Comparison of electrochemical behaviors of Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe and Ti-6Al-4V titanium alloys in NaNO₃ solution

Abstract

The Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe (β-CEZ) alloy is considered as a potential structural material in the aviation industry due to its outstanding strength and corrosion resistance. Electrochemical machining (ECM) is an efficient and low-cost technology for manufacturing the β-CEZ alloy. In ECM, the machining parameter selection and tool design are based on the electrochemical dissolution behavior of the materials. In this study, the electrochemical dissolution behaviors of the β-CEZ and Ti-6Al-4V (TC4) alloys in NaNO₃ solution are discussed. The open circuit potential (OCP), Tafel polarization, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and current efficiency curves of the β-CEZ and TC4 alloys are analyzed. The results show that, compared to the TC4 alloy, the passivation film structure is denser and the charge transfer resistance in the dissolution process is greater for the β-CEZ alloy. Moreover, the dissolved surface morphology of the two titanium-based alloys under different current densities are analyzed. Under low current densities, the β-CEZ alloy surface comprises dissolution pits and dissolved products, while the TC4 alloy surface comprises a porous honeycomb structure. Under high current densities, the surface waviness of both the alloys improves and the TC4 alloy surface is flatter and smoother than the β-CEZ alloy surface. Finally, the electrochemical dissolution models of β-CEZ and TC4 alloys are proposed.

Keywords

electrochemical machining / dissolution behavior / β-CEZ titanium alloy / polarization curve / current efficiency

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