Dissolution Resistance of Spontaneously Formed and Anodic Passive Films Upon Compositionally Complex Alloy 45.5Ti-45.5V-4.5Cr-4.5Al (at.%)

Abstract

A lightweight compositionally complex alloy Ti45.5V45.5Cr4.5Al4.5 (at.%) was investigated. Scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction measurements revealed its homogeneous microstructure. The anodic behavior in 0.6 M NaCl was explored via linear sweep voltammetry, chronoamperometry, Mott-Schottky analysis, and spectroscopy of electrochemical impedance and complex capacitance. The passive films were characterized in terms of their thickness, resistance, resistivity at the outer interface, and charge carrier concentrations. The passive current density lowered from 1.6 to 1.2 μA cm –2 during potentiodynamic polarization. It decreased by another order of magnitude upon a potentiostatic hold. Depassivation occurred at +2.7 V NHE . The passive region was at least 2.3 V wide. The passive layer thickness, resistance (~10 4 –10 5 Ω cm 2 ), and resistivity at the outer interface (~10 6 Ω cm) increased, whereas the charge carrier concentrations (~10 20 –10 21 cm –3 ) decreased as the formation potential rose up to +1.0 V NHE . The surface film thickness was 2.4, 5.2, and 14.5 nm under free corrosion conditions, at +1.0, and +1.9 V NHE , respectively. However, the film resistance and its boundary resistivity declined at +1.9 V NHE (15.1 kΩ cm 2 and 72.3 kΩ cm, respectively). This implied a deterioration in the passive film properties, albeit the overall protective ability remained considerable.