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Fireside corrosion behavior of Inconel 740H superalloy was studied at 750 °C in simulated coal ash/flue gas environments by means of XRD, SEM and EDS. The results indicated that the corrosion behavior was strongly related to the SO2 levels and was significantly affected by NaCl additions. In presence of the atmospheres with 0.1 % SO2, the alloy exhibited the highest corrosion resistance due to formation of a stable and dense Cr2O3 film. In presence of the atmosphere with 1.5 % SO2, however, a non-coherent and porous Cr2O3 film was formed. The thickness of film and internal sulfides were substantially increased. The NaCl additions significantly accelerated the corrosion process. A non-protective outer oxide film was formed, composed by multiple layers with serious inner sulfide and spallation. The depths of internal oxidizing and sulfuration zones were significantly increased. The mechanism of ash corrosion formation was also discussed.

Inconel 740H is a nickel-based alloy for pressure components of ultra-supercritical boilers. Its chemical composition and strengthened matrix, as well as corrosion resistance, provide the highest creep resistance among the materials recommended for use in high-performance pressure components of power units. This paper investigates the changes in the microstructure and mechanical properties after ageing at 700 and 750 &deg, C for 1000, 10,000, 20,000, and 30,000 h. Observation of the microstructure was performed using scanning and transmission electron microscopy. The identification of existing precipitates was conducted by X-ray phase analysis. The effects of time and ageing at elevated temperatures on the mechanical properties and precipitation process in the test alloy are discussed. The presented results are part of the material characteristics of the new-generation alloys to be used in the design of pressure equipment for steam boilers, as well as in diagnostic work during operation.