Selective corrosion in sodium chloride aqueous solution of cupronickel alloys with aluminum and iron additions

• Published in: Corrosion (Houston, Tex.) Vol. 63; no. 3; pp. 211 - 219
• Main Authors: LIBERTO, R. C. N, MAGNABOSCO, R, ALONSO-FALLEIROS, N
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.03.2007
• Subjects: Alloys; Aluminium; Aluminum; Analytical methods; Applied sciences; Aqueous solutions; Cooling systems; Copper; Corrosion; Corrosion mechanisms; Corrosion products; Cupronickel; Electron microscopy; Exact sciences and technology; Iron; Light microscopy; Localized corrosion; Metals. Metallurgy; Microscopy; Nickel; Optical microscopy; Polarization; Scanning electron microscopy; Sodium; Sodium chloride; Spectroscopy; Iron addition; Chlorides; cupronickel alloys; potentiodynamic polarization; Selective corrosion; Aluminium addition; Aqueous solution; Sodium chloride; denickelification
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3278345

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 (Epb) was determined in all solutions, related to the initiation of selective corrosion of nickel. When submitted to cyclic potentiodynamic polarization, alloys with higher Epb 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.