Evaluation of Hot Corrosion of Hot Dip Aluminized Coated Superalloy IN738LC in Melted Na2SO4-25wt% NaCl Salt

Superalloy IN738LC is categorized as one of the most frequently utilized nickel base superalloys in the production of hot section components due to its multiphase microstructure maximizing its strength under elevated temperatures. In this study, a hot dip diffusion coating of aluminum was employed on the nickel-base superalloy Inconel 738LC substrate to enhance the hot corrosion resistance required for high-temperature applications, such as turbine blades. The aluminizing salt bath included Al powder with a particular composition, NaCl, KCl, Na3AlF6, and NaF. A thickness of about 48 µm was attained by applying the coating for 30 minutes at 720 °C. Bare and aluminized coated specimens were subjected to hot corrosion assessment in molten salt, with a composition of Na2SO4-25wt% NaCl at 720 C being exposed for 60 and 140 hours. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were conducted on the coating sample to ensure the successful deposition of the hot dip aluminized layer. The aluminized sample exhibited excellent corrosion resistance owing to the formation of an Al2O3 layer, which meant that after 140 hours of testing; very little coating deterioration was detected. In contrast, the naked sample suffered severe degradation and showed poor hot corrosion resistance. It was thought that the aluminized sample’s superior hot corrosion resistance resulted from the uniform and dense growth of an Al2O3 protective scale without any cracks on the superalloy surface