Tribological performance of Zr–O–N coating in marine environment fabricated by arc ion plating

Zr–O–N coatings with varying oxygen contents were fabricated through arc ion plating, and their microstructure, mechanical properties and tribological behaviour in a seawater environment were evaluated. Zr–O–N composite coatings were fabricated by introducing oxygen elements during the deposition of ZrN coatings. The oxygen content of the coatings increased to 46.88 at% as the oxygen flow rate increased from 0 to 180 sccm. The coatings consisted of ZrN and ZrO₂ phases. Grain size decreased from the micron to the nanometer scale when the oxygen flow rate exceeded 120 sccm. In scratch tests, the coatings prepared with a flow rate of 60 sccm exhibited the remarkable presence of debris and cracks, whereas only microcracks were observed in the coatings deposited under flow rates exceeding 120 sccm. Additionally, all coatings showed no signs of peeling even when subjected to a load of 100 N. The highest hardness value of 26.11 GPa was achieved by the composite coatings deposited under a flow rate of 60 sccm. However, hardness consistently decreased as the oxygen flow rate increased, reaching 17.68 GPa in the coatings deposited under a flow rate of 180 sccm. The tribological behaviour and failure mechanism of the coatings in a seawater environment were also analysed. The composite coatings deposited at 120 sccm exhibited the lowest friction coefficient of 0.19, whereas the those deposited at 180 sccm demonstrated the minimal wear rate of 5.65 × 10⁻⁸ mm³/(N m). When the coating with high oxygen content was rubbed in the seawater environment, the coating components underwent a tribochemical reaction with water to generate Zr–OH and O–OH, which exerted lubricating effects during friction and greatly reduced the friction coefficient and wear rate. The introduction of the appropriate amount of oxygen improved the tribological performance of the Zr–O–N coatings in marine environments effectively.