Tribological behavior of eco-friendly MoS2-hBN solid lubricants for aerospace applications

Solid lubricants are widely used in the aerospace industry with the main purpose to reduce friction and wear on contacting surfaces. MoS₂ – based solid lubricants, in particular, are commonly employed in such harsh environments, mainly due to their favorable lubricating behavior. However, pure MoS₂ is environmentally sensitive, and in the presence of humidity, it is vulnerable to oxidation, leading to an unexpected failure. Thus, the addition of dopants in the form of single elements or compounds could overcome some of these challenges. For instance, Pb-based compounds and Sb₂O₃ are frequently added to MoS₂ – based lubricants in order to improve their load carrying capability and their performance in humid environments. However, due to their toxic nature, there is a strong desire to replace these compounds with eco-friendly alternatives. The main purpose of this study is to critically evaluate the tribological behavior of three different compositions of hexagonal boron nitride (hBN) in MoS₂-hBN as a "green" lubricant. A ball-on-flat tribometer is used for the wear and friction tests with varying contact conditions in order to characterize and compare the worn and unworn coating under different loads, ex-situ analysis such as Scanning Electron Microscopy, Atomic Force Microscopy, and micro-Raman are performed.