Abstract
Ni⁻Co alloy and Ni⁻Co⁻Y₂O₃ multiple coatings refined with nano-Y₂O₃ particles were fabricated by ultrasonic-assisted electrochemical deposition in an acid sulfamate bath. Linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) techniques were applied to investigate the nucleation/growth process of composite coatings in co-deposition. The LSV results indicated that the incorporation of nano-Y₂O₃ particles with the Ni⁻Co matrix shifted the initial deposition potential to a more positive potential and decreased cathodic polarization. For both coatings, the nucleation/growth process approximately agreed with the Scharifker⁻Hill instantaneous nucleation model. Nucleation parameters, including active nucleation sites (N₀) and nucleation rate (A) of the composite, were higher when the measured potential range was between −1.05 V (vs. SCE) and −1.20 V vs. SCE, when compared with the Ni⁻Co alloy, and the observed AFM images of the coatings were in good agreement with the calculated nucleation parameters (using the Marquardt⁻Levenberg algorithm) of experimental curves. EIS testing indicated that the charge transfer resistance of the composite was lower in electrodeposition. The incorporation of nano-Y₂O₃ particles in the matrix changed the preferred orientation of coatings and produced a more uniform and compact deposit layer with finer grains.