Mechanistic study on the corrosion resistance of Cr/N films prepared by plasma-based ion implantation and deposition

To mitigate the severe corrosion of M50 bearing steel in chloride-containing environments, Cr/N multilayer films were fabricated via plasma-based ion implantation and deposition (PBIID). By combining magnetron sputtering with high-energy nitrogen ion implantation, a hybrid microstructure consisting of nanocrystalline CrN, Cr, and Cr₂N phases, together with partially disordered regions, was obtained. The effects of multilayer architecture and ion implantation on corrosion behavior were systematically investigated using XRD, TEM, and electrochemical techniques. The results show that increasing the implantation dose suppresses Cr₂N formation while promoting preferred orientations of CrN(220) and Cr(110). The optimized sample exhibits an ultralow corrosion current density of 3.93 × 10⁻⁸ A·cm⁻² and excellent passivation stability in 3.5 wt% NaCl solution. Corrosion is found to initiate preferentially at martensite–carbide interfaces due to local electric-field intensification and chloride accumulation. Furthermore, negatively charged Cr₂O₃ nanoparticles undergo electrophoretic migration and redeposition, forming a secondary passivation layer that effectively suppresses corrosion propagation.