Effect of different chemical conversion coatings on the tribological performance of cylindrical thrust roller bearings under conditions of dry friction and solid lubrication

Abstract

The chemical conversion coating technology, as a surface technique, can effectively reduce surface wear. In this study, the chemical conversion coating technique was implemented to acquire three distinct coating variations on the surface of cylindrical thrust roller bearings (CTRBs). Nanoindentation tests were conducted to analyze the mechanical features of the coatings, specifically targeting the elastic modulus and nanohardness. To evaluate the surface properties of the coatings, a 3D profilometer was employed. Moreover, the tribological behavior of the CTRBs, subsequent to the application of the coatings, was examined under conditions of dry friction and solid lubrication using a vertical friction and wear testing apparatus. A theoretical framework was established to elucidate the initial phase of transfer film spreading and determine the friction coefficient (COF). The impact of mechanical properties, surface characterization, and crystal structure of the coatings on the tribological performance, both under dry friction and polytetrafluoroethylene (PTFE) solid lubrication conditions, was thoroughly investigated. The findings revealed that, when subjected to dry friction, the dominant factor influencing the tribological performance of the coatings was surface roughness. The addition of solid lubricants can effectively improve the friction performance, resulting in a maximum reduction in bearing wear of 83.9 % and a minimum reduction of 13.0 %. By analyzing the worn surfaces and bearing vibration signals, the influence of coating characterization on the wear and anti-friction performance of solid lubricants is discussed.