Abstract
The influence of the electrode potential on the corrosion behavior of a series of nickel- and cobalt-base gas turbine alloys has been investigated in a (mole %) 53Na2SO4+7CaSO4+40MgSO4 melt at 1073 and 1173 K and in a 90Na2SO4+10K2SO4 melt at 1173 K. Only acidic fluxing is observed in the (Na2,Ca, Mg)SO4 melt at positive potentials while a protective scale rich in MgO is formed on all alloys at negative potentials. This scale prevents basic fluxing because MgO is insoluble in neutral and basic melts. The breakthrough potential for acidic fluxing is a function of the material composition. Increasing chromium content of the alloys extends the potential range of protective film formation. Acidic and basic fluxing are observed in the (Na, K)2SO4 melt. Acidic fluxing occurs at positive and basic fluxing at negative potentials. A protective scale is formed in an intermediate (neutral) potential range on the high-chromium alloys IN-597 and IN-738 LC. Here, too, the breakthrough potentials for acidic and basic fluxing are influenced by the composition of the alloys.
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