Special Issue "High-Entropy Materials"

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

Deadline for manuscript submissions: closed (30 November 2019).

Special Issue Editors

Prof. Dr. Hyoung Seop Kim
Website
Guest Editor
Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea
Interests: mechanical behavior of metallic materials; plasticity theory; constitutive modelling; high-entropy alloy; porous materials; severe plastic deformation; processing simulation
Prof. Jien-Wei Yeh
Website
Guest Editor
Materials Science & Technology Building R505, National Tsing Hua University, Hsinchu 30013, Taiwan
Interests: High-entropy materials, Functional coatings, Functional composites
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

“High-entropy alloys” has become an exciting and vibrant field of materials science and engineering since the concept was first proposed more than a decade ago. Symposia, conferences and workshops on topics of high-entropy alloys or high-entropy materials (HEMs) are being held, and a rapid increase in the number of journal publications and citations is evident. This design concept allows compositions beyond the scope of traditional materials, and offers unprecedented properties and opportunities for a wide range of structural and functional applications. The 2nd International Conference on High-Entropy Materials (ICHEM2) was thus held on Jeju island, South Korea, from 9‒12 December, 2018. It gathered research groups from around the world to present the latest development in HEMs. It also offered a platform for networking, collaboration, and information exchange in the community. To deliver the excellent research works presented at ICHEM2 to global audiences and to accelerate the development of HEMs, the SCI journal Entropy (MDPI) has planned to publish a Special Issue on “High-Entropy Materials” in 2019. The main aspects of these materials are covered, including synthesis, microstructures, properties, mechanisms, and applications of HEMs. The Special Issue will hence provide the latest research results and a state-of-the-art overview of technology in the exciting and rapidly evolving field of HEMs. This Special Issue welcomes all submissions from authors in the field of high-entropy materials.

Prof. Dr. Hyoung Seop Kim
Prof. Jien-Wei Yeh
Guest Editors

Manuscript Submission Information

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Keywords

  • High-entropy materials/alloys
  • Medium-entropy alloy
  • Alloy design
  • Microstructure
  • Properties
  • Modeling and simulation

Published Papers (9 papers)

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Research

Open AccessArticle
Development of Novel Lightweight Dual-Phase Al-Ti-Cr-Mn-V Medium-Entropy Alloys with High Strength and Ductility
Entropy 2020, 22(1), 74; https://doi.org/10.3390/e22010074 - 06 Jan 2020
Abstract
A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequiatiomic approach and alloys were produced through arc melting and drop casting. These alloys comprised a body-centered cubic (BCC) and face-centered cubic (FCC) dual phase with a density of approximately 4.5 [...] Read more.
A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequiatiomic approach and alloys were produced through arc melting and drop casting. These alloys comprised a body-centered cubic (BCC) and face-centered cubic (FCC) dual phase with a density of approximately 4.5 g/cm3. However, the fraction of the BCC phase and morphology of the FCC phase can be controlled by incorporating other elements. The results of compression tests indicated that these Al-Ti-Cr-Mn-V alloys exhibited a prominent compression strength (~1940 MPa) and ductility (~30%). Moreover, homogenized samples maintained a high compression strength of 1900 MPa and similar ductility (30%). Due to the high specific compressive strength (0.433 GPa·g/cm3) and excellent combination of strength and ductility, the cast lightweight Al-Ti-Cr-Mn-V MEAs are a promising alloy system for application in transportation and energy industries. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Effects of Al Addition on Microstructures and Mechanical Properties of CoCrFeMnNiAlx High Entropy Alloy Films
Entropy 2020, 22(1), 2; https://doi.org/10.3390/e22010002 - 18 Dec 2019
Cited by 2
Abstract
CoCrFeMnNiAlx (x = 0, 0.07, 0.3, 0.6, 1.0, 1.3) high-entropy alloy films (HEAFs) were processed by co-sputtering of CoCrFeMnNi alloy and Al targets. The effects of Al content on the microstructures and mechanical properties of HEAFs were studied. The XRD results [...] Read more.
CoCrFeMnNiAlx (x = 0, 0.07, 0.3, 0.6, 1.0, 1.3) high-entropy alloy films (HEAFs) were processed by co-sputtering of CoCrFeMnNi alloy and Al targets. The effects of Al content on the microstructures and mechanical properties of HEAFs were studied. The XRD results indicated that the crystalline structure changed from the single face-centered cubic (FCC) phase for x = 0 and 0.07 to duplex FCC + body-centered cubic (BCC) phases for x = 0.3 and 0.6, and eventually, to a single BCC phase for x = 1.0 and 1.3, which agreed with the corresponding selected-area electron diffraction patterns. Also, nanotwins were observed in the FCC phase. Mechanical properties of films were studied using nanoindentation and micropillar compression tests. The hardness increased from 5.71 GPa at x = 0 to 8.74 GPa at x = 1.3. The compressive yield strength increased from 1.59 GPa to 3.73 GPa; however, the fracture strain decreased from 20.91% (no fracture) to 13.78% with the increasing Al content. Both nanotwins and BCC phase contributed to the strengthening effects for CoCrFeMnNiAlx HEAFs. Also, compared to the bulk CoCrFeMnNiAlx counterpart, the film exhibited much higher hardness and strength because of the much smaller grain size and the presence of nanotwins. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Dynamic Mechanical Properties and Microstructure of an (Al0.5CoCrFeNi)0.95Mo0.025C0.025 High Entropy Alloy
Entropy 2019, 21(12), 1154; https://doi.org/10.3390/e21121154 - 26 Nov 2019
Abstract
The dynamic mechanical properties and microstructure of the (Al0.5CoCrFeNi)0.95Mo0.025C0.025 high entropy alloy (HEA) prepared by powder extrusion were investigated by a split Hopkinson pressure bar and electron probe microanalyzer and scanning electron microscope. The (Al0.5 [...] Read more.
The dynamic mechanical properties and microstructure of the (Al0.5CoCrFeNi)0.95Mo0.025C0.025 high entropy alloy (HEA) prepared by powder extrusion were investigated by a split Hopkinson pressure bar and electron probe microanalyzer and scanning electron microscope. The (Al0.5CoCrFeNi)0.95Mo0.025C0.025 HEA has a uniform face-centered cubic plus body-centered cubic solid solution structure and a fine grain-sized microstructure with a size of about 2 microns. The HEA possesses an excellent strain hardening rate and high strain rate sensitivity at a high strain rate. The Johnson–Cook plastic model was used to describe the dynamic flow behavior. Hat-shaped specimens with different nominal strain levels were used to investigate forced shear localization. After dynamic deformation, a thin and short shear band was generated in the designed shear zone and then the specimen quickly fractured along the shear band. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Effect of Solution Treatment on the Shape Memory Functions of (TiZrHf)50Ni25Co10Cu15 High Entropy Shape Memory Alloy
Entropy 2019, 21(10), 1027; https://doi.org/10.3390/e21101027 - 22 Oct 2019
Cited by 2
Abstract
This study investigated the effects of solution treatment at 1000 °C on the transformation behaviors, microstructure, and shape memory functions of a novel (TiZrHf)50Ni25Co10Cu15 high entropy shape memory alloy (HESMA). The solution treatment caused partial dissolution [...] Read more.
This study investigated the effects of solution treatment at 1000 °C on the transformation behaviors, microstructure, and shape memory functions of a novel (TiZrHf)50Ni25Co10Cu15 high entropy shape memory alloy (HESMA). The solution treatment caused partial dissolution of non-oxygen-stabilized Ti2Ni-like phase. This phenomenon resulted in the increment of (Ti, Zr, Hf) content in the matrix and thus increment of the Ms and Af temperatures. At the same time, the solution treatment induced a high entropy effect and thus increased the degree of lattice distortion, which led to increment of the friction force during martensitic transformation, resulting in a broad transformation temperature range. The dissolution of the Ti2Ni-like phase also improved the functional performance of the HESMA by reducing its brittleness and increasing its strength. The experimental results presented in this study demonstrate that solution treatment is an effective and essential way to improve the functional performance of the HESMA. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
High-Temperature Wear Behaviour of Spark Plasma Sintered AlCoCrFeNiTi0.5 High-Entropy Alloy
Entropy 2019, 21(6), 582; https://doi.org/10.3390/e21060582 - 12 Jun 2019
Cited by 4
Abstract
In this study, the wear behaviour of a powder metallurgically produced AlCoCrFeNiTi0.5 high-entropy alloy (HEAs) is investigated at elevated temperatures. Spark plasma sintering (SPS) of inert gas atomised feedstock enables the production of dense bulk material. The microstructure evolution and phase formation [...] Read more.
In this study, the wear behaviour of a powder metallurgically produced AlCoCrFeNiTi0.5 high-entropy alloy (HEAs) is investigated at elevated temperatures. Spark plasma sintering (SPS) of inert gas atomised feedstock enables the production of dense bulk material. The microstructure evolution and phase formation are analysed. The high cooling rate in the atomisation process results in spherical powder with a microstructure comprising two finely distributed body-centred cubic phases. An additional phase with a complex crystal structure precipitates during SPS processing, while no coarsening of microstructural features occurs. The wear resistance under reciprocating wear conditions increases at elevated temperatures due to the formation of a protective oxide layer under atmospherical conditions. Additionally, the coefficient of friction (COF) slightly decreases with increasing temperature. SPS processing is suitable for the production of HEA bulk material. An increase in the wear resistance at elevated temperature enables high temperature applications of the HEA system AlCoCrFeNiTi0.5. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Solidification Microstructures of the Ingots Obtained by Arc Melting and Cold Crucible Levitation Melting in TiNbTaZr Medium-Entropy Alloy and TiNbTaZrX (X = V, Mo, W) High-Entropy Alloys
Entropy 2019, 21(5), 483; https://doi.org/10.3390/e21050483 - 10 May 2019
Cited by 6
Abstract
The solidification microstructures of the TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, and W) high-entropy alloys (HEAs), including the TiNbTaZrMo bio-HEA, were investigated. Equiaxed dendrite structures were observed in the ingots that were prepared by arc melting, regardless of the position [...] Read more.
The solidification microstructures of the TiNbTaZr medium-entropy alloy and TiNbTaZrX (X = V, Mo, and W) high-entropy alloys (HEAs), including the TiNbTaZrMo bio-HEA, were investigated. Equiaxed dendrite structures were observed in the ingots that were prepared by arc melting, regardless of the position of the ingots and the alloy system. In addition, no significant difference in the solidification microstructure was observed in TiZrNbTaMo bio-HEAs between the arc-melted (AM) ingots and cold crucible levitation melted (CCLM) ingots. A cold shut was observed in the AM ingots, but not in the CCLM ingots. The interdendrite regions tended to be enriched in Ti and Zr in the TiNbTaZr MEA and TiNbTaZrX (X = V, Mo, and W) HEAs. The distribution coefficients during solidification, which were estimated by thermodynamic calculations, could explain the distribution of the constituent elements in the dendrite and interdendrite regions. The thermodynamic calculations indicated that an increase in the concentration of the low melting-temperature V (2183 K) leads to a monotonic decrease in the liquidus temperature (TL), and that increases in the concentration of high melting-temperature Mo (2896 K) and W (3695 K) lead to a monotonic increase in TL in TiNbTaZrXx (X = V, Mo, and W) (x =  0 − 2) HEAs. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Mechanical Properties and Corrosion Resistance of NbTiAlSiZrNx High-Entropy Films Prepared by RF Magnetron Sputtering
Entropy 2019, 21(4), 396; https://doi.org/10.3390/e21040396 - 13 Apr 2019
Cited by 1
Abstract
In this study, we designed and fabricated NbTiAlSiZrNx high-entropy alloy (HEA) films. The parameters of the radio frequency (RF) pulse magnetron sputtering process were fixed to maintain the N2 flux ratio at 0%, 10%, 20%, 30%, 40%, and 50%. Subsequently, NbTiAlSiZrN [...] Read more.
In this study, we designed and fabricated NbTiAlSiZrNx high-entropy alloy (HEA) films. The parameters of the radio frequency (RF) pulse magnetron sputtering process were fixed to maintain the N2 flux ratio at 0%, 10%, 20%, 30%, 40%, and 50%. Subsequently, NbTiAlSiZrNx HEA films were deposited on the 304 stainless steel (SS) substrate. With an increasing N2 flow rate, the film deposited at a RN of 50% had the highest hardness (12.4 GPa), the highest modulus (169 GPa), a small roughness, and a beautiful color. The thicknesses of the films were gradually reduced from 298.8 nm to 200 nm, and all the thin films were of amorphous structure. The electrochemical corrosion resistance of the film in a 0.5 mol/L H2SO4 solution at room temperature was studied and the characteristics changed. The HEA films prepared at N2 flow rates of 10% and 30% were more prone to corrosion than 304 SS, but the corrosion rate was lower than that of 304 SS. NbTiAlSiZrNx HEA films prepared at N2 flow rates of 20%, 40%, and 50% were more corrosion-resistant than 304 SS. In addition, the passivation stability of the NbTiAlSiZrNx HEA was worse than that of 304 SS. Altogether, these results show that pitting corrosion occurred on NbTiAlSiZrNx HEA films. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
A Study on the Hall–Petch Relationship and Grain Growth Kinetics in FCC-Structured High/Medium Entropy Alloys
Entropy 2019, 21(3), 297; https://doi.org/10.3390/e21030297 - 19 Mar 2019
Cited by 5
Abstract
The recrystallization behavior, grain growth kinetics, and corresponding hardness variation of homogenized and 80% cold-rolled FeCoNiCrPd, FeCoNiCrMn, and their quaternary/ternary FCC-structured high/medium entropy alloys (H/MEAs) annealed under different conditions were investigated. Experimental results indicate that the grain size and hardness of these H/MEAs [...] Read more.
The recrystallization behavior, grain growth kinetics, and corresponding hardness variation of homogenized and 80% cold-rolled FeCoNiCrPd, FeCoNiCrMn, and their quaternary/ternary FCC-structured high/medium entropy alloys (H/MEAs) annealed under different conditions were investigated. Experimental results indicate that the grain size and hardness of these H/MEAs follow the Hall–Petch equation, with the Hall–Petch coefficient KH value being mainly dominated by the alloy’s stacking fault energy and shear modulus. The FeCoNiCrPd alloy exhibits the highest hardness of the H/MEAs at the same grain size due to the largest Young’s modulus difference between Cr and Pd. The grain growth exponent n, kinetic constant k, and activation energy for grain growth QG of all H/MEAs are calculated. The k can be expressed by the Arrhenius equation with QG, which is attributed to the diffusion rate. The results demonstrate that the QG values of these H/MEAs are much higher than those of conventional alloys; most notable is FeCoNiCrPd HEA, which has an unusually lattice distortion effect that hinders grain growth. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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Open AccessArticle
Infrared Brazing of CoCrFeMnNi Equiatomic High Entropy Alloy Using Nickel-Based Braze Alloys
Entropy 2019, 21(3), 283; https://doi.org/10.3390/e21030283 - 15 Mar 2019
Cited by 1
Abstract
Infrared vacuum brazing of CoCrFeMnNi high entropy alloy (HEA) using BNi-2 and MBF601 fillers has been investigated. Both brazes show poor wettability at temperatures only 20 °C above their liquidus temperatures. However, the wettability of BNi-2 and MBF601 fillers on CoCrFeMnNi HEA is [...] Read more.
Infrared vacuum brazing of CoCrFeMnNi high entropy alloy (HEA) using BNi-2 and MBF601 fillers has been investigated. Both brazes show poor wettability at temperatures only 20 °C above their liquidus temperatures. However, the wettability of BNi-2 and MBF601 fillers on CoCrFeMnNi HEA is greatly improved with increasing the test temperatures, 50 °C above their liquidus temperatures. The BNi-2 brazed joints are dominated by Ni-rich matrix with huge CrB and a few tiny boride precipitates. Average shear strengths of joints increase with increasing brazing temperature and/or time, and fracture location changes from blocky CrB in the brazed zone to grain boundary boride in the substrate. The MBF601 brazed joints are composed of CoCrFeMnNi-based matrix, particles of B/Co/Cr/Fe/Mn/Ni/P compounds, and some phosphides form along the grain boundaries of the substrate. The specimen brazed with MBF601 filler foil at 1050 °C for 600 s has the highest average shear strength of 321 MPa, while that brazed at 1080 °C for 600 s has a lower average shear strength of 271 MPa due to the presence of solidification shrinkage voids. Full article
(This article belongs to the Special Issue High-Entropy Materials)
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