Nanomechanical and analytical investigations of tribological layers for wear protection in slow-running roller bearings

Abstract

In a tribological system consisting of roller thrust bearings and various lubricants, we investigated reaction layers formed in the presence of lubricants with low wear protection, high wear and fatigue protection as well as high wear but low fatigue protection. The bearings were tested under heavy-duty conditions in an FE-8 test rig in order to rapidly asses the efficiency of different reaction layer systems. Chemical composition and microstructure analysis of the layers was subsequently carried out by transmission electron microscopy on thin cross-sections prepared by the focused ion beam technique. The nanomechanical properties of the different tribological layers were analyzed by nanoindentation. The formation and structure of the layered system, and thus the ability to protect against wear and fatigue, depends on the lubricants and additives, respectively. Our results indicate that wear protection not only relies on the reaction layer itself but also on the properties of the combined system of the reaction layer and an underlying tribomutation layer.