The Effect of Oleic Acid-Treated ZrO2 Particles on the Tribological and Corrosion Resistance of Lithium Grease

Oleic acid-treated ZrO2 particles were added to lithium grease at 0, 0.2, 0.4, 0.6, and 0.8 wt.%. Friction and wear were evaluated by reciprocating ball-on-disc tests using a GCr15 steel ball (6 mm) and GCr15 disc under 10 N, 3 Hz, 5 mm stroke, 30 min, and 25 ± 2 °C. The 0.4 wt.% formulation gave the lowest average coefficient of friction (0.058, 34.1% lower than the base grease), the smallest wear-scar width (331.05 μm, 17.5% lower), and the lowest wear volume (0.0017 mm3, 73.4% lower). After 360 h of intermittent salt-spray exposure, the 0.4 wt.% group showed the least visible rust, and its corrosion current density in 3.5 wt.% NaCl was 6.77 × 10−10 A·cm−2, the lowest among the tested formulations. Increasing the content to 0.6–0.8 wt.% increased the coefficient of friction, wear, and corrosion current density again. Thus, within the tested range, 0.4 wt.% oleic acid-treated ZrO2 simultaneously improves the friction-reducing, anti-wear, and anticorrosion performance of lithium grease. The mechanism still requires verification by particle-dispersion characterization, tribofilm composition analysis, and coating microstructure testing.