Abstract
Surface reactive additives are crucial in the lubrication of surfaces experiencing cyclic contact. The combination of additives in the lubricant, on the material surface and the complex tribo-contact conditions hinders the design of additive packages which can simultaneously protect steel surfaces from wear and fatigue. Amine-based Organic Friction Modifiers (OFMs) influence the tribological performance of steel surfaces. This study investigates the tribochemical impact of three amine-based OFMs in combination with Zinc DialkylDithioPhosphate (ZDDP) on tribological performance, particularly surface fatigue, for steel surfaces in severe rolling–sliding contacts. The thickness of reaction films was tracked throughout experiments and the chemistry of reaction films was examined using X-ray Photoelectron Spectroscopy (XPS). Results highlight the impact of the OFM polar moiety on tribological performance and its influence on chemical composition of tribo-reaction films and their formation kinetics. The combination of selected OFMs with ZDDP reduces frictional forces and can mitigate surface fatigue under certain conditions.Graphic
Highlights
Premature failures and surface fatigue of bearings in wind turbine gearboxes significantly decrease their lifespan
Base Oil (BO) + Zinc DialkylDithioPhosphate (ZDDP) generated a 65-nm-thick film at the initial Stribeck curve measurement, followed by a further 80-nanometer film which was formed subsequent to a 5-min Constant Entrainment-Speed (CES) step resulting in an ultimate 145-nm-thick film
At the same time TDP + ZDDP induced a few nanometer-thick film, while there was no Spacer Layer Image Mapping (SLIM)-sensitive film on the surface of Ethoxylated (2) Tallowalkyl-Amine (ETA) + ZDDP and a film started to emerge from TA + ZDDP
Summary
Premature failures and surface fatigue of bearings in wind turbine gearboxes significantly decrease their lifespan. The effect of different OFMs on surface fatigue, cannot be generalised to be detrimental or beneficial owing to the broad OFM category encompassing molecules with different polar head chemistry. This can be evidenced from results showing an oleic acid OFM was not effective to inhibit micropitting in harsh tribo-contacts, while signs of improvement were observed in less severe contacts [3]. The chemical composition of OFMs has an impact on surface fatigue performance, and more systematic studies are required to reveal the impact of different chemistries of amine-based OFMs on micropitting performance of wind turbine gearbox lubricants. This study elucidates the tribochemical influence of amine-based OFMs in combination with ZDDP anti-wear additive
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