Electrodeposition of nanocrystalline Ni-Mo alloys in pyrophosphate baths

Abstract

Nanocrystalline Ni-Mo alloy coatings with excellent brightness, high hardness, and corrosion resistance were prepared. Nanocrystalline Ni-Mo alloy coating with a Mo content of 14.94 at% was electrodeposited on the copper foil substrate under the optimized conditions with the current efficiency of 51.64%. The electrodeposition behavior of Ni-Mo alloy coatings was studied by cathodic polarization curve and chronopotentiometry. Chronopotentiometry showed that the nucleation rate of Ni-Mo alloys can be accelerated with the increase of current density. Meanwhile, the cathodic polarization curves show that the additives can effectively inhibit the electrodeposition of Ni-Mo alloys. The (2 0 0) and (2 2 0) diffraction peaks of Ni gradually disappeared and the grain size gradually decreased with the increase of Mo content in the alloy coating according to XRD and TEM analysis. Scanning electron microscope (SEM) and confocal microscope observation results show that the coating becomes smoother and denser with the increase of Mo content when Mo content was lower than 14.94 at%, after which the density of the coating saw a decline due to the intensified hydrogen evolution reaction. The microhardness results of the alloy coating show that the microhardness of the alloy coating is related to the solid solution strengthening, texture evolution, and plastic deformation of the alloy. Meanwhile, the alloy coating has a Hall-Petch relationship and inverse Hall-Petch relationship, and the critical grain size is 5.5 nm. The corrosion resistance of Ni-Mo alloy coating is better than that of pure Ni coating, and the corrosion resistance is optimal when the Mo content is about 15 at%. In addition, in the plating solution containing additives, the deposited Ni-Mo alloy coating is smoother and denser, and the hardness and corrosion resistance of the alloy coating is also greatly improved.