High‐entropy alloys (HEAs) in which interesting physical, chemical, and structural properties are being continuously revealed have recently attracted extensive attention. Body‐centered cubic (bcc) ...HEAs, particularly those based on refractory elements are promising for high‐temperature application but generally fail by early cracking with limited plasticity at room temperature, which limits their malleability and widespread uses. Here, the “metastability‐engineering” strategy is exploited in brittle bcc HEAs via tailoring the stability of the constituent phases, and transformation‐induced ductility and work‐hardening capability are successfully achieved. This not only sheds new insights on the development of HEAs with excellent combination of strength and ductility, but also has great implications on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
The “metastability‐engineering” strategy is exploited in brittle body‐centered cubic high‐entropy alloys (HEAs) via tailoring the thermal and mechanical stability of the constituent phases, and consequently, transformation‐induced ductility and work hardening capability are successfully achieved. This not only has important implications for developing high‐performance HEAs, but also sheds light on overcoming the long‐standing strength–ductility tradeoff of metallic materials in general.
High‐entropy alloys (HEAs) are based on five or more principal elements with equal or nearly equal molar fractions and possess many significant advantages over traditional alloys, including high ...strength and hardness, excellent corrosion resistance, outstanding thermal stability, and irradiation resistance. Phase structure plays a vital role in determining the property of HEAs. For further enhancing the performance of HEAs in various application fields, a controllable synthesis with desired phases is required. In this review, the diverse phase structures of HEAs and the related properties are first introduced. Then, alternative tuning strategies to promote the desired phase structure of HEAs are focused upon. Property adjusting of phase‐engineered HEAs is also discussed in depth. Lastly, some insights into the challenges and future prospects in this rapidly emerging research field are provided.
Phase engineering of high‐entropy alloys (HEAs) is comprehensively reviewed. HEAs with rich constituent elements exhibit many remarkable properties that are greatly influenced by phase structure. For further exploring the properties of HEAs, controllable synthesis with desired phases is required. The diverse phase structures, phase‐tuning strategies, and property adjusting of phase‐engineered HEAs is presented and discussed in depth.
High‐entropy alloys (HEAs) are expected to function well as electrocatalytic materials, owing to their widely adjustable composition and unique physical and chemical properties. Recently, HEA ...catalysts are extensively studied in the field of electrocatalysis; this motivated the authors to investigate the relationship between the structure and composition of HEAs and their electrocatalytic performance. In this review, the latest advances in HEA electrocatalysts are systematically summarized, with special focus on nitrogen fixation, the carbon cycle, water splitting, and fuel cells; in addition, by combining this with the characterization and analysis of HEA microstructures, rational design strategies for optimizing HEA electrocatalysts, including controllable preparation, component regulation, strain engineering, defect engineering, and theoretical prediction are proposed. Moreover, the existing issues and future trends of HEAs are predicted, which will help further develop these high‐entropy materials.
In this review, the latest advances in high‐entropy alloy (HEA) electrocatalysts for electrochemical energy storage and conversion are systematically summarized. Moreover, combining the characterization and analysis of HEA microstructures, rational design strategies are proposed for optimizing HEAs electrocatalysts, covering controllable preparation, component regulation, strain engineering, defect engineering, and theoretical prediction.
One important goal of the current electrocatalysis is to develop integrated electrodes from the atomic level design to multilevel structural engineering in simple ways and low prices. Here, a series ...of oxygen micro‐alloyed high‐entropy alloys (O‐HEAs) is developed via a metallurgy approach. A (CrFeCoNi)97O3 bulk O‐HEA shows exceptional electrocatalytic performance for the oxygen evolution reaction (OER), reaching an overpotential as low as 196 mV and a Tafel slope of 29 mV dec−1, and with stability longer than 120 h in 1 m KOH solution at a current density of 10 mA cm−2. It is shown that the enhanced OER performance can be attributed to the formation of island‐like Cr2O3 microdomains, the leaching of Cr3+ ions, and structural amorphization at the interfaces of the domains. These findings offer a technological‐orientated strategy to integrated electrodes.
A new class of bulk electrodes is designed by incorporating oxide microdomains into the so‐called high‐entropy alloys (HEAs). From these, unprecedented oxygen evolution reaction (OER) activity is achieved, with an ultralow overpotential of 196 mV and a Tafel slope of 29 mV dec−1, and with stability longer than 120 h in 1 m KOH solution at current density of 10 mA cm−2.
Boosted by the success of high‐entropy alloys (HEAs) manufactured by conventional processes in various applications, the development of HEAs for 3D printing has been advancing rapidly in recent ...years. 3D printing of HEAs gives rise to a great potential for manufacturing geometrically complex HEA products with desirable performances, thereby inspiring their increased appearance in industrial applications. Herein, a comprehensive review of the recent achievements of 3D printing of HEAs is provided, in the aspects of their powder development, printing processes, microstructures, properties, and potential applications. It begins with the introduction of the fundamentals of 3D printing and HEAs, as well as the unique properties of 3D‐printed HEA products. The processes for the development of HEA powders, including atomization and mechanical alloying, and the powder properties, are then presented. Thereafter, typical processes for printing HEA products from powders, namely, directed energy deposition, selective laser melting, and electron beam melting, are discussed with regard to the phases, crystal features, mechanical properties, functionalities, and potential applications of these products (particularly in the aerospace, energy, molding, and tooling industries). Finally, perspectives are outlined to provide guidance for future research.
3D printing of high‐entropy alloys (HEAs) has great potential for manufacturing geometrically complex and/or customized HEA products with desirable performances, inspiring their increased appearance in industrial applications. A comprehensive review of the recent advances on the 3D printing of HEAs is provided, with regard to the aspects of their powder development, printing processes, microstructures, mechanical properties, functionalities, and potential applications.
Refractory high‐entropy alloys (RHEAs) show promising applications at high temperatures. However, achieving high strengths at elevated temperatures above 1173K is still challenging due to heat ...softening. Using intrinsic material characteristics as the alloy‐design principles, a single‐phase body‐centered‐cubic (BCC) CrMoNbV RHEA with high‐temperature strengths (beyond 1000 MPa at 1273 K) is designed, superior to other reported RHEAs as well as conventional superalloys. The origin of the high‐temperature strength is revealed by in situ neutron scattering, transmission‐electron microscopy, and first‐principles calculations. The CrMoNbV's elevated‐temperature strength retention up to 1273 K arises from its large atomic‐size and elastic‐modulus mismatches, the insensitive temperature dependence of elastic constants, and the dominance of non‐screw character dislocations caused by the strong solute pinning, which makes the solid‐solution strengthening pronounced. The alloy‐design principles and the insights in this study pave the way to design RHEAs with outstanding high‐temperature strength.
Structural materials with exceptional high‐temperature strengths are highly desirable for high‐temperature applications. In this work, three alloy‐design principles of the large atomic‐size and elastic‐modulus mismatches, the insensitive temperature‐dependence of elastic properties, and the dominance of non‐screw dislocations are used to design a CrMoNbV refractory high‐entropy alloy, which exhibits outperforming high‐temperature strengths.
Mixing multimetallic elements in hollow‐structured nanoparticles is a promising strategy for the synthesis of highly efficient and cost‐effective catalysts. However, the synthesis of multimetallic ...hollow nanoparticles is limited to two or three elements due to the difficulties in morphology control under the harsh alloying conditions. Herein, the rapid and continuous synthesis of hollow high‐entropy‐alloy (HEA) nanoparticles using a continuous “droplet‐to‐particle” method is reported. The formation of these hollow HEA nanoparticles is enabled through the decomposition of a gas‐blowing agent in which a large amount of gas is produced in situ to “puff” the droplet during heating, followed by decomposition of the metal salt precursors and nucleation/growth of multimetallic particles. The high active sites per mass ratio of such hollow HEA nanoparticles makes them promising candidates for energy and electrocatalysis applications. As a proof‐of‐concept, it is demonstrated that these materials can be applied as the cathode catalyst for Li–O2 battery operations with a record‐high current density per catalyst mass loading of 2000 mA gcat.−1, as well as good stability and durable catalytic activity. This work offers a viable strategy for the continuous manufacturing of hollow HEA nanomaterials that can find broad applications in energy and catalysis.
The rapid and continuous synthesis of hollow high‐entropy‐alloy (HEA) nanoparticles by a “droplet‐to‐particle” nanomanufacturing method is reported. The formation of hollow HEA nanoparticles is enabled by the introduction of a blowing agent. The high active sites per mass ratio of such hollow HEA nanoparticles makes them promising candidates for electrocatalysis.
The lack of strength and damage tolerance can limit the applications of conventional soft magnetic materials (SMMs), particularly in mechanically loaded functional devices. Therefore, strengthening ...and toughening of SMMs is critically important. However, conventional strengthening concepts usually significantly deteriorate soft magnetic properties, due to Bloch wall interactions with the defects used for hardening. Here a novel concept to overcome this dilemma is proposed, by developing bulk SMMs with excellent mechanical and attractive soft magnetic properties through coherent and ordered nanoprecipitates (<15 nm) dispersed homogeneously within a face‐centered cubic matrix of a non‐equiatomic CoFeNiTaAl high‐entropy alloy (HEA). Compared to the alloy in precipitate‐free state, the alloy variant with a large volume fraction (>42%) of nanoprecipitates achieves significantly enhanced strength (≈1526 MPa) at good ductility (≈15%), while the coercivity is only marginally increased (<10.7 Oe). The ordered nanoprecipitates and the resulting dynamic microband refinement in the matrix significantly strengthen the HEAs, while full coherency between the nanoprecipitates and the matrix leads at the same time to the desired insignificant pinning of the magnetic domain walls. The findings provide guidance for developing new high‐performance materials with an excellent combination of mechanical and soft magnetic properties as needed for the electrification of transport and industry.
Ultrastrong and ductile bulk high‐entropy alloys with excellent soft magnetic properties are achieved by introducing a high volume fraction of coherent and ordered nanoprecipitates into the alloy matrix. The high lattice coherency between the homogeneously dispersed nanoprecipitates and the alloy matrix creates only negligible distortion fields on magnetic domain wall motion and contributes significantly to the strength of the material.
Electrocatalytic hydrogen evolution in alkaline and neutral media offers the possibility of adopting platinum‐free electrocatalysts for large‐scale electrochemical production of pure hydrogen fuel, ...but most state‐of‐the‐art electrocatalytic materials based on nonprecious transition metals operate at high overpotentials. Here, a monolithic nanoporous multielemental CuAlNiMoFe electrode with electroactive high‐entropy CuNiMoFe surface is reported to hold great promise as cost‐effective electrocatalyst for hydrogen evolution reaction (HER) in alkaline and neutral media. By virtue of a surface high‐entropy alloy composed of dissimilar Cu, Ni, Mo, and Fe metals offering bifunctional electrocatalytic sites with enhanced kinetics for water dissociation and adsorption/desorption of reactive hydrogen intermediates, and hierarchical nanoporous Cu scaffold facilitating electron transfer/mass transport, the nanoporous CuAlNiMoFe electrode exhibits superior nonacidic HER electrocatalysis. It only takes overpotentials as low as ≈240 and ≈183 mV to reach current densities of ≈1840 and ≈100 mA cm−2 in 1 m KOH and pH 7 buffer electrolytes, respectively; ≈46‐ and ≈14‐fold higher than those of ternary CuAlNi electrode with bimetallic Cu–Ni surface alloy. The outstanding electrocatalytic properties make nonprecious multielemental alloys attractive candidates as high‐performance nonacidic HER electrocatalytic electrodes in water electrolysis.
Nonprecious nanoporous multielemental alloy electrodes composed of electroactive surface high‐entropy CuNiMoFe alloy hold great promise as cost‐effective electrocatalysts for hydrogen evolution reaction (HER) in nonacidic media. Associated with hierarchical nanoporous architecture to facilitate electron transfer and offer abundant high‐entropy CuNiMoFe active sites, the nanoporous CuAlNiMoFe hybrid electrode exhibits remarkably enhanced HER activity and durability.
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