Electrically promoted tribological changes at diamond-like carbon/steel interface under lubrication conditions

Abstract

In modern machinery, the electrified contacts introduce novel lubrication challenges for sliding components. It is vital to understand the electrified tribological characteristics of tribo-materials. This work studied the electrified tribological changes at a DLC/steel sliding interface when lubricated with base oils. The results showed that electric current induced sticking friction, resulting in a friction reduction of approximately 5% to 20% when using mineral, PAO6, and castor oils in short-duration tests, conversely, a slight increase in friction with rapeseed oil. The electric current triggered the growth of a graphite-like tribo-layer on the DLC surface, particularly in ester-lubricated interfaces, which mitigated the wear of DLC. As sliding progressed, DLC film experienced peeling wear under electrified conditions, especially at high currents and loads. The tribo-layer, formed from tribo-oxidation of steel pair and lubricant degradation, was correlated with electrified tribological behavior. The enhanced adhesive and molecular interactions caused by the electric field across the contact were deemed to contribute to the sticking friction under electrified conditions. These findings validate the electrically caused tribological changes in lubricated DLC/steel contacts and indicate the necessity of a novel DLC film design to counteract electrified-induced damage.