Evaluation of wear and corrosion resistance in acidic and chloride solutions of Cathodic Arc PVD chromium nitride coatings on untreated and plasma nitrided AISI 4140 steel

Chromium nitride ceramic like coatings are well known for their hardness and wear resistance, especially under severe conditions. When deposited on mild steel, nitriding is required for such applications to create a gradient hardness profile and improve the coating adhesion and the system's mechanical properties. Corrosion resistance is also necessary since these chromium coatings are recommended for applications in the plastic mould and injection industry. Therefore, in this work, the combination of a nitriding without white layer pretreatment and CrN coating was studied in a chloride and an acidic electrolyte, to asses if the diffusion layer also plays an important role as a corrosion protection treatment. Coating microstructure, adhesion to both nitrided and nonnitrided steel, wear resistance, and corrosion resistance in chloride and acidic media were evaluated. For comparison, bare and nitrided steel were also examined. Results indicated an improvement in the adhesion for the duplex treatment (nitriding + CrN). The CrN coating demonstrated a considerably lower coefficient of friction and wear rate compared to both non-nitrided and nitrided steel. Regarding corrosion, the iron nitride layer provides some protection in chloride environments; however, in acidic media, only the CrN coating plays a protective role. In both media, localized attack occurred at sites where the coating had defects, such as pores or pinholes through which the electrolyte comes into contact with the substrate. The duplex treatment proved to be the most effective surface treatment for AISI 4140, achieving excellent tribological properties, good adhesion, and high corrosion resistance in both neutral chloride and acidic solutions.