Structural and corrosion behavior of Ni-Cu and Ni-Cu/ZrO2 composite coating electrodeposited from sulphate-citrate bath at low Cu concentration with additives

Abstract

Ni-Cu and Ni-Cu/ZrO2 composite coatings were electrodeposited by addition of Cu, Cu and ZrO2 in Ni deposit from a sulphate-citrate bath at low Cu concentration with additives. Effects of the added Cu atoms and zirconia (ZrO2) particles on surface morphology and structural properties of Ni matrix were examined with various methods. The effects of deposition parameters like current density, duty cycle and their combination on corrosion behavior of Ni-Cu/ZrO2 coating were examined. The hardness was evaluated by Vickers hardness tester. Results indicated that the presence of Cu and ZrO2 changes the texture of nickel and reduces its crystallite size. The corrosion resistance of Ni deposit has been enhanced by the formation of Ni-Cu or Ni-Cu/ZrO2 composite coating. The average roughness values (Ra) of the Ni-Cu, Ni-Cu/ZrO2 coating is about 4–5 nm, 16–20 nm, respectively, indicating the rougher surface of Ni-Cu/ZrO2 in comparison with Ni-Cu alloy. Ni-Cu/ZrO2 composite coating presents higher hardness than Ni and Ni-Cu alloys. It was found that not only the current density, duty cycle, but also their combination affects the corrosion properties of the composites. Compared to others, Ni-Cu/ZrO2 coating electrodeposited at duty cycle of 30% has the highest impedance value. Also, the higher corrosion-resistant property of Ni–Cu/ZrO2 composites were obtained under the parameter combination of 3 A dm−2, 80% and 8 A dm−2, 40% in comparison with other parameter combination.