Influence of Two Different Salt Mixture Combinations of Na2SO4-NaCl-NaVO3 on Hot Corrosion Behavior of Ni-Base Superalloy Nimonic263 at 800 °C

Isothermal hot corrosion behavior of Nimonic263 alloy was studied under the influence of two different salt mixtures of 87.5 wt.% Na2SO4 + 5 wt.% NaCl + 7.5 wt.% NaVO3 (3SM) and 74 wt.% Na2SO4 + 21.7 wt.% NaCl + 4.3 wt.% NaVO3 (3SM-A) and also without salt mixtures up to 500 h at 800 °C. Corrosion kinetics showed that 3SM-A is more aggressive than 3SM. Multiple oxides, spinels, sulfides, vanadate compounds, and volatile compounds were observed during various hot corrosion reactions. The volatile compounds NaClO3 and CrMoO3, and SO3 gas are attributed to the weight loss under both 3SMs. The Na2SO4 of 3SM prevailed till 400 h, but that of 3SM-A disappeared within 5 h, as established conclusively by Raman spectra analysis. The sulfides plus internal oxide zone increased with the increased exposure duration as evident from the extensive EPMA analysis. Based on the critical analysis of corrosion kinetics and detailed microstructural characterization, fluxing and sulfidation followed by oxidation are identified as plausible hot corrosion mechanisms under both 3SMs. Besides, chlorination and high-temperature oxidation mechanisms occur under 3SM-A condition.