Insights into corrosion resistance enhancement of nickel–phosphorus metallic glass in acid environment by the incorporation of copper

Abstract

The corrosion resistance of a Ni–P metallic glass could be enhanced significantly by the addition of Cu. However, the mechanism of corrosion resistance remains unclear. In this study, Ni–Cu–P amorphous coatings with different Cu contents were chemically deposited on mild steel. The effects of the Cu content on the morphology, composition, microstructure, thermal stability and corrosion resistance of the coatings were investigated through scanning electron microscopy, energy-dispersive spectroscopy, X–ray diffraction analysis, differential scanning calorimetry, and electrochemical tests. The corrosion products on the coating in the acid corrosion medium were analyzed through X–ray photoelectron spectroscopy. The cluster size in the Ni–Cu–P amorphous coating initially decreased and then increased with an increase in Cu content. An amorphous coating with relatively smaller ordered clusters showed better corrosion resistance. In 5 wt% H2SO4 solution, the compact phosphate and hypophosphate passive film was generated on the Ni–Cu–P coating with n–type semiconductor characteristics.