Comparison of chromium coatings and electrochemical behaviour with direct current and pulse current deposition in trivalent chromium formate urea bath as alternative to conventional Cr coatings

Abstract

Alternative process to hexavalent chromium (Cr) plating, substitute materials and new designs are urgently needed owing to the requirement of ‘clean’ manufacture. Trivalent Cr coatings with thickness of 29·7 μm, Hardness (HV 1131) and acceptable quality that can be used for wear resistance as well as corrosion resistance purposes were produced successfully in the present work. The results show that the coatings exhibited crack free surface and amorphous/microcrystalline structure. The effect of direct current (DC) and pulse current (PC) on the thickness, hardness and current efficiencies were compared with DC and PC deposition. The Cr coatings were characterised by scanning electron microscope, atomic force microscopy and X-ray diffraction. The morphology of Cr deposits obtained in the formate urea electrolyte is a typical nodular and fine grained structure. As regards to the electrochemical behaviour, the deposited Cr by PC and DC coatings exhibited better corrosion resistance than the mild steel. Therefore, the electroplated Cr coatings are environmentally acceptable to replace the conventional Cr coatings.

Keywords

Trivalent Cr bath Direct current Pulse current Average current On-time Off-time Duty cycle Urea Amorphous/microcrystalline Formate

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