Ultra-thin carbon-based nanocomposite coatings for superior wear resistance under lubrication with nano-diamond additives

Ultra-thin carbon-based nanocomposite coatings comprised of graphite nanocrystals embedded in diamond-like carbon (DLC) matrix were deposited on stainless steel substrates by the C₆₀ ion beam method, as a wear protective coating. Increasing the C₆₀ irradiation energy and deposition temperature led to the formation of graphite nanocrystals with a size of less than 2 nm. The wear characteristics of the coatings were investigated in the presence of engine base oil with nano-diamond particle (NDP) additives that are commonly used to lower friction and wear. The nanocomposite coating deposited at 5 keV, 300 °C showed the highest sp³ content and the best tribological characteristics. A minimum coefficient of friction of 0.07 and a wear rate of 1.8 × 10^-12 mm³ N^-1 mm^-1 could be achieved which was lower than the best previously reported data considering that the contact pressure was greater than 1 GPa. Such a high wear resistance of the nanocomposite coating was attributed to their unique structure that simultaneously provided high hardness and elasticity while in contact with nano-diamond particles.