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Special Issue "High Entropy Alloys"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 31 December 2018

Special Issue Editor

Guest Editor
Prof. Michael Regev

Department of Mechanical Engineering, ORT Braude College of Engineering, Karmiel, Israel
Website | E-Mail
Interests: metallurgy; magnesium alloys; amorphous alloys; friction stir welding; high temperature mechanical properties; high entropy alloys

Special Issue Information

Dear Colleagues,

The search for new materials with improved properties, as we all know, never stops. High Entropy Alloys (HEAs) are among the new and promising material groups, alloys, that have been attracting attention since the beginning of the 21st Century.

Historically, alloys have consisted of one, sometimes two, or even three, major elements, together with minor ones. HEAs, in contrast, contain at least five principal elements in equal, or near equal atomic percentage.

HEAs are known for their attractive physical and mechanical properties. It should be noted that some HEAs show unique properties, such as high-strength at room temperature, as well as at elevated temperatures. Their room temperature yield strength can vary from 300 MPa for FCC-structured alloys to about 3000 MPa for BCC-structured alloys. As for elevated temperatures, some refractory HEAs can sustain their high specific strength up to 1800 K. Certain HEAs also possess both high fatigue resistance and high wear resistance. Other HEAs exhibit excellent paramagnetic, ferromagnetic and soft magnetic properties together with high irradiation resistance and high corrosion resistance. Four core effects are responsible for the superior properties of some HEAs: the high mixing entropy effect, the sluggish diffusion effect, the lattice distortion effect and the cocktail effect, which says that the properties of HEAs cannot just be taken from averaging the properties of the constituting elements.

HEAs have potentially a wide range of applications, such as in functional and structural materials. Among many other applications one can mention their potential in the nuclear and at the aerospace industries, as well as in the production of heat-resistant and wear-resistant coatings and joining processes.

It is my pleasure to invite you to submit manuscripts on the subject of HEAs for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Michael Regev
Guest Editor

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 papers will be 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 monthly 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 1600 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

  • Advanced Materials

  • Mechanical Properties

  • Physical Properties

  • Characterization

  • Microstructure

  • Elevated temperature properties

Published Papers (4 papers)

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Research

Open AccessArticle Enhanced Strength of a Mechanical Alloyed NbMoTaWVTi Refractory High Entropy Alloy
Materials 2018, 11(5), 669; https://doi.org/10.3390/ma11050669
Received: 10 April 2018 / Revised: 23 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
A NbMoTaWVTi refractory high entropy alloy (HEA) has been successfully synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure and mechanical properties of this alloy are investigated. It is observed that only two types of body-centered cubic (BCC) solid solutions
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A NbMoTaWVTi refractory high entropy alloy (HEA) has been successfully synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure and mechanical properties of this alloy are investigated. It is observed that only two types of body-centered cubic (BCC) solid solutions are formed in the powders after ball milling for 40 h. However, a new face-centered cubic (FCC) precipitated phase is observed in the BCC matrix of bulk material consolidated by SPS. The FCC precipitated phase is identified as TiO, due to the introduction of O during the preparing process of HEA. The compressive yield strength, fracture strength, and total fracture strain of the consolidated bulk HEA are 2709 MPa, 3115 MPa, and 11.4%, respectively. The excellent mechanical properties can be attributed to solid solution strengthening and grain boundary strengthening of the fine-grained BCC matrix, as well as the precipitation strengthening owing to the formation of TiO particles. Full article
(This article belongs to the Special Issue High Entropy Alloys)
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Open AccessFeature PaperArticle Microstructural Evolution and Phase Formation in 2nd-Generation Refractory-Based High Entropy Alloys
Materials 2018, 11(2), 175; https://doi.org/10.3390/ma11020175
Received: 27 December 2017 / Revised: 16 January 2018 / Accepted: 22 January 2018 / Published: 23 January 2018
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Abstract
Refractory-based high entropy alloys (HEAs) of the 2nd-generation type are new intensively-studied materials with a high potential for structural high-temperature applications. This paper presents investigation results on microstructural evolution and phase formation in as-cast and subsequently heat-treated HEAs at various temperature-time regimes. Microstructural
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Refractory-based high entropy alloys (HEAs) of the 2nd-generation type are new intensively-studied materials with a high potential for structural high-temperature applications. This paper presents investigation results on microstructural evolution and phase formation in as-cast and subsequently heat-treated HEAs at various temperature-time regimes. Microstructural examination was performed by means of scanning electron microscopy (SEM) combined with the energy dispersive spectroscopy (EDS) mode of electron probe microanalysis (EPMA) and qualitative X-ray diffraction (XRD). The primary evolutionary trend observed was the tendency of Zr to gradually segregate as the temperature rises, while all the other elements eventually dissolve in the BCC solid solution phase once the onset of Laves phase complex decomposition is reached. The performed thermodynamic modelling was based on the Calculation of Phase Diagrams method (CALPHAD). The BCC A2 solid solution phase is predicted by the model to contain increasing amounts of Cr as the temperature rises, which is in perfect agreement with the actual results obtained by SEM. However, the model was not able to predict the existence of the Zr-rich phase or the tendency of Zr to segregate and form its own solid solution—most likely as a result of the Zr segregation trend not being an equilibrium phenomenon. Full article
(This article belongs to the Special Issue High Entropy Alloys)
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Open AccessArticle Microstructures, Hardness and Corrosion Behaviors of FeCoNiNb0.5Mo0.5 and FeCoNiNb High-Entropy Alloys
Materials 2018, 11(1), 16; https://doi.org/10.3390/ma11010016
Received: 3 December 2017 / Revised: 17 December 2017 / Accepted: 21 December 2017 / Published: 23 December 2017
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Abstract
This study investigates the effects of niobium and molybdenum on FeCoNi alloy, including on the microstructures and hardness of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys, and the polarization behaviors of these alloys in 1 M sulfuric acid and 1 M sodium chloride
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This study investigates the effects of niobium and molybdenum on FeCoNi alloy, including on the microstructures and hardness of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys, and the polarization behaviors of these alloys in 1 M sulfuric acid and 1 M sodium chloride solutions. The results in this study indicate that both FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys had a dual-phased dendritic microstructure; all of the phases in these alloys were solid solution phases, and no ordering was observed. Therefore, the solid solution effect significantly increased the hardness of these two alloys; in particular, FeCoNiNb alloy had the highest hardness of the alloys of interest. The corrosion resistance of FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys was less than that of FeCoNi alloy because of their dual-phased dendritic microstructures. The corrosion resistance of the FeCoNiNb0.5Mo0.5 alloy exceeded that of the FeCoNiNb alloy in these solutions. However, FeCoNiNb0.5Mo0.5 and FeCoNiNb alloys exhibited a favorable combination of corrosion resistance and hardness. Full article
(This article belongs to the Special Issue High Entropy Alloys)
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Open AccessArticle Microstructure, Tensile and Creep Properties of Ta20Nb20Hf20Zr20Ti20 High Entropy Alloy
Materials 2017, 10(8), 883; https://doi.org/10.3390/ma10080883
Received: 5 July 2017 / Revised: 26 July 2017 / Accepted: 27 July 2017 / Published: 31 July 2017
Cited by 1 | PDF Full-text (13758 KB) | HTML Full-text | XML Full-text
Abstract
This paper examines the microstructure and mechanical properties of Ta20Nb20Hf20Zr20Ti20. Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current
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This paper examines the microstructure and mechanical properties of Ta20Nb20Hf20Zr20Ti20. Two casting processes, namely, gravity casting and suction-assisted casting, were applied, both followed by Hot Isostatic Pressing (HIP). The aim of the current study was to investigate the creep and tensile properties of the material, since the literature review revealed no data whatsoever regarding these properties. The main findings are that the HIP process is responsible for the appearance of a Hexagonal Close Packed (HCP) phase that is dispersed differently in these two castings. The HIP process also led to a considerable increase in the mechanical properties of both materials under compression, with values found to be higher than those reported in the literature. Contrary to the compression properties, both materials were found to be highly brittle under tension, either during room temperature tension tests or creep tests conducted at 282 °C. Fractography yielded brittle fracture without any evidence of plastic deformation prior to fracture. Full article
(This article belongs to the Special Issue High Entropy Alloys)
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