Hot corrosion behavior of aluminized and Si-modified aluminized coated IN-738LC produced by a novel hot-dip process

Abstract

Hot-dip aluminum and Si-modified aluminum diffusion coatings were applied on the substrate of nickel-base superalloy IN-738LC to enhance its hot corrosion behavior for high-temperature applications. Aluminizing salt bath consisted of KCl, NaCl, NaF, Na3AlF6, and Al powder, while the Si-modified salt bath contained NaCl, NaF, KCl, Na2SiF6, and Na3AlF6. A temperature of 750 °C and an operating time of 30 min were applied for coating. At this condition, the thicknesses of about 48 and 35 µm were achieved for aluminum and Si-modified aluminum coatings, respectively. All coated samples were immersed in the molten salt of Na2SO4–25 wt%NaCl composition for 60 and 140 h for the hot corrosion test. It was found that the Si-modified coated samples had better corrosion resistance. The high hot corrosion resistance was believed to be due to the formation of the protective and continuous scale of Al2O3 and SiO2 and no sign of sulfidation was detected at 750 °C.