Hot Corrosion Performance of Single-Crystal CMSX-4 and CMSX-486 Superalloys in the Mixture of Na2SO4-NaCl Melts

A modification in the chemistry of single-crystal CMSX-4 to produce CMSX-486 superalloy has been reported in the literature to be accomplished without degradation in high-temperature mechanical performance. However, adequate attention has not yet been focussed on the hot corrosion response of the alloy considering its chemical composition modification. This paper reports for the first time that a considerable degradation in the hot corrosion resistance of CMSX-4 occurs by the modification of its chemistry. Corrosion tests at different salt concentrations and temperatures showed that the hot corrosion resistance of CMSX-486 is worse than the conventional CMSX-4 alloy. The difference in the corrosion resistance characteristics of the two alloys is attributable to the nature of the protective oxide layer formed on the materials during hot corrosion. Characterization using various advanced techniques revealed that the oxide layer formed on CMSX-486 consists of less amount of protective and coherent Al2O3 and Cr2O3 film than CMSX-4, and this is the reason for its poor hot corrosion resistance.