Roles of Graphene Additives in Optimizing the Microstructure and Properties of Ni-Cr-Graphene Coatings

The electrodeposition technique was used to fabricate graphene and Cr particle-reinforced Ni-Cr-graphene coatings. The Rietveld refinement was utilized to analyze the microstructure of Ni deposits in the coatings. The properties including micro-hardness and corrosion behaviors of the coatings were also tested. Results showed that the addition of graphene particles contributed to the dendrite like structure on the surface of the Ni-Cr-graphene coating. The crystallite size and [200] texture of the Ni deposits in the Ni-Cr-graphene coatings were significantly decreased by the graphene particles. The crystallite size of 149.8 nm in the Ni-25-Cr-0-graphene coating was reduced to 35 nm in the Ni-25-Cr-8-graphene coating due to the addition of 8 g/L graphene to the electrolyte. The microstructure evolution of the Ni-Cr-graphene coatings brought about an enhancement in micro-hardness and corrosion resistance of the coatings. The micro-hardness of the coatings was improved from 260.1 HV0.2 of the pure Ni coating to 285.9 HV0.2 of the Ni-25-Cr-0-graphene coating and continually to 461.8 HV0.2 of the Ni-25-Cr-8-graphene coating. In corrosion solution (3.5 wt.% NaCl), the corrosion current (6.22 mu A/cm(2)) of the Ni-25-Cr-0-graphene coating could be decreased by about an order of magnitude through the addition of graphene particles, which was 0.33 mu A/cm(2) for the Ni-25-Cr-8-graphene coating.