Environmentally friendly bonded MoS2 solid film lubricants for aerospace applications: Closing the gap

Abstract

Solid lubricants have been extensively used in the aerospace industry with the main purpose to reduce friction and wear in such demanding environments. One such solid lubricant is MoS2, which is being widely used in tribological applications due to its low friction behavior. This study mainly aims to evaluate the influence of the carrier system (i.e., solvent and water) on the tribological behavior of bonded MoS2 solid film lubricants in order to close the gap with green alternatives. Two bonded MoS2 based solid lubricants were critically evaluated in terms of their tribological behavior, with one lubricant containing a solvent-borne carrier and the other lubricant with a water-borne carrier. The tribological tests were performed using a ball-on-disc tribometer against the alumina (Al2O3) counter face by varying applied load. Ex-situ analysis was carried out using scanning electron microscope (SEM), micro-Raman spectroscopy and Fourier transform Infrared Spectroscopy (FTIR) in order to understand the interfacial processes and chemical composition of the solid lubricants. Overall, the wear rate of both lubricants (i.e., solvent- and water-borne) was equivalent when testing using lower normal loads (i.e., up to 8 N). However, the solvent-borne solid lubricant showed better load carrying capabilities and performed better in terms of the tribological behavior (lower friction and wear) with higher normal loads, which was attributed to the formation of uniform transfer film. The findings of the interfacial phenomenon have provided critical information to further improve the load carrying capability of lubricants without any toxic compounds in order to achieve sustainable environment.