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 Cr₂O_3, 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.

Key Words: Superalloys, Hot corrosion, Oxidation, Molten salt environment