The hot corrosion of nickel-based ternary alloys and superalloys for gas turbine applications. II. The mechanism of corrosion in SO2/O2 atmospheres

A stage-by-stage mechanism is proposed for the corrosion of Ni-20Cr-X ternary alloys in SO2/O2 (in equilibrium with SO3) atmospheres. Stage 1 represents the building of the initial oxide layer which takes place immediately. Stage 2 elaborates on the build-up of external oxide layers and sulphide areas and can be applied to both NiSO4 or non-NiSO4 forming conditions. Stage 3 elucidates the development of the internal striated sulphide structure. The beneficial effect of the ternary additions of Al, V and Si is related to the mechanism.