Electrotribochemical formation of abrasive nano-carbon particles under electrified conditions on lubricated sliding contacts

Electric vehicle (EV) mobility represents a transformative shift in achieving better energy security, environmental cleanliness, and economic prosperity. Despite recent advancements in EV technology, several challenges persist in tribology and lubrication fronts that can hamper their long-term reliability, performance, and efficiency. In this work, we explored the tribological performance of four commercially available driveline lubricants under non-electrified and electrified sliding conditions using AISI 52100 bearing steel. The results confirmed that passing of electricity through the contact interface exacerbate the wear damage (causing as much as a 5-fold increase in wear volume). Using Raman Spectroscopy, XPS, SEM, ToF-SIMS, and HRTEM, we confirmed that such accelerated wear primarily results from the formation of highly abrasive soot-like amorphous carbon, iron carbide, and other carbonaceous products which result from the decomposition of long-chain hydrocarbon molecules of lubricating oils under electrification. These findings confirm the existence of very complex wear mechanisms in electrified contacts and suggest the need for much improved lubricants and/or materials for future EV applications.