Electrification effects on dry and lubricated sliding wear of bearing steel interfaces

In electric vehicles' powertrains, bearings can be susceptible to failure more rapidly than some of the other components mainly because of accelerated fatigue, corrosion and wear. Specifically, due to much severe operating conditions (including high speeds, torques, temperatures) of such vehicles combined with the presence of an electrical environment in which uncontrollable or stray electrical currents discharge through the contact interfaces can further exacerbate the situation and reduce their service lives by triggering much severe adhesive, abrasive and oxidative wear. In this work, we explore the effects of DC current discharges through the contact interfaces of AISI 52100 bearing steel using a novel two-electrode cell-based micro-abrasion tester under electrified dry and boundary lubricated contact conditions. A mineral base oil (as a reference), a gear oil and an automatic transmission fluid (ATF) with different dielectric strengths were tested under unelectrified and DC electrified (1.5 A) conditions. Overall, our test results suggest that passing DC current increases coefficient of friction (CoF) and wear of dry sliding contacts while it slightly reduces CoF but increases wear significantly for lubricated contacts due to accelerated oxidation by electrification. SEM, Raman spectroscopy and non-contact optical profilometry were used for analyzing the physical and chemical nature of worn surfaces and understanding of the specific wear modes and mechanisms.