The Structure and Texture Development of Ni Alloy Electrodeposits. 1. Nickel-Iron Electrodeposits

SUMMARY

Electrodeposited nickel-iron alloys have been studied using ‘direct’ methods e.g. X-ray diffraction and transmission electron microscopy on coatings having different thicknesses, deposited on copper substrates at different current densities. The work has confirmed and extended the ideas of Finch et al^1.21.22 and Pangarov^16.23.24 to alloy deposition. It has been shown that a better understanding, particularly of the initial deposition stages, can be obtained by considering crystallographic, energy and electrochemical effects in combination rather than individually. Initially alloy is deposited on a ‘foreign’ substrate i.e. copper but subsequently the alloy deposit serves as the ‘substrate’. Similarly ‘old’ crystallites have to compete for growth with ‘newly’ nucleated ones as the deposit develops. The three stages of growth observed in nickel-iron are discussed

Whereas during initial nucleation the original substrate surface is the dominating influence, in the later stages the electrolytic parameters determine the structure of the deposit. If the crystallographic structure of the outer deposit differs markedly from that of the initial stages, then a transitional growth stage is involved. For example, in bcc nickel-iron deposits the film formed at the substrate/coating interface develops with a {110} texture, at intermediate thickness (0·5 μm to 1·0 μm) the {211} texture predominates whereas in ‘bulk deposits’ above 1·5 μm the {111} texture predominates. Furthermore, the structures of deposits studied in the present work tended to be fine grained in the initial stages but developed a coarser columnar structure due to selected grain growth with favoured grains becoming broader during the intermediate and final stage of growth.