Selective Corrosion in Sodium Chloride Aqueous Solution of Cupronickel Alloys with Aluminum and Iron Additions

Cupronickel pipes are widely used in cooling systems. Under this application, localized corrosion is observed, particularly associated with selective corrosion of nickel (denickelification). This work studied the denickelification process in solution-treated cupronickel alloys 90-10 (Cu-10wt%Ni), with aluminum and iron additions, in 0.01 M, 0.1 M, or 0.6 M sodium chloride (NaCl) aqueous solutions. Polished surfaces of the studied materials were submitted to potentiodynamic polarization, and after that, the polarized surfaces were studied using optical microscopy (OM) and scanning electron microscopy (SEM) assisted by energy-dispersive spectroscopy (EDS). A passivity break potential (E_pb) was determined in all solutions, related to the initiation of selective corrosion of nickel. When submitted to cyclic potentiodynamic polarization, alloys with higher E_pb showed the higher nickel losses in localized spots. However, potentiodynamic polarization tests conducted in 0.01 M NaCl until current densities of 10⁻¹ A/cm² were reached showed that the selective corrosion process was stopped by the formation of copper-rich corrosion products over the surface.