High-entropy Alloys Research Articles

Flocculent-structured high-entropy-alloy anode electrocatalyst for direct ethylene glycol fuel cells

The Pt-based alloys catalysts with special morphology attract great attention. Herein, a flocculent-structured high-entropy-alloy (HEA) (named as F-PtBiCuCoMo/C) electrocatalyst is prepared by co-reduction, which can greatly improve the overall catalytic performance and reduce Pt-usage. In ethylene glycol oxidation reaction (EGOR), it has mass activity of 1.08Amg-1Pt, which also has a good durability with high residual current density (0.27Amg-1Pt after 3000s). Notably, the power density reached 17.9mWcm-2 in as-assembled direct ethylene glycol fuel cells (DEGFC), which exceeded commercial Pt/C references by 2.4 times. Thence, this F-PtBiCuCoMo/C electrocatalyst would be a good option for the advancement of DEGFC technology.

Radiation Shielding Properties of Composites of TiZrNbHfTa Refractory High Entropy Alloy Reinforced with TiZrNbHfTaOx High-Entropy Oxide

Radiation shielding materials play a critical role in advancing the next generation of nuclear reactors. Among these, high-entropy materials with refractory properties emerge as a new category for radiation shielding applications. This study introduces TiZrNbHfTa-TiZrNbHfTaOx composites tailored for such purposes. Initially, a TiZrNbHfTa refractory high-entropy alloy (RHEA) is synthesized via mechanical alloying, followed by the oxidation of the alloy to obtain its refractory high-entropy oxide (RHEO), TiZrNbHfTaOx. Composites are then prepared by blending 5%, 10%, and 20% weight fractions of RHEO with RHEA using mechanical alloying. Comparative analysis of shielding properties reveals a decrease in mass attenuation coefficient and effective atomic number with increasing RHEO content. While RHEA exhibits superior shielding performance against photons and neutrons, the composite containing 20% RHEO emerges as the optimal shield against alpha and proton irradiations. A comparison between the shielding properties of composites with those of the RHEA and the HEO confirmed that among the tested samples, RHEA is superior in terms of gamma shielding, but the composite with 20% HEO is the best shielding material against alpha and proton particles. Also, the equivalent neutron dose rate and removal cross section values are obtained 49.812% and 0.14214 for 20% HEO sample, respectively. These findings, supported by computational simulations in this study, contribute valuable insights for the advancement of novel shielding materials crucial for future nuclear reactor technologies.

The role of the preparation route on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Nearly equiatomic AlCoCrFeNi alloy samples were prepared by induction melting and mechanical alloying (MA) combined with spark plasma sintering (SPS). The cast sample showed a dendritic microstructure composed of spinodally decomposed nanometric constituents of the B2 and BCC phases. The spark plasma sintered sample exhibited an ultrafine-grained microstructure of B2 phase and FCC solid solution and Cr23C6 carbides. The MA+SPS sample was strengthened by compressive stress-strain test up to a yield strength of 2029 ± 5 MPa, resulting significantly higher compared to 1366 ± 32 MPa of the cast sample. In addition to the higher compressive yield strength, the sintered sample exhibited a hardness of more than 130 HV higher compared to the cast alloy. On the other hand, the cast alloy showed high plastic deformation (29%) and significantly high ultimate compressive strength of 3072 ± 122 MPa. Together with these mechanical characteristics, the MA+SPS sample showed good thermal stability while preserving the mechanical properties even after annealing at 800 °C. This was not the case with the cast sample, in which ductility and ultimate strength significantly decreased upon annealing at 800 °C. A substantial yield strength reduction of both MA+SPS and cast samples was recorded when tested at 800 °C. Nevertheless, stress-strain curve trends were observed to be quite different between the two samples, thus suggesting dissimilar deformation mechanisms under high-temperature compression.

Deformation mechanism and microstructure evolution during superplastic deformation of friction stir processed CoCrFeNiMn high entropy alloy

Since superplastic formation offers a significant advantage in preparing the complex structure parts of HEAs, the study of their superplastic behavior is extremely important. Using friction stir processing (FSP) with an improved convex hemispherical shape tool, this study reported for the first time an equiaxed ultrafine-grained CoCrFeNiMn HEA (489 nm) with a maximum elongation of 870% at 675 °C and 3 × 10−4 s−1. This superplastic property is much larger than ever reported in the CoCrFeNiMn HEA, which is even larger than that of the nano-sized CoCrFeNiMn HEA (10 nm) prepared by the high-pressure torsion. A high proportion of high angle grain boundaries and twin boundaries, a hard Cr-rich phase, and the sluggish diffusion effect of the CoCrFeNiMn HEA were primarily responsible for the exceptional superplasticity. Additionally, this study provides the first elucidation of the mechanism underlying Cr precipitation and Cr-rich phase growth, as well as the function of low-energy annealed twins during superplastic deformation. The diffusion of Cr along dislocations and grain boundaries facilitated grain boundary sliding as the predominant deformation mechanism. This study elucidates the superplastic deformation mechanism and microstructure evolution, thereby furnishing theoretical guidance for the practical implementation of superplastic forming of complex components of HEAs. Additionally, it presents an efficient method for fabricating such components.

Molecular dynamics investigation of wear mechanisms in drilling motion for FeCrNiCoAl high-entropy alloy

This work employed molecular dynamics (MD) to investigate the wear mechanism in the drilling motion of FeCrNiCoAl high entropy alloy. MD simulations reveal a reduction in tangential force upon applying torque to the tool, attributed to the synergy between rotational and thermal effects. Entropy generation analysis indicates that below 20GHz, rotational effects prevail, while conversely, thermal effects take precedence. Furthermore, the correlation between wear volume and rotation frequency exhibits non-monotonic characteristics, which suggests that fine-tuning material wear can be achieved through adjustments to the rotation frequency. An in-depth analysis of the strain energy and the Bejan number allows the categorization of wear into three modes: rotation-dominant, transitional, and thermal-dominant.

Simultaneous realization of high power factor and low thermal conductivity in medium-entropy La-doped (Sr1/3Ba1/3Ca1/3)1-xLaxTiO3 oxides with porous structure

Some studies have proven the effectiveness of high-entropy alloying in reducing lattice thermal conductivity; however, the synchronous degradation in carrier mobility limits the thermoelectric properties of high-entropy materials. Herein, we present a series of medium-entropy oxides (Sr1/3Ba1/3Ca1/3)1-xLaxTiO3 (x = 0.05, 0.1, 0.15) with different levels of La doping, breaking the trade-off between carrier and phonon transport. The medium-entropy design helps keep the carrier mobility at a moderate level while modulating the carrier concentration through La3+ doping, thereby yielding a peak power factor value of 1842 μW/(m⋅K2) at 773 K. Meanwhile, the incorporation of nano-micro-porous structure and medium entropy effect leads to a significant reduction in lattice thermal conductivity, reaching 2.3 W/(m⋅K) at 1073 K. Consequently, a ZTmax value of 0.67 is obtained for the MEP-10La sample at 1073 K, which is one of the state-of-the-art ZT values reported for the SrTiO3-based materials. The present work provides a viable approach for the development of thermoelectric materials with enhanced performance.

Integration of high-entropy nanozyme and hollow In2S3 nanotube heterostructure decorated with WO3 for ultrasensitive PEC aptasensing of highly toxic mycotoxin

As a highly toxic mycotoxin, patulin threatens human and animal health. Herein, a new signal amplification strategy was designed for photoelectrochemical (PEC) analysis of patulin based on nanotube-like In2S3/WO3 heterostructures with the assistance of PtRuFeCoW high-entropy alloy nanorods (HEANRs). Specifically, the prominent photoactivity of the In2S3/WO3 was investigated by UV−vis diffuse reflectance and photoluminescence spectroscopy, coupled by elaborating the photoelectron transport mechanism in detail. Simultaneously, the excellent peroxidase-like activity of the PtRuFeCoW HEANRs was certificated mainly by UV-vis absorption spectroscopy. On such foundation, the PtRuFeCoW HEANRs modified capture DNA was cast onto the In2S3/WO3 based photoanode for catalyzing 4-chloro-1-naphthol (4-CN) oxidation to form insoluble benz-4-chloro-hexadienone (4-CD) precipitate in the presence of H2O2, ultimately weakening the PEC currents. The resulting PEC sensor exhibited a wider detection range from 0.1pgmL−1 to 500ngmL−1 and a lower detection limit was down to 0.063pgmL−1 (S/N = 3). The HEANRs nanozyme assisted PEC method holds great promise for ultrasensitive detection of environmental pollutants in practice.

Structural insights, synthesis, and electrocatalysis of high entropy nanoparticles for fuel cell, metal-air battery, and water-splitting applications

High-entropy alloy nanoparticles (HEA-NPs) have recently sparked great interest in materials science. Their solid-solution states, derived from distinct HEA configurations, make them promising candidates for catalysts with exceptional activity, stability, and tunable performance. However, a comprehensive understanding of the underlying mechanisms governing their electrocatalytic behavior is still lacking, hindering the rational design of HEA electrocatalysts. This review summarizes the fundamental knowledge of HEA-NPs, including the structure-activity correlations of HEA-NPs, diverse synthesis strategies, and applications in electrochemical catalysis. The design strategies for guiding improvements in tunable performance were highlighted. The article concludes with insights, perspectives, and future directions, encapsulating the state-of-the-art knowledge and paving the way for further exploration in this dynamic field.

AB-type dual-phase high-entropy alloys as negative electrode of Ni-MH batteries: Impact of interphases on electrochemical performance

High-entropy alloys (HEAs) and their corresponding high-entropy hydrides are new potential candidates for negative electrode materials of nickel-metal hydride (Ni-MH) batteries. This study investigates the cyclic electrochemical hydrogen storage performance of two AB-type HEAs (A: hydride-forming elements, B: non-hydride-forming elements) in Ni-MH batteries. TiV2ZrCrMnFeNi with a dual-phase structure shows a fast activation and a low charge transfer impedance with a discharge capacity of 150 mAhg−1, while TiV1.5Zr1.5CrMnFeNi with a single phase shows a slow activation and a capacity of only 60 mAhg−1. The better electrochemical performance of TiV2ZrCrMnFeNi was attributed to its higher vanadium/zirconium ratio and abundant interphase boundaries, which act as hydrogen paths and heterogeneous hydride nucleation sites. These results suggest the high potential of dual-phase HEAs as new active electrode materials for Ni-MH batteries.

The mechanism on surface integrity and fatigue performance of double‐sided micro‐cutting enhanced FeCoCrNiAl0.6 high entropy alloy

AbstractThis study examines the impact of cutting parameters on the fatigue properties of FeCoCrNiAl0.6 high‐entropy alloy under bi‐directional micro‐cutting. Utilizing Abaqus/fe−safe for analysis, we evaluated surface roughness, internal stress distribution, and fatigue longevity. Enhanced cutting speed resulted in smoother surfaces, whereas increased cut depth intensified surface roughness. Optimal cutting at 60,000 mm/min and 40 μm depth yielded a notable 91% rise in compressive stress (207 MPa) compared to slower speeds (108 MPa at 30,000 mm/min). Yield strength remained stable at 700 MPa across conditions. Fatigue resistance improved post‐bi‐directional cutting, with a 21.8–26.6% boost in life cycles, highlighting a consistent 10% advantage over single‐direction cutting.

Diffusion coefficients and atomic mobilities in the BCC phase of the Al–Nb–V system

Diffusion coefficients in the BCC phase of the Al–Nb–V ternary system are studied for the first time, including an assessment of the atomic mobilities. Ternary interdiffusion coefficients are obtained from the intersecting diffusion paths of several sets of diffusion couples that are annealed at both 1100 °C and 1200 °C. Existing experimental data from the pertinent binary systems are also employed for the assessments of atomic mobilities using the 1-parameter Z-Z-Z binary diffusion coefficient model developed by Zhong et al [1]. Interdiffusion coefficients in the BCC region of the Al–V system are also extracted through a forward-simulation analysis and incorporated into the mobility modeling. A complete description of diffusion in the BCC phase of the Al–Nb–V system is presented following the Binary and Cross-Binary Parameters Only (BCBPO) model developed by Zhong and Zhao [2]. Our data will be valuable input to diffusion-related simulation of refractory high entropy alloys containing aluminum.

Distinguishing Elements at the Sub-Nanometer Scale on the Surface of a High Entropy Alloy.

Materials in crystalline form possess translational symmetry (TS) when the unit cell is repeated in real space with long- and short-range orders. The periodic potential in the crystal regulates the electron wave function and results in unique band structures, which further define the physical properties of the materials. Amorphous materials lack TS due to the randomization of distances and arrangements between atoms, causing the electron wave function to lack a well-defined momentum. High entropy materials provide another way to break the TS by randomizing the potential strength at periodic atomic sites. The local elemental distribution has a great impact on physical properties in high entropy materials. It is critical to distinguish elements at the sub-nanometer scale to uncover the correlations between the elemental distribution and the material properties. Here, the use of synchrotron X-ray scanning tunneling microscopy (SX-STM) with sub-nm scale resolution in identifying elements on a high entropy alloy (HEA) surface is demonstrated. By examining the elementally sensitive X-ray absorption spectra with an STM tip to enhance the spatial resolution, the elemental distribution on an HEA's surface at a sub-nm scale is extracted. These results open a pathway towardsquantitativelyunderstanding high entropy materials and their material properties.

Microstructure Evolution and Enhanced Wear Resistance of Al2CrFeNiMo High Entropy Alloy Coating Fabricated by Laser Cladding

Microstructure Evolution and Enhanced Wear Resistance of Al2CrFeNiMo High Entropy Alloy Coating Fabricated by Laser Cladding

Cooling Curves of Concentrated Alloys, Steelmaking Slag, and Lithium Iron Phosphate

AbstractOver the past few years, a variety of melting casting projects have been performed, in collaboration with industries and universities. Concentrated alloys and nonmetallic compounds were studied including high-Si cast iron, high-Mn steel, Al-added stainless steel, high-entropy alloy, Permalloy 80 Ni alloy, Stellite Co alloy, steelmaking slag, and lithium iron phosphate (LFP). A melt synthesis of LFP was developed. Cooling curves were measured using the thermal analysis cup method and differential thermal analysis. In addition, the phase diagrams of alloys were calculated using Thermo-Calc. This paper draws on some examples of the measured cooling curves to illustrate the thermal behaviors of melts, along with a quick review of each project.

Effect of Copper and Silicon on the Corrosion Properties of the AlCrFeMnNi High Entropy Alloy

Effect of Copper and Silicon on the Corrosion Properties of the AlCrFeMnNi High Entropy Alloy

In-situ EBSD investigation of excellent strength-ductility synergy mechanism achieved by thermal-mechanical processing of Al0·25FeCoNiV high-entropy alloy

The development of high-entropy alloys (HEAs) is plagued by a trade-off between strength and ductility. In this study, we investigated the effects of different cold rolling ratios and subsequent heat treatments on the microstructures and mechanical properties of the Al0·25FeCoNiV HEA. An efficient and economical thermal-mechanical processing route was successfully explored to prepare multiscale, multiphase heterogeneous structures consisting of heterogeneous grain structures and duplex structures. Yield strength, ultimate tensile strength, and fracture elongation of 1277.3 MPa, 1633.6 MPa, and 26.4 %, respectively, could be achieved. The strength-ductility trade-off was avoided. Detailed information on the evolution of grain boundary distribution, grain orientation changes, and grain rotation under stress and strain fields were obtained with in-situ electron backscatter diffraction (EBSD) tensile tests. The mechanism of coordinated plastic deformation and the intrinsic mechanism of excellent strength and ductility were investigated by quantitatively calculating the activation of the slip system, slip transfer at the phase boundaries, and grain rotation paths. It was found that the excellent mechanical properties can be attributed to multistage hetero-deformation-induced (HDI) strengthening and strain-hardening coupling mechanisms. In this study, an effective method for designing novel HEAs with excellent strength-ductility combinations and an analytical method based on in-situ tests are proposed.

Computational insights into gas atomization of FeCoNiCrMoBSi high-entropy alloy: From droplet formation to rapid solidification

The intricate processes governing the gas atomization of molten metal droplets and their subsequent solidification hold paramount significance in materials science. Computational fluid dynamics simulations have emerged as indispensable tools for unraveling the complexities inherent in metal melt atomization. This study employed the volume of fluid method and the shear-stress transport k-ω turbulence model to simulate the primary atomization process of a FeCoNiCrMoBSi high-entropy alloy. Subsequently, the discrete phase model and Taylor analogy breakup model, based on the gas Weber number and incorporating primary atomization outcomes as initial conditions, were utilized to simulate droplet formation during the secondary atomization process. Analysis of the particle size distribution at the outlet of the geometric model demonstrated excellent agreement with experimental data for gas-atomized FeCoNiCrMoBSi high-entropy alloy powder. Furthermore, comprehensive characterization analyses were conducted to probe the phase constitution and structure of FeCoNiCrMoBSi powder produced by gas atomization. The results revealed that, irrespective of particle size, the powder exhibited a face-centered cubic structure and distinctive eutectic microstructural characteristics. The numerical simulation provided insights into the solidification process of secondary droplets by integrating inverse pole figure data for gas-atomized powder across varying particle sizes. The estimated cooling rate of secondary droplets ranged from 1.22 × 104 K/s to 2.64 × 105 K/s. These findings significantly advance the understanding of the gas atomization mechanism of the FeCoNiCrMoBSi high-entropy alloy, paving the way for the development of more efficient manufacturing processes for advanced materials.

The Effect of Laser Remelting during SLM on Microstructure and Mechanical Properties of CoCrFeNiNb0.25.

A sub-eutectic high-entropy alloy composed of CoCrFeNiNb0.25 was prepared using a combination of mechanical powder mixing and selective laser melting (SLM). The mechanical properties of the alloy were enhanced by employing an interlayer laser remelting process. This study demonstrates the feasibility of using mechanical mixing and SLM to form an CoCrFeNiNb0.25 alloy. The interlayer laser remelting process can effectively promote the melting of Nb particles introduced by mechanical mixing, release the stresses near the unfused Nb particles, and reduce their degradation of the specimen properties. The results indicate that the CoCrFeNiNb0.25 alloy, prepared using the interlayer laser remelting process, had an average microhardness of 376 HV, a tensile strength of 974 MPa, and an elongation at break of 10.51%. This process offers a viable approach for rapidly adjusting the composition of high-entropy alloys for SLM forming.

Self-Encapsulation of High-Entropy Alloy Nanoparticles inside Carbonized Wood for Highly Durable Electrocatalysis.

High-entropy alloy nanoparticles (HEAs) show great potential in emerging electrocatalysis due to their combination and optimization of multiple elements. However, synthesized HEAs often exhibit a weak interface with the conductive substrate, hindering their applications in long-term catalysis and energy conversion. Herein, a highly active and durable electrocatalyst composed of quinary HEAs (PtNiCoFeCu) encapsulated inside the activated carbonized wood (ACW) is reported. The self-encapsulation of HEAs is achieved during Joule heating synthesis (2060 K, 2 s) where HEAs naturally nucleate at the defect sites. In the meantime, HEAs catalyze the deposition of mobile carbon atoms to form a protective few-layer carbon shell during the rapid quenching process, thus remarkably strengthening the interface stability between HEAs and ACW. As a result, the HEAs@ACW shows not only favorable activity with an overpotential of 7mV at 10mA cm-2 for hydrogen evolution but also negligible attenuation during a 500 h stability test, which is superior to most reported electrocatalysts. The design of self-encapsulated HEAs inside ACW provides a critical strategy to enhance both activity and stability, which is also applicable to many other energy conversion technologies.

Laser Powder Bed Fusion Processing of Low Cost CoCrFeNiMoxNby High Entropy Alloys with Promising High-Temperature Properties via In Situ Alloying Commercial Powders

A blend of only commercial powders, including Ni625, CoCrF75, and 316L, were used as the raw material for fabricating non-equiatomic CoCrFeNiMoxNby high entropy alloys (HEAs) through laser powder bed fusion (PBF-LB/M) via in situ alloying, instead of using pure elemental powders, thus reducing the raw materials cost. The rapid cooling inherent in the PBF-LB/M process facilitated the dissolution of Mo and Nb, resulting in a single FCC phase characterized by high relative densities. High-temperature tensile tests were conducted at room temperature, 700 °C, 800 °C, and 900 °C, revealing mechanical properties that surpassed those reported in existing HEA literature. The remarkable strength of the HEAs developed in this study primarily stemmed from the incorporation of Mo and Nb, leading to the precipitation of Mo and Nb-rich lave phases at elevated temperatures. While constraining elongation when confined to grain boundaries, these precipitates enhanced strength without compromising elongation when distributed throughout the matrix. This work is a feasibility study to explore the usage of commodity compositions from the market to develop HEAs using PBF-LB/M, which opens the possibility of using scraps to further the development of new materials. Consequently, this study presents a rapid and cost-effective approach for HEA development, improving efficiency and sidestepping the direct utilization of critical raw metals for sustainable manufacturing. Moreover, this work also underscores the outstanding mechanical performance of these HEAs at high temperatures, paving the way for the design of innovative alloys for future high-temperature applications.