Investigation of Microstructure and Properties of Ni/CNT Nanocrystalline Coating Deposited by Brush Plating

Nickle-carbon nanotube (Ni/CNT) nanocrystalline coatings with different parameter were prepared by brush plating. The carbon nanotubes were added into common nickel solution for brush plating and ball milling was used to disperse the carbon nanotubes in the solusion. The concentration of carbon nanotubes in the solution was 3 g/l. The SEM and XRD were applied to investigate the grain size, microstructure and morphology of the coatings. The hardness and the wear mass loss of the coatings were examined on micro hardness tester and ball on disk tribotester. The results show that under a direct-current source, the grain size of the Ni/CNT coating was about 20 nm. Under a pulse-current source, the grain size of the Ni/CNT coatings decreased and the coatings gained smoother surface when the pulse-width became shorter. The grain size of the Ni/CNT coating increased with the heating temperature increasing and the average grain size of the coating heated at 500 degrees centigrade was over 50 nm. The microhardness of the Ni/CNT coating under a pulse-current source was higher than that of the coating under a direct-current source. Under a pulse-current source, the microhardness of the Ni/CNT coating increased when the pulse-width became shorter. The microhardness of the Ni/CNT coating changed slightly below 300 degrees centigrade, while decreased obviously after heated up to 400 degrees centigrade. The wear resistance of the Ni/CNT coating under a pulse-current was higher than that of the coating under a direct-current. Under a pulse-current, the wear resistance of the Ni/CNT coating increased when the pulse-width became shorter.