Clarification of the Corrosion and Frictional Behavior of Nitrogen-Doped ta-C Coating in Nitride Acid Solution

The ta-C coating, characterized by a high fraction of sp3 hybridized structure, was considered as a potential protective film for preventing bearing steel corrosion in acidic environments due to its chemical inertness. In this study, it was suggested that incorporating nitrogen into the ta-C coating could increase fracture toughness, ultimately enhancing corrosion resistance and frictional performance in nitric acid solutions. As the nitric acid solution’s concentration increased to pH1, the surface of the ta-C coating exhibited a significant increase in cracks and pitting. Raman spectroscopy revealed the incorporation of nitrogen resulted in an increased sp2 structure, enhancing electronic conductivity, and inversely reducing the corrosion resistance of the ta-C coating in the acid solution. SEM observation unveiled the corrosion process, involving small pitting, crack propagation, and delamination. Ultimately, the rough surface corroded by pH1 HNO3 solution resulted in a higher friction coefficient of 0.083 (with Si3N4 ball as the counterpart), indicating the compromised efficacy of the ta-C coating under pH1 conditions.