Hot corrosion mechanism of intermetallic compound Ni3Al

The molten salt-induced oxidation/sulfidation (hot corrosion) on nickel alummide intermetallic compound (Ni3Al, Ni-11.7 wt.%Al-0.6 wt.%Zr-0.01 wt.%B) has been studied in the 1%SO2/air gas mixtures. X-ray analyses for the hot-corroded specimen tested at different period of time show only NiO formed at 605 degreesC, and NiO and NiAl2O4 at 800 and 1000 degreesC. EDAX analyses reveal that AIS(x) and/or NiS, are produced beneath the oxide scales at all temperatures. From the experimental results, the hot corrosion mechanism can be described as follows. NiO oxide formation consumes oxygen in molten salt. The consumption of oxygen will locally reduce the oxygen and increase the sulfur partial pressure in molten salt. This partial pressure change can be represented by the stability diagram. As the increased sulfur partial pressure reaches the equilibrium partial pressure region of NiSx and/or AlSx, NiSx and/or AlSx will form at the salUalloy interface through sulfidation reaction. The consumption of sulfur will balance out the sulfur and oxygen partial pressure increases in molten salt. This will force NiO to form again. This process also suggests that NiO and NiSx and/or AlSx will be produced simultaneously. Since the produced sulfide is thermodynamically unstable when the oxygen potential increases, it is possible for sulfide to convert into oxides (NiO, Al2O3, and NiAl2O4) through the necessary reactions. There are two possibilities for the formation of spinel phase, which is produced either through the reaction of Al and Ni with oxygen in the molten salt or through the evolution of sulfides. (C) 2002 Elsevier Science B.V. All right reserved.