Pitting corrosion mechanism of Cl-- and S2--induced by oxide inclusions in Fe-based amorphous metallic coatings

Fe-based amorphous metallic coatings (AMCs) were prepared by activated combustion-high velocity air fuel (AC-HVAF) method. The corrosion mechanism of AMCs under different corrosion conditions was investigated using corrosion electrochemical tests. The process of pitting corrosion induced by oxide inclusions was uncovered by molecular dynamics (MD) simulation. Results show that the passivation current density of the AMCs increases with increasing concentration of S2-. After adding NaCl, variation in the concentration of S2- shows minimal effect on the corrosion. Cl- is the main factor that affects the pitting corrosion of the AMCs when Cl- and S2- coexist. The pitting corrosion of AMCs is related to oxides of Fe, Cr and Mo. Cr2O3 inclusion is one of the sensitive phases to induce the pitting initiation for AMCs. Cl- and S2- exhibit the strongest diffusion force and the greatest negative adsorption energy on the (001) surface of Cr2O3 inclusion during the MD calculation. Pitting corrosion induced by Cl- occurs through the penetration mechanism and adsorption at the interface with metal oxides. The addition of S2- does not affect the molecular force and pitting tendency between Cr2O3 inclusion and NaCl. Hence, Cl- primarily affects the pitting corrosion of AMCs in mixed solutions. Results of simulation and experiment provide a suitable method for solving the sensitive location of pitting initiation induced by oxide inclusions in Fe-based AMCs.