Special Issue "High-Entropy Alloys (HEAs)"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 July 2017)

Special Issue Editors

Guest Editor
Dr. Michael C. Gao

AECOM|Contractor for the US DEPT of ENERGY, National Energy Technology Laboratory (Albany), 1450 Queen Ave SW, Albany, OR 97321, USA
Website | E-Mail
Guest Editor
Prof. Junwei Qiao

Laboratory of Applied Physics and Mechanics of Advanced Materials, College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
Website | E-Mail

Special Issue Information

Dear Colleagues,

Originated from the idea of multi-principal-element solid solution, the field of “high-entropy alloys (HEAs)” has attracted intense and increasing interest from academia and industries worldwide. Outstanding (physical, mechanical, and functional) properties have been reported for a variety of HEAs. In order to balance the properties for targeted applications, the microstructure of HEAs can be a single phase or composite, and traditional physical metallurgy principles have been applied to develop unique HEAs, including high-entropy stainless steels, high-entropy superalloys, high-entropy refractory alloys, high-entropy light-weight alloys, high-entropy oxides, high-entropy metallic compounds, etc. As presented in a recent comprehensive review on HEAs (High-Entropy Alloys: Fundamentals and Applications (2016). 1st edn. Gao MC, Yeh JW, Liaw PK, Zhang Y (eds). Springer International Publishing, Cham, Switzerland. doi:10.1007/978-3-319-27013-5), great challenges remain in fundamental understanding of HEAs formation and their properties, and potential high-performance HEAs are yet to be explored. The objective of this Special Issue is to timely disseminate the rapid progress in fundamental understanding and applications of HEAs.

Specific topics of interest include (but are not limited to):

  • Accelerated alloy design using combinatorial approach, models or others
  • Structure/processing/properties relationships
  • Advanced characterization including neutron scattering, 3-dimension scanning electron microscopy, high-resolution transmission electron microscopy, etc.
  • Mechanical, electrochemical, physical, anti-irradiation, thermodynamic, kinetic, and other properties
  • Computational modeling: first-principles density functional theory, molecular dynamics, Monte Carlo simulations, phase field, finite element methods, CALPHAD, etc.

Dr. Michael C. Gao
Professor Junwei Qiao
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 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
  • computational modeling
  • mechanical properties
  • alloy design
  • thermodynamics

Published Papers (10 papers)

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Research

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Open AccessArticle The Phase Composition and Microstructure of AlxCoCrFeNiTi Alloys for the Development of High-Entropy Alloy Systems
Metals 2017, 7(5), 162; doi:10.3390/met7050162
Received: 3 April 2017 / Revised: 3 May 2017 / Accepted: 4 May 2017 / Published: 9 May 2017
Cited by 1 | PDF Full-text (3765 KB) | HTML Full-text | XML Full-text
Abstract
Alloying aluminum offers the possibility of creating low-density high-entropy alloys (HEAs). Several studies that focus on the system AlCoCrFeNiTi differ in their phase determination. The effect of aluminum on the phase composition and microstructure of the compositionally complex alloy (CCA) system Alx
[...] Read more.
Alloying aluminum offers the possibility of creating low-density high-entropy alloys (HEAs). Several studies that focus on the system AlCoCrFeNiTi differ in their phase determination. The effect of aluminum on the phase composition and microstructure of the compositionally complex alloy (CCA) system AlxCoCrFeNiTi was studied with variation in aluminum content (molar ratios x = 0.2, 0.8, and 1.5). The chemical composition and elemental segregation was measured for the different domains in the microstructure. The crystal structure was determined using X-ray diffraction (XRD) analysis. To identify the spatial distribution of the phases found with XRD, phase mapping with associated orientation distribution was performed using electron backscatter diffraction. This made it possible to correlate the chemical and structural conditions of the phases. The phase formation strongly depends on the aluminum content. Two different body-centered cubic (bcc) phases were found. Texture analysis proved the presence of a face-centered cubic (fcc) phase for all aluminum amounts. The hard η-(Ni, Co)3Ti phase in the x = 0.2 alloy was detected via metallographic investigation and confirmed via electron backscatter diffraction. Additionally, a centered cluster (cc) with the A12 structure type was detected in the x = 0.2 and 0.8 alloys. The correlation of structural and chemical properties as well as microstructure formation contribute to a better understanding of the alloying effects concerning the aluminum content in CCAs. Especially in the context of current developments in lightweight high-entropy alloys (HEAs), the presented results provide an approach to the development of new alloy systems. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Investigating the Wear Behavior of Fe-Based Amorphous Coatings under Nanoscratch Tests
Metals 2017, 7(4), 118; doi:10.3390/met7040118
Received: 23 January 2017 / Revised: 23 March 2017 / Accepted: 24 March 2017 / Published: 29 March 2017
PDF Full-text (4479 KB) | HTML Full-text | XML Full-text
Abstract
The wear behavior of two coatings (Fe49.7Cr18Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 and Fe40Cr23Mo14C15B6Y2) sprayed by high-velocity air fuel technology was
[...] Read more.
The wear behavior of two coatings (Fe49.7Cr18Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 and Fe40Cr23Mo14C15B6Y2) sprayed by high-velocity air fuel technology was investigated through nanoscratch tests under ramping loads. Compared with the substrate, the Fe-based amorphous coatings exhibit lower penetration depth, higher elastic recovery, and lower wear volume, indicating the excellent wear resistance of the coatings. This behavior is related to the high hardness and high hardness/elastic modulus ratio (H/E) of the Fe-based amorphous coatings. From the scanning electron microscopy images of the scratch grooves, it is found out that ploughing governs the wear behavior of the coatings and substrate. In addition, spalling wear easily occurs in the pore regions of the coatings. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Deformation Behavior of Al0.25CoCrFeNi High-Entropy Alloy after Recrystallization
Metals 2017, 7(4), 111; doi:10.3390/met7040111
Received: 27 December 2016 / Revised: 12 March 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
PDF Full-text (11114 KB) | HTML Full-text | XML Full-text
Abstract
Cold rolling with subsequent annealing can be used to produce the recrystallized structure in high entropy alloys (HEAs). The Al0.25CoCrFeNi HEAs rolled to different final thickness (230, 400, 540, 800, 1000, 1500 μm) are prepared to investigate their microstructure evolutions and
[...] Read more.
Cold rolling with subsequent annealing can be used to produce the recrystallized structure in high entropy alloys (HEAs). The Al0.25CoCrFeNi HEAs rolled to different final thickness (230, 400, 540, 800, 1000, 1500 μm) are prepared to investigate their microstructure evolutions and mechanical behaviors after annealing. Only the single face-centered cubic phase was obtained after cold rolling and recrystallization annealing at 1100 °C for 10 h. The average recrystallized grain size in this alloy after annealing ranges from 92 μm to 136 μm. The annealed thin sheets show obviously size effects on the flow stress and formability. The yield strength and tensile strength decrease as t/d (thickness/average grain diameter) ratio decreases until the t/d approaches 2.23. In addition, the stretchability (formability) decreases with the decrease of the t/d ratio especially when the t/d ratio is lower than about 6. According to the present results, yield strength can be expressed as a function of the t/d ratio. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle The BCC/B2 Morphologies in AlxNiCoFeCr High-Entropy Alloys
Metals 2017, 7(2), 57; doi:10.3390/met7020057
Received: 31 December 2016 / Revised: 7 February 2017 / Accepted: 9 February 2017 / Published: 15 February 2017
Cited by 6 | PDF Full-text (3678 KB) | HTML Full-text | XML Full-text
Abstract
The present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in AlxNiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases,
[...] Read more.
The present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in AlxNiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases, which is sensitive to Al. There are two types of microscopic BCC/B2 morphologies in this HEA series: one is the weave-like morphology induced by the spinodal decomposition, and the other is the microstructure of a spherical disordered BCC precipitation on the ordered B2 matrix that appears in HEAs with a much higher Al content. The mechanical properties, including the compressive yielding strength and microhardness of the AlxNiCoFeCr HEAs, are also discussed in light of the concept of the valence electron concentration (VEC). Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Phase Evolution of the AlxNbTiVZr (x = 0; 0.5; 1; 1.5) High Entropy Alloys
Metals 2016, 6(12), 298; doi:10.3390/met6120298
Received: 26 October 2016 / Revised: 19 November 2016 / Accepted: 21 November 2016 / Published: 25 November 2016
PDF Full-text (4135 KB) | HTML Full-text | XML Full-text
Abstract
AlxNbTiVZr (x = 0; 0.5; 1; 1.5) high entropy alloys were fabricated by vacuum arc melting and annealed at 1200 °C for 24 h. The NbTiVZr alloy had single body centered cubic (bcc) solid solution phase after annealing at 1200
[...] Read more.
AlxNbTiVZr (x = 0; 0.5; 1; 1.5) high entropy alloys were fabricated by vacuum arc melting and annealed at 1200 °C for 24 h. The NbTiVZr alloy had single body centered cubic (bcc) solid solution phase after annealing at 1200 °C, while, in the Al-containing alloys, C14 Laves and Zr2Al-type phases are found. The alloys were subjected to annealing at 800 °C and 1000 °C. It was shown that annealing temperature (800 °C or 1000 °C) weakly affected the produced phases but the Al content had pronounced effect on structure of the annealed alloys. The NbTiVZr alloy decomposed into bcc, Zr-rich hexagonal close-packed (hcp), and C15 Laves phases. In the Al0.5NbTiVZr alloy, the bcc matrix phase also decomposed into a mixture of bcc and C14 Laves phases. In the AlNbTiVZr alloy, annealing resulted in an increase of volume fraction of Zr2Al-type phase. Finally, in the Al1.5NbTiVZr alloy, formation of AlNb2-type phase was observed. The highest fraction of second phases appeared after annealing in the NbTiVZr alloy. It is demonstrated that the strong chemical affinity and high enthalpy of formation of intermetallic phases in Al-Zr atomic pair govern the intermetallic phase formation in the alloys at 1200 °C. Increase of volume fraction of second phases in the alloys due to annealing at 800 °C and 1000 °C is in proportion to the decrease of Zr concentration in the bcc matrix phase. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Hot Deformation Behavior of As-Cast and Homogenized Al0.5CoCrFeNi High Entropy Alloys
Metals 2016, 6(11), 277; doi:10.3390/met6110277
Received: 10 September 2016 / Revised: 3 November 2016 / Accepted: 4 November 2016 / Published: 15 November 2016
Cited by 1 | PDF Full-text (3249 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The hot deformation behavior of as-cast and homogenized Al0.5CoCrFeNi high entropy alloys (HEAs) during isothermal compression was investigated as a function of temperature and strain rate. Results indicated that flow stress in a homogenized state was always higher than that in
[...] Read more.
The hot deformation behavior of as-cast and homogenized Al0.5CoCrFeNi high entropy alloys (HEAs) during isothermal compression was investigated as a function of temperature and strain rate. Results indicated that flow stress in a homogenized state was always higher than that in an as-cast state under the same deformation conditions. Moreover, the optimum thermo-mechanical processing (TMP) conditions for the hot working of the homogenized state were identified as 945–965 °C and 10−1.7–10−1.1 s−1 and were easier to determine in practice. Constitutive equations, for both states, correlating the flow stress of Al0.5CoCrFeNi with strain rate and deformation temperature were also determined. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Influence of Annealing on the Microstructures and Oxidation Behaviors of Al8(CoCrFeNi)92, Al15(CoCrFeNi)85, and Al30(CoCrFeNi)70 High-Entropy Alloys
Metals 2016, 6(9), 222; doi:10.3390/met6090222
Received: 28 July 2016 / Revised: 2 September 2016 / Accepted: 5 September 2016 / Published: 12 September 2016
Cited by 3 | PDF Full-text (3401 KB) | HTML Full-text | XML Full-text
Abstract
The understanding of the oxidation behaviors of as-cast and annealed high-entropy alloys (HEAs) is currently limited. This work systematically investigates the influence of annealing on the microstructures and oxidation behaviors of AlCoCrFeNi-based HEAs. Annealing was found to alter the distribution of Al-rich phases
[...] Read more.
The understanding of the oxidation behaviors of as-cast and annealed high-entropy alloys (HEAs) is currently limited. This work systematically investigates the influence of annealing on the microstructures and oxidation behaviors of AlCoCrFeNi-based HEAs. Annealing was found to alter the distribution of Al-rich phases which caused a change in the oxidation mechanisms. In general, all three of the investigated HEAs displayed some degree of transient oxidation at 1050 °C that was later followed by protective, parabolic oxide growth. The respective oxidation behaviors are discussed relative to existing oxide formation models for Ni–Cr–Al alloys. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Serration Behavior in Pd77.5Cu6Si16.5 Alloy
Metals 2016, 6(8), 191; doi:10.3390/met6080191
Received: 18 May 2016 / Revised: 1 August 2016 / Accepted: 1 August 2016 / Published: 17 August 2016
PDF Full-text (4197 KB) | HTML Full-text | XML Full-text
Abstract
The strain-rate-dependent plasticity under uniaxial compression at the strain rates of 2 × 10−3, 2 × 10−4 and 2 × 10−5 s−1 in a Pd77.5Cu6Si16.5 alloy is investigated. At different strain rates, the
[...] Read more.
The strain-rate-dependent plasticity under uniaxial compression at the strain rates of 2 × 10−3, 2 × 10−4 and 2 × 10−5 s−1 in a Pd77.5Cu6Si16.5 alloy is investigated. At different strain rates, the serration events exhibit different amplitudes and time scales. The intersection effects take place obviously, and the loading time is much longer than the relaxation time in the serration event at three strain rates. However, the time intervals between two neighboring serrations lack any time scale, and the elastic energy density displays a power-law distribution at the strain rate of 2 × 10−3 s−1, which means that the self-organized critical (SOC) behavior emerges with increasing strain rates. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Review

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Open AccessFeature PaperReview Corrosion-Resistant High-Entropy Alloys: A Review
Metals 2017, 7(2), 43; doi:10.3390/met7020043
Received: 30 December 2016 / Revised: 29 January 2017 / Accepted: 2 February 2017 / Published: 5 February 2017
Cited by 8 | PDF Full-text (2256 KB) | HTML Full-text | XML Full-text
Abstract
Corrosion destroys more than three percent of the world’s gross domestic product. Therefore, the design of highly corrosion-resistant materials is urgently needed. By breaking the classical alloy-design philosophy, high-entropy alloys (HEAs) possess unique microstructures, which are solid solutions with random arrangements of multiple
[...] Read more.
Corrosion destroys more than three percent of the world’s gross domestic product. Therefore, the design of highly corrosion-resistant materials is urgently needed. By breaking the classical alloy-design philosophy, high-entropy alloys (HEAs) possess unique microstructures, which are solid solutions with random arrangements of multiple elements. The particular locally-disordered chemical environment is expected to lead to unique corrosion-resistant properties. In this review, the studies of the corrosion-resistant HEAs during the last decade are summarized. The corrosion-resistant properties of HEAs in various aqueous environments and the corrosion behavior of HEA coatings are presented. The effects of environments, alloying elements, and processing methods on the corrosion resistance are analyzed in detail. Furthermore, the possible directions of future work regarding the corrosion behavior of HEAs are suggested. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessFeature PaperReview An Insight into Evolution of Light Weight High Entropy Alloys: A Review
Metals 2016, 6(9), 199; doi:10.3390/met6090199
Received: 14 July 2016 / Revised: 18 August 2016 / Accepted: 19 August 2016 / Published: 26 August 2016
Cited by 3 | PDF Full-text (961 KB) | HTML Full-text | XML Full-text
Abstract
High Entropy Alloys (HEAs) are the most recently developed new class of materials, which are known for their unique structural properties. Lightweight materials are currently in excessive demand for transportation and energy saving applications. In this review, efforts have been made to summarize
[...] Read more.
High Entropy Alloys (HEAs) are the most recently developed new class of materials, which are known for their unique structural properties. Lightweight materials are currently in excessive demand for transportation and energy saving applications. In this review, efforts have been made to summarize the work done towards the development of HEAs targeting lightweight applications. Some new synthesis techniques are suggested for the fabrication of lightweight HEAs (LWHEAs). The concept of porous structure fabrication, microwave sintering of green compact, casting by disintegration melt deposition and advanced manufacturing using additive manufacturing are discussed as future directions of LWHEAs synthesis. LWHEAs for potential biomedical applications have also been addressed. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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