Cyclic oxidation behavior of Ni- and Fe-based superalloys in air and Na2SO4-25%NaCl molten salt environment at 800 oC

Abstract

The present investigation aims to evaluate the high-temperature oxidation and hot corrosion behaviour of Ni-based
superalloy (Superni 75) and Fe-based superalloy (Superfer 800H). The superalloy specimens were exposed to air and
molten salt (Na2SO4-25%NaCl) environment at 800 °C under cyclic conditions. The thermogravimetric technique was
used to establish the kinetics of corrosion. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron
probe micro analyser (EPMA) techniques were used to characterize the corrosion products. The hot corrosion
resistance of Ni-based superalloys was found to be better than that of Fe-based superalloys. The formation of scale
rich in Cr2O3, NiO and spinel NiCr2O4 has contributed for the better oxidation and hot corrosion resistance of Superni
75, whereas relatively lesser hot corrosion resistance of Superfer 800H is due to the formation of non-protective oxide
of iron, and sulphides of iron and nickel.