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High Entropy Alloys

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

Deadline for manuscript submissions: closed (30 November 2013) | Viewed by 190471

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Materials Science & Technology Building R505, National Tsing Hua University, Hsinchu 30013, Taiwan
Interests: high-entropy materials; functional coatings; functional composites
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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

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Published Papers (12 papers)

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Research

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2016 KiB  
Article
Microstructures and Crackling Noise of AlxNbTiMoV High Entropy Alloys
by Shu Ying Chen, Xiao Yang, Karin A. Dahmen, Peter K. Liaw and Yong Zhang
Entropy 2014, 16(2), 870-884; https://doi.org/10.3390/e16020870 - 13 Feb 2014
Cited by 139 | Viewed by 11901
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) crystal [...] 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)
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1916 KiB  
Article
Exploration and Development of High Entropy Alloys for Structural Applications
by Daniel B. Miracle, Jonathan D. Miller, Oleg N. Senkov, Christopher Woodward, Michael D. Uchic and Jaimie Tiley
Entropy 2014, 16(1), 494-525; https://doi.org/10.3390/e16010494 - 10 Jan 2014
Cited by 753 | Viewed by 35715
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 uses [...] 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)
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3028 KiB  
Article
Nanomechanical Properties and Deformation Behaviors of Multi-Component (AlCrTaTiZr)NxSiy High-Entropy Coatings
by Shao-Yi Lin, Shou-Yi Chang, Chia-Jung Chang and Yi-Chung Huang
Entropy 2014, 16(1), 405-417; https://doi.org/10.3390/e16010405 - 31 Dec 2013
Cited by 23 | Viewed by 8646
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 characterized [...] 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)
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704 KiB  
Article
Atomic Structure Modeling of Multi-Principal-Element Alloys by the Principle of Maximum Entropy
by Shaoqing Wang
Entropy 2013, 15(12), 5536-5548; https://doi.org/10.3390/e15125536 - 13 Dec 2013
Cited by 76 | Viewed by 16292
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 these [...] 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)
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Graphical abstract

2008 KiB  
Article
Microstructures and Mechanical Properties of TiCrZrNbNx Alloy Nitride Thin Films
by Chun-Huei Tsau and Yu-Hsin Chang
Entropy 2013, 15(11), 5012-5021; https://doi.org/10.3390/e15115012 - 18 Nov 2013
Cited by 24 | Viewed by 6796
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 effect [...] 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)
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2546 KiB  
Article
Searching for Next Single-Phase High-Entropy Alloy Compositions
by Michael C. Gao and David E. Alman
Entropy 2013, 15(10), 4504-4519; https://doi.org/10.3390/e15104504 - 18 Oct 2013
Cited by 272 | Viewed by 20030
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 on [...] 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)
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1339 KiB  
Article
Entropies in Alloy Design for High-Entropy and Bulk Glassy Alloys
by Akira Takeuchi, Kenji Amiya, Takeshi Wada, Kunio Yubuta, Wei Zhang and Akihiro Makino
Entropy 2013, 15(9), 3810-3821; https://doi.org/10.3390/e15093810 - 12 Sep 2013
Cited by 103 | Viewed by 10765
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 of [...] 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)
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1782 KiB  
Article
Phase Composition of a CrMo0.5NbTa0.5TiZr High Entropy Alloy: Comparison of Experimental and Simulated Data
by Oleg N. Senkov, Fan Zhang and Jonathan D. Miller
Entropy 2013, 15(9), 3796-3809; https://doi.org/10.3390/e15093796 - 12 Sep 2013
Cited by 59 | Viewed by 8389
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 BCC1 [...] 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)
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702 KiB  
Article
Microstructure of Laser Re-Melted AlCoCrCuFeNi High Entropy Alloy Coatings Produced by Plasma Spraying
by Tai M. Yue, Hui Xie, Xin Lin, Haiou Yang and Guanghui Meng
Entropy 2013, 15(7), 2833-2845; https://doi.org/10.3390/e15072833 - 19 Jul 2013
Cited by 89 | Viewed by 8905
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 obtained. [...] 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)
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Review

Jump to: Research

6174 KiB  
Review
Multicomponent and High Entropy Alloys
by Brian Cantor
Entropy 2014, 16(9), 4749-4768; https://doi.org/10.3390/e16094749 - 26 Aug 2014
Cited by 477 | Viewed by 24653
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 speed [...] 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)
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847 KiB  
Review
Alloying and Processing Effects on the Aqueous Corrosion Behavior of High-Entropy Alloys
by Zhi Tang, Lu Huang, Wei He and Peter K. Liaw
Entropy 2014, 16(2), 895-911; https://doi.org/10.3390/e16020895 - 14 Feb 2014
Cited by 179 | Viewed by 13724
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 corrosion, [...] 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)
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752 KiB  
Review
Physical Properties of High Entropy Alloys
by Ming-Hung Tsai
Entropy 2013, 15(12), 5338-5345; https://doi.org/10.3390/e15125338 - 3 Dec 2013
Cited by 268 | Viewed by 22187
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 on [...] 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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