Friction and wear property of lithium grease contained with copper oxide nanoparticles

In general, the friction and wear property of lubricating grease has great influence on the usability of bearings. Copper oxide (CuO) was added in the base grease to prepare composite grease, followed by the investigation of anti-fraction properties to analyze the role of CuO and identify the optimum content. CuO nanoparticles were characterized first by series of techniques, including surface area and micropore analysis, particle size analysis, X-ray diffraction (XRD) analysis, atomic force microscope (AFM) scanning, infrared and Raman spectroscopic analysis. Composite greases were prepared by added CuO nanoparticles into the base grease, then examined via AFM and infrared spectrum. The friction and wear property of composite greases was investigated by friction test on a four-ball friction test machine. Scanning electron microscope (SEM) and three-dimensional (3D) profilometer were utilized to observe the wear surface and helped to unravel the anti-friction mechanism. The formation of oil films on wear surface was identified and investigated by Raman spectrum and 3D morphology height, demonstrating the anti-friction effect. When CuO content was 0.60 wt%, only a small number of furrows were observed on the wear surface. The composite grease showed the lowest average friction coefficient and wear scar diameter, which were 30% and 13% lower than the base grease, respectively. According to 3D morphology scanning and Raman spectrum, CuO-contained oil films were detected on the wear surface. This lowered furrow number and the roughness of wear surface, demonstrating the great role of CuO in the enhanced anti-friction property of composite grease.