta substrate in molten CaCl 2 -CaC 2 at 850 °C for 4 h. In the molten salt electrolyzer, the Ta plate served as the anode where C 2 2− was oxidized and simultaneously reacted with Ta to form a TaC layer, and Ca 2+ was reduced and alloyed with C to form CaC 2 that can replenish the C 2 2− . The electrolytic TaC exhibited an average hardness of 962 HV that was 6 times of the bare Ta substrate. In the 3.5 wt% NaCl solution, the TaC coating displayed a higher corrosion potential and lower corrosion current density (0.48 V, 1.59 μA cm −2 ) than Ta substrate (0.35 V, 1.85 μA cm −2 ) and the mixtures of TaC and Ta 2 C (0.35 V, 1.78 μA cm −2 ), indicating its better corrosion resistance. The molten salt anodic carbidation may lead to a general way to prepare transition metal carbide coatings with enhanced carburizing kinetics at < 1000 °C. Graphical abstract