Composition and structure of thin electrodeposited zinc-nickel coatings

The initial stages of Zn-Ni electrodeposition have been investigated through a study of composition and structure of thin deposits on copper and iron substrates. Compositional gradients through the 0.05 μm thick deposits formed at 10 and 60 mA cm−2 have been obtained using Glow Discharge Optical Emission Spectrometry (GDOES) and Scanning Transmission Electron Microscopy (STEM). The results obtained by GDOES show the influence of the substrate material on composition of the deposits, which may also be inferred from the STEM results. Glancing angle X-ray diffraction (GAXRD) patterns confirm the formation of a complex γ phase structure in all the nickel-zinc deposits even though at the coating/substrate interface in the coating deposited on mild steel at 10 mA cm−2 the nickel content approached 60 wt.% and therefore one would expect α Zn-Ni phase to be formed. The formation of γ phase rather than the α phase was discussed in terms of substrate effects.