Effects of Substrate Material, Surface Preparation, and Operating Conditions on the Surface Characteristics and Tribological Performance of MoS2 Dry Film Lubricants

Molybdenum disulfide (MoS2) dry film lubricants (DFLs) are widely used in aerospace mechanisms when conventional liquid lubricants are impractical. While the effects of environment on MoS2 are well established, the influence of substrate characteristics and operating conditions remains less understood. In this work, three commercial MoS2-based DFLs (Lube-Lok 4396, Everlube 620C, and Everlube 9002) were applied to five aerospace-relevant substrate materials and characterized in terms of surface roughness, flatness, coating thickness, friction, wear life, and load-carrying capacity. Vendor surface preparation and DFL deposition increased roughness, reduced flatness, and shifted the surface toward a more peak-dominated morphology, with the magnitude of these changes depending on both the substrate and coating. Tribological performance was evaluated for a subset of the samples which showed that friction was substantially lower in dry nitrogen than in ambient air, increasing contact pressure reduced friction, and sliding speed had little effect. Lube-Lok 4396 exhibited the longest wear life and highest load-carrying capacity, while Everlube 620C exhibited the lowest friction. Measured friction, wear life, and load-carrying capacity also differed from vendor specifications. These results highlight the effects of substrate material, surface preparation, and operating conditions on the surface characteristics and tribological performance of commercial MoS2 DFLs for aerospace applications.