The texture–surface morphology relationship in zinc–iron electrolytic coatings


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Abstract

A combination of X-ray texture measurements and atomic force microscopy topographical analysis was used to characterize the growth surface of Zn–Fe alloys electrolytically deposited on cold rolled steel substrates. Deposits, which initially exhibited a morphology of approximately 20 nm thick platelets inclined 10°–20° to the substrate surface, subsequently evolved either into triangular pyramids or hexagonal columnar crystals depending on the presence of Sn2+ ions in the sulphate electrolyte. The morphology of the triangular pyramids, formed in the absence of Sn2+ ions, had (1 0 ˙ 0) and (0 0 ˙ 1) planes of η (hcp) phase tilted to the substrate surface. For the morphology of hexagonal columnar crystals, formed in the presence of Sn2+ ions, the (0 0 · 1) basal planes of η phase were aligned parallel to the substrate surface. The macro and nano-size steps of growth were identified on both morphologies in order to locate the active growth front. It is concluded that the lateral growth on the same (0 0 · 1) basal planes of η phase led to the formation of essentially different morphologies and textures of the Zn–Fe deposits.

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