Effect of carbamide concentration on electrodeposition and tribological properties of Al^sub 2^O^sub 3^ nanoparticle reinforced nickel nanocomposite coatings

Ni-Al2O3 nanocomposite coatings were electrodeposited from Watt's bath containing alumina nanoparticles, dispersed with the aid of carbamide. The effect of carbamide concentration on the amount of embedded alumina nanoparticles, zeta potential, microstructure, microhardness and tribological behavior of nanocomposite coatings were investigated. The results revealed that using of carbamide in the range of 10-15 g/L increased the microhardness up to 85% compared with the coating fabricated without carbamide. The adsorption of alumina nanoparticles increased from 4.6 vol% to 11.3 vol% by the aid of carbamide and it also caused grain refinement in the nickel matrix. Increasing the carbamide concentration up to 15 g/L led to decrease in the wear rate, approximately to 30% of the coating electrodeposited without carbamide.