Type-I Hot Corrosion of Ni-Base Superalloy CM247LC in Presence of Molten Na2SO4 Film

Type-I hot corrosion behavior of CM247LC superalloy is evaluated in the air at 950 °C against low (3 to 4), intermediate (7 to 9), and high (12 to 14 mg cm−2) Na2SO4 deposits. Duration of thermal exposure is varied from a very short duration of 5 minutes to long duration of 1000 hours. The alloy shows poor corrosion resistance and undergoes complete disintegration after 500 hours of thermal exposure. Degradation of alloy increases with the increase in the duration of exposure as well as the initially deposited amount of the salt. Based on the systematic analysis of the corrosion scale, degradation mechanisms supported by the microstructural evidence are proposed. Fluxing, sulfidation-oxidation, and sulfide-undercutting are reported as the primary degradation mechanisms for CM247LC alloy in the presence of Na2SO4. Self-sustaining degradation of alloy leading to complete disintegration of specimen is caused by the changeover of fluxing mechanism from basic fluxing to alloy-induced fluxing.