Passivation effects on corrosion and cavitation erosion resistance of UNS S32205 duplex alloy in 3.5% NaCl

The electrochemical and electronic properties of UNS S32205 duplex alloy passive film were studied with EIS and Mott-Schottky techniques, respectively. The role of Fe and Cr oxides in the passive film formation was checked using XPS. The cavitation behaviour was evaluated using an optical microscope OM. The studies were carried out in a 3.5% NaCl solution saturated with CO2 on various types of passive films: the air-formed (AF), the long-term aged (LTA), and the passivated (P1 and P2). The results showed that the electrochemical passivation treatment at passive region 1 improved the corrosion and cavitation behaviour compared to AF, while the long-term aging process made it worse. Passivation at passive region 2 was harmful and recorded the worst results under corrosion and cavitation erosion conditions. Thus, exposing the equipment made of this alloy to the passivation treatment at special conditions makes it more resistant to corrosion and cavitation erosion.