ABSTRACT Solid lubricants have long been used to combat friction and wear, especially under harsh operating conditions of numerous moving mechanical systems. In this study, we explored the effect of another harsh condition, i.e., electrical current, on the friction and wear performance of two solid lubricants: one with very high electrical conductivity (i.e., graphite) and one with very low electrical conductivity (i.e., boric acid (H 3 BO 3 )). They were applied as solution‐processed powder coatings on AISI 52100 steel discs and tested against uncoated 52100 steel balls with and without contact electrification. The main goal was to determine whether electrical conductivity plays a critical role in the tribological performance of these solid lubricants. Results showed that graphite was very effective in reducing friction and wear under non‐electrified conditions. Specifically, it reduced the coefficients of friction (COFs) of steel test pairs by about 75% and the wear volume of the balls by a factor of more than 50 compared to the uncoated unelectrified condition. However, under contact electrification, the reduction in COF was about 60%, and the wear volume of the balls increased significantly, but graphite was still able to reduce the wear volume by fourfold compared to uncoated electrified steel. On the other hand, the COF and wear volume of the balls tested against the boric acid coated disc were about 75% and 1227 times lower, respectively, than that of the ball tested against uncoated and unelectrified disc. However, under electrification, the friction coefficient did not change much, while the wear volume of the balls went up but was still 20 times lower than that of the balls slid against uncoated electrified disc. Post‐test microscopic and chemical analyses showed that boric acid remained structurally and chemically intact under electrified and non‐electrified conditions and thus effectively protected the sliding surfaces against wear. Conversely, graphite was partially worn out or removed from the sliding surfaces when tested under electrified conditions and thus provided marginal benefits. The superior friction and wear performance of boric acid is attributed to its low shear strength and highly insulating nature, demonstrating its potential applications in electric vehicle drivetrains.
Komurlu et al. (Sun,) studied this question.