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Improvement of the electrochemical behavior of steel surfaces using a [Ti-Al/Ti-Al-N]<inf>n</inf> multilayer system

Abstract:

The aim of this work is to improve the corrosion resistance of AISI D3 steel surfaces using a [Ti-Al/Ti-Al-N]n multilayer system deposited with different periods (λ) and bilayer numbers (n), via magnetron co-sputtering pulsed d.c. procedure, from a metallic (Ti-Al) binary target. The multilayer coatings were characterized by cross-sectional scanning electron microscopy that showed the modulation and microstructure of the [Ti-Al/Ti-Al-N]n multilayer system. The composition of the single Ti-Al and Ti-Al-N layer films was studied via x-ray photoelectron spectroscopy, where typical signals for Ti2p1/2, Ti2p, N1s, and Al2p3/2 were detected. The electrochemical properties were evaluated by electrochemical impedance spectroscopy and Tafel polarization curves. The optimal electrochemical behavior was obtained for the [Ti-Al/Ti-Al-N]n mul-tilayered period of λ = 25 nm (100 bilayers). At these conditions, the maximum polarization resistance (1719.32 kΩ cm2) and corrosion rate (0.7 μmy) were 300 and 35 times higher than that of uncoated AISI D3 steel substrate (5.61 kOmega; cm 2 and 25 μmy, respectively). Finally, scanning electron microscopy was used to analyze the [Ti-Al/Ti-Al-N]n multilayered surface after the corrosive attack. The improvement effects in the electrochemical behavior of the AISI D3 coated with the [Ti-Al/Ti-Al-N]n multilayered coatings could be attributed to the number of interfaces that act as obstacles for the inward and outward diffusions of Cl2 ions, generating an increment in the energy or potential required for translating the corrosive ions across the coating/substrate interface. © ASM International.