Tribological Evaluation of Eco-friendly MoS2 based Solid Lubricants for Gas Turbine Engines

Solid lubricants such as MoS₂ have been widely used in the aerospace industry with the primary purpose of reducing the friction and wear of tribological interfaces. MoS₂ based lubricants are generally doped with other compounds, which can help overcome some of their limitations related to environmental conditions. For instance, compounds like Pb and Sb₂O₃ have been traditionally used to improve the endurance life of these lubricants. However, with the recent zest in transferring to eco-friendly lubricants, there is a strong push to eliminate Pb based compounds. The main purpose of this work is to better understand the influence of Pb based compounds on the tribological behavior of MoS₂-based solid lubricants as well as to evaluate the performance of Pb free lubrication strategies critically. More specifically, the baseline lubricant was doped with Pb compound and Sb₂O₃ (Lube-Lok 5306), and the Pb compound in the alternative lubricant was replaced by more Sb₂O₃ (Everlube 620C). The wear test was done using ball-on-disk tribometer for specific loads and 5000 cycles. Ex-situ analysis was conducted using Scanning Electron Microscope, Atomic Force Microscopy, and micro-Raman to capture the interfacial processes of these coatings at different loads. Overall, the Lube-Lok 5306 performed better in tribological aspects due to the transfer film formation and basally oriented MoS₂ crystallites on the worn surface.