Abstract
Increasing concern over toxic wastes produced by nickel–chromium (Ni–Cr) plating industries has resulted in strong research efforts to replace conventional plating by physical vapour deposition techniques like evaporation and sputtering. Ni–Cr coatings on mild steel substrates produced by an electron beam evaporation process with layer thickness of ∼8–10 m m have been investigated with regard to the structural and corrosion properties. The structure of the coating was evaluated by X-ray diffractometer (XRD). The (110) Cr and (200) Ni predominant peaks with the crystallite size in the range of 25–30 nm was observed from XRD pattern. The electrochemical polarisation studies performed on samples showed the corrosion resistant nature of the evaporated Cr coating with Ni underlayer on mild steel substrates. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the surface characteristics of the samples before and after the electrochemical corrosion tests. The localised corrosion through a micropore in the evaporated Cr deposit and its penetration to the Ni layer was observed from SEM. The smaller change in roughness observed from AFM reflects the resistance of this coating to corrosion breakdown.
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