Hot corrosion behaviors of 921A alloy and HVAF-sprayed Fe-based amorphous coating covered with KCl-ZnCl₂ salts

Hot corrosion behaviors of the 921A alloy and Fe-based amorphous coating induced by KCl-10% ZnCl2 and KCl-55% ZnCl2 salts at 450 & DEG;C in air for 40 h were investigated. Results show that the 921A alloy suffers more serious corrosion damage than the coating and KCl-55% ZnCl2 salts are more corrosive than KCl-10% ZnCl2 salts. In the two salts, an Fe2O3 layer is formed on the 921A alloy surface, while an outer Fe-rich oxide layer and an inner Cr-rich oxide layer are formed on the surface of the coating. Moreover, a certain amount of metal chloride can be found at the oxide/alloy (coating) interface, which can be explained by "active oxidation". However, the corrosion resistance of the Fe-based amorphous coating did not achieve the desired results, probably because the intersplats in the coating serve as corrosion diffusing channels, which facilitate the corrosion damage rate. Nevertheless, the coating is still in amorphous state after hot corrosion exposure.