Optimization of electrodeposition nanocrytalline Ni-Fe alloy coatings for the replacement of Ni coatings

Fabricating nanocrystalline Ni-Fe alloy coatings with excellent brightness and corrosion resistance could reduce the use of Ni and benefit economically. Nanocrystalline Ni-Fe alloy coatings were electrodeposited on steel substrates and the coatings with 34.55% Fe content were achieved at the optimized conditions with the current efficiency high up to 80.30%. The electrodeposition behavior of Ni-Fe coatings was investigated by cyclic voltammetry (CV), chronopotentiometry and chronoamperometry. CV tests illustrate that Ni²⁺ and Fe²⁺ are co-electrodeposited to form single phase and the deposition of Ni is inhibited by the presence of Fe²⁺ while the deposition of Fe is boosted by the Ni²⁺ according to chronopotentiometry. The nucleation and growth of nanocrystalline Ni-Fe alloy coatings is 3D diffusion-controlled instantaneous nucleation process. Intermetallic compound, namely Ni₃Fe phase, was formed according to XRD analysis and TEM analysis, while the mean grain size is 4.79 nm. SEM and AFM images demonstrate that nanocrystalline and compact surface were fabricated and the roughness is lower than 5 nm, better than pure Ni coating. Due to the nanocrystalline and compact surface, the i_corr and R_ct of nanocrystalline Ni-Fe alloy coating are 0.7544 μA cm⁻² and 8560 Ω respectively, indicating that Ni-Fe alloy coating is of good corrosion resistance.