Electrodeposition and characterization of Ni-Co-carbon nanotubes composite coatings

Ni-Co-carbon nanotubes composite coatings were prepared by electrodeposition in a Ni-Co plating bath containing carbon nanotubes (CNTs) to be co-deposited. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni-Co-CNTs composite coatings were evaluated on a UMT-2MT test rig in a ball-on-disk contact mode. The morphologies of the original and worn surfaces of the composite coatings were observed on an atom force microscope (AFM) and scanning electron microscope. It was found that the introduction of the carbon nanotubes in the electrolyte caused the shift towards larger negatives of the reduction potential of the Ni-Co alloy coating, and the co-deposited CNTs had no significant effect on the electrodeposition process of the Ni-Co alloy coating. However, the co-deposited CNTs led to changes in the composition and structure of the composite coatings as well. Namely, the peak width of the Ni-Co solid solution for the composite coating is broader than that of the Ni-Co alloy coating and the composite coating possess higher microhardness and elastic modulus than Ni-Co alloy coating. The co-deposited CNTs were uniformly distributed in the Ni-Co matrix and contributed to greatly increase the microhardness and tribological properties of the Ni-Co alloy coating.