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Special Issue "High Entropy Alloys"

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A special issue of Entropy (ISSN 1099-4300).

Deadline for manuscript submissions: closed (30 November 2013)

Special Issue Editor

Guest Editor
Prof. Dr. Jien-Wei Yeh (Website)

Materials Science & Technology Building R505, National Tsing Hua University, Taiwan
Interests: high-entropy alloys; reciprocating extrusion process; light alloys; superplasticity; metal matrix composites; composites

Special Issue Information

Dear Colleagues,

“High-entropy Alloys (HEAs)” has become an emerging field from the efforts of many researchers since 1995. Its design concept is beyond the conventional scope of materials design, and was hardly noticed previously. In principle, HEAs are alloys that have at least five major elements and thus have high mixing entropy at the liquid state or random state. High mixing entropy can enhance the formation of solution-type phases, and in general leads to simpler microstructure. HEAs have a broad range of structure and properties and may find applications in structural, electrical, magnetic, high-temperature, wear-resistant, corrosion-resistant, and oxidation-resistant components. Among numerous possibilities of HEAs or other HE-related materials, one might design suitable compositions and processes to research for desired phenomena, properties, mechanisms, theories, and applications. The central scheme of this special issue comprises thermodynamics, kinetics, structure, microstructure, properties, applications, alloy design, modeling, and simulation, which can provide our further understanding and manipulation on this new material world.

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

 

  • thermodynamics and kinetics
  • structure, microstructure, and properties
  • mechanisms
  • simulation and modeling
  • alloy design
  • applications
  • HE materials based on HEAs

 

Prof. Jien-Wei Yeh
Guest Editor

Submission

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. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as 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 refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy 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 1400 CHF (Swiss Francs).

Published Papers (12 papers)

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Research

Jump to: Review

Open AccessArticle Microstructures and Crackling Noise of AlxNbTiMoV High Entropy Alloys
Entropy 2014, 16(2), 870-884; doi:10.3390/e16020870
Received: 28 October 2013 / Revised: 5 February 2014 / Accepted: 6 February 2014 / Published: 13 February 2014
Cited by 11 | PDF Full-text (2016 KB) | HTML Full-text | XML Full-text
Abstract
A series of high entropy alloys (HEAs), AlxNbTiMoV, was produced by a vacuum arc-melting method. Their microstructures and compressive mechanical behavior at room temperature were investigated. It has been found that a single solid-solution phase with a body-centered cubic (BCC) [...] Read more.
A series of high entropy alloys (HEAs), AlxNbTiMoV, was produced by a vacuum arc-melting method. Their microstructures and compressive mechanical behavior at room temperature were investigated. It has been found that a single solid-solution phase with a body-centered cubic (BCC) crystal structure forms in these alloys. Among these alloys, Al0.5NbTiMoV reaches the highest yield strength (1,625 MPa), which should be attributed to the considerable solid-solution strengthening behavior. Furthermore, serration and crackling noises near the yielding point was observed in the NbTiMoV alloy, which represents the first such reported phenomenon at room temperature in HEAs. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Exploration and Development of High Entropy Alloys for Structural Applications
Entropy 2014, 16(1), 494-525; doi:10.3390/e16010494
Received: 31 October 2013 / Revised: 27 November 2013 / Accepted: 20 December 2013 / Published: 10 January 2014
Cited by 78 | PDF Full-text (1916 KB) | HTML Full-text | XML Full-text
Abstract
We develop a strategy to design and evaluate high-entropy alloys (HEAs) for structural use in the transportation and energy industries. We give HEA goal properties for low (≤150 °C), medium (≤450 °C) and high (≥1,100 °C) use temperatures. A systematic design approach [...] Read more.
We develop a strategy to design and evaluate high-entropy alloys (HEAs) for structural use in the transportation and energy industries. We give HEA goal properties for low (≤150 °C), medium (≤450 °C) and high (≥1,100 °C) use temperatures. A systematic design approach uses palettes of elements chosen to meet target properties of each HEA family and gives methods to build HEAs from these palettes. We show that intermetallic phases are consistent with HEA definitions, and the strategy developed here includes both single-phase, solid solution HEAs and HEAs with intentional addition of a 2nd phase for particulate hardening. A thermodynamic estimate of the effectiveness of configurational entropy to suppress or delay compound formation is given. A 3-stage approach is given to systematically screen and evaluate a vast number of HEAs by integrating high-throughput computations and experiments. CALPHAD methods are used to predict phase equilibria, and high-throughput experiments on materials libraries with controlled composition and microstructure gradients are suggested. Much of this evaluation can be done now, but key components (materials libraries with microstructure gradients and high-throughput tensile testing) are currently missing. Suggestions for future HEA efforts are given. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Nanomechanical Properties and Deformation Behaviors of Multi-Component (AlCrTaTiZr)NxSiy High-Entropy Coatings
Entropy 2014, 16(1), 405-417; doi:10.3390/e16010405
Received: 27 September 2013 / Revised: 20 November 2013 / Accepted: 18 December 2013 / Published: 31 December 2013
Cited by 1 | PDF Full-text (3028 KB) | HTML Full-text | XML Full-text
Abstract
In this study multi-component (AlCrTaTiZr)NxSiy high-entropy coatings were developed by co-sputtering of AlCrTaTiZr alloy and Si in an Ar/N2 mixed atmosphere with the application of different substrate biases and Si-target powers. Their nanomechanical properties and deformation behaviors were [...] Read more.
In this study multi-component (AlCrTaTiZr)NxSiy high-entropy coatings were developed by co-sputtering of AlCrTaTiZr alloy and Si in an Ar/N2 mixed atmosphere with the application of different substrate biases and Si-target powers. Their nanomechanical properties and deformation behaviors were characterized by nanoindentation tests. Because of the effect of high mixing entropies, all the deposited multi-component (AlCrTaTiZr)NxSiy high-entropy coatings exhibited a simple face-centered cubic solid-solution structure. With an increased substrate bias and Si-target power, their microstructures changed from large columns with a [111] preferred orientation to a nanocomposite form with ultrafine grains. The hardness, H/E ratio and H3/E2 ratio of (AlCrTaTiZr)N1.07Si0.15 coating reached 30.2 GPa, 0.12 and 0.41 GPa, respectively, suggesting markedly suppressed dislocation activities and a very high resistance to wear and plastic deformation, attributable to grain refinements and film densification by the application of substrate bias, a nanocomposite structure by the introduction of silicon nitrides, and a strengthening effect induced by severe lattice distortions. In the deformed regions under indents, stacking faults or partial dislocations were formed, while in the stress-released regions, near-perfect lattices recovered. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Atomic Structure Modeling of Multi-Principal-Element Alloys by the Principle of Maximum Entropy
Entropy 2013, 15(12), 5536-5548; doi:10.3390/e15125536
Received: 20 September 2013 / Revised: 19 November 2013 / Accepted: 25 November 2013 / Published: 13 December 2013
Cited by 6 | PDF Full-text (704 KB) | HTML Full-text | XML Full-text
Abstract
Atomic structure models of multi-principal-element alloys (or high-entropy alloys) composed of four to eight componential elements in both BCC and FCC lattice structures are built according to the principle of maximum entropy. With the concept of entropic force, the maximum-entropy configurations of [...] Read more.
Atomic structure models of multi-principal-element alloys (or high-entropy alloys) composed of four to eight componential elements in both BCC and FCC lattice structures are built according to the principle of maximum entropy. With the concept of entropic force, the maximum-entropy configurations of these phases are generated through the use of Monte Carlo computer simulation. The efficiency of the maximum-entropy principle in modeling the atomic structure of random solid-solution phases has been demonstrated. The bulk atomic configurations of four real multi-principal-element alloys with four to six element components in either BCC or FCC lattice are studied using these models. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Figures

Open AccessArticle Microstructures and Mechanical Properties of TiCrZrNbNx Alloy Nitride Thin Films
Entropy 2013, 15(11), 5012-5021; doi:10.3390/e15115012
Received: 20 September 2013 / Revised: 10 November 2013 / Accepted: 13 November 2013 / Published: 18 November 2013
Cited by 3 | PDF Full-text (2008 KB) | HTML Full-text | XML Full-text
Abstract
The pure elements Ti, Zr, Cr, Nb were selected to produce an TiCrZrNb alloy target and deposited thin films thereof by a reactive high vacuum DC sputtering process. Nitrogen was used as the reactive gas to deposit the nitride thin films. The [...] Read more.
The pure elements Ti, Zr, Cr, Nb were selected to produce an TiCrZrNb alloy target and deposited thin films thereof by a reactive high vacuum DC sputtering process. Nitrogen was used as the reactive gas to deposit the nitride thin films. The effect of nitriding on the properties of the TiCrZrNbNx film was tested by changing the nitrogen ratio of the atmosphere. All of the as-deposited TiCrZrNbNx nitride films exhibited an amorphous structure. The film thickness decreases by increasing the N2 flow rate, because the Ar flow rate decreased and the target was poisoned by nitrogen. The hardness and Young’s modulus were also measured by a nano-indenter. The hardness and Young’s modulus of the TiCrZrNbNx nitride films were all lower than those of a TiCrZrNb metallic film. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Searching for Next Single-Phase High-Entropy Alloy Compositions
Entropy 2013, 15(10), 4504-4519; doi:10.3390/e15104504
Received: 22 September 2013 / Revised: 11 October 2013 / Accepted: 16 October 2013 / Published: 18 October 2013
Cited by 51 | PDF Full-text (2546 KB) | HTML Full-text | XML Full-text
Abstract
There has been considerable technological interest in high-entropy alloys (HEAs) since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based [...] Read more.
There has been considerable technological interest in high-entropy alloys (HEAs) since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new single-phase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Phase Composition of a CrMo0.5NbTa0.5TiZr High Entropy Alloy: Comparison of Experimental and Simulated Data
Entropy 2013, 15(9), 3796-3809; doi:10.3390/e15093796
Received: 7 August 2013 / Revised: 2 September 2013 / Accepted: 9 September 2013 / Published: 12 September 2013
Cited by 17 | PDF Full-text (1782 KB) | HTML Full-text | XML Full-text
Abstract
Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified and heat treated conditions. In the as-solidified condition, the alloy consisted of two disordered BCC phases and an ordered cubic Laves phase. The [...] Read more.
Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified and heat treated conditions. In the as-solidified condition, the alloy consisted of two disordered BCC phases and an ordered cubic Laves phase. The BCC1 phase solidified in the form of dendrites enriched with Mo, Ta and Nb, and its volume fraction was 42%. The BCC2 and Laves phases solidified by the eutectic-type reaction, and their volume fractions were 27% and 31%, respectively. The BCC2 phase was enriched with Ti and Zr and the Laves phase was heavily enriched with Cr. After hot isostatic pressing at 1450 °C for 3 h, the BCC1 dendrites coagulated into round-shaped particles and their volume fraction increased to 67%. The volume fractions of the BCC2 and Laves phases decreased to 16% and 17%, respectively. After subsequent annealing at 1000 °C for 100 h, submicron-sized Laves particles precipitated inside the BCC1 phase, and the alloy consisted of 52% BCC1, 16% BCC2 and 32% Laves phases. Solidification and phase equilibrium simulations were conducted for the CrMo0.5NbTa0.5TiZr alloy using a thermodynamic database developed by CompuTherm LLC. Some discrepancies were found between the calculated and experimental results and the reasons for these discrepancies were discussed. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Entropies in Alloy Design for High-Entropy and Bulk Glassy Alloys
Entropy 2013, 15(9), 3810-3821; doi:10.3390/e15093810
Received: 19 July 2013 / Revised: 10 September 2013 / Accepted: 10 September 2013 / Published: 12 September 2013
Cited by 25 | PDF Full-text (1339 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
High-entropy (H-E) alloys, bulk metallic glasses (BMGs) and high-entropy BMGs (HE-BMGs) were statistically analyzed with the help of a database of ternary amorphous alloys. Thermodynamic quantities corresponding to heat of mixing and atomic size differences were calculated as a function of composition [...] Read more.
High-entropy (H-E) alloys, bulk metallic glasses (BMGs) and high-entropy BMGs (HE-BMGs) were statistically analyzed with the help of a database of ternary amorphous alloys. Thermodynamic quantities corresponding to heat of mixing and atomic size differences were calculated as a function of composition of the multicomponent alloys. Actual calculations were performed for configurational entropy (Sconfig.) in defining the H-E alloys and mismatch entropy (Ss) normalized with Boltzmann constant (kB), together with mixing enthalpy (DHmix) based on Miedema’s empirical model and Delta parameter (d) as a corresponding parameter to Ss/kB. The comparison between DHmixd and DHmix–  diagrams for the ternary amorphous alloys revealed Ss/kB ~ (d /22)2. The zones S, S′ and B’s where H-E alloys with disordered solid solutions, ordered alloys and BMGs are plotted in the DHmixd diagram are correlated with the areas in the DHmixSs /kB diagram. The results provide mutual understandings among H-E alloys, BMGs and HE-BMGs. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessArticle Microstructure of Laser Re-Melted AlCoCrCuFeNi High Entropy Alloy Coatings Produced by Plasma Spraying
Entropy 2013, 15(7), 2833-2845; doi:10.3390/e15072833
Received: 23 May 2013 / Revised: 2 July 2013 / Accepted: 10 July 2013 / Published: 19 July 2013
Cited by 8 | PDF Full-text (702 KB) | HTML Full-text | XML Full-text
Abstract
An AlCoCrCuFeNi high-entropy alloy (HEA) coating was fabricated on a pure magnesium substrate using a two-step method, involving plasma spray processing and laser re-melting. After laser re-melting, the microporosity present in the as-sprayed coating was eliminated, and a dense surface layer was [...] Read more.
An AlCoCrCuFeNi high-entropy alloy (HEA) coating was fabricated on a pure magnesium substrate using a two-step method, involving plasma spray processing and laser re-melting. After laser re-melting, the microporosity present in the as-sprayed coating was eliminated, and a dense surface layer was obtained. The microstructure of the laser-remelted layer exhibits an epitaxial growth of columnar dendrites, which originate from the crystals of the spray coating. The presence of a continuous epitaxial growth of columnar HEA dendrites in the laser re-melted layer was analyzed based on the critical stability condition of a planar interface. The solidification of a columnar dendrite structure of the HEA alloy in the laser-remelted layer was analyzed based on the Kurz–Giovanola–Trivedi model and Hunt’s criterion, with modifications for a multi-component alloy. Full article
(This article belongs to the Special Issue High Entropy Alloys)

Review

Jump to: Research

Open AccessReview Multicomponent and High Entropy Alloys
Entropy 2014, 16(9), 4749-4768; doi:10.3390/e16094749
Received: 4 February 2014 / Revised: 31 July 2014 / Accepted: 12 August 2014 / Published: 26 August 2014
Cited by 25 | PDF Full-text (6174 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high [...] Read more.
This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessReview Alloying and Processing Effects on the Aqueous Corrosion Behavior of High-Entropy Alloys
Entropy 2014, 16(2), 895-911; doi:10.3390/e16020895
Received: 24 September 2013 / Revised: 9 January 2014 / Accepted: 5 February 2014 / Published: 14 February 2014
Cited by 18 | PDF Full-text (847 KB) | HTML Full-text | XML Full-text
Abstract
The effects of metallurgical factors on the aqueous corrosion behavior of high-entropy alloys (HEAs) are reviewed in this article. Alloying (e.g., Al and Cu) and processing (e.g., heat treatments) effects on the aqueous corrosion behavior of HEAs, including passive film formation, galvanic [...] Read more.
The effects of metallurgical factors on the aqueous corrosion behavior of high-entropy alloys (HEAs) are reviewed in this article. Alloying (e.g., Al and Cu) and processing (e.g., heat treatments) effects on the aqueous corrosion behavior of HEAs, including passive film formation, galvanic corrosion, and pitting corrosion, are discussed in detail. Corrosion rates of HEAs are calculated using electrochemical measurements and the weight-loss method. Available experimental corrosion data of HEAs in two common solutions [sulfuric acid (0.5 M H2SO4) and salt water (3.5 weight percent, wt.%, NaCl)], such as the corrosion potential (Ecorr), corrosion current density (icorr), pitting potential (Epit), and passive region (ΔE), are summarized and compared with conventional corrosion-resistant alloys. Possible directions of future work on the corrosion behavior of HEAs are suggested. Full article
(This article belongs to the Special Issue High Entropy Alloys)
Open AccessReview Physical Properties of High Entropy Alloys
Entropy 2013, 15(12), 5338-5345; doi:10.3390/e15125338
Received: 26 September 2013 / Revised: 20 November 2013 / Accepted: 24 November 2013 / Published: 3 December 2013
Cited by 14 | PDF Full-text (752 KB) | HTML Full-text | XML Full-text
Abstract
The majority of studies on high-entropy alloys are focused on their phase, microstructure, and mechanical properties. However, the physical properties of these materials are also encouraging. This paper provides a brief overview of the physical properties of high-entropy alloys. Emphasis is laid [...] Read more.
The majority of studies on high-entropy alloys are focused on their phase, microstructure, and mechanical properties. However, the physical properties of these materials are also encouraging. This paper provides a brief overview of the physical properties of high-entropy alloys. Emphasis is laid on magnetic, electrical, and thermal properties. Full article
(This article belongs to the Special Issue High Entropy Alloys)

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