Electrodeposition of nickel-zinc alloy coatings with high nickel content

The electrodeposition of Ni–Zn alloy coatings with high nickel content from a Watts type bath was studied. The investigation was performed by means of cyclic voltammetry, potentiostatic electrodeposition, X-ray diffraction, energy dispersive X-ray analysis, scanning electron microscopy and transmission electron microscopy. The effect of the experimental parameters (deposition potential, bath temperature, zinc concentration, presence of additives) on the coating composition, morphology and structure was studied. The obtained results show that the addition of Zn2+ to the deposition bath leads to a strong decrease in the cathodic current density indicating a remarkable inhibition of Ni reduction. Even if anomalous codeposition was observed for all the studied experimental conditions, nickel rich alloys were obtained due to the mass transport control of zinc deposition. A strong decrease in the current efficiencies was observed when Zn percentage in the deposit was higher than 7wt.%. The incorporation of Zn in the fcc Ni lattice leads to a remarkable decrease in the grain size. The presence of nanocrystalline Ni–Zn beta-phase was observed in the alloys having Zn content higher than about 8 wt.%.