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High-Entropy Alloys and High-Entropy-Related Materials

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

Deadline for manuscript submissions: closed (31 July 2016) | Viewed by 138371

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Prof. Dr. An-Chou Yeh

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Frontier Materials & Engineering Alloys Laboratory, High Entropy Materials Center, Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
Interests: alloy design; superalloys; high entropy alloys; additive manufacturing; microstructure engineering
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Special Issue Information

Dear Colleague,

Considerable interest has been shown over the last few years in exploring new alloy compositions using the high-entropy alloy (HEA) design concept. This is because of the four core effects which can bring various advantages to the HEAs. For example, high entropy effect can reduce the number of constituent phases and facilitate the design of the microstructure. Sluggish diffusion effect can reduce the phase transformation rate and stabilize the microstructure at elevated temperatures. Significant strengthening can be enhanced by severe lattice distortion effect. And, the cocktail effect enables tailor-made properties to be realized by choosing the right alloying constituents. The HEA alloy design approach has broadened the scope of composition design and new types of HEAs and high-entropy-related materials (HEMs) have been developed, such as high-entropy superalloys, high-entropy refractory alloys, high-entropy bulk metallic glasses, high-entropy carbides, high-entropy nitrides, high-entropy oxides, and high-entropy composites.

Most importantly, these HEMs can be fabricated and processed by similar routes as those of conventional materials. Also, characterization techniques for conventional materials can be employed for HEMs. For these reasons, HEMs have attracted more and more scientists from various disciplines to undertake such research activities. The combinations of compositions in the scope of HEMs and processing routes can potentially lead to a wide range of microstructures and properties. Many preliminary studies have shown evidence of their potentials to replace conventional materials for industrial applications.

The continued importance and interest in this research field is evident based on the rapid increase in the number of scientific journal publications. In this Special Issue of High-Entropy Alloys and High-Entropy-Related Materials, the aim is to gather the latest developments in HEAs and HEMs, and make the fundamental materials science more comprehensive, so that the R&D of HEAs and HEMs can be accelerated to develop a sustainable and eco-friendly society. Specific topics of interest include (but are not limited to):

Alloy design of HEAs and HEMs
Simulation and modeling
Processing
Thermodynamics and kinetics
Structure, microstructure and properties
Characterization
Mechanisms
Applications

Dr. An-Chou Yeh
Guest Editor

Relevant Special issue: https://0-www-mdpi-com.brum.beds.ac.uk/journal/entropy/special_issues/high-entropy-alloys

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Keywords

high-entropy alloys
high-entropy-related materials
alloy design
processing
crystal structure
microstructure
property
simulations
phase transformation
characterization
applications

Published Papers (13 papers)

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Research

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17446 KiB

Open AccessArticle

Isothermal Oxidation of Aluminized Coatings on High-Entropy Alloys

by Che-Wei Tsai, Kuen-Cheng Sung, Kzauki Kasai and Hideyuki Murakami

Entropy 2016, 18(10), 376; https://0-doi-org.brum.beds.ac.uk/10.3390/e18100376 - 20 Oct 2016

Cited by 6 | Viewed by 4813

Abstract

The isothermal oxidation resistance of Al_0.2Co_1.5CrFeNi_1.5Ti_0.3 high-entropy alloy is analyzed and the microstructural evolution of the oxide layer is studied. The limited aluminum, about 3.6 at %, leads to the non-continuous alumina. The present alloy is insufficient for severe circumstances only due to chromium oxide that is 10 μm after 1173 K for 360 h. Thus, the aluminized high-entropy alloys (HEAs) are further prepared by the industrial packing cementation process at 1273 K and 1323 K. The aluminizing coating is 50 μm at 1273 K after 5 h. The coating growth is controlled by the diffusion of aluminum. The interdiffusion zone reveals two regions that are the Ti-, Co-, Ni-rich area and the Fe-, Cr-rich area. The oxidation resistance of aluminizing HEA improves outstandingly, and sustains at 1173 K and 1273 K for 441 h without any spallation. The alumina at the surface and the stable interface contribute to the performance of this Al_0.2Co_1.5CrFeNi_1.5Ti_0.3 alloy. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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4197 KiB

Open AccessArticle

Design of Light-Weight High-Entropy Alloys

by Rui Feng, Michael C. Gao, Chanho Lee, Michael Mathes, Tingting Zuo, Shuying Chen, Jeffrey A. Hawk, Yong Zhang and Peter K. Liaw

Entropy 2016, 18(9), 333; https://0-doi-org.brum.beds.ac.uk/10.3390/e18090333 - 13 Sep 2016

Cited by 170 | Viewed by 14886

Abstract

High-entropy alloys (HEAs) are a new class of solid-solution alloys that have attracted worldwide attention for their outstanding properties. Owing to the demand from transportation and defense industries, light-weight HEAs have also garnered widespread interest from scientists for use as potential structural materials. Great efforts have been made to study the phase-formation rules of HEAs to accelerate and refine the discovery process. In this paper, many proposed solid-solution phase-formation rules are assessed, based on a series of known and newly-designed light-weight HEAs. The results indicate that these empirical rules work for most compositions but also fail for several alloys. Light-weight HEAs often involve the additions of Al and/or Ti in great amounts, resulting in large negative enthalpies for forming solid-solution phases and/or intermetallic compounds. Accordingly, these empirical rules need to be modified with the new experimental data. In contrast, CALPHAD (acronym of the calculation of phase diagrams) method is demonstrated to be an effective approach to predict the phase formation in HEAs as a function of composition and temperature. Future perspectives on the design of light-weight HEAs are discussed in light of CALPHAD modeling and physical metallurgy principles. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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1131 KiB

Open AccessArticle

Lattice Distortions in the FeCoNiCrMn High Entropy Alloy Studied by Theory and Experiment

by Hyun Seok Oh, Duancheng Ma, Gerard Paul Leyson, Blazej Grabowski, Eun Soo Park, Fritz Körmann and Dierk Raabe

Entropy 2016, 18(9), 321; https://0-doi-org.brum.beds.ac.uk/10.3390/e18090321 - 02 Sep 2016

Cited by 144 | Viewed by 13172

Abstract

Lattice distortions constitute one of the main features characterizing high entropy alloys. Local lattice distortions have, however, only rarely been investigated in these multi-component alloys. We, therefore, employ a combined theoretical electronic structure and experimental approach to study the atomistic distortions in the FeCoNiCrMn high entropy (Cantor) alloy by means of density-functional theory and extended X-ray absorption fine structure spectroscopy. Particular attention is paid to element-resolved distortions for each constituent. The individual mean distortions are small on average, <1%, but their fluctuations (i.e., standard deviations) are an order of magnitude larger, in particular for Cr and Mn. Good agreement between theory and experiment is found. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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1181 KiB

Open AccessArticle

Interplay between Lattice Distortions, Vibrations and Phase Stability in NbMoTaW High Entropy Alloys

by Fritz Körmann and Marcel H.F. Sluiter

Entropy 2016, 18(8), 403; https://0-doi-org.brum.beds.ac.uk/10.3390/e18080403 - 20 Aug 2016

Cited by 63 | Viewed by 10360

Abstract

Refractory high entropy alloys (HEA), such as BCC NbMoTaW, represent a promising materials class for next-generation high-temperature applications, due to their extraordinary mechanical properties. A characteristic feature of HEAs is the formation of single-phase solid solutions. For BCC NbMoTaW, recent computational studies revealed, however, a B2(Mo,W;Nb,Ta)-ordering at ambient temperature. This ordering could impact many materials properties, such as thermodynamic, mechanical, or diffusion properties, and hence be of relevance for practical applications. In this work, we theoretically address how the B2-ordering impacts thermodynamic properties of BCC NbMoTaW and how the predicted ordering temperature itself is affected by vibrations, electronic excitations, lattice distortions, and relaxation energies. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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1758 KiB

Open AccessArticle

Soft Magnetic Properties of High-Entropy Fe-Co-Ni-Cr-Al-Si Thin Films

by Pei-Chung Lin, Chun-Yang Cheng, Jien-Wei Yeh and Tsung-Shune Chin

Entropy 2016, 18(8), 308; https://0-doi-org.brum.beds.ac.uk/10.3390/e18080308 - 18 Aug 2016

Cited by 28 | Viewed by 7621

Abstract

Soft magnetic properties of Fe-Co-Ni-Al-Cr-Si thin films were studied. As-deposited Fe-Co-Ni-Al-Cr-Si nano-grained thin films showing no magnetic anisotropy were subjected to field-annealing at different temperatures to induce magnetic anisotropy. Optimized magnetic and electrical properties of Fe-Co-Ni-Al-Cr-Si films annealed at 200 °C are saturation magnetization 9.13 × 10⁵ A/m, coercivity 79.6 A/m, out-of-plane uniaxial anisotropy field 1.59 × 10³ A/m, and electrical resistivity 3.75 μΩ·m. Based on these excellent properties, we employed such films to fabricate magnetic thin film inductor. The performance of the high entropy alloy thin film inductors is superior to that of air core inductor. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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17050 KiB

Open AccessArticle

Microstructures of Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ High-Entropy Alloy and Its Polarization Behaviors in Sulfuric Acid, Nitric Acid and Hydrochloric Acid Solutions

by Chun-Huei Tsau and Po-Yen Lee

Entropy 2016, 18(8), 288; https://0-doi-org.brum.beds.ac.uk/10.3390/e18080288 - 08 Aug 2016

Cited by 6 | Viewed by 6257

Abstract

This paper investigates the microstructures and the polarization behaviors of Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ high-entropy alloy in 1M (1 mol/L) deaerated sulfuric acid (H₂SO₄), nitric acid (HNO₃), and hydrochloric acid (HCl) solutions at temperatures of 30–60 °C. The three phases of the Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ high-entropy alloy are body-centered cubic (BCC) dendrites, face-centered cubic (FCC) interdendrites, and ordered BCC precipitates uniformly dispersed in the BCC dendrites. The different phases were corroded in different acidic solutions. The passivation regions of the Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ alloy are divided into three and two sub-regions in the solutions of H₂SO₄ and HNO₃ at 30–60 °C, respectively. The passivation region of the Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ alloy is also divided into two sub-domains in 1M deaerated HCl solution at 30 °C. The Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ alloy has almost equal corrosion resistance in comparison with 304 stainless steel (304SS) in both the 1M H₂SO₄ and 1M HCl solutions. The polarization behaviors indicated that the Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ alloy possessed much better corrosion resistance than 304SS in 1M HNO₃ solution. However, in 1M NaCl solution, the corrosion resistance of the Al_7.5Cr_22.5Fe₃₅Mn₂₀Ni₁₅ alloy was less than 304SS. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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2563 KiB

Open AccessArticle

Nano-Crystallization of High-Entropy Amorphous NbTiAlSiW_xN_y Films Prepared by Magnetron Sputtering

by Wenjie Sheng, Xiao Yang, Cong Wang and Yong Zhang

Entropy 2016, 18(6), 226; https://0-doi-org.brum.beds.ac.uk/10.3390/e18060226 - 13 Jun 2016

Cited by 80 | Viewed by 10242

Abstract

High-entropy amorphous NbTiAlSiW_xN_y films (x = 0 or 1, i.e., NbTiAlSiN_y and NbTiAlSiWN_y) were prepared by magnetron sputtering method in the atmosphere of a mixture of N₂ + Ar (N₂ + Ar = 24 standard cubic centimeter per minute (sccm)), where N₂ = 0, 4, and 8 sccm). All the as-deposited films present amorphous structures, which remain stable at 700 °C for over 24 h. After heat treatment at 1000 °C the films began to crystalize, and while the NbTiAlSiN_y films (N₂ = 4, 8 sccm) exhibit a face-centered cubic (FCC) structure, the NbTiAlSiW metallic films show a body-centered cubic (BCC) structure and then transit into a FCC structure composed of nanoscaled particles with increasing nitrogen flow rate. The hardness and modulus of the as-deposited NbTiAlSiN_y films reach maximum values of 20.5 GPa and 206.8 GPa, respectively. For the as-deposited NbTiAlSiWN_y films, both modulus and hardness increased to maximum values of 13.6 GPa and 154.4 GPa, respectively, and then decrease as the N₂ flow rate is increased. Both films could be potential candidates for protective coatings at high temperature. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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7432 KiB

Open AccessArticle

MoNbTaV Medium-Entropy Alloy

by Hongwei Yao, Jun-Wei Qiao, Michael C. Gao, Jeffrey A. Hawk, Sheng-Guo Ma and Hefeng Zhou

Entropy 2016, 18(5), 189; https://0-doi-org.brum.beds.ac.uk/10.3390/e18050189 - 19 May 2016

Cited by 107 | Viewed by 11376 | Correction

Abstract

Guided by CALPHAD (Calculation of Phase Diagrams) modeling, the refractory medium-entropy alloy MoNbTaV was synthesized by vacuum arc melting under a high-purity argon atmosphere. A body-centered cubic solid solution phase was experimentally confirmed in the as-cast ingot using X-ray diffraction and scanning electron microscopy. The measured lattice parameter of the alloy (3.208 Å) obeys the rule of mixtures (ROM), but the Vickers microhardness (4.95 GPa) and the yield strength (1.5 GPa) are about 4.5 and 4.6 times those estimated from the ROM, respectively. Using a simple model on solid solution strengthening predicts a yield strength of approximately 1.5 GPa. Thermodynamic analysis shows that the total entropy of the alloy is more than three times the configurational entropy at room temperature, and the entropy of mixing exhibits a small negative departure from ideal mixing. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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3134 KiB

Open AccessArticle

On the Path to Optimizing the Al-Co-Cr-Cu-Fe-Ni-Ti High Entropy Alloy Family for High Temperature Applications

by Anna M. Manzoni, Sheela Singh, Haneen M. Daoud, Robert Popp, Rainer Völkl, Uwe Glatzel and Nelia Wanderka

Entropy 2016, 18(4), 104; https://0-doi-org.brum.beds.ac.uk/10.3390/e18040104 - 23 Mar 2016

Cited by 61 | Viewed by 14231

Abstract

The most commonly investigated high entropy alloy, AlCoCrCuFeNi, has been chosen for optimization of its microstructural and mechanical properties by means of compositional changes and heat treatments. Among the different available optimization paths, the decrease of segregating element Cu, the increase of oxidation protective elements Al and Cr and the approach towards a γ-γ′ microstructure like in Ni-based superalloys have been probed and compared. Microscopical observations have been made for every optimization step. Vickers microhardness measurements and/or tensile/compression test have been carried out when the alloy was appropriate. Five derived alloys AlCoCrFeNi, Al₂₃Co₁₅Cr₂₃Cu₈Fe₁₅Ni_16, Al₈Co₁₇Cr₁₇Cu₈Fe₁₇Ni_33, Al₈Co₁₇Cr₁₄Cu₈Fe₁₇Ni_34.8Mo_0.1Ti₁W_0.1 and Al₁₀Co₂₅Cr₈Fe₁₅Ni₃₆Ti₆ (all at.%) have been compared to the original AlCoCrCuFeNi and the most promising one has been selected for further investigation. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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6815 KiB

Open AccessArticle

Development of a Refractory High Entropy Superalloy

by Oleg N. Senkov, Dieter Isheim, David N. Seidman and Adam L. Pilchak

Entropy 2016, 18(3), 102; https://0-doi-org.brum.beds.ac.uk/10.3390/e18030102 - 17 Mar 2016

Cited by 218 | Viewed by 15396

Abstract

Microstructure, phase composition and mechanical properties of a refractory high entropy superalloy, AlMo_0.5NbTa_0.5TiZr, are reported in this work. The alloy consists of a nano-scale mixture of two phases produced by the decomposition from a high temperature body-centered cubic (BCC) phase. The first phase is present in the form of cuboidal-shaped nano-precipitates aligned in rows along <100>-type directions, has a disordered BCC crystal structure with the lattice parameter a₁ = 326.9 ± 0.5 pm and is rich in Mo, Nb and Ta. The second phase is present in the form of channels between the cuboidal nano-precipitates, has an ordered B2 crystal structure with the lattice parameter a₂ = 330.4 ± 0.5 pm and is rich in Al, Ti and Zr. Both phases are coherent and have the same crystallographic orientation within the former grains. The formation of this modulated nano-phase structure is discussed in the framework of nucleation-and-growth and spinodal decomposition mechanisms. The yield strength of this refractory high entropy superalloy is superior to the yield strength of Ni-based superalloys in the temperature range of 20 °C to 1200 °C. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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10038 KiB

Open AccessArticle

High Temperature Oxidation and Corrosion Properties of High Entropy Superalloys

by Te-Kang Tsao, An-Chou Yeh, Chen-Ming Kuo and Hideyuki Murakami

Entropy 2016, 18(2), 62; https://0-doi-org.brum.beds.ac.uk/10.3390/e18020062 - 22 Feb 2016

Cited by 76 | Viewed by 13233

Abstract

The present work investigates the high temperature oxidation and corrosion behaviour of high entropy superalloys (HESA). A high content of various solutes in HESA leads to formation of complex oxides, however the Cr and Al activities of HESA are sufficient to promote protective chromia or alumina formation on the surface. By comparing the oxidation and corrosion resistances of a Ni-based superalloy—CM247LC, Al₂O₃-forming HESA can possess comparable oxidation resistance at 1100 °C, and Cr₂O₃-forming HESA can exhibit superior resistance against hot corrosion at 900 °C. This work has demonstrated the potential of HESA to maintain surface stability in oxidizing and corrosive environments. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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Review

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1193 KiB

Open AccessReview

Three Strategies for the Design of Advanced High-Entropy Alloys

by Ming-Hung Tsai

Entropy 2016, 18(7), 252; https://0-doi-org.brum.beds.ac.uk/10.3390/e18070252 - 15 Jul 2016

Cited by 65 | Viewed by 11272

Abstract

High-entropy alloys (HEAs) have recently become a vibrant field of study in the metallic materials area. In the early years, the design of HEAs was more of an exploratory nature. The selection of compositions was somewhat arbitrary, and there was typically no specific goal to be achieved in the design. Very recently, however, the development of HEAs has gradually entered a different stage. Unlike the early alloys, HEAs developed nowadays are usually designed to meet clear goals, and have carefully chosen components, deliberately introduced multiple phases, and tailored microstructures. These alloys are referred to as advanced HEAs. In this paper, the progress in advanced HEAs is briefly reviewed. The design strategies for these materials are examined and are classified into three categories. Representative works in each category are presented. Finally, important issues and future directions in the development of advanced HEAs are pointed out and discussed. Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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153 KiB

Open AccessCorrection

Correction to Yao, H.; Qiao, J.-W.; Gao, M.C.; Hawk, J.A.; Ma, S.-G.; Zhou, H. MoNbTaV Medium-Entropy Alloy. Entropy 2016, 18, 189

by Hongwei Yao, Jun-Wei Qiao, Michael C. Gao, Jeffrey A. Hawk, Sheng-Guo Ma and Hefeng Zhou

Entropy 2016, 18(8), 289; https://0-doi-org.brum.beds.ac.uk/10.3390/e18080289 - 09 Aug 2016

Cited by 3 | Viewed by 3878

Abstract

The authors wish to make the following correction to their paper [1].[...] Full article

(This article belongs to the Special Issue High-Entropy Alloys and High-Entropy-Related Materials)

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