Sulfidation behavior in low-temperature hot corrosion of single crystal superalloy DD421 without SO_<i>x</i> atmosphere

Abstract

The hot corrosion behavior of the second generation nickel base single crystal superalloy DD421 coated with 90%(mass fraction) Na2SO4+10%NaCl (molten at 750 ℃) and pure Na2SO4 (solid state at 750 ℃) was investigated by salt coating method in 750 ℃ atmosphere (without SOx atmosphere). The results show that in the corrosion medium of molten mixed salt, the sulfidation reaction is mainly caused by the corrosion of liquid molten salt. After 100 h of hot corrosion, the main corrosion products are typical simple oxides (Al2O3, Cr2O3, TiO2) and Ni/Cr/Ti sulfides. However, in the pure Na2SO4 solid salt hot corrosion experiment, the corrosion products of the alloy after 100 h of hot corrosion are basically the same as those in the mixed salt test, but the thickness of the corrosion layer is relatively thinner and the size of sulfide is relatively larger. Combined with thermodynamics and microstructure analysis, it is clear that the alloy elements can react with solid Na2SO4 salt in the corrosion environment without SOx atmosphere.

Keywords

• superalloy
• hot corrosion
• sulfidation
• solid-state reaction