The Structure and Texture Development of Ni Alloy Electrodeposits—III Nickel-Zinc Electrodeposits

Abstract

SUMMARYElectrodeposited nickel-zinc alloys have been studied using ‘direct’ methods e.g. x-ray diffraction and transmission electron microscopy on coatings having different thicknesses, deposited on mild steel and copper substrates at current densities of 10 and 60 mA cm2. In all cases the coatings evolved with a complex bcc gamma phase. The work has confirmed and extended the ideas of Finch et al.1 3 and Pangarov4-6 to alloy deposition. It has been shown that a better understanding, particularly of the initial deposition stages, can be obtained by considering both strain and surface energy effects. In all cases the film formed at the coating/substrate interface develops with a {110} texture on both mild steel and copper substrates at current densities of 10 and 60 mA cm2. From surface energy considerations a {110} texture would be expected as in bcc metals this orientation has the lowest surface energy. XRD measurements by glancing angle indicate that in the initial stage of deposition, the zinc and nickel atoms deposit in the recesses in the {110) plane of the mild steel as the initially formed deposit had a d-spacing similar to that of the mild steel. Similar effects were also indicated for the nickel-zinc film deposited on copper substrates indicating that ‘templating’ occurs during deposition on both mild steel and copper substrates. A semi-quantitative model based on surface energy and strain energy considerations has been used to explain the texture development. Furthermore, the structures of deposits studied in the present work tended to be fine grained in the initial stages but developed coarser columnar due to selected grain growth with favoured grains becoming broader during the intermediate and final of growth. However, unlike previous work on bcc nickel-zinc alloys7 which developed a {111} texture in thicker films the {110} texture remained dominant in the majority of the films examined and the final texture in 20 μm bulk films was a {110}.