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The electrification of vehicles has introduced additional tribological challenges caused by stray currents and voltage surges that accelerate bearing degradation. This study investigates the effects of viscosity and other characteristics of three base greases on their frictional and wear behaviors under direct current (DC). The representative greases, lithium complex, aluminum complex, and calcium sulfonate, formulated with a common ISO VG 100 base oil, were comparatively studied. Results reveal that the rheological behavior, dielectric response, and charge-transfer kinetics of the greases collectively determine the overall tribological performance under electrified conditions. Across Hertzian contact pressures of 822 MPa, 1116 MPa, and 1405 MPa (loads of 2 N, 5 N, 10 N), calcium grease delivered the most stable friction behavior (COF 0.12–0.16) and the minimal wear increases (99–451%), while lithium grease showed the strongest sensitivity to electrification, with friction rising up to 72% and wear increasing by 1248–1684%. Aluminum grease exhibited intermediate responses. SEM analyses revealed deep grooves, arc-induced pits, and extensive debris for lithium and aluminum greases under current, whereas calcium grease maintained narrower, shallower tracks. Adhesion measurements showed that Li and Al greases possessed higher adhesive energies (7.008–7.477 J/m 2 ) compared with Ca grease (3.422 J/m 2 ), and in situ contact resistance measurements confirmed consistently higher average interfacial resistance for Ca grease (0.326 Ω vs. 0.259–0.268 Ω). It was discovered that the electrified wear of steels was a linear function of combined factors, normal load, grease adhesive energy, and electrical potential. This could be used to predict the electrified performance of grease-lubricated steels. This work provides benchmark data and mechanistic insight into lubricant selection and formulation in electric-vehicle components.
Bons et al. (Sat,) studied this question.