The Preparation And Electrochemical Behavior Of Supercritical Nickel-based Graphene Composite Coating

Electrodeposition technology is one of the important approaches to prepare metal matrix composites in superior performance based on low cost.Because of its high hardness,excellent wear resistance and corrosion resistance,much attention has been attracted in composite coatings.Compared with the traditional electrodeposition technology,the composite electrodeposition technology,which uses the nanomaterials as the strengthening phase,can achieve co-deposition of the nanosheets and matrix metal for obtaining some composite coatings with special function.Graphene is the hexagonal arrangement of carbon atoms forming a one-atom thick planar sheet.These nano-materials exhibit superior thermal,electrical and mechanical properties.The composite coatings with superior properties can be prepared by the introduction of graphene as a second phase additive into the metal matrix composites.But the structure of graphene is easy to destruction when conventional processes（such as EDM sintering,hot pressing sintering,etc.）was used to prepare graphene composites.Howeve,graphene composites prepared by electrodeposion can enhance the properties of composites while protecting the unique structure of graphene.The agglomeration and uneven distribution of graphene is the main problem when using electrodeposition enhanced by graphene.In this paper,the combination of high mass transfer and miscibility of supercritical fluids with pulsed electrodeposition techniques was use to solve the above phenomenon.And the study on pulse composite electrodeposition of Nickel-Graphene with supercritical fluid was carried out.The main contents of this paper are as follows:1.Study on electrochemical behavior of graphene composite electrodepositionThe effect of process factors on the electrode potential of the bath was studied by Open Circuit Potential.The Electrochemical behavior of Ni-GO composite electrodeposition was studied by Cyclic Voltammetry Potentiostatic,Chronoamperometry and AC Impedance Spectra.The effects of graphene on the process of electrodeposition reduction and the nucleation and growth of Ni crystal were investigated.The results show that the introduction of graphene oxide is conducive to the crystal deposition of Ni and hinders the growth of Ni grains.2.Study on microstructure of Ni-GO composite coatingThe binding energy,crystal orientation and microstructure of the graphene electrodeposition were analyzed by XPS,XRD and SEM.Before and after the crystallization of graphene composites,the combination modes and chemical bonds of C and O were investigated.The surface energy of the coatings were analyzed by XRD for studing the the texture coefficients and crystal orientation of different coatings.Finally,the microstructure of the coating was observed by SEM.The results show that graphene oxide was reduced to graphene during the electrodeposition.The reduced graphene changed the optimal orientation of Ni and refined the grain size of the composite coating.3.Study on the process of Ni-GO composite coatingThe effects of average current density,pulse duty cycle and pulse frequency on the mechanical properties and microstructure of Ni-GO composite coatings were investigated.The optimum process parameters for the preparation of Ni-GO composite coating are summarized as follows:average current density J_m=6 A·dm^-2,pulse duty cycle r=0.3 and pulse frequency f=2000 Hz.4.Study on the properties of Ni-GO composite coatingsThe wear resistance and corrosion resistance of Ni-GO composite coating were studied,and compared with the pure nickel coating under supercritical carbon dioxide and the graphene composite coating under normal conditions.The effects of supercritical fluid and graphene on the properties of composite coatings were analyzed.The electrochemical behavior of Ni-GO composite coating in 3.5%NaCl corrosion solution was analyzed by Polarization Curve and AC Impedance Spectra.The results show that the wear resistance and corrosion resistance of the composite coatings were improved by both supercritical fluid and graphene.In addition,the phenomenon of concentration polarization was inhibited with the introduction of graphene during electrodeposition.