Ni-W coatings electrodeposited on carbon steel: Chemical composition, mechanical properties and corrosion resistance

Abstract

Hard, ductile and adherent nanostructured Ni-W coatings were electrodeposited on carbon steel fromelectrolyte solutions containing sodium tungstate, nickel sulfate and sodium citrate, using different current pulse programs. Current pulse frequency was the dominant factor to define chemical composition,grain size, thickness and hardness. According to the electrodeposition conditions the deposited coatings showed 15-30 at% W, the grain size ranged from 65 to 140 nm, and the hardness varied from 650 to850 Hv. Tungsten carbide also present in the coating contributed to its hardness. The corrosion resistanceof the Ni-W coated steel was tested by potentiodynamic polarization in a neutral medium containingsulphate ions. The Ni-W coating protected the carbon steel from localized corrosion induced by sulphate anions.