High-entropy Alloys For Applications Research Articles

Nanoporous High Entropy Alloy Al-Pt-Pd-Ru as an Efficient Catalyst for One-Pot Reductive Amination of Nitroarenes.

High entropy alloys (HEAs) are promising heterocatalysts because of their unique physicochemical properties, but research on HEA-catalyzed tandem reactions is lacking. Moreover, limited research on HEAs for molecular transformation has hindered their development. Herein, an unsupported nanoporous HEA Al-Pt-Pd-Ru (HEANPore) prepared using a top-down dealloying method is reported. The Lewis acidity and electron redistribution of the noble metals Pt, Pd, and Ru are identified to be intrinsic of high activity and selectivity of HEANPore in the one-pot reductive amination of nitroarenes. The competitive adsorption of the reactant and corresponding reaction mechanism are investigated using DFT. This study demonstrates the exceptional performance of the HEANPore in tandem reactions, presenting new possibilities for the application of HEAs in the field of catalysis.

Ultrasmall High-Entropy-Alloy Nanozyme Catalyzed In Vivo ROS and NO Scavenging for Anti-Inflammatory Therapy.

High-entropy alloy (HEA) nanoparticles possess finely tunable and multifunctional catalytic activity due to their extremely diverse adsorption sites. Their unique properties enable HEA nanoparticles to mimic the complex interactions of the redox homeostasis system, which is composed of cascade and multiple enzymatic reactions. The application of HEAs in mimicking complex enzymatic systems remains relatively unexplored, despite the importance of regulating biological redox reactions. Here, it is reported that ultra-small (<10 nm in a diameter) HEA nanozymes consisting of five platinum-group metals with tunable morphologies from planar to dendritic structures are synthesized. The synthesized HEA nanozymes exhibited higher peroxidase-like activity compared to monometallic platinum-group nanoparticles. Additionally, HEA nanoparticles effectively mimicked RONS-regulation metabolism in cascade reactions involving superoxide dismutase and catalase, as well as in multiple reactions including HORAC and NO scavenging. As a result, the HEA nanozyme exhibited superior anti-inflammatory efficacy both in vitro and in vivo. The findings underscore the effectiveness of the high-entropy alloy structure in restoring in vivo enzymatic systems through intrinsic activity enhancements and cascade reaction mechanisms.

Clarifying the effects of composition and phase stabilization on the oxidation resistance in AlCoCrFeNiTi series high-entropy alloys at 1100 °C

The application of high entropy alloys in thermal barrier coating (TBC) systems offers a viable solution for mitigating interfacial instability arising from the elevated-temperature interdiffusion within the bonding layer/matrix. Nevertheless, the elucidation of the phase stability under elevated temperatures and the intricate interplay among thermal-mechanical-chemical factors in HEAs remain lacks clarity. Herein, a set of AlxCo10.5Cr10Fe25Ni(50-x)Ti4.5 HEAs featuring desirable high-temperature phase stability, oxidation resistance, and spalling resistance at 1100 °C were meticulously designed. And the effects of phase composition and thermodynamics on the evolution of surface oxides in these HEAs were investigated. Specifically, the formation of the unfavorable σ phase between 860 and 1200 °C is avoided through the composition adjustment. The oxidation resistance is governed by the presence of large-size columnar grains and the spalling resistance of the Al2O3 oxide film. The spalling resistance is mainly linked to the configuration sequence (Spinel→FeAlTiO5→TiO2) of the outer oxide layer and the phase transition of the matrix either to FCC or BCC. Meanwhile, the formation of FeAlTiO5 assumes a crucial role in the optimization of spalling (>770 h) and oxidation resistance (2.6×10−12 g2·cm−4·s−1) within an Al20Co10.5Cr10Fe25Ni30Ti4.5 alloy. These findings provide guidance for the development of TBC systems endowed with exceptional properties tailored for engineering applications.

Vacuum brazing of Al0.3CoCrFeNi high-entropy alloys with CoCrFeNiNb0.5 eutectic filler metal for wide-temperature range application

The service conditions of high-entropy alloys (HEAs) joints brazed with conventional filler metals (FMs) can be confined because few HEAs phases generate in the braze zone. In this study, a multicomponent CoCrFeNiNb0.5 eutectic HEAs (EHEAs) FM was developed to braze Al0.3CoCrFeNi HEAs in vacuum, the braze zone mainly consisted of face-centered cubic (FCC) and Laves lamellar structure, exhibiting a superior metallurgical compatibility with the Al0.3CoCrFeNi base metals (BMs). The shear strength and shear displacement of brazed joints reached 461 MPa/1.35 mm at room temperature (RT), 741 MPa/1.42 mm at −196 °C and 380 MPa/1.62 mm at 700 °C, respectively. This strategy can stimulate the fabrication and wide-temperature range applications of HEAs brazed components by exploiting the structural and performance merits of EHEAs FMs.

Obtaining in-situ reacted Fe–W–Ni–Cr–Cu high-entropy alloy within the interlayer of dissimilar Cf/SiC-GH3536 joint by designing non-high-entropy Cu–Ti–W composite filler

In aerospace applications, the development of high-entropy alloys (HEAs) filler is an effective strategy to obtain reliable Cf/SiC nozzles and GH3536 thrust chambers components. Considering the high costs and extended preparation times with HEA fillers, utilizing non-HEA fillers to generate HEAs within brazing seam offers significant advantages. This study successfully joined Cf/SiC with GH3536 using a non-HEA Cu–Ti–W composite filler that facilitated the in-situ formation of Fe–W–Ni–Cr–Cu HEA during the brazing process. Furthermore, the formation and accompanying martensite phase transformation were revealed. The microstructure characteristic of W reinforcements/HEA/Cu(s,s) was ultimately formed in the brazing seam. The atomic structure of the HEA, confirmed to be hexagonal close-packed, was elucidated using spherical aberration-corrected transmission electron microscopy. Additionally, a martensite phase transformation was observed in the HEA, involving two adjacent layers of (0 0 0 1) atomic planes that sheared and move a3 distance alon g [10–10] in opposite directions, resulting in the formation of M-HEA. The inclusion of HEA and M-HEA in the Cf/SiC-GH3536 joint, brazed with Cu–Ti–W composite filler, increased its shear strength to 84.8 MPa, which was 2.15 times higher than that of joints without the W reinforcements. This study offers new insights into the design of composite fillers and the application of HEAs.

Effects of strain rate and low temperature on dynamic behaviors of additively manufactured CoCrFeMnNi high-entropy alloys

With the increasing demand for high-performance alloys in extreme environments, there has been an active development of new materials. High-entropy alloys (HEAs) are considered a promising choice due to their exceptional properties. Even though HEAs exhibit remarkable mechanical properties, only a limited number of studies have explored the mechanical properties and microstructures of additively manufactured HEAs under extreme conditions. In this work, the dynamic mechanical properties at high strain rates and different temperatures (i.e., 293 K and 77 K), as well as quasi-static mechanical properties for the CoCrFeMnNi HEAs fabricated by selective laser melting (SLM) are investigated. Microstructure observations have demonstrated that the as-printed sample displays a single face-centered cubic (FCC) phase with a columnar dendrite feature. Within dendrites, a large number of dislocations and substructures appear due to the applied high cooling rates during the SLM process. The as-printed sample exhibits a significant strain rate dependence from quasi-static to dynamic loading during deformation. Compared to the quasi-static mechanical properties, the as-printed HEA reveals higher dynamic yield strength (e.g., ∼1081 MPa and ∼1020 MPa along the build and scanning directions under 2800 s−1, respectively), more pronounced strain-hardening behavior, and larger remarkable plasticity under dynamic loading at cryogenic temperatures. When subjected to increasing strain rates ranging from 0.001 s−1 to 3500 s−1 at 293 K, the yield strength of the as-printed HEAs exhibits a notable enhancement, increasing from ∼517 MPa to ∼723 MPa along the BD direction, and from ∼545 MPa to ∼667 MPa along the SD direction. The corresponding variation in the strength of the BD samples is more pronounced than that of the SD samples. The enhancement in strength should be attributed to the differences in the features of grain orientation and dislocation distribution along different build directions, as well as the strain rate dependence. During plastic deformation, the dominant mechanisms of dislocation slips and deformation twins (DTs) are transformed into multi-stage-twin-controlled ones at cryogenic temperatures, which is beneficial to improve the strain hardening rate and plasticity. The present studies provide a deep understanding of the deformation mechanism of HEAs under extreme conditions and help promote the application of HEAs in the future.

Accelerating the Exploration of High‐Entropy Alloys: Synergistic Effects of Integrating Computational Simulation and Experiments

High‐entropy alloys (HEAs) are novel materials composed of multiple elements with nearly equal concentrations and they exhibit exceptional properties such as high strength, ductility, thermal stability, and corrosion resistance. However, the intricate and diverse structures of HEAs pose significant challenges to understanding and predicting their behavior at different length scales. This review summarizes recent advances in computational simulations and experiments of structure‐property relationships in HEAs at the nano/micro scales. Various methods such as first‐principles calculations, molecular dynamics simulations, phase diagram calculations, and finite element simulations are discussed for revealing atomic/chemical and crystal structures, defect formation and migration, diffusion and phase transition, phase formation and stability, stress‐strain distribution, deformation behavior, and thermodynamic properties of HEAs. Emphasis is placed on the synergistic effects of computational simulations and experiments in terms of validation and complementarity to provide insights into the underlying mechanisms and evolutionary rules of HEAs. Additionally, current challenges and future directions for computational and experimental studies of HEAs are identified, including accuracy, efficiency, and scalability of methods, integration of multiscale and multiphysics models, and exploration of practical applications of HEAs.

Phase Engineering of High-Entropy Alloy for Enhanced Electrocatalytic Nitrate Reduction to Ammonia.

Directly electrochemical conversion of nitrate (NO3 -) is an efficient and environmentally friendly technology for ammonia (NH3) production but is challenged by highly selective electrocatalysts. High-entropy alloys (HEAs) with unique properties are attractive materials in catalysis, particularly for multi-step reactions. Herein, we first reported the application of HEA (FeCoNiAlTi) for electrocatalytic NO3 - reduction to NH3 (NRA). The bulk HEA is active for NRA but limited by the unsatisfied NH3 yield of 0.36 mg h-1 cm-2 and Faradaic efficiency (FE) of 82.66 %. Through an effective phase engineering strategy, uniform intermetallic nanoparticles are introduced on the bulk HEA to increase electrochemical active surface area and charge transfer efficiency. The resulting nanostructured HEA (n-HEA) delivers enhanced electrochemical NRA performance in terms of NH3 yield (0.52 mg h-1 cm-2) and FE (95.23 %). Further experimental and theoretical investigations reveal that the multi-active sites (Fe, Co, and Ni) dominated electrocatalysis for NRA over the n-HEA. Notably, the typical Co sites exhibit the lowest energy barrier for NRA with *NH2 to *NH3as the rate-determining step.

The comparative research on tribological behavior of carbon-doped CoCrFeNiV high entropy alloys in air and vacuum environments

In the field of aviation and aerospace engineering, the application of high-entropy alloys (HEAs) is inevitably needs to withstand the damage of both wear and adhesion in vacuum. Herein, the vacuum tribological behavior of a high performance Co21Cr21Fe21Ni21V14.5C1.5 HEAs (C12) were investigated. In this study, the hardness and compressive strength, significantly improved for Co21Cr21Fe21Ni21V14.5C1.5 (1200 °C, C12) HEA compared to the CoCrFeNiV (C0) base alloy. The focus was put on the effect of C element and sintering temperature at 1000 ℃ and1200 ℃ (C10 and C12) on the microstructure and vacuum tribological mechanisms of the alloy. It was found that the friction coefficient of the C12 alloy under air can be minimized to lower than 0.37. The wear rate of C12 alloy ((1.31–2.67)× 10−4 mm3/Nm) is 2–4 times lower than that of C10 alloy (2.91–8.31)× 10−4 mm3/Nm). The wear-resistance of Co21Cr21Fe21Ni21V14.5C1.5 alloy at sinter temperature 1200 °C (C12) is significantly higher than that of alloy sinter temperature at 1000 °C (C10). Therefore, C12 alloy exhibited optimal vacuum tribological properties. This work provides helpful guidance for material design and wear resistance in the field of space tribology.

A Modern Approach to HEAs: From Structure to Properties and Potential Applications

High-entropy alloys (HEAs) are advanced materials characterized by their unique and complex compositions. Characterized by a mixture of five or more elements in roughly equal atomic ratios, these alloys diverge from traditional alloy formulations that typically focus on one or two principal elements. This innovation has paved the way for subsequent studies that have expanded our understanding of HEAs, highlighting the role of high mixing entropy in stabilizing fewer phases than expected by traditional phase prediction methods like Gibbs’s rule. In this review article, we trace the evolution of HEAs, discussing their synthesis, stability, and the influence of crystallographic structures on their properties. Additionally, we highlight the strength–ductility trade-off in HEAs and explore strategies to overcome this challenge. Moreover, we examine the diverse applications of HEAs in extreme conditions and their promise for future advancements in materials science.

Phase Engineering of High‐Entropy Alloy for Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Directly electrochemical conversion of nitrate (NO3−) is an efficient and environmentally friendly technology for ammonia (NH3) production but is challenged by highly selective electrocatalysts. High‐entropy alloys (HEAs) with unique properties are attractive materials in catalysis, particularly for multi‐step reactions. Herein, we first reported the application of HEA (FeCoNiAlTi) for electrocatalytic NO3− reduction to NH3 (NRA). The bulk HEA is active for NRA but limited by the unsatisfied NH3 yield of 0.36 mg h−1 cm−2 and Faradaic efficiency (FE) of 82.66%. Through an effective phase engineering strategy, uniform intermetallic nanoparticles are introduced on the bulk HEA to increase electrochemical active surface area and charge transfer efficiency.The resulting nanostructured HEA (n‐HEA) delivers enhanced electrochemical NRA performance in terms of NH3 yield (0.52 mg h−1 cm−2) and FE (95.23%). Further experimental and theoretical investigations reveal that the multi‐active sites (Fe, Co, and Ni) dominated electrocatalysis for NRA over the n‐HEA. Notably, the typical Co sites exhibit the lowest energy barrier for NRA with *NO + H+ + e− → *NOH as the rate‐determining step.

Synergistic effects of Monel 400 filler wire in gas metal arc welding of CoCrFeMnNi high entropy alloy

Weldability plays a crucial role in the journey of high entropy alloys towards their engineering applications. In this study, gas metal arc welding was performed to join an as-rolled CoCrFeMnNi high entropy alloy using Monel 400 as the filler wire. The present research findings demonstrate a favorable metallurgical chemical reaction between the Monel 400 filler and the CoCrFeMnNi high entropy alloy, resulting in compositional mixing within the fusion zone that promotes a solid-solution strengthening effect, counteracting the typical low hardness associated to the fusion zone of these alloys. The weld thermal cycle induced multiple microstructure changes across the joint, including variations in the grain size, existing phases and local texture. The grain size was seen to increase from the base material toward the fusion zone. An FCC matrix and finely sparse Cr-Mn-based oxides existed in both base material and heat affected zone, while in the fusion zone new FCC phases and carbides were formed upon the mixing of the Monel 400 filler. The role of the filler material on the fusion zone microstructure evolution was rationalized using thermodynamic calculations. Texture shifted from a γ-fiber (in the base material) to a strong cubic texture in the fusion zone. Digital image correlation during tensile testing to fracture coupled with microhardness mapping revealed that, stemming from the process-induced microstructure changes, the micro and macromechanical response differed significantly from the original base material. This study successfully established a correlation between the impact of the process on the developed microstructural features and the resultant mechanical behavior, effectively assessing the processing-microstructure-properties relationships towards an improved understanding of the physical metallurgy associated to these advanced engineering alloys. In conclusion, this work provides an important theoretical framework and practical guidance for optimizing the engineering applications of high entropy alloys.

Effect of Ti additions on the mechanical properties and thermal expansion properties of Ni9Cr9Co9Fe9Tix (x=1, 2, 3) high entropy alloy

The mechanical properties and thermal expansion properties of high entropy alloys (HEAs) are crucial for practical applications. However, there is a scarcity of research on how to optimize the relationship between the mechanical and thermal expansion properties, which currently restricts the application of HEAs as precision structural materials. To address this critical issue, the present study investigates the mechanical properties and thermal expansion properties of Ni9Cr9Co9Fe9Tix (x=1,2,3) HEAs fabricated via repeated arc melting and casting in a vacuum environment. The results show that Ni9Cr9Co9Fe9Tix HEAs exhibit a typical microstructure characteristic of dendritic and inter-dendritic phase, and a small amount of Ni3Ti phase is formed in the Ni9Cr9Co9Fe9Tix HEAs. The addition of Ti notably increases the tensile strength of Ni9Cr9Co9Fe9Tix HEAs, while the presence of the Ni3Ti phase contributes to a reduction in its thermal expansion coefficient. Notably, HEAs with higher Ti content demonstrate increased yield strength but diminished ductility. The primary mechanisms that strengthen the HEA are solid-solution strengthening, secondary phase hardening and dislocations strengthening of the FCC matrix. This study provides superior mechanical properties for HEAs structural components and reduces the thermal expansion coefficient of the matrix alloy, which also indicated the potential of this material for the design and development of HEAs for precision structural components.

Unique Hierarchically Structured High-Entropy Alloys with Multiple Adsorption Sites for Rechargeable Li-CO2 Batteries with High Capacity.

Lithium-carbon dioxide (Li-CO2) batteries offer the possibility of synchronous implementation of carbon neutrality and the development of advanced energy storage devices. The exploration of low-cost and efficient cathode catalysts is key to the improvement of Li-CO2 batteries. Herein, high-entropy alloys (HEAs)@C hierarchical nanosheet is synthesized from the simulation of the recycling solution of waste batteries to construct a cathode for the first time. Owing to the excellent electrical conductivity of the carbon material, the unique high-entropy effect of the HEAs, and the large number of catalytically active sites exposed by the hierarchical structure, the FeCoNiMnCuAl@C-based battery exhibits a superior discharge capability of 27664 mAh g-1 and outstanding durability of 134 cycles as well as low overpotential with 1.05V at a discharge/recharge rate of 100mA g-1. The adsorption capacity of different sites on the HEAs is deeply understood through density functional theory calculations combined with experiments. This work opens up the application of HEAs in Li-CO2 batteries catalytic cathodes and provides unique insights into the study of adsorption active sites in HEAs.

Mechanical-thermal coupling fatigue failure of CoCrFeMnNi high entropy alloy

High entropy alloys exhibit excellent performance under different-temperature conditions. In order to investigate the effect of temperature on the mechanical-thermal coupling fatigue failure of classical CoCrFeMnNi high entropy alloy to accelerate the application of high entropy alloys, the uniaxial tensile and fatigue tests at temperatures ranging from RT to 500 °C were conducted, and statics simulation analysis of fatigue specimens under fatigue loading conditions was conducted. The results of the uniaxial tensile tests illustrated that the yield stress and tensile strength of the alloy decreased with increasing temperature. In contrast, the elongation after the fracture of the alloy increased with temperature. The fatigue test results revealed that the fatigue life decreased as the temperature increased. The fracture morphology of the fatigue specimens and the flank morphology and dislocation distribution near the crack nucleation zone were collected to support the investigation. Accordingly, the reasons for the high-temperature-induced decrease in fatigue crack nucleation and propagation lives were systematically investigated. The main reasons for the higher-temperature-induced decrease in crack nucleation lives were a decrease in the yield stress of the alloy, more easily triggered dislocation motion and stress homogenization. The reasons for the decrease in fatigue crack propagation lives induced by higher temperatures were the more prone occurrence of dislocation motion, a decrease in yield stress, and a decrease in the area of the crack propagation region.

A Prospective on Energy and Environment Applications of High Entropy Alloys

A Prospective on Energy and Environment Applications of High Entropy Alloys

High temperature oxidation behavior of CoCrFeNiMo0.2 high-entropy alloy coatings produced by laser cladding

The oxidation behavior of CoCrFeNiMo0.2 high-entropy alloy laser cladding coatings at 700°C and 900°C was investigated. The oxidation kinetics of the alloys at all temperatures followed a parabolic behavior, with the oxidation rates increasing significantly with increasing temperature. The alloy exhibits excellent oxidation resistance at 700 °C. Compared with the original alloy structure, the segregation of Mo element in the alloy is more serious after high-temperature treatment. Compared with 700 °C, the oxidation degree of the alloy is more intense at 900 °C. The reaction between iron and chromium oxides forms a chromite layer, and the rapid diffusion of iron ions in the layer forms an outer layer of iron oxides. As the oxidation proceeds, the oxide film is separated from the metal, and the chromium oxide layer grows between the spinel layer and the metal. The thermodynamics of the reaction was calculated, the oxidation mechanism of the alloy was explored, and a high-temperature model of the alloy was developed. This study expands the potential applications of high entropy alloys in surface engineering.

Unraveling the oxidation mechanism of Y-doped AlCoCrFeNi high-entropy alloy at 1100 °C

Equimolar AlCoCrFeNi high entropy alloy (HEA) with a coherent dual-phase structure commonly exhibits good strength at high temperatures. Regretfully, the poor oxidation resistance greatly limits its practical application space. In this work, the effect of the reactive element (RE) Y on the oxidation resistance of AlCoCrFeNi HEA is explored. (AlCoCrFeNi)100−xYx (x = 0, 0.1, 0.5 and 1, at.%) were designed and their oxidation mechanisms were unravelled at 1100 °C. Besides the two original B2 phase and A2 phase, the Y-doped HEAs contain (Y, Ni)-rich phase. An appropriate amount of Y blocks the outward Al diffusion and meanwhile inhibits the laterally grown oxides within the existing scale, thereby suppressing the formation of interface pores and rumplings and contributing to superior resistance to oxide scale spallation. However, excessive Y doping causes the formation of (Y, Al)-rich oxide intrusions, which result in the nucleation of cracks near them and thus degrade the interface adherence. The generation and failure mechanisms of oxide scales formed on Y-doped HEAs during 100 h oxidation have been revealed. The presented information proposes new insights to improve the high-temperature oxidation resistance of AlCoCrFeNi HEA and may be useful for assessing the possibility of the practical application of HEAs in aerospace engine components.

High-entropy alloy nanomaterials for electrocatalysis.

High-entropy alloys (HEAs) exhibit a remarkable capacity to modulate geometric and electronic structures for the construction of catalysts with unpredictable and exceptional performance, and have attracted substantial acclaim within the domain of materials science. In this comprehensive review, we present a thorough summary of the synthesis and multiple applications of HEAs in the realm of electrocatalysis. Our review encompasses the diverse synthesis methodologies of HEA nanomaterials and their pivotal roles in amplifying electrocatalytic performance in hydrogen evolution reactions (HERs), oxygen evolution reactions (OERs), oxygen reduction reactions (ORRs), alcohol oxidation reactions (AORs), and CO2 reduction reactions (CO2RRs), and more. Furthermore, we address the intricate challenges and promising avenues that lie ahead in this research area. Reviewing recent breakthroughs, emerging paradigms, and prospects on the horizon, it becomes increasingly evident that HEAs harbor immense potential to reshape the landscape of energy conversion and storage, and emerge as paramount contenders for the development of cutting-edge electrocatalytic materials that hold the key to a sustainable energy future.

Microwave synthesis of high-entropy alloy catalysts on graphene oxide sheets for oxygen reduction and evolution reactions

High-entropy alloys (HEAs) are commonly synthesized through solid-state reactions and solution-mediated techniques. In this work, HEA nanoparticles were synthesized using an ultra-efficient pulse microwave (PM) method at relatively low temperatures (∼100 °C) with superior catalytic activities. During the PM synthesis process, the precursors of the reaction activate and accelerate the reaction owing to the release of localized and excessive energy. This leads to the formation of a crystallized high-entropy alloy (HEA). Pt30Al15Mn15Co10Ni15Cu15 and Pt30Al15Mn15Co10Ni15Fe15 HEA nanoparticles were synthesized without requiring additional external heat treatments. Furthermore, the synthesized entropically stable HEA nanoparticles showed excellent dispersion behavior towards graphene oxide (GO) sheets (particle size: 4–10 nm), this enhanced dispersion resulted in improved catalytic activity and long-term durability for various processes including H2 adsorption/desorption, oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). The robust design of Cu-HEA-GO catalytic nanoparticles leads to increased synergistic interactions, which play a critical role in enhancing the ORR/OER activity. We firmly believe that the framework established in this study paves the way for the development of various high-performance catalysts based on HEAs for applications in fuel cells, metal-air batteries, and other electrochemical devices.