Effect of graphene on tribological properties of Ni based composite coatings prepared by oxidation reduction method

In order to study the effect of graphene on the tribological properties of Ni-based composite coatings, a hydrosol graphene was synthesized by oxidation reduction and then added into an electroplating bath to form Ni-graphene composite coatings. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Thermo-gravimetric analysis (TGA) were used to study the crystal structure, spectral characteristics, reduction degree, lamellar thickness and thermal stability of the prepared products in the reaction. During the oxidation of graphite, a large number of functional groups are bonded in the structural layer, and parts of these stable functional groups remain on the reduced surface. The diffraction peaks of graphene become weaker to a line, and the average particle size is 30nm. Raman show that the D and G peaks of graphene shift to the right and the peak width extends, and the increasing of I-D/I-G value indicates that the higher disorder degree. Graphene has a single layer structure, and its thermal stability is lower than that of graphite. The thickness of Ni-graphene composite coatings with graphene contents (0.1%wt, 0.2%wt and 0.4%wt) is about 40-45 mu m. The friction factor (0.61) and wear rate(1.9 x 10(-4) mm(3)/N.m) of the composite coating with 0.4%wt graphene content are reduced by 31% and 65% than those of the matrix under a load of 300 g. The very thin layer structure of graphene can form deposit layer between friction contact surfaces and reduce oxidation wear and furrow at high temperature, which can effectively improve the wear resistance and friction reduction properties of the matrix. (C) 2020 The Authors. Published by Elsevier B.V.