Self-adaption Ta/TaC multilayer coating with fine grains: toward excellent corrosion resistance in aggressive environment

Since engineering equipment applied in aggressive environment always suffers from severe corrosion, self-adaption protective coatings with the excellent and stable anti-corrosion performance are needed urgently. In this work, TaC and Ta/TaC coatings were prepared by reaction magnetron sputtering on Ti6Al4V substrate and fine grains sized under 10 nm were found in TaC layers which form a physical barrier to corrosive ions (compare to column structure in traditional ceramic coatings). Meanwhile, the hardness of TaC and Ta/TaC coatings is about 20–24 GPa which increased surface strength of bare substrates. In EIS measurements, Ta/TaC multilayer coatings show the most superior corrosion resistance compared to TaC coatings and substrate at different temperatures. Besides, low corrosion current density can be detected from polarization tests of Ta/TaC multilayer coatings and stable passivation regions can be found in polarization curves at different temperatures and pH. Furthermore, the mechanism of the anti-corrosion properties is studied. It is found that passivation film on TaC coating would fracture at over potential. On the contrary, the compact passivation film on Ta/TaC coating can keep the coating in good condition and Ta layer plays a significant role in it. This work provides a new thought to design a self-adaption coating with excellent corrosion resistance applied in aggressive environment.