Effect of applied current on the electrodeposited Ni–Al2O3 composite coatings

Nano-sized Al2O3 ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al2O3 particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm2 was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al2O3 particles (4.3 wt.%) in the coatings. The increase in Al2O3 particles in the coatings increased the mechanical properties of the Ni–Al2O3 composite coatings by grain refining and dispersion strengthening mechanisms.