Growth Kinetics of Multi-Oxide Passive Film Formed Upon the Multi-Principal Element Alloy AlTiVCr: Effect of Transpassive Dissolution of V and Cr

Abstract

The growth kinetics of the surface film formed upon the multi-principal element alloy AlTiVCr under anodic polarisation in 0.6 M NaCl was investigated using atomic emission spectroelectrochemistry (AESEC). The AESEC charge balance analysis revealed that thickness of the barrier layer of the passive film upon the alloy: (1) increases linearly with the increase in anodic potential during potentiodynamic polarisation, and (2) increases logarithmically with exposure time during potentiostatic polarisation. This is consistent with the assumptions of the point defect model, despite the film being a multi-oxide film with transpassive dissolution of V and Cr. The X-ray photoelectron spectroscopy (XPS) analysis suggested that the growth of the film was predominantly due to TiO2 during anodic polarisation. The electric field was found to decrease with enrichment of TiO2 in the barrier layer. The Mott-Schottky analysis revealed that the diffusivity of oxygen vacancies increased with the increase in fraction of TiO2 in the film, which subsequently led to the increase in the growth rate of the barrier layer during transpassive dissolution. The present work is a discrete effort towards understanding the growth behaviour of the passive film experiencing complex and competing interfacial electrochemical processes, upon a multi-principal element alloy.

A computational approach for mapping electrochemical activity of multi-principal element alloys

“…The elemental order for cathodic site as predicted by hydrogen evolution reaction is varied from the systems studied here, in which Ti, V and Cr exhibits the capability to facilitate *H adsorption with negative energies, excluding Al with positive energy. This suggests that Al is more dominant and active towards any oxidation/anodic reaction, which is consistent with experiments 12,13 . Additionally, the role of Ti on the formation of protective oxide layer, including the enrichment of Ti, can be explained from its strong interaction with O 2and Cl -.…”

“…The experimental techniques used to study the passive film characteristics and electrochemical activity, include high resolution X-ray photoelectron spectroscopy (XPS) and atomic emission spectroelectrochemistry. Using AESEC, Choudhary et al 12,13 quantitatively recorded the dissolution and oxidation of AlCrTiV on a 'per element' basis. It was revealed that elemental Al was readily observed to preferentially dissolve (although the alloy has stoichiometrically equal atomic proportion of all constituent elements), as soon as the sample was exposed to the electrolyte, as shown in Fig.…”

“…As a proof of concept, this methodology was explored for an MPEA with the equi-atomic composition AlCrTiV. This alloy was selected as a representative model system, because its electrochemical activity has been thoroughly and well-documented in the literature [10][11][12][13][14] . The 'electrochemistry simulator' is expected to describe the relationship between surface features and surface reactivity.…”

Current state of electrochemical techniques and corrosion rate analysis for next-generation materials

“…Another example is the PDM, originally developed to describe the corrosion mechanism of austenitic alloys. The PDM was recently used to explain the transpassive dissolution mechanism of an AlTiVCr MPEA via conventional Mott-Schottky analysis using EIS, coupled with element-resolved characterization techniques [ 14 ]. However, a general issue of applying the PDM to the multi-principal element alloy systems is that the PDM does not account for the non-constant electric field across the passive film, possible cation migration, and substrate composition.…”

Corrosion Resistance and Corrosion Mechanism of the Superhydrophobic Coating Fabricated on Aluminum Alloy in the Salt Spray Corrosion Environment

“…[1] In the corrosion protection of aluminum alloys, many traditional methods like anodic oxidation, corrosion inhibitor, slippery liquid-infused porous surfaces (SLIPSs), and protective coating were substantially limited by their shortcomings. [2][3][4][5][6][7][8][9][10][11][12] Corrosion inhibitors were toxic and prone to pollute the environment. Ordinary protective coatings had poor durability.…”