Wear control and friction reduction in newly developed multilayer Mg-DLC coatings using organic base oil and sustainable lubrication additives

Two sets of DLC coatings, doped with identical Mg concentrations (6–15 at.%) but exhibiting different monolayer and multilayer microstructures, were deposited via DC magnetron sputtering (DCMS) with varying substrate rotational speeds. The investigation focused mainly on the physical, mechanical, and tribological properties of the coatings. The multilayer coatings demonstrated superior mechanical performance compared to their monolayer counterparts. Specifically, the multilayer coating with 6.1 at.% Mg exhibited a 46 % improvement in reduced modulus and a 26 % increase in hardness compared to monolayer coatings. Furthermore, the multilayer coating with 15 at.% Mg significantly reduced wear on both the disc and ball during testing with a synthetic oil containing an ashless, sulphur-free anti-wear phosphate ester additive with an amine group in its chemical structure. • New Mg-doped DLC coatings were developed having monolayer and nanoscale multilayer microstructures by DCMS. • The multilayer Mg-doped coatings showed improved mechanical properties approaching undoped DLC, contrary to monolayer coatings. • Multilayer coatings showed superior tribological performance with eco-friendly lubricants. • Wear rates of multilayer coatings noticeably reduced when oil formulations of ‘C 12-14 alkyl amine iso octyl phosphate’ were used. • COF was moderately reduced, more prominently with oil formulations of ‘octyl dihydrogen phosphate’.