Future power generation requires gas turbines with high efficiency and fuel flexibility. The latter requirement implies that the turbine components will be exposed to more aggressive service environments. In the present work the oxidation behavior of a commercial, cast Ni-base superalloy was studied in air-SO2 mixture, simulating combustion gases originating from high sulfur containing fuels.
The experiments were performed at 1050°C for various times up to 500 hours duration. For elucidating the mechanisms of corrosion attack, the studied alloy was characterized with a number of analytical methods including SEM / EDX and GDOES after different oxidation times. In the investigated material, internal sulfidation was observed underneath the oxide scale, which led to non-protective, breakaway oxidation after extended exposure times. The corrosion resistance of the studied material in the presence of SO2 could not be explained in terms of the concentrations of the main oxide scale forming elements, Cr and Al. Apart from the latter elements, various strengthening alloying additions including Hf, C and B were found to have a profound effect on the extent of the corrosion attack. The latter element was found to be rapidly enriched in the oxide scale thereby promoting internal oxidation and sulfidation.
Key words: downloadable, Ni-base superalloys, SO2-induced corrosion, Hf, C, B