Improving the corrosion properties of amorphous Ni-P thin films using different additives

Ni-P amorphous coatings are considered as important engineering alloys. In this paper, the effects of various additives on the properties of Ni-P thin films were investigated, including saccharine, glycine, pyridinium propyl sulfonate, coumarin, sodium citrate, and cerium sulfate. Potentiodynamic polarization and electrochemical impedance spectroscopy tests, scanning electron microscopy, X-ray fluorescence and diffraction, and atomic force microscopy were employed to study the properties of the samples. It was found that a proper concentration of these additives, except saccharine, noticeably improved the corrosion resistance, especially at high potentials (about 25% increase in instantaneous corrosion efficiency and about 300% in corrosion efficiency at high potentials) and decreased the surface roughness (by about 10 to 55%) of Ni-P thin films. Thinner, more uniform, and less porous coatings were formed in the presence of additives. Except saccharine, all the additives enhanced the P content of Ni-P films, which thus kept their amorphous structure; saccharine highly suppressed the incorporation of P inside the Ni lattice and a mixed amorphous-crystalline structure was stabilized.