Environmentally Friendly MoS2-hBN Solid Lubricants: A Comprehensive Tribological Evaluation

Abstract

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, Raman spectroscopy, and atomic force microscopy 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.