Atomic-scale investigations of passive film formation on Ti-Nb alloys

This study extensively investigates the passive film formation mechanisms on Ti-xNb alloys by using several electrochemical techniques, including electrochemical impedance spectroscopy (EIS) before and after potentiostatic polarization at the passive zone, and Mott-Schottky (MS) measurements in 9 g/l NaCl electrolyte at 37 °C, together with X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis. Overall, the Ti40Nb presented lower corrosion resistance due to a thinner passive film as compared to commercial pure Ti (grade 2) and Ti12Nb. The passive film formed on Ti12Nb and Ti40Nb alloys at a steady-state condition (+0.5 VAg/AgCl for 60 min) is composed of amorphous phases of TiO, Ti2O3, TiO2, Nb2O5, and crystalline phases of TiO2 (anatase) and Nb2O5.This work is supported by FCT with the reference project UID/EEA/04436/2019, together with M-ERA-NET/0001/2015, and by MINECO (Spain) through the program PCIN-2016-123, the Ramón y Cajal project RYC-2014-15014 and the regional government of Madrid by S2018/NMT-4411, as well, by the CASOLEM project (028917) "Correlated Analysis of Inorganic Solar Cells in and outside an Electron Microscope", co-funded by FCT and ERDF through COMPETE2020