Synergistic effect of ceria-zirconia nanoparticles and hBN nanosheets incorporation on the corrosion resistance of MoS2 solid lubricant coatings

Molybdenum disulphide is a conventional solid lubricant material due to their layered crystal structure enabling easy shearing resulting in low coefficient of friction. Even though MoS2 is highly lubricating, the corrosive nature of this dry solid lubricant limits its application, especially in oxidizing and humid environment. The present work focuses on the improvement of corrosion resistance properties of MoS2 nanosheets coatings, while maintaining its excellent anti-friction properties by incorporating hexagonal boron nitride (hBN) nanosheets and ceriazirconia nanoparticles (CZ NPs). A hybrid structure consisting of MoS2, hBN and CZ NPs was prepared as a composite and multilayer coating. The coatings were characterized by FE-SEM, XRD, Raman spectroscopy and XPS. The inclusion of hBN and CZ NPs did not significantly alter the coefficient of friction (CoF) and wear for the composite and multilayer coatings, as determined by the tribological investigations conducted using high frequency reciprocating rig (HFRR). The MH30-CZ composite coatings showed higher CoF compared to MH30-CZ multilayer coatings, with only 7.75 % increase as compared to pure MoS2 coating. The composite structure and multilayer structure showed high long-term corrosion resistance while the latter had the highest resistance to corrosion and oxidation. The hybrid multilayer structure had the lowest corrosion current density and corrosion rate with 167 % enhancement in total impedance. In the hybrid coating, hBN acts as a physical and insulating barrier to the flow of corrosive ions and charge transfer while CZ NPs forms insoluble precipitates which further impedes the corrosion. The galvanic cell formation of MoS2 with steel was suppressed due to the presence of insulating CZ NPs layers. The synergic effect of hBN and CZ NPs resulted in high long-term corrosion resistance of the coating.