Electrochemical Behavior on Surface Passivation Films of Fe-Me(Me=Co,Ni,Co-Ni) Alloying Layers

Fe-Co, Fe-Ni and Fe-Co-Ni alloying layers were prepared on mild steel by thermal diffusion. Heat treatment of the coated mild steel was performed at 1 000 ℃ for 5 h in hydrogen atmosphere. The composition and microstructure of the alloying layers were analyzed by XRD, EDS and SEM. A series of electrochemical analysis was carried out to examine the passivation behavior of these alloying layers in borate buffer solution (pH=8.4). Results indicated that the Fe-Ni alloy layer and the Fe-Co-Ni alloy layer with high Ni content promoted the formation of compact passive films. The passive films significantly improved the corrosion resistance of mild steel substrate in alkaline solution.