Evolution of the Corrosion Product Film on Nickel-Aluminum Bronze and Its Corrosion Behavior in 3.5 wt % NaCl Solution

The in-situ studies of the corrosion product film on nickel-aluminum bronze are significant for explaining the mechanism of its corrosion resistance. In this paper, the corrosion behavior of nickel-aluminum bronze and the formation process of the protective film in 3.5 wt % NaCl solution are systematically investigated. The results of scanning electron microscope analysis and electrochemical tests indicate that the corrosion resistance of nickel-aluminum bronze is improved due to the formation of the corrosion product film. The change of local electrochemical property on the corrosion product film during the immersion time is evaluated via in-situ scanning vibrating electrode technique, and it reveals the evolution rules of ionic flux in real time. The formation process of the protective film on different phases in nickel-aluminum bronze is observed directly by in-situ atomic force microscopy as height change measurements. The α phases at different locations present different corrosion behaviors, and the lamellar α phase within the α + κ(III) eutectoid structure gets more serious corrosion attack. The κ phases establish a stable and dense protective film in short time, preventing the corrosion attack effectively. The β′ phase, however, suffers the most serious corrosion damage until a protective film is formed after 150 min of immersion.