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Corrosion studies on multicomponent CoCrFeMnNi(C) thin films in acidic environments
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0001-6162-1167
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-9204-5999
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström.
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2022 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 404, article id 139756Article in journal (Refereed) Published
Abstract [en]

The corrosion resistances of near equimolar CoCrFeMnNi magnetron-sputtered thin films with different carbon concentrations were examined in 0.05 M HCl and 0.05 M H2SO4. Polarization curves were recorded with different scan rates with and without reducing the native oxide. The results showed that the carbon concentration and the experimental conditions affected the electrochemical behaviour mainly in the Cr transpassive region. At potentials above 850 mV, the carbon-containing films were more corrosion resistant in 0.05 M HCl than in 0.05 M H2SO4 due to a lower carbon oxidation rate in 0.05 M HCl, facilitating the formation of a Mn-rich oxide layer. (C)& nbsp;2021 The Author(s). Published by Elsevier Ltd.& nbsp;

Place, publisher, year, edition, pages
Elsevier BV Elsevier, 2022. Vol. 404, article id 139756
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-473954DOI: 10.1016/j.electacta.2021.139756ISI: 000778816800008OAI: oai:DiVA.org:uu-473954DiVA, id: diva2:1656704
Funder
Swedish Research CouncilAvailable from: 2022-05-06 Created: 2022-05-06 Last updated: 2024-01-15Bibliographically approved
In thesis
1. Designing multicomponent alloy coatings for corrosion protection
Open this publication in new window or tab >>Designing multicomponent alloy coatings for corrosion protection
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis explores the design of metallic coatings for corrosion protection. The subject of the study was the new class of materials multicomponent alloys (MCAs, also known as high entropy alloys). They consist of near-equal concentrations of many (four or more) metals and are often reported to form a single phase with a simple crystal structure. Due to the complexity and range of possible MCA compositions, there is a need for design principles as guidelines for how the alloying elements can be chosen and combined. This work aimed at finding such principles through the systematic study of the synthesis and properties of three MCA systems. Their compositions were carefully chosen to answer fundamental questions about the materials class and the synthesis method and to generate conclusions that could be generalized to a larger group of MCAs. All three systems were based on the elements Cr, Fe, and Ni, and can therefore be considered an extension of stainless steels.

The first alloy was CoCrFeMnNi, which is well-known as a single-phase bulk MCA. A systematic exploration of the synthesis parameters showed that there are fundamental differences in the phase formation of CoCrFeMnNi through magnetron sputtering compared to typical bulk synthesis. Literature studies revealed that this conclusion can be generalized; single-phase MCAs should not necessarily be expected from magnetron sputtering. It was also shown that the choice of substrate and even the crystal orientation of the individual substrate grains strongly influenced the outcomes of synthesis, including the phase formation, growth rate, morphology, and the formation of stacking fault structures. 

Two novel alloy systems were also explored: CrFeNiTa and CrFeNiW. Ta and W were added to achieve an alloy with higher corrosion resistance than stainless steels and more generally, to examine the interplay between passivating elements in MCAs during corrosion. Based on geometrical considerations, it was predicted that equal amounts of Ta and W would be needed to protect alloys from corroding (less than 20 at%). It was found that the prediction was only valid for the CrFeNiTa alloy system. The reason behind this was explored and a new criterion was then proposed: In an MCA, each passivating element should have similar electrochemical nobility.

Further design possibilities were demonstrated by adding up to 50 at% carbon to the alloys. Thermodynamic calculations predicted decomposition into multiple metallic and carbide phases. However, the limited diffusion during magnetron sputtering suppressed the segregation. At lower carbon contents, the carbon-containing alloys were single-phase and amorphous. At higher carbon contents they formed alloy/amorphous carbon nanocomposites. The addition of carbon made the alloys stronger, more corrosion resistant, and more crack resistant. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2023. p. 117
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2222
Keywords
corrosion, thin films, coatings, magnetron sputtering, high entropy alloy, percolation theory, mechanical tests
National Category
Materials Chemistry Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-489916 (URN)978-91-513-1670-3 (ISBN)
Public defence
2023-02-03, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Available from: 2023-01-11 Created: 2022-12-06 Last updated: 2023-01-11

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Paschalidou, Eirini-MariaLindblad, RebeckaZendejas Medina, LeónJansson, UlfNyholm, Leif

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