Improvement of corrosion resistance and research on corrosion mechanism after depositing Ni-Y2O3/Ni-graphene composite coatings on NdFeB magnets

In this paper, we studied the corrosion resistance of the composite deposition of Y2O3 and graphene on nickel coating. The corrosion resistance of the coating was significantly improved after the composite deposition, especially for the Ni-graphene coating with the addition of 0.05 g/L graphene. The Ecorr and Icorr of the coating were optimized to 404.340 mV and 0.24 × 10−8 A cm−2. The surface morphology, microstructure, passivation behavior, and corrosion products of the coating were analyzed, and the mechanism of corrosion resistance enhancement was revealed. The results show that the deposition of the Y2O3 and graphene composite can decrease the surface roughness of the coating. The graphene composite effect is the most significant and greatly reduces the contact area between the coating and the medium. In addition, the particle composite deposition can also yield grain refinement. The graphene composite deposition reduces the grain size from 75.3 to 18.9 nm, significantly improving the nucleation and formation of the passivation film. The uniform deposition of graphene at grain boundaries can also hinder the infiltration of corrosive media into the interior region. Upon the composite deposition, the improved corrosion resistance of magnets significantly increases their performance and service life, facilitating their railway applications.