Evolution of Passivity for the Multi-Principal Element Alloy CoCrFeNi with Potential, pH, and Exposure in Chloride Solution

The evolution of passivity of the multi-principal element alloy (MPEA) CoCrFeNi was studied as a function of potential, pH, and exposure duration in 0.1 M NaCl. It was shown that CoCrFeNi exhibits excellent passivity irrespective of pH, revealing a multi-oxide passive film enriched with Cr(III) oxide. Electrochemical impedance spectroscopy suggests that the passive film thickness and polarization resistance increase with increasing pH and exposure duration, whereby the growth behavior of the passive film was consistent with the assumptions of the point defect model. X-ray photoelectron spectroscopy analysis suggested that the fraction of Co(II) and Ni(II) oxides in the passive film, and their contributions to the passivity of the alloy, increased with increase in pH of the electrolyte. The present work explores the complex synergy between composition, thermodynamics, and kinetics on the resultant passivity of a MPEA

On the origin of passive film breakdown and metastable pitting for stainless steel 316L

On the origin of passive film breakdown and metastable pitting for stainless steel 316

Growth kinetics of multi-oxide passive film formed upon the multi-principal element alloy AlTiVCr: Effect of transpassive dissolution of V and Cr

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 perspective on corrosion of multi-principal element alloys

Metallic alloys are critical to essentially all advanced technologies and engineered systems. The well-documented impact of corrosion (and oxidation) of alloys, remains a significant industrial and economic challenge, year on year. Recent activity in the field of metallurgy has revealed a class of metallic alloys, termed multi principal element alloys (MPEAs) that present unique physical properties. Such MPEAs have in many instances also demonstrated a high resistance to corrosion – which may permit the broader use of MPEAs as corrosion resistant alloys (CRAs) in harsh environments. Herein, the progress in MPEA research to date, along with prospects and challenges, are concisely reviewed—with potential future lines of research elaborated

Corrosion protection enhancement of Mg alloy WE43 by in-situ synthesis of MgFe LDH/citric acid composite coating intercalated with 8HQ

A composite coating consisting of Mg-Fe LDH intercalated with 8-hydroxyquinoline (8HQ) and modified with citric acid (CA) layer is constructed on Mg alloy WE43 via combination of electrodeposition, hydrothermal and anion-exchange. In view of CA and their small “island-shaped” surface morphology, the CA coating could provide MgFe LDH film with physical and chemical shielding. The intercalation of 8HQ into the MgFe LDH/0.05CA saw further enhancement in corrosion resistance as 8HQ hinders anodic and cathodic dissolution reaction. Furthermore, the MgFe-8HQ LDH/0.05CA coating presented a possible self-healing based on the 7-day EIS study, establishing as a potential coating for biomedical implant applications

Element-resolved electrochemical analysis of the passivity of additively manufactured stainless steel 316L

The dissolution and passivation behavior of additively manufactured stainless steel 316L (AM-316L) prepared via selective laser melting was studied in quiescent 0.6 M NaCl. In a detailed comparison with the wrought stainless steel 316L (W-316L), it was determined via mass spectroelectrochemistry and x-ray photoelectron spectroscopy (XPS), that AM-316L exhibited a unique passive film relative to W-316L, resulting in a lower dissolution rate. The dissolution and enrichment of all alloying elements at open circuit potential and during polarisation were studied and elaborated

Recent insights in corrosion science from atomic spectroelectrochemistry

A fundamental understanding of corrosion mechanisms is the key to developing suitable corrosion protection approaches, and for the prediction of service life of metallic structures. However, conventional corrosion testing methods such as mass loss and electrochemical testing do not guarantee estimation of "true" corrosion rate and often mask the underlying mechanisms, due to either low sensitivity or a lack of element-resolved information. Relatively recent work in corrosion science has led to the development of a new class of corrosion testing approaches, namely atomic spectroelectrochemistry; whereby direct insight of dissolution and corrosion mechanisms can be obtained during electrochemical testing. Atomic spectroelectrochemistry provides real-time and element resolved dissolution rate of material via coupling electrochemical flow cell with inductively coupled plasma – atomic spectroscopy. This concise review discusses the basic working principle of atomic spectroelectrochemistry and its recent applications in corrosion science to understand the true underlying corrosion mechanisms of a range of metallic materials

On the corrosion of a high solute Al-Zn-Mg alloy produced by laser powder bed fusion

An additively manufactured aluminium alloy with very high solute content, Al-14Zn-3Mg (wt. %), was studied herein. Compared to wrought AA7075-T6 as a benchmark, Al-14Zn-3Mg revealed a lower rate of corrosion, attributed to its microstructure and solute content. Specifically, the lack of coarse intermetallic particles in the Al-14Zn-3Mg led to reduced cathodic kinetics relative to AA7075-T6. Potentiodynamic polarisation tests and electrochemical impedance spectroscopy analysis was performed, along with XPS studies of the corresponding surface films. The findings herein demonstrate the corrosion behaviour of a new high solute aluminium alloy manufactured in net shape through LPBF

On the dynamic passivity and corrosion resistance of a low cost and low density multi-principal-element alloy produced via commodity metals

Recent exploration of multi-principal-element alloys (MPEAs), which include the so-called high-entropy alloys, has revealed hitherto unreported properties and phenomena arising from investigation of broader compositional space. Herein, a low cost and lightweight alloy (equiatomic AlFeMnSi) is presented that exhibits exceptional corrosion resistance in 0.6 M NaCl solution, despite a multiphase structure and the absence of well-known passivating elements (such as Cr, Mo, Ti and Nb). In-line inductively-coupled plasma mass spectroscopy (ICP-MS) analysis of alloy dissolution and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) of the surface film revealed that the alloy passivates by a unique mechanism involving dissolution–precipitation of Si. The dynamic precipitation of a Si hydroxide surface film results in excellent passivity of the alloy, revealing the possibility of developing low-cost corrosion-resistant alloys from metals available from waste streams

Towards equity: a qualitative exploration of the implementation and impact of a digital educational intervention for pharmacy professionals in England.

Background: Patients belonging to marginalised (medically under-served) groups experience problems with medicines (i.e. non-adherence, side effects) and poorer health outcomes largely due to inequitable access to healthcare (arising from poor governance, cultural exclusion etc.). In order to promote service equity and outcomes for patients, the focus of this paper is to explore the implementation and impact of a new co-produced digital educational intervention on one National Health Service (NHS) funded community pharmacy medicines management service.Methods: Semi-structured interviews with a total of 32 participants. This included a purposive sample of 22 community pharmacy professionals, (16 pharmacists and 6 pharmacy support staff) all who offered the medicine management service. In order to obtain a fuller picture of the barriers to learning, five professionals who were unable to complete the learning were also included. Ten patients (from a marginalised group) who had received the service (as a result of the digital educational intervention) were also interviewed. Drawing on an interpretative analysis, Normalisation Process Theory (NPT) was used as a theoretical framework.Results: Three themes are explored. The first is how the digital learning intervention was implemented and applied. Despite being well received, pharmacists found it challenging completing and cascading the learning due to organisational constraints (e.g. lack of time, workload). Using the four NPT constructs (coherence, cognitive participation, collective action and reflexive monitoring) the second theme exposes the impact of the learning and the organisational process of ‘normalisation’. Professional reflective accounts revealed instances where inequitable access to health services were evident. Those completing the intervention felt more aware, capable and better equipped to engage with the needs of patients who were from a marginalised group. Operationally there was minimal structural change in service delivery constraining translation of learning to practice. The impact on patients, explored in our final theme, revealed that they experience significant disadvantage and problems with their medicines. The medication review was welcomed and the discussion with the pharmacist was helpful in addressing their medicine-related concerns.Conclusions: The co-produced digital educational intervention increases pharmacy professionals’ awareness and motivation to engage with marginalised groups. However structural barriers often hindered translation into practice. Patients reported significant health and medicine challenges that were going unnoticed. They welcomed the additional support the medication review offered. Policy makers and employers should better enable and facilitate ways for pharmacy professionals to better engage with marginalised groups. The impact of the educational intervention on patients’ health and medicines management could be substantial if supported and promoted effectively.</p