The Effect Of Electrodeposition Parameters On The Performance And Properties Of Nickel- Graphene Composite Coatings

Composite electrodeposition is a process which introduces different solid reinforcers in a plating bath, and the reinforcers combine into the metal matrix when the metal ions reduce on the cathode. So the composite deposits are metal matrix composite materials, which consist of a metal continuous phase and reinforcer discontinuous phase. The Nickel-Graphene composite have the high-intensity, high modulus and tremendous self-lubricating properties of Graphene and the pyrolytic stability as well as corrosion resistance of nickel. So Ni-Graphene composite has been paid more attention by researcher in recent years. But the existed references only have limited and simple researches on this nanocomposite. So, a systematic research about the effect of each aspect of the electrodeposited nanocomposite was performed in this thesis. On the basis of this new research, the each factor about growth mechanism of nickel-graphene nanao composite coating was firstly found during the electrodeposition. A conventional Watts bath with treated graphene was used as the electroplating cell. The cathodic E-i curves, hardness test, surface morphology, elements analysis, tensile test, polarization curves and electrochemical impedance spectrum (EIS) were performed to determine the factors influencing on the performance and properties of the composite coatings. The results showed that the graphene platelets uniformly distributed in composite coatings and the dispersed graphene platelets combined tightly with nickel matrix. The electrodeposited composite coatings have a compact structure, fine grain size and uniform thickness. This synthesizes composite coatings also has higher hardness and good adhesion strength than pure nickel coating. In the following experiments it has been found that increasing the concentration of graphene keeps improve the sedimentation velocity and cohesion of composite coatings.The increasing of current density of deposit makes the coating's surface coarser. The hardness, adhesion, erosion and corrosion resistance firstly increases with the increasing of current density and then decrease after reaching the peak value at 9A/dm2. Higher bath temperature can increase the sedimentation velocity as well as coating's hardness. A smooth surface can be obtained in either higher or lower bath temperature. The stirring also effect on the properties of composite coatings and the increasing of agitation speed can improve the sedimentation velocity and hardness of composite coating slightly. The effect of anion surfactant on the graphene content, hardness, adhesion, surface morphology and corrosion resistance of composite coatings were studied and compared with the coatings without the assistance of surfactant. The results showed the addition of surfactant improved the mechanical properties of composite coatings. The anion surfactant increases the graphene content in coatings because of the electrostatic repletion between graphene platelets and leads to prevent the agglomeration of graphene platelets. The graphene because of anion surfactant also accelerate the nickel ions reduction on the cathode, to improve the roughness of composite coatings. Surfactant can reduce the nickel grain size and transform the texture coefficient of crystal plane. The anionic surfactant can improve the composite coating's hardness and the adhesion between the composite coatings and the carbon steel. Anionic surfactant improves the Corrosion resistance of composite coatings. The deposition mechanism of the nickel matrix composite was also discussed in this thesis.