Research On The Corrosion Behavior Of Fe-based Amorphous Metallic Coatings Under Mechanical Factors

Fe-based amorphous coatings exhibit enhanced mechanical properties, excellent corrosion resistance, highly cost-effective and strong ability of amorphous formation, which can be applied in corrosive and/or abrasive environments. Recently, activated combustion high-velocity air fuel(AC-HVAF) technique has been developed to prepare highly qulity of amorphous coatings with higher spraying rate and deposition efficiency compared to conventional high-velocity oxygen fuel(HVOF) spraying technology, which can broaden the application of amorphous metallic coatings in corrosive and/or abrasive environments.The AC-HVAF amorphous coatings serviced in corrosive environments were studied in this paper. The effects of residual stresses on the stability of passivation of amorphous coatings were studied by electrochemical methods. The failure mechanism of amorphous coatings under the action of residual stress was obtained. Based on the jet impact platform,the erosion-corrosion behavior and rules of amorphous coatings were investigated. The erosion-corrosion failure mechanism was determined. This research can lay solid theoretical foundation for the application of amorphous coatings in mechanical and corrosive environments.The amorphous coatings prepared by AC-HVAF methods exhibited high amorphous phase content, also including a small amount of Fe2 C, Cr7C3, M23C6, Cr2 B and little oxides.The coatings showed compact structure and good bonding in interface.The spray processing and coatings thickness affected the performance of amorphous coating. The passivation current density of amorphous coatings increased with the increasing of [H+]/[Cl-] and temperature. Different from the deteriorated unform corrosion resistance, the pitting resistance of coatings was not sensitive to parameters of environments, which showed that coatings possesed excellent local corrosion resistance.The passivation current density of amorphous coatings with residual stress was closely related with the stress, [H+] and temperature. The passivation current density increased with the residual stress, and the higher residual stress can decrease its ability to resist uniform and pitting corrosion. During the immersing corrosion period, the uniform corrosion process accelerated and the pitting corrosion tendency increased. The stability of the passive films formed on the coatings mainly depends on the composition and structural properties of the film, especially the structural properties. The higher donor density of the film formed on the high tensile residual stress coatings might also be responsible for the lower localized corrosion resistance.The AC-HVAF amorphous coatings exhibited higher uniform corrosion and pitting corrosion resistance than that of HVOF coaitngs for the lower porosity and compact structure.The passivation current density of AC-HVAF coatings was sensitive to the temperature andpH values. The enhanced erosion–corrosion resistance of the AC-HVAF coatings relative to the HVOF coatings could mainly be related to the high hardness and compact structure. The erosion-corrosion damage of the AMC is dominated by the mechanical damage resulting from erosion. The enhanced erosion-corrosion resistance of AC-HVAF coatings can be considerably due to the high hardness, low porosity and little oxides existed in the coatings..