Effects of solid NaCl deposit and water vapor on corrosion resistance of K452 superalloy and aluminized coating

Abstract

Aluminized coating was prepared on K452 superalloy by chemical vapor deposition (CVD) technique. The oxidation/corrosion behavior of alloy and coating were investigated at 750 ℃ in air, air with solid NaCl deposit and moist air with solid NaCl deposit, respectively. The microstructure and composition of samples were characterized by SEM/EDS and XRD techniques. The results demonstrated that aluminized coating exhibited better oxidation/corrosion resistance than K452 alloy in the three environments above. And the main oxidation and corrosion products of alloy were Cr2O3 and NiO, respectively. This indicated that Ni participated in the corrosion process due to the depletion of Cr during accelerated corrosion. Therefore, the established corrosion scale was non-protective, which could not protect underlying alloy from accelerated corrosion. Contrarily, the main oxidation and corrosion products of coating were protective Al2O3, which acted as a barrier to separate coating from NaCl and oxygen, interrupting the self-sustainable accelerated corrosion. Additionally, the presence of water vapor was beneficial in reducing the spallation of corrosion products within a short time. The mechanisms of K452 alloy and aluminized coating in the three environments above were discussed in detail.