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

In this work, the authors studied the corrosion resistance of composite deposits of yttrium (III) oxide (Y2O3) and graphene on a nickel (Ni) coating. The corrosion resistance of the coating was significantly improved after the composite deposition, particularly for the nickel–graphene coating with the addition of 0.05 g/l graphene. The E corr and I corr of the coating were optimized to 404.340 mV and 0.24 × 10−8 A/cm2, respectively. 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 deposition of the yttrium (III) oxide and graphene composite can decrease the surface roughness of the coating. The graphene composite has a more significant effect and greatly reduces the contact area between the coating and the medium. Moreover, particle composite deposition can also lead to grain refinement. Graphene composite deposition reduces the grain size from 75.3 to 18.9 nm, significantly improving the nucleation and formation of the passivation film. Uniform deposition of graphene at grain boundaries can also hinder the infiltration of corrosive media into the interior region. Upon composite deposition, the improved corrosion resistance of magnets significantly increases their performance and service life, facilitating their railway applications.