Superlubricity of multilayer titanium doped DLC coatings by using low SAPS organic additives in base oil

This study systematically investigates the tribological performance of titanium doped diamond-like carbon monolayer and multilayer coatings with superior mechanical properties. The coatings were lubricated in poly alpha olefin grade 4 (PAO4) base oil, containing three concentrations of two organic, ashless, and sulfur free (low SAPS) antiwear, and extreme pressure additives with different amounts of phosphorus and nitrogen (Duraphos (R) 178 and Duraphos (R) OAP). The multilayer Ti-doped DLC coatings exhibited superior tribological performance compared to uncoated steel, undoped DLC, and monolayer Ti-DLC coatings. They exhibited coefficient of friction values which were in the range of 0.013 and 0.006 (superlubricity) for formulations with Duraphos (R) OAP. Duraphos (R) 178 significantly lowered the specific wear rates of both the monolayer and multilayer coatings.