Investigating the Microstructure and Anti-corrosion Behavior of the Electroless Ni-P-Y2O3 Composite Coatings

This research focuses on evaluating the effects of Y2O3 nano-particles on the microstructure, and the corrosion resistance of the Ni-P-Y2O3 composite coatings deposited from a surfactant-free solution containing 0.5, 1, 2, or 3 g/l particles by electroless deposition method. In this regard, various techniques including scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, x-ray diffraction, Tafel polarization, and electrochemical impedance spectroscopy were conducted. It was observed that the nanoparticles were uniformly distributed on the surface of the composite coating produced with 0.5 g/l Y2O3. However, the composite coatings produced with 2 or 3 g/l Y2O3 were very thin with some surface defects. In the absence of Y2O3, the phosphorous content of the Ni-P coating was 12.08 wt.%, which decreased to 11.1 wt.% in the presence of 3 g/l Y2O3. Hence, the embedment of the Y2O3 particles did not alter the amorphous structure of the coatings. Among the produced coatings immersed in 3.5 wt.% NaCl electrolyte, the coatings produced with 1 g/l Y2O3 had the highest corrosion resistance. This coating exhibited the lowest corrosion current density of 0.251 mu A cm-2 and the highest charge transfer resistance of 17488 Omega cm2 calculated using the Tafel polarization and the Nyquist graphs, respectively.