MoS₂-based solid lubricants have obtained significant attention and are extensively employed in the aerospace industry due to their desirable tribological performance. However, to enhance their performance in humid environments, MoS₂ is often doped with Pb-based compounds. Considering the health and environmental concerns associated with Pb, it is necessary to develop eco-friendly alternatives. In this study, hexagonal boron nitride (hBN) has been used as a potential substitute for Pb-based dopants in MoS₂-based solid lubricants and coatings with varying hBN contents (9.5, 11.5, 13.5, 15.5, and 17.5 wt.%) were applied to stainless steel substrates using a spray bonding technique. The friction and wear characteristics of the coatings were analyzed by using a ball-on-flat tribometer, employing constant load conditions. Subsequently, ex-situ analysis techniques such as scanning electron microscopy (SEM), raman spectroscopy, and atomic force microscopy (AFM) were used to characterize the coatings. The results showed that the coating with a lower hBN concentration presented improved tribological properties, which was correlated with the development of an effective MoS₂-based transfer/tribo-film. This suggests that optimizing hBN content is crucial for enhancing the lubrication performance.

To elucidate the role of environmentally friendly oxide additives in a molybdenum disulfide (MoS₂)-based solid lubricant, this study investigates the tribological behavior of a MoS₂–TiO₂ coating deposited via a spray-bonding process and compares it with a commercial Sb₂O₃-containing formulation (Everlube 620C). Interfacial characteristics and wear-related mechanisms were systematically analyzed using scanning electron microscopy (SEM), focused ion beam (FIB), Raman spectroscopy, and X-ray diffraction (XRD). The MoS₂–TiO₂ coating exhibited a higher steady-state coefficient of friction (0.35–0.45) and wear compared to the baseline. Its wear behavior was governed by fracture-induced three-body abrasion, driven by the hard and brittle nature of TiO₂, which promotes stress concentration at particle–matrix interfaces, crack initiation, particle pull-out, and debris generation. These processes suppress the formation of a desirable MoS₂-rich tribo/transfer film, leading to deformation-dominated friction. Overall, the findings indicate that the intrinsic mechanical properties and interfacial behavior of TiO₂ limit its effectiveness as an additive in MoS₂-based coatings, highlighting the importance of additive selection and compatibility in achieving optimal tribological performance. Notably, this study was performed at an additive volume fraction equivalent to that of Sb₂O₃ in Everlube 620C, serving as a foundation and indicating that further optimization of TiO₂ particle size and concentration is required to achieve comparable performance.