Reassessment of the Zn-Fe phases in electrodeposited Zn-Fe layers

In the present study, a detailed investigation of the structure and morphology of electrodeposited zinc-iron layers is presented. Both the influence of plating conditions and the Fe content of the deposits on the phase composition are examined and the mechanisms for the observed morphological changes are discussed. The phase identification in the electroplated zinc-iron layers confirmed the coexistence of several metastable compounds in the deposit. The phase distribution depends mainly on the Fe content in the deposit, yet the process parameters and the composition of the electrolyte can influence the phase fractions. At low Fe contents the as-deposited layers consist of both pure zinc and a Fe supersaturated η phase which is characterized by a c/a ratio lower than that of pure zinc. Small amounts of δ and Γ/Γ1 are present in the deposits. As the Fe content in the layer increases the δ and Γ/Γ1 phase fractions increase while the amount of η decreases. A close investigation of the X-ray spectra showed that Γ phase particles initiate the Γ/Γ1 phase growth after epitaxial nucleation on the η phase ledges. When the Γ/Γ1 phase fraction increases, Γ1 is the main component. Annealing of the as-deposited layers, however, causes the η phase to transform to δ, while Γ1 partly changes to the more stable Γ phase. The ζ phase, commonly observed in zinc-iron diffusion alloys, remained absent even after annealing of the deposits.