Effect of Sulfur on Hot Corrosion Behavior of Nickel-Based Superalloys at 900 °C

Nickel-based superalloys are extensively used in fabricating high-temperature gas turbine components, owing to their superior high-temperature strength, excellent structural stability, and remarkable hot corrosion resistance. The influence of impurity sulfur content on their hot corrosion performance is a core scientific issue in hot-end component compositional design and smelting. This study investigated chromium (Cr)-rich nickel-based superalloys with sulfur (S) contents of 3 ppm, 16 ppm, and 42 ppm via XRD, SEM, and an EPMA, focusing on their hot corrosion behavior under a 100% Na2SO4 deposit at 900 °C. The results indicated that their hot corrosion products were basically identical, forming a Cr-dominated outer oxide layer rich in Ti, Co, and Ni, an Al2O3-based inner corrosion zone, and a CrSx-dominated sulfide layer. With increasing sulfur content, the outer layer thickness decreased from approximately 30 μm to less than 20 μm, pores in the outer oxide layer increased in quantity and size, and internal sulfides and nitrides accumulated. The average depth of spallation increased from 55 μm for the S3 alloy to 80 μm for the S16 alloy, with the S42 alloy showing even more extensive spallation. The alloy’s hot corrosion performance deteriorated notably with increasing S content. The mechanism of sulfur’s effect on hot corrosion behavior is that sulfur in the alloy segregates at oxide film defects, enhancing defect stability and increasing their quantity and size. These defects serve as rapid diffusion channels for corrosive media, thereby accelerating the alloy’s hot corrosion rate.