Study On Pitting Behavior Of Oxide Inclusions In Amorphous Metallic Coatings

Pitting damage is one of the most difficult problems in material research because of its great concealment and abruptness.Fe-based amorphous alloy coatings have excellent corrosion resistance and wear resistance,which makes them have very important application prospects in the industry.However,the structure of oxide inclusions increases the pitting sensitivity.The metastable nature of amorphous makes the experimental study of pitting process difficult.How to clarify the role of oxide inclusions in the pitting process of amorphous coating by effective means is particularly important for understanding the pitting mechanism of amorphous materials.This paper mainly uses the method of combining the macro experimental analysis with the micro simulation calculation.The Fe-based amorphous alloy coating was prepared by Activated combustion high velocity air fuel?AC-HVAF?.The passivation and pitting behavior of the amorphous coating in the corrosive medium containing Cl^-and S^2-were studied by means of corrosion electrochemical test technology.Based on the molecular dynamics simulation,the adsorption model of aggressive anion and oxide surface was established,and the interaction between Cl^-and S^2-aggressive anion and oxide inclusions in amorphous coating was analyzed.There are a lot of pores and oxide crystal phase in Fe-based amorphous coating.In the solution of Na Cl,Na₂S and their mixtures,the pitting corrosion of the amorphous coating is obvious,and the passivation current density increases with the increase of Na₂S concentration.After adding 3.5%Na Cl,the change of Na₂S concentration has little effect on the corrosion,and Cl^-in the mixed solution is the main factor affecting the pitting corrosion of the coating.Pitting corrosion is mainly caused by coating pores and oxide inclusions.There are many defects and vacancies in passivation film,which provide diffusion channel for Cl^-and lead to local corrosion under corrosion products.For the oxide inclusions of Fe,Cr and Mo with different valence states in the amorphous coating,the molecular dynamics simulation shows that Cl^-,S^2-have the strongest diffusion force and the largest negative adsorption energy on the?001?surface of the inclusion phase Cr₂O₃,and the oxide of Cr is one of the sensitive phases easy to cause pitting corrosion of the amorphous coating.In the mixed solution,the addition of S^2-does not affect the molecular force with Cr₂O₃,and Cl^-is the dominant factor.The chemisorption mainly occurs between S^2-and Cr₂O₃ surface,while Cl^-mainly induces pitting through permeation mechanism and interface with metal oxide.This result provides a strong theoretical background for the local dissolution of oxide inclusions in Fe-based amorphous coatings.