Tribological Properties of Ti-Doped Diamond-Like Carbon Coatings Under Boundary Lubrication With ZDDP

Abstract

Abstract Diamond-like carbon (DLC) coatings containing 0.7%, 5.8%, and 23.3% Ti were deposited via pulsed cathodic arc deposition and magnetron sputtering on AISI 316L stainless steel substrates. The varied Ti content was controlled by setting Ti target current at 3, 5, and 7A. The composition, microstructure, mechanical, and tribological properties of Ti-doped DLC (Ti-DLC) coatings were investigated using X-ray photoelectron spectroscopy, Raman spectroscopy, nanoindentation, and ball-on-disc tribometer. The results show that TiC formed when Ti content in the coating was higher than 5.8 at% and the ID/IG ratios increased gradually with the increasing Ti content. Ti-DLC with 0.7 at% Ti had the highest H/E and H3/E2 ratios and exhibited optimal tribological properties under lubrication, especially when zinc dialkyldithio-phosphate (ZDDP) was contained in the oil. Furthermore, ZDDP tribofilms played an important role in wear reduction by protecting the rubbing surfaces against the adhesion and suppressing the tribo-induced graphitization of DLC coatings.