Abstract
The influence of the electrode potential on the corrosion behavior of a series of Ni-base superalloys has been investigated in a (mole %) 90Na2SO4-10K2SO4 melt at 1173 K. Acidic fluxing occurs at positive potentials and basic fluxing at negative potentials. A protective scale is formed in an intermediate (neutral) potential range on high chromium-containing alloys such as IN-738LC, IN-939, IN-597, and IN-657. The breakthrough potentials for acidic and basic fluxing depend on the composition of the alloy. Alloys with low chromium contents such as IN-100 and IN-713LC do not form stable protective scales at any potential. Numerous sulfide phases have been identified in the scale and subscale, depending on potential, severity of attack, and material composition. NaCrS2 only forms under basic fluxing conditions. Its presence can therefore be considered as an indication that basic fluxing conditions have existed.
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