Influence of Ti content on the structure and tribological properties of Ti-DLC coatings in water lubrication

The Ti-DLC coatings with varying Ti content were deposited on Si(100) wafers and 316 L stainless steel substrates using unbalanced magnetron sputtering (UMS) from Ti and C elemental targets at different Ti target currents. The influence of Ti content on the microstructure and phase composition of Ti-DLC films were studied systematically. The tribological properties of Ti-DLC coatings sliding against Al2O3 balls in water were investigated using ball-on-disc tribometer, and the worn surfaces on Ti-DLC coatings were analyzed using scanning electronic microscopy and non-contact profilometer. It was revealed that the sp3/sp2 carbon ratio first increased as the Ti content increased in the DLC films and then tended to decrease with the further increase of Ti content. TiC nanocrystallites were generated in the DLC coatings. It was also demonstrated that the Ti-DLC coatings with moderate Ti content exhibited enhanced mechanical properties, such as higher hardness and improved tribological behaviors as sliding against Al2O3 balls in water lubrication.

► Ti-DLC coatings were deposited using unbalanced magnetron sputtering.
► The D and G peaks' intensities all decreased with Ti element content.
► TiC nano-crystalline was formed at the current of Ti target beyond 1 A.
► Ti-DLC coatings deposited at 0.5 A possessed the excellent tribological properties in water.