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

In modern machinery, electrified contacts present novel lubrication challenges for sliding components. Understanding the electrified tribological characteristics of tribomaterials is vital. This work studied the electrified tribological changes at a diamond-like carbon (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%–20% when mineral, PAO6, and castor oils were used in short-duration tests; conversely, there was 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 at the ester-lubricated interfaces, which mitigated the wear of the DLC. As sliding progressed, the DLC film experienced peeling wear under electrified conditions, especially at high currents and loads. The tribo-layer, formed from tribo-oxidation of the 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 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.