The Corrosion Performance and Mechanical Properties of Mg-Zn Based Alloys—A Review

Magnesium alloys have shown great potential for applications as both structural and biomedical materials due to their high strength-to-weight ratio and good biodegradability and biocompatibility, respectively. Among them, Mg-Zn based alloys are attracting increasing interest for both applications. As such, this article provides a review of the corrosion performance and mechanical properties of Mg-Zn based alloys, including the influence of environment and processing on both of them. The strategies for tailoring corrosion resistance and/or mechanical properties by microstructure adjustment and surface treatment are discussed

Controllable Degradable Plasma Electrolytic Oxidation Coated Mg Alloy for Biomedical Application

A controllable degradable coating on Mg alloy based on plasma electrolytic oxidation (PEO) process is reported for the first time. The reported results show that introduction of silica nanoparticles into PEO electrolytes leads to their reactive incorporation in coatings and thus influencing the degradation behavior. Dissolution of amorphous phases facilitates chemical reaction with components of simulated body fluid, resulting in self-healing effect via redeposition of insoluble conversion products. The dynamic balance between dissolution of the original coating and reconstruction of corrosion layer is mainly determined by the phase composition of the coating as well as the surrounding corrosive medium

Role of Phase Composition of PEO Coatings on AA2024 for In-Situ LDH Growth

Plasma electrolytic oxidation (PEO) is an environmentally friendly anodizing technique leading to the formation of a ceramic-like coatings under high-voltage discharges. Layered double hydroxides (LDHs) were grown directly on γ, α, and amorphous Al2O3 powders, respectively, in order to investigate the phase responsible for in-situ LDH growth on PEO coating. Furthermore, it is shown that LDH growth is limited by the high tortuosity of the PEO layer and the accessibility of Al(OH) − 4 anions from the substrate covered with thin amorphous aluminum oxide, through the pores

Small-angle neutron scattering and magnetically heterogeneous state in Sr2FeMoO6–δ

Single-phase strontium ferromolybdate (Sr2FeMoO6–δ) samples with different degrees of the superstructural ordering of the Fe/Mo cations were obtained from partially reduced SrFeO3–х, SrMoO4 precursors by the solid-state technology. The study of the temperature dependences of the magnetization measured in the field-cooling and zero-field-cooling regimes indicated an inhomogeneous magnetic state of the samples. The presence of magnetic regions of different nature has also been revealed by the small-angle neutron scattering. For the Sr2FeMoO6–δ samples with different superstructural ordering of the Fe/Mo cations and for all values of the magnetic field induction in the range up to 1.5 T and of the scattering vector in the interval 0.1 >q >0.005 Å–1, the analytical dependence I ~ q–α obeys the Porod law (α ≈ 4), which corresponds to an object with a smooth and well-marked surface and polydisperse grain size. Deviations from the Porod law in the q > 0.1 Å–1 region and a weakening of the neutron scattering in applied magnetic fields may be ascribed to magnetic inhomogeneities with diameters D <6 nm, which are partially destroyed /oriented by magnetic fields В ≥1.5 T.publishe

Redução electroquímica de iões de terras raras e o seu efeito na corrosão de metais

RESUMO: Os iões de terras raras estão entre os inibidores de corrosão de nova geração mais promissores. No entanto, foram encontradas condições onde a corrosão é acelerada na presença destes iões [1]. O caso mais relevante devido à sua importância é o aumento da corrosão do zinco no par galvânico zinco-ferro. Esse aumento está associado a uma reacção catódica adicional inesperada que é observada nas curvas de polarização obtidas experimentalmente. Esta nova redução corresponde a corrente catódica adicional que aumenta a oxidação do ânodo do par galvânico. Nesta comunicação analisa-se o impacto prático desta aceleração no par Zn-Fe e no aço galvanizado e procura-se identificar a natureza da nova reacção catódica.info:eu-repo/semantics/publishedVersio

Evaporation of Electrolyte During SVET Measurements: The Scale of the Problem and the Solutions

The objective of this work is to investigate the scale of the effect of spontaneous solution evaporation during SVET (Scanning Vibrating Electrode Technique) measurements and demonstrate how it biases the final results. When SVET maps are continuously acquired for more than several hours, the measured currents are smaller than expected. This is attributed to solvent (typically water) evaporation which leads to an increase in solution conductivity over time. If this is not considered when converting the measured potential differences into the local current densities, the SVET results display currents smaller than the true ones. Here, this effect is studied with a platinum disk electrode as source of a constant current and a model corroding system consisting of the AA2024/CFRP galvanic couple. Corrective actions are proposed to mitigate the problem, either in the experimental set‐up or as numerical correction

Ontology Assisted Modelling of Galvanic Corrosion of Magnesium

Multi-physics and multiscale modelling frameworks, especially for the computer based analysis of surface damage and corrosion, requires not only robust computational tools but also an efficient data-centric architecture for handling information exchange at different modelling scales. The issue to exchange data provided by different computational solvers as well as required and used in different programming languages forms a request in specific formats signifying a strong non-uniformity for an easy nexus with other solvers. This non-uniformity has created a need to focus on intermittent state-of-theart data-centric software tools, which aim to bridge data exchange technology, to ensure heterogeneity across a wide range of solvers [1]. Moreover, data organization in the form of ontological representation and metadata structures are necessary to be prepared as a standard for a coherent representation of information regardless of the diverse nature of data formats specific to a scientific discipline. A domain ontology based on the European Materials &amp; Modelling Ontology (EMMO) for galvanic corrosion is outlined and connected to corresponding concepts in a galvanic corrosion model. This fundamental work provides and discusses the concept, underlying terminology and working mechanism of a data-centric architecture for exchanging and interfacing data-flow between data sources/sinks and solvers. It realizes an ontological representation of physics and chemistry of galvanic corrosion. Thus, it is a nuclei for further improvement&#39;s of interoperability between complex corrosion related phenomena and models. It paves the way for accurate computational corrosion engineering

Comparison of 2D and 3D Plasma Electrolytic Oxidation (PEO)-Based Coating Porosity Data Obtained by X-ray Tomography Rendering and a Classical Metallographic Approach

In this work, the porosity of plasma electrolytic oxidation (PEO)-based coatings on Al- and Mg-based substrates was studied by two imaging techniques-namely, SEM and computer microtomography. Two approaches for porosity determination were chosen; relatively simple and fast SEM surface and cross-sectional imaging was compared with X-ray micro computed tomography (microCT) rendering. Differences between 2D and 3D porosity were demonstrated and explained. A more compact PEO coating was found on the Al substrate, with a lower porosity compared to Mg substrates under the same processing parameters. Furthermore, huge pore clusters were detected with microCT. Overall, 2D surface porosity calculations did not show sufficient accuracy for them to become the recommended method for the exact evaluation of the porosity of PEO coatings; microCT is a more appropriate method for porosity evaluation compared to SEM imaging. Moreover, the advantage of 3D microCT images clearly lies in the detection of closed and open porosity, which are important for coating properties

Biocompatible and biodegradable functional coatings with natural occurring materials for the corrosion protection of Mg alloys

Magnesium alloys are amidst the most innovative materials for biomedical applications, as they show a set of unique properties, namely appropriate mechanical properties and biodegradability, when compared to other alloys. Although these properties make them suitable for medical implants, the main challenge is the uncontrolled corrosion. Mg degradation is fast, inhomogeneous, localized and often accompanied by hydrogen formation which can lead to complications in vivo. Here, we propose the development of a functional coating, containing natural-based capsules for the controlled release of biocompatible corrosion inhibitors and well known pharmaceutical agents. Empty and loaded capsules toxicity tests were performed as a first step for materials selection. Subsequently, they were incorporated into polyetherimide (PEI) coatings and tested using electrochemical impedance spectroscopy (EIS) under aggressive conditions. The obtained results showed a successful synthesis of natural-based microcapsules, constituting a fast, simple and environmentally friendly method. Additionally, the high cell proliferation observed in the presence of the aforementioned materials demonstrates their low toxicity. Preliminary results carried out with capsule-modified coatings show that the incorporation of Ca2+-loaded gelatin capsules in PEI coatings leads to barrier and active corrosion protection properties improvement and that anti-inflammatory agent ibuprofen may have a role in active corrosion protection as well.publishe

The Role of Cu-Based Intermetallic on the Direct Growth of a ZnAl LDH Film on AA2024

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement