Abstract
Corrosion rates have been measured electrochemically for IN 738 and FSX 414 gas turbine alloys in molten alkali metal sulphates at 1100 K under 1 atm. (101 kNm−2) of oxygen and 1·95 × 10−4 atm. (19·8 Nm−2) SO3 for periods of up to 2500 h. Initially protective scale formation, suggested by decreasing corrosion rate, was observed, but this wasfollowed by an increasing corrosion rate associated with failure of the protective scale. Microscopic examination of corroded specimens revealed a sulphide phase beneath the oxide layer penetrating along grain boundaries into the substrate metal.
The effect of oxidation reactions, other than the corrosion of the metal, on the determination of the corrosion current has been considered. Under some conditions the corrosion potential approaches the redox potential of the melt and oxidation reactionsfor the molten sulphate contribute significantly to the apparent corrosion current. A correction for this effect is described.
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