Effect of Y2O3 nanoparticles on the microstructure and corrosion resistance of electrodeposited Ni-Mo-Y2O3 nanocomposite coatings

In this study, a composite coating for corrosion protection was successfully prepared on Q235 steel under neutral conditions by means of the DC electrodeposition technique. According to the results of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electrochemical tests, the effects of different additions of yttrium oxide nanoparticles in the electrolyte on the surface morphology, phase structure and corrosion resistance of nickel-molybdenum alloys were analyzed, and the deposition mechanism of yttrium oxide nanoparticles in the bath was proposed. The average grain size of the composite coating was reduced from 6.9 nm to 4 nm due to the grain refining effect of yttrium oxide nanoparticles in the coatings. The content of yttrium oxide in the coating increased with its concentration in the electrolyte, while the content of Mo atoms increased first and then decreased, reaching a peak when the addition of Y2O3 reached 2 g/L. To facilitate the study of the corrosion behavior of the coating after the introduction of the added phase, an equivalent series circuit was also proposed to fit the EIS test results, and it was hypothesized that a corrosion microcell was formed between the nanoparticles and the Ni-Mo alloy when the electrolyte solution uniformly penetrated the film. Based on the results of the electrochemical tests in 3.5 wt% NaCl solution, it was shown that it was not the case that the higher the amount of yttrium oxide added was, the better the corrosion resistance of the coating. Among all samples, Ni-Mo-Y2O3-2 g/L had the most positive corrosion potential (−0.54 V) and the best corrosion current density of 2.452 μA cm−2, which was 52.8 % lower than that of the Ni-Mo alloy coating.