Effect of ZDDP and ashless triphenyl phosphorothionate (TPPT) as lubricant additives on tribological performance of Cr-N coatings

In recent years, there has been significant attention paid to the effect of lubricant additives on the tribological properties of advanced surface coatings. However, not many research papers have addressed the influence of additives on the tribological performance of chromium nitride (Cr-N) coatings. In this study, lubricants containing zinc dialkyl dithiophosphate (ZDDP) or triphenyl phosphorothionate (TPPT) were used to conduct tribological tests based on a disc on cylinder tribometer. The wear scars formed on the Cr-N coated discs were analysed using surface sensitive analytical techniques such as field emission scanning electron microscope and energy dispersive X-ray spectroscopy. Results showed that both ZDDP and TPPT (to a lesser extent) enhanced friction reduction compared to pure base oil on the Cr-N surface. Results also indicated that both antiwear additives helped to improve wear protection on the Cr-N coating. At the same treat rate, TPPT gave better antiwear performance than ZDDP.