Formation Of Compact Passive Film Research Articles

Preparation of passive Cu–Ni–Fe coating on low-carbon steel for improving corrosion resistance

Cu–Ni–Fe alloy coating was prepared on low-carbon steel by surface alloying. The surface heat treatment of coated low-carbon steel was performed at 700°C, 800°C, 900°C and 1000°C for 3h under hydrogen atmosphere. The structure and microstructure of coatings were separately analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A series of electrochemical analysis was carried out to examine the corrosion resistance of Cu–Ni–Fe alloy coatings in borate buffer solution. Results indicated that a uniform and homogeneity Cu–Ni–Fe alloy coating constituted of γ-phases was prepared on the surface of low-carbon steel at 1000°C, which promoted the formation of compact passive film. The passive film significantly improved the substrate's corrosion resistance in alkaline solution.

Influence of Cold Working and Grain Size on Pitting Corrosion Resistance of Ferritic Stainless Steel

The influence of cold working and grain size on the pitting corrosion resistance of Fe-Cr-Nb-Mo ferritic stainless steel is investigated using optical microscope and electrochemical methods. The pitting corrosion resistance firstly decreases with increasing the cold-rolling reduction from 0% to 30% due to the number of nucleation site increasing. With increasing the cold-rolling reduction from 40% to 60%, the disappearance of grain boundaries, stacked dislocation and uniform microstructure results in the pitting corrosion resistance of the steel. With prolonging the annealing time, the grain size of the steel grows, and the pitting potential of the steel decrease. The smaller grain size promotes the formation of compact passive film and improves the pitting corrosion resistance.

Influence of grain size on the corrosion behavior of a Ni-based superalloy nanocrystalline coating in NaCl acidic solution

The effects of grain size on the electrochemical corrosion behavior of a Ni-based superalloy nanocrystalline (NC) coating fabricated by a magnetron sputtering technique, has been investigated in 0.5 M NaCl + 0.05 M H 2SO 4 solution. Coatings with grain sizes 10 nm, 50 nm and 100 nm were fabricated on glass and the superalloy substrates. The results indicate that a passive film with porous property, n-type semiconductive property and incorporation of chloride ions formed on the NC coating with 100 nm grain size, which increased the susceptibility to pitting corrosion. The NC coatings with 10 nm and 50 nm grain size formed compact, non-porous and p-type passive films without chloride ions, which improved resistance to pitting corrosion. The smaller grain size of the material decrease the amount of chloride ions adsorbed on the surface and promoted the formation of compact passive film, which significantly increased the material's resistance to pitting corrosion in acidic solution.