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Recent Advances in Refractory High Entropy Alloys

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A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Multidisciplinary Applications".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 16667

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Prof. Dr. Yucheng Wu

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Guest Editor

School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China
Interests: tungsten alloys; refractory high entropy alloys; fusion materials; non-ferrous metals; plasma-facing tungsten-based composites; functional nanomaterials; energy-related materials

Prof. Dr. Shunhua Chen

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Guest Editor

School of Mechanical Engineering, Hefei University of Technology, Hefei 230009, China
Interests: refractory high entropy alloys; mechanical properties; advanced manufacturing technology; bulk metallic glasses; deformation mechanism; processing

Special Issue Information

Dear Colleagues,

During the past two decades, high entropy alloys (HEAs), consisting of multi-principal elements rather than one or two principal elements that exist in traditional alloys, have attracted increasing research interest due to their unique combinations of excellent properties. Through the introduction of refractory elements, refractory high entropy alloys (RHEAs) have been developed since 2010, demonstrating excellent mechanical and functional properties superior to conventional alloys, especially at elevated temperatures. Numerous studies have shown that RHEAs, with high melting points as well as high strength and good corrosion, oxidation and irradiation resistance, have great potential for use in high-temperature applications, such as turbine engines and nuclear reactors.

Although efforts have been devoted to the development of new systems of RHEAs, the investigation of their microstructure and mechanical properties and the exploration of their possible structural and functional applications, these efforts are still far from those necessary for the development of next-generation high-temperature materials. For example, the mechanisms of phase formation, plastic deformation, strengthening and high-temperature oxidation are still under debate. Similarly, the development of tungsten-containing RHEAs, which are extremely suitable for harsh environments such as in nuclear fusion reactors, is still in progress. This Special Issue aims to include the recent progress in the development, deformation mechanisms, functional properties as well as the applications of RHEAs, especially tungsten-containing RHEAs. All original research work and review articles related to the following aspects are welcome and appreciated:

Design and development of new RHEAs;
Mechanical properties and deformation mechanisms of RHEAs;
Functional properties of RHEAs, such as oxidation, corrosion and irradiation resistance;
Fabrication and processing of RHEAs;
Development, characterization, processing and application of tungsten alloys;
Advances in other refractory alloys and HEAs.

Prof. Dr. Yucheng Wu
Prof. Dr. Shunhua Chen
Guest Editors

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Published Papers (10 papers)

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Research

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14 pages, 4741 KiB

Open AccessArticle

Irradiation-Hardening Model of TiZrHfNbMo_0.1 Refractory High-Entropy Alloys

by Yujun Fan, Xuejiao Wang, Yangyang Li, Aidong Lan and Junwei Qiao

Entropy 2024, 26(4), 340; https://0-doi-org.brum.beds.ac.uk/10.3390/e26040340 - 17 Apr 2024

Viewed by 332

Abstract

In order to find more excellent structural materials resistant to radiation damage, high-entropy alloys (HEAs) have been developed due to their characteristics of limited point defect diffusion such as lattice distortion and slow diffusion. Specially, refractory high-entropy alloys (RHEAs) that can adapt to [...] Read more.

{T i Z r H f N b M o}_{0.1}

RHEAs are selected for irradiation and nanoindentation experiments. We combined the mechanistic model for the depth-dependent hardness of ion-irradiated metals and the introduction of the scale factor

f

to modify the irradiation-hardening model in order to better describe the nanoindentation indentation process in the irradiated layer. Finally, it can be found that, with the increase in irradiation dose, a more serious lattice distortion caused by a higher defect density limits the expansion of the plastic zone. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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17 pages, 5040 KiB

Open AccessArticle

High-Temperature Mechanical Properties of NbTaHfTiZrV_0.5 Refractory High-Entropy Alloys

by Zhangquan Liu, Xiaohui Shi, Min Zhang and Junwei Qiao

Entropy 2023, 25(8), 1124; https://0-doi-org.brum.beds.ac.uk/10.3390/e25081124 - 26 Jul 2023

Viewed by 1180

Abstract

The NbTaHfTiZrV_0.5 is a refractory multi-principal-element alloy with high strength and good ductility at room temperature. It is important for possible high-temperature applications to investigate the deformation mechanism of the NbTaHfTiZrV_0.5 alloy at different temperatures using tensile tests. In this investigation, the tensile tests were conducted at room temperature to 1273 K on sheet materials fabricated by cold rolling combined with annealing treatments. At 473 K, the NbTaHfTiZrV_0.5 alloy exhibited a high tensile ductility (12%). At a testing temperature range of 673~873 K, the ductility was reduced, but the yield strength remained above 800 MPa, which is rare in most other alloys. The TEM investigations revealed that a dislocation slip controlled the plastic deformation, and the degree of deformation was closely related to the dislocation density. The true stress–strain curves of the alloy under different deformation conditions were obtained by tensile deformation at different deformation temperatures (673~873 K) and strain rates (0.001~0.0005 s⁻¹). Experimental results were utilized to construct the parameters of a constitutive model based on a traditional mathematical model to predict the flow behavior at high temperatures. The excellent high-temperature mechanical properties of the NbTaHfTiZrV_0.5 alloy will enable it to be used in several engineering applications. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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14 pages, 8131 KiB

Open AccessArticle

Hydrogen Embrittlement of CrCoNi Medium-Entropy Alloy with Millimeter-Scale Grain Size: An In Situ Hydrogen Charging Study

by Shaohua Yan, Xipei He and Zhongyin Zhu

Entropy 2023, 25(4), 673; https://0-doi-org.brum.beds.ac.uk/10.3390/e25040673 - 18 Apr 2023

Cited by 3 | Viewed by 1646

Abstract

In this study, we examined the effect of charging current density on the hydrogen embrittlement (HE) of MEA and the associated HE mechanisms using electron backscattered diffraction (EBSD). Results show that MEA is susceptible to HE, but is stronger than as-rolled and 3D-printed Cantor alloy and stainless steel. The HE susceptibility of MEA decreases with increasing current density. Ductile fracture with transgranular dimples switches to intergranular brittle fracture with clear slip bands in the interior of grains. EBSD results uncovered that hydrogen facilitates localized slips and deformation twins. Hydrogen-enhanced localized plasticity and hydrogen decohesion are the possible HE mechanisms. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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22 pages, 19700 KiB

Open AccessArticle

Interdiffusion in Refractory Metal System with a BCC Lattice: Ti/TiZrHfNbTaMo

by Mikhail I. Razumovsky, Boris S. Bokstein, Alexey O. Rodin and Alexandra V. Khvan

Entropy 2023, 25(3), 490; https://0-doi-org.brum.beds.ac.uk/10.3390/e25030490 - 12 Mar 2023

Viewed by 1475

Abstract

Interdiffusion of the elements in a diffusion pair consisting of Ti and an equiatomic high-entropy alloy (HEA) TiZrHfNbTaMo in the temperature range of 1473–1673 K has been studied. A calculated results phase diagram of the alloy by Thermo-Calc 2021-B software as used to determine the temperature stability range of the β-phase in the alloy. Ti–HEA diffusion pairs were obtained by low = temperature welding and then diffusion annealing was carried out at temperatures of 1473, 1573, and 1673 K during 12, 9, and 6 h, respectively. The interdiffusion zone was profiled using electron probe microanalysis (EPMA). The diffusion parameters of the HEA’s elements were obtained using Hall’s method. An experimental results discussion is given. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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17 pages, 4762 KiB

Open AccessArticle

Microstructure and Mechanical Properties of High-Specific-Strength (TiVCrZr)_100−xW_x (x = 5, 10, 15 and 20) Refractory High-Entropy Alloys

by Haitao Wang, Kuang Xu, Juchen Zhang and Junsheng Zhang

Entropy 2023, 25(1), 100; https://0-doi-org.brum.beds.ac.uk/10.3390/e25010100 - 03 Jan 2023

Cited by 1 | Viewed by 1493

Abstract

With the increasing demand for high-specific-strength materials for high-temperature applications, particularly in the aerospace field, novel (TiVCrZr)_100−xW_x (x = 5, 10, 15 and 20) refractory high-entropy alloys (RHEAs) were developed. The phase formation, microstructure, and mechanical properties were studied. The (TiVCrZr)_100−xW_x RHEAs exhibit a relatively high specific strength and low density compared with the W-containing RHEAs and most of the W-free RHEAs. In (TiVCrZr)_100−xW_x RHEAs, Laves, BCC and Ti-rich phases are formed, where the Laves phase is the major phase, and the volume fraction of the BCC phase increases with increasing W content. (TiVCrZr)_100−xW_x RHEAs exhibit dendrite structures, where W is enriched in the dendrite region, and increasing W-rich precipitations corresponding to the BCC phase are observed. The improvement of the strength and hardness of RHEAs is mainly attributed to the evolution of the microstructure and corresponding strengthening effect of W. The empirical parameters and calculated phase diagram were investigated, which further explain and verify the formation and variation of phases. The present findings give more insights into the formation of multi phases in (TiVCrZr)_100−xW_x RHEAs, and explore their application potential in the aerospace industry and nuclear reactors due to their high specific strength and low-activation constituent elements. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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22 pages, 6856 KiB

Open AccessArticle

On the WEDM of WNbMoTaZr_x (x = 0.5, 1) Refractory High Entropy Alloys

by Shunhua Chen, Kuang Xu, Weijie Chang, Yong Wang and Yucheng Wu

Entropy 2022, 24(12), 1796; https://0-doi-org.brum.beds.ac.uk/10.3390/e24121796 - 08 Dec 2022

Cited by 2 | Viewed by 1259

Abstract

As a potential candidate for the next generation of high-temperature alloys, refractory high entropy alloys (RHEAs) have excellent mechanical properties and thermal stability, especially for high-temperature applications, where the processing of RHEAs plays a critical role in engineering applications. In this work, the wire electrical discharge machining (WEDM) performance of WNbMoTaZr_x (x = 0.5, 1) RHEAs was investigated, as compared with tungsten, cemented carbide and industrial pure Zr. The cutting efficiency (CE) of the five materials was significantly dependent on the melting points, while the surface roughness (Ra) was not. For the RHEAs, the CE was significantly affected by the pulse-on time (ON), pulse-off time (OFF) and peak current (IP), while the surface roughness was mainly dependent on the ON and IP. The statistical analyses have shown that the CE data of RHEAs have relatively-smaller Weibull moduli than those for the Ra data, which suggests that the CE of RHEAs can be tuned by optimizing the processing parameters. However, it is challenging to tune the surface roughness of RHEAs by tailoring the processing parameters. Differing from the comparative materials, the WEDMed surfaces of the RHEAs showed dense spherical re-solidified particles at upper recast layers, resulting in larger Ra values. The proportion of the upper recast layers can be estimated by the specific discharge energy (SDE). Following the WEDM, the RHEAs maintained the main BCC1 phase, enriched with the W and Ta elements, while the second BCC2 phase in the Zr1.0 RHEA disappeared. Strategies for achieving a better WEDMed surface quality of RHEAs were also proposed and discussed. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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13 pages, 3393 KiB

Open AccessArticle

Lightweight Multiprincipal Element Alloys with Excellent Mechanical Properties at Room and Cryogenic Temperatures

by Gongxi Lin, Ruipeng Guo, Xiaohui Shi, Lina Han and Junwei Qiao

Entropy 2022, 24(12), 1777; https://0-doi-org.brum.beds.ac.uk/10.3390/e24121777 - 05 Dec 2022

Cited by 2 | Viewed by 1356

Abstract

Lightweight multiprincipal element alloys (MPEAs) are promising candidates for potential application as engineering materials due to their high strength and low density. In this work, lightweight Ti₇₀Al₁₅V₁₅ and Ti₈₀Al₁₀V₁₀ MPEAs were fabricated via vacuum arc melting. The phases of the Ti₇₀Al₁₅V₁₅ alloys consisted of a BCC phase and a small amount of B2 phase while the Ti₈₀Al₁₀V₁₀ alloys displayed a dual-phase structure with BCC and HCP phases. The different phase compositions led to differences in their mechanical properties. When the temperature changed from 298 K to 77 K, the strength of the alloys further increased and maintained a certain plasticity. This is attributed to the increasing lattice friction stress at cryogenic temperature. TEM observation demonstrated that dislocation played a crucial role in plastic deformation for both the Ti₇₀Al₁₅V₁₅ and Ti₈₀Al₁₀V₁₀ alloys. In addition, Ti₈₀Al₁₀V₁₀ exhibited significant work-hardening capabilities. By analyzing the strengthening mechanism of the alloys, the theoretical yield strength was calculated, and the results agreed with the experimental values. The present results provide new insight into developing lightweight MPEAs containing Ti and Al. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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17 pages, 5068 KiB

Open AccessFeature PaperArticle

Microstructure and Mechanical Properties of Novel High-Strength, Low-Activation W_x(TaVZr)_100−x (x = 5, 10, 15, 20, 25) Refractory High Entropy Alloys

by Jingsai Zhang, Shunhua Chen, Jiaqin Liu, Zhenhua Qing and Yucheng Wu

Entropy 2022, 24(10), 1342; https://0-doi-org.brum.beds.ac.uk/10.3390/e24101342 - 23 Sep 2022

Cited by 7 | Viewed by 1499

Abstract

In this work, novel high-strength, low-activation W_x(TaVZr)_100−x (x = 5, 10, 15, 20, 25) refractory high entropy alloys (RHEAs) were prepared by vacuum arc melting. Their microstructure, compressive mechanical properties, hardness, and fracture morphology were investigated and analyzed. The results show that the RHEAs possess a disordered BCC phase, ordered Laves phase, and Zr-rich HCP phase. Their dendrite structures were observed, and the distribution of dendrites became gradually more dense with an increase in W content. The RHEAs demonstrate high strength and hardness, with these properties being higher than in most reported tungsten-containing RHEAs. For example, the typical W₂₀(TaVZr)₈₀ RHEA has a yield strength of 1985 MPa and a hardness of 636 HV, respectively. The improvement in terms of strength and hardness are mainly due to solid solution strengthening and the increase in dendritic regions. During compression, with the increase in the applied load, the fracture behavior of RHEAs changed from initial intergranular fractures to a mixed mode combining both intergranular and transgranular fractures. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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20 pages, 10093 KiB

Open AccessArticle

Effects of Nb Additions and Heat Treatments on the Microstructure, Hardness and Wear Resistance of CuNiCrSiCoTiNb_x High-Entropy Alloys

by Denis Ariel Avila-Salgado, Arturo Juárez-Hernández, María Lara Banda, Arnoldo Bedolla-Jacuinde and Francisco V. Guerra

Entropy 2022, 24(9), 1195; https://0-doi-org.brum.beds.ac.uk/10.3390/e24091195 - 26 Aug 2022

Viewed by 1419

Abstract

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb_0.5 (H-0.5Nb) and CuNiCrSiCoTiNb₁ (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm³. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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Review

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38 pages, 7983 KiB

Open AccessReview

Recent Advances in W-Containing Refractory High-Entropy Alloys—An Overview

by Shunhua Chen, Chen Qi, Jiaqin Liu, Jingsai Zhang and Yucheng Wu

Entropy 2022, 24(11), 1553; https://0-doi-org.brum.beds.ac.uk/10.3390/e24111553 - 28 Oct 2022

Cited by 16 | Viewed by 3370

Abstract

During the past decade, refractory high-entropy alloys (RHEA) have attracted great attention of scientists, engineers and scholars due to their excellent mechanical and functional properties. The W-containing RHEAs are favored by researchers because of their great application potential in aerospace, marine and nuclear equipment and other high-temperature, corrosive and irradiated fields. In this review, more than 150 W-containing RHEAs are summarized and compared. The preparation techniques, microstructure and mechanical properties of the W-containing RHEAs are systematically outlined. In addition, the functional properties of W-containing RHEAs, such as oxidation, corrosion, irradiation and wear resistance have been elaborated and analyzed. Finally, the key issues faced by the development of W-containing RHEAs in terms of design and fabrication techniques, strengthening and deformation mechanisms, and potential functional applications are proposed and discussed. Future directions for the investigation and application of W-containing RHEAs are also suggested. The present work provides useful guidance for the development, processing and application of W-containing RHEAs and the RHEA components. Full article

(This article belongs to the Special Issue Recent Advances in Refractory High Entropy Alloys)

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