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Advances in High Entropy Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Metals and Alloys".

Deadline for manuscript submissions: closed (20 March 2024) | Viewed by 10287

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Dr. Zhaobing Cai

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Guest Editor

Key Laboratory of Metallurgical Equipment and Control Technology, Wuhan University of Science and Technology, Ministry of Education, Wuhan, Hubei 430081, China
Interests: laser cladding; PVD; high-entropy alloy coating/film; wear; corrosion

Special Issue Information

Dear Colleagues,

Since the discovery of high-entropy alloys 20 years ago, this field has been developing rapidly, and the research scope of high entropy has also expanded, prompting the emergence of several new developments, such as high-entropy metallic glass, ceramics, perovskite, polymers, composites, catalysts and films and coatings. This broadening of the field of materials science with unexpected results has had a significant influence on and even changed our knowledge of this area.

This Special Issue presents a compilation of the most recent developments in the properties and application of high-entropy alloys. The articles presented in this Special Issue will cover a wide scope, with topics including, but not limited to: material design, preparation methods, mechanical behavior, physical and chemical properties and other behaviors of the above-mentioned high-entropy materials. Papers on new structures (such as dual-phase, eutectic, particle-reinforced and oxide-dispersion structures), innovative technologies (such as 3D printing, plasma spray–physical vapor deposition, cold spraying and ultra-high speed laser cladding) and their applications in particular environments (such as under vacuum, ocean, high-speed, heavy-duty and nuclear conditions) are welcome and will be given priority for this Special Issue.

Dr. Zhaobing Cai
Guest Editor

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Keywords

high-entropy material
new structure
new technology
special environment
material design
preparation method
properties

Published Papers (7 papers)

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Research

11 pages, 9531 KiB

Open AccessArticle

Suppressed Plastic Anisotropy via Sigma-Phase Precipitation in CoCrFeMnNi High-Entropy Alloys

by Tae Hyeong Kim, Jaimyun Jung and Jae Wung Bae

Materials 2024, 17(6), 1265; https://doi.org/10.3390/ma17061265 - 08 Mar 2024

Viewed by 422

Abstract

The effect of sigma-phase precipitation on plastic anisotropy of the equiatomic CoCrFeMnNi high-entropy alloy was investigated. Annealing at 700 °C after cold-rolling leads to the formation of the Cr-rich σ phase with a fraction of 2.7%. It is experimentally found that the planar anisotropy (∆r = −0.16) of the CoCrFeMnNi alloy annealed at 700 °C is two times lower than that of the alloy annealed at 800 °C (∆r = −0.35). This observation was further supported by measuring the earing profile of cup specimens after the deep drawing process. The plastic strain ratio, normal anisotropy, and planar anisotropy were also predicted using the visco-plastic self-consistent model. The results indirectly indicated that the reduction of plastic anisotropy in alloy annealed at 700 °C can be attributed to the formation of the σ phase. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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18 pages, 6237 KiB

Open AccessArticle

Structural Stability of Titanium-Based High-Entropy Alloys Assessed Based on Changes in Grain Size and Hardness

by Dominika Górniewicz, Krzysztof Karczewski, Zbigniew Bojar and Stanisław Jóźwiak

Materials 2023, 16(23), 7361; https://doi.org/10.3390/ma16237361 - 27 Nov 2023

Viewed by 713

Abstract

The thermal stability of the grain structure and mechanical properties of the high-entropy two-phase TiCoCrFeMn alloy produced by powder metallurgy, assessed based on microhardness measurements, was analyzed in this work. For this purpose, material obtained via sintering using the U-FAST method was subjected to long-term heating at a temperature of 1000 °C for up to 1000 h in an argon atmosphere. For homogenization times of 1, 10, 20, 50, 100, and 1000 h, grain size changes in the identified phase components of the matrix were assessed, and microhardness measurements were conducted using the Vickers method. It has been shown that the changes in the analyzed parameters are closely correlated with non-monotonic modifications in the chemical composition. It was found that the tested alloy achieved structural stability after 100 h of annealing. A stable grain size was obtained in the BCC solid solution of approximately 2 µm and the two-phase BCC+C14 mixture of roughly 0.4 µm. Long-term heating for up to 1000 h caused the grain structure to grow to 2.7 µm and 0.7 µm, respectively, with a simultaneous decrease in hardness from 1065 HV to 1000 HV. The chromium and titanium diffusion coefficient values responsible for forming the BCC solid solution and the Laves C14 phase, including the material matrix, were also determined at this level to be D_Cr = 1.28 × 10⁻¹⁹ (m²·s⁻¹) and D_Ti = 1.04 × 10⁻¹⁹ (m²·s⁻¹), demonstrating the sluggish diffusion effect typical of high-entropy alloys. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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10 pages, 5354 KiB

Open AccessArticle

Microstructural Changes and Mechanical Properties of Precipitation-Strengthened Medium-Entropy Fe_71.25(CoCrMnNi)_23.75Cu₃Al₂ Maraging Alloy

by Unhae Lee and Jae Wung Bae

Materials 2023, 16(9), 3589; https://doi.org/10.3390/ma16093589 - 07 May 2023

Viewed by 1162

Abstract

Metal alloys with enhanced mechanical properties are in considerable demand in various industries. Thus, this study focused on the development of nanosized precipitates in Fe_71.25(CoCrMnNi)_23.75Cu₃Al₂ maraging medium-entropy alloy (MEA). The Fe-based alloying design in the MEA samples initially formed a body-centered cubic (BCC) lath martensite structure. After a subsequent annealing process at 450 °C for varying durations (1, 3, 5, and 7 h), nanosized precipitates (B2 intermetallic) enriched with Cu and with a diameter of approximately 5 nm formed, significantly increasing the hardness of the alloy. The highest Vickers microhardness of 597 HV, along with compressive yield strength and ultimate compressive strength of 2079 MPa and 2843 MPa, respectively, was achieved for the Aged_7h sample. Therefore, the BCC lath martensite structure with B2 intermetallics leads to remarkable mechanical properties. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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10 pages, 2561 KiB

Open AccessArticle

Estimation of Shear Modulus and Hardness of High-Entropy Alloys Made from Early Transition Metals Based on Bonding Parameters

by Ottó Temesi, Lajos K. Varga, Xiaoqing Li, Levente Vitos and Nguyen Q. Chinh

Materials 2023, 16(6), 2311; https://doi.org/10.3390/ma16062311 - 13 Mar 2023

Cited by 1 | Viewed by 1397

Abstract

The relationship between the tendencies towards rigidity (measured by shear modulus, G) and hardness (measured by Vickers hardness, HV) of early transition metal (ETM)-based refractory high-entropy alloys (RHEA) and bond parameters (i.e., valence electron concentration (VEC), enthalpy of mixing (ΔH_mix)) was investigated. These bond parameters, VEC and ΔH_mix, are available from composition and tabulated data, respectively. Based on our own data (9 samples) and those available from the literatures (47 + 27 samples), it seems that for ETM-based RHEAs the G and HV characteristics have a close correlation with the bonding parameters. The room temperature value of G and HV increases with the VEC and with the negative value of ΔH_mix. Corresponding equations were deduced for the first time through multiple linear regression analysis, in order to help design the mechanical properties of ETM refractory high-entropy alloys. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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14 pages, 12022 KiB

Open AccessArticle

Phase Transformations Caused by Heat Treatment and High-Pressure Torsion in TiZrHfMoCrCo Alloy

by Alena S. Gornakova, Boris B. Straumal, Alexander I. Tyurin, Natalia S. Afonikova, Alexander V. Druzhinin, Gregory S. Davdian and Askar R. Kilmametov

Materials 2023, 16(4), 1354; https://doi.org/10.3390/ma16041354 - 05 Feb 2023

Cited by 1 | Viewed by 1517

Abstract

In this work the high-entropy alloy studied contained six components, Ti/Zr/Hf/Mo/Cr/Co, and three phases, namely one phase with body-centered cubic lattice (BCC) and two Laves phases C14 and C15. A series of annealings in the temperature range from 600 to 1000 °C demonstrated not only a change in the microstructure of the TiZrHfMoCrCo alloy, but also the modification of phase composition. After annealing at 1000 °C the BCC phase almost fully disappeared. The annealing at 600 and 800 °C leads to the formation of new Laves phases. After high-pressure torsion (HPT) of the as-cast TiZrHfMoCrCo alloy, the grains become very small, the BCC phase prevails, and C14 Laves phase completely disappears. This state is similar to the state after annealing at high effective temperature T_eff. The additional annealing at 1000 °C after HPT returns the phase composition back to the state similar to that of the as-cast alloy after annealing at 1000 °C. At 1000 °C the BCC phase completely wets the C15/C15 grain boundaries (GBs). At 600 and 800 °C the GB wetting is incomplete. The big spread of nanohardness and Young’s modulus for the BCC phase and (C15 + C14) Laves phases is observed. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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16 pages, 8166 KiB

Open AccessArticle

Atomic Interactions and Order–Disorder Transition in FCC-Type FeCoNiAl_1−xTi_x High-Entropy Alloys

by Ying Wu, Zhou Li, Hui Feng and Shuang He

Materials 2022, 15(11), 3992; https://doi.org/10.3390/ma15113992 - 03 Jun 2022

Cited by 2 | Viewed by 2353

Abstract

Single-phase high-entropy alloys with compositionally disordered elemental arrangements have excellent strength, but show a serious embrittlement effect with increasing strength. Precipitation-hardened high-entropy alloys, such as those strengthened by L1₂-type ordered intermetallics, possess a superior synergy of strength and ductility. In this work, we employ first-principles calculations and thermodynamic simulations to explore the atomic interactions and order–disorder transitions in FeCoNiAl_1−xTi_x high-entropy alloys. Our calculated results indicate that the atomic interactions depend on the atomic size of the alloy components. The thermodynamic stability behaviors of L1₂ binary intermetallics are quite diverse, while their atomic arrangements are short-range in FeCoNiAl_1−xTi_x high-entropy alloys. Moreover, the order–disorder transition temperatures decrease with increasing Ti content in FeCoNiAl_1−xTi_x high-entropy alloys, the characteristics of order–disorder transition from first-principles calculations are in line with experimental observations and CALPHAD simulations. The results of this work provide a technique strategy for proper control of the order–disorder transitions that can be used for further optimizing the microstructure characteristics as well as the mechanical properties of FeCoNiAl_1−xTi_xhigh-entropy alloys. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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13 pages, 4224 KiB

Open AccessArticle

Study on Stability of Mechanical Properties for Porous Fe-Cr-Al Alloys after Long-Term Aging

by Huibin Zhang, Junliang Ma, Zhencheng Gao, Fei Guo, Shenghang Xu, Guangya Hou and Guoqu Zheng

Materials 2022, 15(10), 3718; https://doi.org/10.3390/ma15103718 - 22 May 2022

Cited by 4 | Viewed by 1643

Abstract

Nowadays, both the ferrite phase and B2-structured intermetallic in the Fe-Cr-Al alloy system are developed as porous materials, which have been further applied as high-temperature filter materials in industry. This work presents a comparative study of the mechanical properties of porous Fe20Cr5Al, Fe10Cr10Al and Fe10Cr20Al aged at 480 °C for 500 h. The changes in tensile strength, elongation and hardness were determined, and the microstructure changes as well as slight oxidation states of the aged samples were investigated. The results show that the precipitated Cr-rich phase in porous Fe20Cr5Al can increase the hardness and decrease the ductility, while intergranular oxidation can degrade the mechanical performance of the three porous Fe-Cr-Al materials. It is noted that porous Fe10Cr20Al exhibits relatively superior mechanical stability during long-term aging. Meanwhile, by introducing boron, the mechanical performance of the aged porous Fe-Cr-Al alloys can be stabilized since the possible internal oxidation of the exposed grain boundaries is inhibited. Full article

(This article belongs to the Special Issue Advances in High Entropy Materials)

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