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High-Entropy Alloy and Compositionally Complex Alloys: Challenges and Prospects for Applications in Corrosive Environments

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Corrosion".

Deadline for manuscript submissions: closed (15 December 2021) | Viewed by 9244

Special Issue Editors


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Guest Editor
Department of Industrial Engineering, Mechanical Engineering and Computer Science, School of Engineering and Natural Sciences, University of Iceland, Reykjavík, Sæmundargata 2, 102 Reykjavik, Iceland
Interests: high-entropy alloys; compositionally complex alloys; microstructure; corrosion; corrosion and scaling in geothermal environments; corrosion resistance of coatings; tribological and mechanical properties

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Guest Editor
Department of Engineering and Management of Metallic Materials Production, Materials Science and Engineering Faculty, University Politehnica Bucharest, Bucharest, Splaiul Independetei 313, County 6, 060042 Bucharest, Romania
Interests: coatings; compositionally complex alloys; corrosion and scaling in aggressive environments; coatings characterization; microstructure; mechanical properties

Special Issue Information

Dear Colleagues,

In the last decade, high-entropy alloys (HEAs) have gained increased attention as a new class of metallic materials with improved mechanical properties and corrosion resistance for environments where high-temperature strength and corrosive challenges prevail. HEAs are multi-component alloys which consist of equiatomic mixtures or near-equal proportions of five or more elements. They tend to form simple solid-solution structures due to their high mixing entropy, with single-phase crystal structures being more studied. The sluggish diffusion and severe lattice distortions of HEAs have a large effect on their microstructures and properties. These characteristics are considered to be of critical importance for providing the good properties of HEAs, such as high hardness and strength, corrosion, and wear resistance.

Recently, distinction has been made between single-phase high-entropy alloys and multi-phase compositionally complex alloys (CCAs), which both fulfill the initial definition criteria. There are many different kinds of multi-component alloys. Whether they have a large number of components in equal or near-equal proportions depends on their alloying method, constituent species, manufacturing method, and resulting phase structure and microstructure. The combination of the unique structure, excellent mechanical properties, and corrosion and oxidation resistance have given these materials a position as promising candidates for structural applications in corrosive environments. These application fields can be various, including: geothermal, oil and gas, and nuclear industry, biomedical coatings, electronics industry, and lightweight casing for mobile facilities, battery anode materials, and the transportation industry.

The requirement for near-equiatomic mixtures can also lead to the high cost of these alloys if more exotic or costly elements are required. The deposition of HEAs and CCAs as a coating onto an inexpensive substrate could be an economical way to exploit the advantageous properties of these materials.

This Special Issue welcomes original research on topics concerning the microstructure, corrosion resistance, and mechanical properties of different types of bulk HEA and CCA materials, as well as coatings based on these constitutes. This includes characterization of the HEAs obtained from the thermodynamical point of view, microstructural (SEM/EDS) and crystal structural (XRD) analysis, as well as mechanical and corrosion testing, or any relevant test that will prove the hypothesis and results presented.

We hope that this Special Issue will provide a platform to share new results on the properties and structure of HEAs and CCAs for coatings and bulk materials.

Prof. Dr. Sigrún Nanna Karlsdóttir
Prof. Ioana Csaki
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • high-entropy alloys
  • complex compositionally alloys
  • corrosion resistance
  • oxidation resistance
  • mechanical properties
  • tribological properties
  • microstructure
  • alloying
  • thermal spray coatings
  • various coating processes using high-entropy alloys
  • microscopic analysis (e.g. optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM))
  • chemical compositional analysis (e.g., X-ray energy dispersive spectroscopy (EDS) and EPMA)
  • Crystal structure analysis (e.g., XRD—X-ray diffraction)

Published Papers (3 papers)

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Research

10 pages, 6946 KiB  
Article
New HfNbTaTiZr High-Entropy Alloy Coatings Produced by Electrospark Deposition with High Corrosion Resistance
by Ciprian Alexandru Manea, Mirela Sohaciu, Radu Stefănoiu, Mircea Ionuț Petrescu, Magdalena Valentina Lungu and Ioana Csaki
Materials 2021, 14(15), 4333; https://doi.org/10.3390/ma14154333 - 3 Aug 2021
Cited by 7 | Viewed by 3502
Abstract
The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity [...] Read more.
The aim of the present paper is to investigate an innovative high corrosion resistance coating realized by electrospark deposition. The coating material was fabricated from HfNbTaTiZr high-entropy alloy. HEA was produced by the mechanical alloying of Hf, Nb, Ta, Ti, and Zr high-purity powders in a planetary ball mill, achieving a good homogenization and a high alloying degree, followed by spark plasma sintering consolidation. The electrodes for electrospark deposition were cut and machined from the bulk material. Stainless steel specimens were coated and electrochemically tested for corrosion resistance in a 3.5% NaCl saline solution. Full article
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11 pages, 3731 KiB  
Article
Mechanically Alloyed CoCrFeNiMo0.85 High-Entropy Alloy for Corrosion Resistance Coatings
by Laura Elena Geambazu, Cosmin Mihai Cotruţ, Florin Miculescu and Ioana Csaki
Materials 2021, 14(14), 3802; https://doi.org/10.3390/ma14143802 - 7 Jul 2021
Cited by 15 | Viewed by 2073
Abstract
High-entropy alloys could provide a solution for corrosion resistance due to their impressive properties. Solid-state processing of high purity Co, Cr, Fe, Ni and Mo metallic powders and consolidation resulted in a bulk material that was further machined into electro spark deposition electrodes. [...] Read more.
High-entropy alloys could provide a solution for corrosion resistance due to their impressive properties. Solid-state processing of high purity Co, Cr, Fe, Ni and Mo metallic powders and consolidation resulted in a bulk material that was further machined into electro spark deposition electrodes. After the stainless steel substrate surface preparation, thin successive layers of the high-entropy alloy were deposited and Pull-Off testing was performed on the newly obtained coating, for a better understanding of the adhesion efficiency of this technique. Good adhesion of the coating to the substrate was proved by the test and no cracks or exfoliations were present. Corrosion resistance testing was performed in a liquid solution of 3.5 wt.% NaCl for 6 h at room temperature and the results obtained validated our hypothesis that CoCrFeNiMo0.85 high-entropy alloys could provide corrosion resistance when coating a stainless steel substrate. Full article
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17 pages, 10780 KiB  
Article
Erosion and Corrosion Resistance Performance of Laser Metal Deposited High-Entropy Alloy Coatings at Hellisheidi Geothermal Site
by Andri Isak Thorhallsson, Francesco Fanicchia, Emily Davison, Shiladitya Paul, Svava Davidsdottir and Dagur Ingi Olafsson
Materials 2021, 14(11), 3071; https://doi.org/10.3390/ma14113071 - 4 Jun 2021
Cited by 9 | Viewed by 2759
Abstract
Geothermal process equipment and accessories are usually manufactured from low-alloy steels which offer affordability but increase the susceptibility of the materials to corrosion. Applying erosion-corrosion-resistant coatings to these components could represent an economical solution to the problem. In this work, testing of two [...] Read more.
Geothermal process equipment and accessories are usually manufactured from low-alloy steels which offer affordability but increase the susceptibility of the materials to corrosion. Applying erosion-corrosion-resistant coatings to these components could represent an economical solution to the problem. In this work, testing of two newly developed laser metal deposited high-entropy alloy (LMD-HEA) coatings—CoCrFeNiMo0.85 and Al0.5CoCrFeNi, applied to carbon and stainless steels—was carried out at the Hellisheidi geothermal power plant. Tests in three different geothermal environments were performed at the Hellisheidi site: wellhead test at 194 °C and 14 bar, erosion test at 198 °C and 15 bar, and aerated test at 90 °C and 1 bar. Post-test microstructural characterization was performed via Scanning Eletron Microscope (SEM), Back-Scattered Electrons analysis (BSE), Energy Dispersive X-ray Spectroscopy (EDS), optical microscopy, and optical profilometry while erosion assessment was carried out using an image and chemical analysis. Both the CoCrFeNiMo0.85 and Al0.5CoCrFeNi coatings showed manufacturing defects (cracks) and were prone to corrosion damage. Results show that damage in the CoCrFeNiMo0.85-coated carbon steel can be induced by manufacturing defects in the coating. This was further confirmed by the excellent corrosion resistance performance of the CoCrFeNiMo0.85 coating deposited onto stainless steel, where no manufacturing cracks were observed. Full article
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