Hot corrosion behavior of a centimeter Fe-based amorphous composite coating prepared by laser cladding in molten Na2SO4Â +Â K2SO4 salts

An Fe-based amorphous composite coating with a thickness of 15 mm was prepared by laser cladding method. Hot corrosion behavior of the composite coating in the molten Na2SO4 + K2SO4 at 650 °C was investigated by the weight change kinetics, X-ray diffraction (XRD), scanning electron microscopy (SEM) as well as energy dispersive X-ray spectroscopy (EDS). The mass gain measurements were performed after each cycle to establish the kinetics of corrosion using the thermogravimetric technique. The coating consisted of an Fe-Cr-rich amorphous matrix and several kinds of borides. Compared to the microstructure of the substrate specimens, no spallation or crack of the oxide scales was observed on the coating surface, indicating that the thermal stresses on the composite coating are lower than the substrate specimens. The results indicated that the composite coating exhibited high hot corrosion resistance in the molten Na2SO4 + K2SO4 due to the amorphous composite microstructure, which is in favor of the formation of a continuous and protective Cr2O3 oxide scale. Usually, the Cr2O3 oxide scale acts as an effective barrier to the inward diffusion of corrosive species during the hot corrosion process.