Electrodeposition of nanocrystalline Zn/Ni multilayer coatings from single bath: Influences of deposition current densities and number of layers on characteristics of deposits

Abstract

Zn/Ni nanocrystalline multilayer coatings were electrodeposited using single bath method and switching current densities. Effect of deposition current densities (i1 and i2) and number of layers (n) on composition, surface morphology and roughness, microhardness, phase structure and corrosion resistance of Zn/Ni multilayers were studied and compared with that of single layer. Analyzing and optimizing the influences of mentioned parameters on corrosion resistance of multilayers carried out through Response Surface Methodology. The model based on RSM results demonstrated that improvement in corrosion resistance due to increase in “difference of deposition current densities” was more effective in higher number of layers. Also, as the mentioned difference surpassed from a defintie value, the reduction trend of corrosion current density approximately stopped. The overall Ni content of the multilayer with least corrosion current was less than that of specimens with higher Ni content. Increase in number of layers could enhance the microhardness more than 50%. Also, layering leaded to finer surface morphology as well as lower roughness. The interfaces in deposited multilayers comprised of same crystall structure (Ni2Zn11) but different composition and crystallite size.