Direct and pulse current electrodeposition of Ni-W-TiO2 nanocomposite coatings

Ni-W-TiO2 nanocomposite coatings have been obtained on mild steel surface by direct current (DC) and pulse current (PC) electrodeposition from Watts bath containing an ammonical citrate complexing agent. The morphology of the coatings was explored by scanning electron microscopy (SEM), atomic force microscopy (AFM) and the composition of the electrodeposits was analyzed by energy dispersive X-ray analysis (EDX). Surface morphology studies revealed that Ni-W alloy surface was covered by long needle like crystals and Ni-W-TiO2 composite coatings with smaller spherical sized grains. The coated surface contained 25.55% W and 5.55% Ti. XRD studies revealed that (111) plane was predominant in both Ni-W alloy deposits and Ni-W-TiO2 composite coatings. The patterns of the electrodeposits confirmed only fcc frame work structure. Microhardness values increased with TiO2 addition in the alloy. The corrosion resistance of Ni-W alloy deposit and TiO2 incorporated coatings was evaluated by Potentiodynamic polarization studies in 3.5% NaCl solutions. Corrosion current densities decreased with TiO2 inclusion in the alloy deposit. Electrochemical impedance studies revealed that the charge transfer resistance increased with TiO2 inclusion in the alloy deposits while the double layer capacitance decreased. The PC composites coatings offer uniform surface, high microhardness and enhanced corrosion resistance than DC composites coatings. Crown Copyright (c) 2012 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.