Study On Preparation And Performance Of Ni-Fe-Graphene Protective Coating

Steel 45 is a medium carbon steel with moderate strength,toughness and good welding performance.It is widely used in section steel,structural parts processing,mechanical manufacturing and other fields.The damage of modern machines is mostly due to the failure of parts,The failure forms of parts mainly include friction wear and corrosion,and steel 45 has poor corrosion resistance,which is easy to be oxidized and corroded under normal temperature conditions,resulting in the failure of parts or equipment composed of steel 45,which leads to irreparable losses.On the other hand,as the human science and technology improves and the industrialization advances,the requirements of human beings are getting higher and higher,so there is a higher expectation in traditional materials.Electrodeposition can deposit one or more layers of coating on the base metal.The hardness,strength and other properties of the coating are generally higher than that of the base metal,so that the mechanical parts are protected from corrosion,wear and other damage.Given the wide range of application of steel 45,in this paper,the Ni-Fe-graphene single/multilayer coating was prepared by DC electrodeposition based on steel 45.Raman spectrum,XRD,SEM and EDS were used to characterize the composition,phase structure,surface micro morphology and elements of the composite coating.Orthogonal test was used to optimize the process parameters.Single factor test was used to explore the influence of different factors on the hardness,wear resistance and corrosion resistance of the composite coating.The results show that:(1)The optimal process parameters for the preparation of Ni-Fe-graphene protective coating are:stirring rate 300r/min,time 90min,temperature 50℃,current density 5A/dm~2,graphene concentration 1g/L.The microhardness of the composite coating reaches 1083.88HV in this optimal parameters,which is 260.78%higher than that of the steel 45 substrate and 104.27%higher than that of the Ni-Fe coating.The average friction coefficient achieves 0.2321,which is 65.60%lower than that of the steel 45 substrate and 48.62%lower than that of the Ni-Fe coating.(2)According to the analysis of Raman spectrum and XRD spectrum,the characteristic peak of graphene appears in the figure,which proves that the graphene nano flakes are embedded in the Ni-Fe-graphene protective coating;The coating shows a face centered cubic structure,with the strongest diffraction peak in(111)face coating,followed by the sub strong peak(200)face.After adding graphene,the average grain size of the composite coating decreased by 38.91%,from 48.08nm to29.37nm.It is because the addition of graphene makes the coating nucleate at the graphene,and increases the nucleation center,so that inhibits the growth of grains,leads to the refinement of grains and improves the mechanical properties.(3)Under the above-mentioned preparation process,the optimal coating configuration is three-layer coating and the Ni-Fe-graphene layer is on the top layer.At this time,the microhardness reaches 1132.47HV and the friction coefficient is0.2078,which is increased by 4.48%and decreased by 10.47%compared with the single-layer Ni-Fe-graphene coating,respectively;Under the same conditions,the microhardness of four-layer coating is 1076.54HV,which is 4.84%lower than that of three-layer coating,the friction coefficient of the four-layer coating is 0.2403,which is lower than that of the three-layer coating(0.2078).By analyzing the location of graphene layer of the multilayer coating,it is found that the comprehensive performance of the composite coating is the best when it is used as the top layer.(4)With the increase of graphene concentration,current density and temperature,the microhardness of the coating shows a trend of increasing first and then decreasing.The friction coefficient of the coating is consistent with the change trend of the wear rate.Both increase with the increase of graphene concentration,current density,temperature,and then decline.(5)The corrosion resistance of the single-layer coating with 1g/L graphene and the multilayer coating with the same concentration of graphene is the best,the corrosion resistance grade is 4,and the corrosion resistance grade of the Ni-Fe coating is 2.Microhardness of all coatings is greatly reduced before and after corrosion.The multi-layer coating with 1g/L graphene and the single-layer coating with the same concentration had the smallest decrease in microhardness after corrosion,which is 657.55HV and 608.32HV,with 38.92%and 39.68%lower than before corrosion.While the microhardness of the Ni-Fe coating decreased the most after corrosion,which is 63.17%.Graphene has a strong chemical stability,which can be used as a physical barrier to isolate the substrate and the active medium in the environment,and also can effectively prevent corrosive media such as water molecules and oxygen in the environment from contacting the substrate.Therefore,graphene particles embedded in the Ni-Fe-graphene plating layer can effectively protect the substrate.On the other hand,the embedding of graphene can also passivate the substrate and improve the corrosion resistance of the coating.