Excellent Lubricating Ability of Functionalization Graphene Dispersed in Perfluoropolyether for Titanium Alloy

The dispersibility of graphene family nanomaterials in base oil is a crucial factor for their application as lubricating additive in oil-based fluids. Here, the 1H,1H-perfluorooctylamine (FOA) was covalently grafted onto the GO surfaces and then the product was reduced by hydrazine monohydrate for synthesizing a modified graphene nanomaterial of FOA-rGO. Various techniques including transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to characterize the as-prepared FOA-rGO nanomaterial. The test results demonstrate that the long fluorocarbon chains of FOA are successfully linked to the edges of GO surfaces by covalent functionalization, which corresponds to the excellent dispersibility of the resulting FOA-rGO in a space lubricating oil of perfluoropolyethers (PFPE). The tribological properties of FOA-rGO as nanoadditive in PFPE for lubricating Ti6Al4V/steel friction pairs were systemically evaluated by a UMT tribometer. The results show that the FOA-rGO dispersed in PFPE displays remarkable antiwear and friction-reducing ability for Ti6Al4V/steel friction pairs. The friction coefficient is reduced by 52.7% and the wear rate is reduced by almost 5 orders of magnitude, when compared to the pure PFPE. The superior lubricating ability of the FOA-rGO additive is closely related to its excellent dispersibility in PFPE that favors the formation of a thin, durable, and stable boundary tribofilm between the contact surfaces