Corrosion behaviour of sediment electro-codeposited Ni–Al2O3 composite coatings

• Ni–Al2O3 composite coatings with 12–18 vol.% particles are produced by SECD.
• Al2O3 particles do not affect corrosion behaviour at OCP and low anodic potentials.
• Composite coatings exhibit deteriorated corrosion resistance at high anodic potentials.
• Composite coatings show deteriorated corrosion resistance with prolonged anodic polarization.

Ni–Al2O3 composite coatings were produced by the sediment electro-codeposition (SECD) technique at various particle loadings and current densities. The submicron Al2O3 particles were found to distribute uniformly in the coating, and 12–18 vol.% particles can be incorporated in the coating depending on deposition current density and particle loading in the plating bath. Electrochemical corrosion testing was conducted in 0.9 wt.% NaCl solution. The results show that the incorporation of Al2O3 particles in the coating did not affect the general corrosion behaviour of the Ni coating. However, at higher anodic potentials approaching the breakdown potential and with prolonged polarization, the composite coatings showed deteriorated corrosion resistance in terms of increased anodic current density, reduced pitting potential and quicker breakdown of the passive film. The detrimental effects of Al2O3 particle incorporation could be explained by the existence of numerous boundaries between the particles and the matrix, which would serve as active sites for anodic dissolution and micro-pit formation.