Synergistic lubrication effect of OLC and MoDTC for reducing friction and wear of MAO ceramic coating on TC4 alloy

Abstract

TC4 titanium alloy has been widely used in the automotive field due to its exceptional properties. However, inherent defects such as low hardness and poor wear resistance for TC4 alloy limited its wider application. The microarc oxidation (MAO) technique was employed in this paper to prepare MAO coatings on TC4 titanium alloy. The microstructure, phase structure, mechanical properties, and tribological performance were systematically evaluated. The results show that the coating contains a large amount of rutile TiO2 hard phase after MAO treatment, which significantly improves the mechanical properties of the substrate. The hardness of the MAO coating can reach 581 HV.05. Furthermore, the synergistic lubrication effect of onion‐like carbon (OLC) nanoparticles and organic molybdenum dithiocarbamate (MoDTC) in PAO oil was observed for MAO‐treated TC4. Particularly, when .01 wt.% OLC is used with 1 wt.% MoDTC oil, the coefficient of friction (COF) decreases to .062, and the wear rate decreases to 4.3 × 10−7 mm3/Nm. Combined Raman and X‐ray photoelectron spectroscopy (XPS) analysis indicate that OLC is deposited on coating area to form a lubricating carbon film. Additionally, OLC can promote the decomposition of MoDTC during sliding to generate a tribofilm containing MoS2.