Hot Corrosion Study of TiO2-ZrO2 Coating on Inconel 601 Alloy in NaVO3 Molten Salt

Abstract

The corrosion resistance effect of a ceramic coating applied on –Inconel-601 alloy immerse in molten salts was studied. The development of ceramic coating was obtained by sol-gel synthesis of TiO2-ZrO2, FTIR analysis was used to characterize the resultant sol. The dip-coating technique was used to coating application using the sol solution and Inconel-601 substrate set previously in an alumina tube with the cylindrical side exposed. The molten salt of metavanadate of sodium (NaVO3) at 700 °C was used as corrosive electrolyte, the electrochemical cell consisted uncoated and coated samples as working electrode and two platinum wire as references and auxiliary electrodes. Those last were placed inside to alumina tubes in order to isolate the non-immersed part from air. Potentiodynamic long polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques were used to study the corrosion behavior of samples. Potentiodinamic test were applied at -500 to 1500 mV vs open corrosion potential (OCP) with a 1 mV/s scan rate. LPR was realized within a ± 15 mV vs OCP at 1 mV/s scan rate each 15 minutes during 24 h. The EIS was realized in the frequency of from 25 kHz to 0.01 Hz with a potential signal amplitude of 30 mV vs OCP. Potentiodynamic results did not showed a substantial difference on the current densities, but some passive steps were presented by the coated sample, however the coated sample showed a higher corrosion resistance kinetic than uncoated sample with average values 160 ohm cm2 and 40 ohm cm2 respectively. EIS results present the active mechanism of the uncovered Inconel at the first time of immersion followed by diffusion increasing with the corrosion products, however coated sample showed a mixture of capacitive and diffusion mechanism since the first time of immersion with higher resistance values as RPL results. Those results were complemented by the cross section characterization by SEM and EDS, showing a reduction of salt species penetration from 48.5 to 21.3 µm in deep. Chemical mapping was obtained also. Scanning electron microscopy observation and chemical analysis by energy dispersive spectroscopy were used to characterize the as received and after corroded materials in order to complement the corrosion behavior study. Keywords: TiO2-ZrO2 coating; Inconel 601 alloy; electrochemical techniques; NaVO3 Molten Salt Acknowledgements The present research was supported by CONACYT for the project financing number: CB-2014-01-243236, I0017 Fund.