Effect of phosphonate additives with hydroxy groups on tribological properties of ta-C coatings under boundary lubrication

Abstract

In recent years, the range of applications of DLC coatings has been expanding, and finding the optimal additives for DLC coatings is an urgent issue. In this study, friction tests were conducted on ta-C/ta-C tribopair using a phosphonate additive with hydroxy groups, which is a combination of GMO (an additive that reduces friction of DLC) and ZDDP (an additive that reduces wear), and tribolayers after friction tests were analyzed using AFM, XPS and ToF-SIMS. The results showed that the phosphonate additive with hydroxy groups tribochemically reacted with the ta-C coating to form a low-shear, hard triblayer on the surface, thereby reducing the friction and wear of the ta-C coating.This indicates that additives with phosphonate structures and hydroxy groups are effective for DLC coatings.