Insights into the degradation mechanism of Fe-40Ni-15Co superalloy exposed to marine atmospheric and high-temperature conditions

Abstract This study investigated the corrosion and oxidation mechanism of the Cr-free Fe-40Ni-15Co superalloy with exposure to a tropical marine atmosphere for one year and a subsequent high temperature of 650 °C for 300 h. The degradation behavior of the samples was evaluated based on surface characterization and analysis. In the tropical marine atmospheres, the corrosion process of the Fe-40Ni-15Co superalloy presented an initial localized type after one month of exposure and gradually developed into uniform. The corrosion products were mainly comprised of Fe2O3 and NiO, suppressing the pitting process. During the high-temperature oxidation process, all samples presented super-parabolic oxidation kinetics. Except for the initial active oxidation due to salt deposits, the corrosion products after atmospheric exposure could significantly enhance the oxidation resistance at 650 °C. An explanation for the degradation mechanism of the Fe-40Ni-15Co superalloy was developed based on the synergistic effects of atmospheric corrosion and high-temperature oxidation.