High Entropy Research Articles

Advancements in machine learning for predicting phases in high-entropy alloys: a comprehensive review

High entropy alloys (HEAs) are distinguished by their enhanced physicochemical properties, attributed to the formation of various phases such as solid solution (SS), intermetallic (IM), or a combination (SS + IM). These phases contribute distinctively to the microstructure of the alloys. A critical aspect of alloy design revolves around accurately predicting these phases, which has led to the integration of sophisticated data vetting methods and Machine Learning (ML) algorithms in recent research. This review paper aims to provide a comprehensive analysis of the advancements in phase prediction accuracy within HEAs, an essential component in the development of these alloys. HEAs are known for their intricate compositions, offering a wide spectrum of material properties, making them particularly relevant for applications aimed at future sustainability. Phase engineering in HEAs unlocks the potential for creating materials tailored to eco-friendly technologies and energy-efficient solutions. The challenge in predicting phase selection in HEAs is accentuated by the limited data available on these complex materials. This review delves into how advanced data vetting techniques and ML algorithms are being employed to overcome these challenges, thus contributing significantly to sustainable material design. The paper examines various algorithms used in HEA phase prediction, including KNN (K-Nearest Neighbors), SVM (Support Vector Machines), ANN (Artificial Neural Networks), GNB (Gaussian Naive Bayes), and RF (Random Forest). It discusses the testing accuracy of these algorithms in classifying HEA phases, revealing variations in their effectiveness. The review highlights the superior accuracy of ANNs, followed closely by KNN and SVM, while noting the comparatively lower accuracy of GNB. This comprehensive review synthesizes current research efforts in utilizing computational methods to design HEAs, underlining their broader implications in expediting the discovery and development of diverse metal alloys. These efforts are pivotal in meeting the evolving demands of modern engineering applications, thereby contributing to the advancement of materials science.

Multiscale chromatin dynamics and high entropy in plant iPSC ancestors.

Plant protoplasts provide a starting material to induce pluripotent cell masses in vitro competent for tissue regeneration. Dedifferentiation is associated with large-scale chromatin reorganisation and massive transcriptome reprogramming, characterized by stochastic gene expression. How this cellular variability reflects on chromatin organisation in individual cells and what are the factors influencing chromatin transitions during culturing is largely unknown. High-throughput imaging and a custom, supervised image analysis protocol extracting over 100 chromatin features unravelled a rapid, multiscale dynamics of chromatin patterns which trajectory strongly depends on nutrients availability. Decreased abundance in H1 (linker histones) is hallmark of chromatin transitions. We measured a high heterogeneity of chromatin patterns indicating an intrinsic entropy as hallmark of the initial cultures. We further measured an entropy decline over time, and an antagonistic influence by external and intrinsic factors, such as phytohormones and epigenetic modifiers, respectively. Collectively, our study benchmarks an approach to understand the variability and evolution of chromatin patterns underlying plant cell reprogramming in vitro.

Microstructure Evolution and Strengthening Mechanism of AlCrFe2NiCuMox High Entropy Alloys

Microstructure Evolution and Strengthening Mechanism of AlCrFe2NiCuMox High Entropy Alloys

Quantifying Actinide HEA Superconducting Secrets: A Compositional Odyssey

The superconductivity in the actinide-based high entropy alloy superconductor (AHEASC) (TaNb)x(TiUHf)[Formula: see text] is studied in the framework of Bardeen–Cooper–Schrieffer (BCS) theory, and McMillan’s formalism has been studied for the investigation of superconducting state (SC) parameters, viz., Coulomb pseudopotential [Formula: see text], electron–phonon coupling strength [Formula: see text], SC transition temperature [Formula: see text], interaction strength [Formula: see text], band gap [Formula: see text], energy or mass renormalization parameter [Formula: see text], and isotope effect exponent [Formula: see text]. BCS theory in conjunction with McMillan’s formalism has been used for the investigation. The study indicates a strong correlation between the electron–phonon interaction, and the superconducting properties of the high entropy alloy (TaNb)x(TiUHf)[Formula: see text] are highly dependent on its composition. An abrupt change in the isotope effect exponent suggests the presence of additional mechanisms such as magnetic interactions, spin fluctuations, or strong electron correlations.

Overcoming strength-ductility tradeoff with high pressure thermal treatment

Conventional material processing approaches often achieve strengthening of materials at the cost of reduced ductility. Here, we show that high-pressure and high-temperature (HPHT) treatment can help overcome the strength-ductility trade-off in structural materials. We report an initially strong-yet-brittle eutectic high entropy alloy simultaneously doubling its strength to 1150 MPa and its tensile ductility to 36% after the HPHT treatment. Such strength-ductility synergy is attributed to the HPHT-induced formation of a hierarchically patterned microstructure with coherent interfaces, which promotes multiple deformation mechanisms, including dislocations, stacking faults, microbands and deformation twins, at multiple length scales. More importantly, the HPHT-induced microstructure helps relieve stress concentration at the interfaces, thereby arresting interfacial cracking commonly observed in traditional eutectic high entropy alloys. These findings suggest a new direction of research in employing HPHT techniques to help develop next generation structural materials.

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.

High-entropy carbide (ZrNbTiCrV)C ceramic composite coating possessing good mechanical properties and wear resistance

High entropy carbide ceramics possess high hardness but suffer from low toughness and densification challenges. A dense (ZrNbTiCrV)C composite coating was fabricated through spraying ZrO2-Nb2O5-TiO2-Cr2O3-V2O5-Al-SiC powders, which was subsequently compared to a (ZrNbTiCrV)C coating produced from binary carbides. Incorporating the V element facilitated the densification and element diffusion. The coating obtained via spraying ZrO2-Nb2O5-TiO2-Cr2O3-V2O5-Al-SiC powders exhibited superior mechanical properties and wear resistance, particularly achieving a 17.2 % increase in fracture toughness and a 73.3 % reduction in wear rate compared to the coating derived from binary carbides. These improved properties were attributed to fine-grained particles and a low porosity of 1.56 %. Wear resistance was also enhanced through rolling friction and the formation of a protective oxide film.

Thermal and electrical properties of single‐phase high entropy carbide ceramics

AbstractThermal and electrical properties were investigated for five nominally phase‐pure high entropy carbide ceramics. The compositions (Hf0.2Nb0.2Ta0.2Ti0.2Zr0.2)C, (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C, (Hf0.2Ta0.2Ti0.2W0.2Zr0.2)C, and (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C were synthesized by carbothermal reduction of oxides. The thermal diffusivity and heat capacity were measured from room temperature to 1800°C. The room temperature thermal conductivity ranged from 5.1 W/mK for (Hf0.2Mo0.2Ti0.2W0.2Zr0.2)C to 9.0 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C. The thermal conductivity increased over the temperature range with maximum conductivities of 19.6 W/mK measured for (Hf0.2Mo0.2Ta0.2Ti0.2Zr0.2)C to 29.7 W/mK for (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)C at 1800°C. The electron contribution to thermal conductivity calculated from measured electrical resistivity varied from 41% to 52% of the total thermal conductivity. The tungsten and molybdenum containing compositions had higher phonon contributions while the niobium and chromium containing compositions had nearly equal electron and phonon contributions to thermal conductivity.

Nanostructured High Entropy Alloys as Structural and Functional Materials.

Since their introduction in 2004, high entropy alloys (HEAs) have attracted significant attention due to their exceptional mechanical and functional properties. Advances in our understanding of atomic-scale ordering and phase formation in HEAs have facilitated the development of fabrication techniques for synthesizing nanostructured HEAs. These materials hold immense potential for applications in various fields including automobile industries, aerospace engineering, microelectronics, and clean energy, where they serve as either structural or functional materials. In this comprehensive Review, we conduct an in-depth analysis of the mechanical and functional properties of nanostructured HEAs, with a particular emphasis on the roles of different nanostructures in modulating these properties. To begin, we explore the intrinsic and extrinsic factors that influence the formation and stability of nanostructures in HEAs. Subsequently, we delve into an examination of the mechanical and electrocatalytic properties exhibited by bulk or three-dimensional (3D) nanostructured HEAs, as well as nanosized HEAs in the form of zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, or two-dimensional (2D) nanosheets. Finally, we present an outlook on the current research landscape, highlighting the challenges and opportunities associated with nanostructure design and the understanding of structure-property relationships in nanostructured HEAs.

Wear performance of FeCuMoTiV high entropy alloy coatings by laser cladding

FeCuMoTiV high-entropy alloy coatings were prepared on the surface of aluminum matrix composites using the laser cladding technique. The physical phase composition of the coating, the hardness of each physical phase, and the friction and wear behavior of the coating were studied in detail. The results show that: From the XRD and TEM analysis, the coating’s physical phases, BCC1(MoV) and BCC2(TiFe), are coherent. From the EBSD analysis, the grains of the coating have no obvious selective orientation, and the average equivalent circle diameter is 26.44 μm. Nanomechanical tests showed that the average hardness of the BCC1 phase in the coating was 7831.2 N mm−2, which provided the coating with excellent abrasion resistance. The average coefficient of friction of the coating showed a tendency to decrease and then increase with the increase of time, and it floated in the range of 0.3 ± 0.05. The coating forms a structure containing Fe2O3, MoO3, CuO, and TiO2 mixed oxide ‘glaze layer’ on the wear surface, which provides good lubrication. Combined with SEM analysis, the wear mechanism of the coating is a mixture of abrasive wear, oxidative wear, adhesive wear, and fatigue wear.

Slurry Jet Erosion Resistance of SS304 Reinforced with High Entropy Alloys through Friction Stir Processing

Slurry Jet Erosion Resistance of SS304 Reinforced with High Entropy Alloys through Friction Stir Processing

Non-precious high entropy alloys and highly alkali-resistant composite membranes based high performance anion exchange membrane water electrolyzers

Cost-effective highly efficient and stable catalysts and alkali-resistant anion exchange membranes (AEMs) are critical for practical applications of anion exchange membrane water electrolyzers (AEMWEs). Here, bifunctional non-precious FeCoNiCuMo high entropy alloys (HEAs), electrochemically deposited on nickel mesh as an anode (FeCoNiCuMo/NM) and on carbon paper as a cathode (FeCoNiCuMo/CP), together with a NiFe layered double hydroxide (LDH) loaded AEM (AEM/LDH), were developed for high performance AEMWEs. The AEMWE thus fabricated delivered an ultrahigh current density of 1777 mA cm−2 at 2 V and exhibited remarkable stability with a less than 0.1% cell voltage increase after a 100-hour operation at 100 mA cm−2 at 50 °C, largely outperforming those of the precious metal based AEMWE, composed of IrO2/NM as the anode and Pt/C/CP as the cathode, 1231 mA cm−2@2 V and 4.57% increase in cell voltages. Composition of the alkali-resistant, hydrophilic, and water electrolysis active NiFe LDH into the AEM improved not only the electrolyte uptake and operational stability, but also the efficiency of the AEMWE, with a 10% boost in current density achieved at 2 V and a reduction in cell voltage increases from 2.94% to 0.0951%. The present development demonstrates the practicality of AEMWEs toward green hydrogen production.

Enhancing sulfur resistance of oxides in carbon monoxide oxidation by a high‐entropy‐stabilized strategy

AbstractIndustrial chemical processes require sulfur‐resistant catalysts, which reduce catalyst replacement costs and simplify process operations. Herein, a high‐entropy‐stabilized strategy was put forward for sulfur‐resistant catalysis. A spinel high entropy (Zn0.2Mg0.2Cu0.2Mn0.2Co0.2Al2O4) was introduced by ball milling process with aluminum isopropoxide as the main precursor. Zn0.2Mg0.2Cu0.2Mn0.2Co0.2Al2O4 possessed a high surface area of 171.2 m2 g−1, higher than typical high‐entropy oxides (HEOs). The high‐entropy spinel catalyst exhibited better SO2‐resistance performance in the oxidation of carbon monoxide, better than the simple oxides. The SO2‐resistance of Zn0.2Mg0.2Cu0.2Mn0.2Co0.2Al2O4 was primarily improved by reinforcing the stability of the oxide using a high‐entropy structure to decrease the absorption of SO2 on its surface. Any adsorbed SO2 on the surface of the HEO was then selectively trapped by sacrificial metal ions with stronger electron‐withdrawing ability, protecting the active center (Cu2+, Co2+) from poisoning. This work reveals the significance of high‐entropy structures in sulfur resistance.

Effect of Nb-content on the corrosion resistance of Co-free high entropy alloys in chloride environment

Effect of Nb-content on the corrosion resistance of Co-free high entropy alloys in chloride environment

Revealing the inhomogeneous nature of microstructure and texture evolution in the cold-rolled CoCrFeMnNi alloy during static recrystallization

In the present investigation, equiatomic CoCrFeMnNi high entropy alloy (HEA) was subjected to 80% cold rolling (as-rolled) followed by isothermal annealing treatment at 700 °C for different time periods. Microstructural characterization was performed using electron back-scattered diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques on the as-rolled and annealed samples. The as-rolled microstructure consisted of elongated grains mainly composed of strong α-fiber and weak γ-fiber textures. The as-rolled sample showed the formation of ingrain SBs in the γ-fiber grains, which served as preferential sites for grain nucleation. The annealing treatment of as-rolled samples at 700 °C cause static recovery (SRV) before 5 minutes of heat-treatment, whereas static recrystallization (SRX) was observed after 5 minutes of heat-treatment in the CoCrFeMnNi alloy samples. A faster rate of recrystallization kinetics was observed after 15 minutes of heat-treatment. The annealing treatment reduced the intensity of α-fiber and enhanced the Copper, Cube and P ({011}<122>) texture components. Copper components originated from coarse recrystallized grains, which were the results of localized grain growth phenomena. Unusual behavior of banded featured α-fiber grains was observed during the annealing process. These banded grains in the partially annealed samples consisted of subgrain-boundaries and showed a delayed response to recrystallization as compared to grains with other orientations. Stored energy (SE) and Taylor factor (M) calculations were also used to understand the delayed recrystallization response of the banded featured/retained deformed grains. The microhardness value of the as-rolled sample was approximately 450 Hv, which decreased to around 230 Hv for the fully recrystallized grains.

A novel L12-strengthened single crystal high entropy alloy with excellent high-temperature mechanical properties

In this work, a novel and low-cost L12-strengthened single crystal high entropy alloy (HEA) was prepared through the seeding method of directional solidification. The microstructures, tensile properties and deformation mechanisms of the single crystal HEA were systematically investigated. The volume fraction of L12 precipitates after heat treatment was almost 80%, which was higher than that of conventional single crystal superalloys. The maximum yield strength, ultimate tensile strength and elongation, which were separately as 897 MPa, 1038 MPa and 37%, were obtained at the intermediate temperature of 800 °C. Moreover, at higher temperature (900 °C and 1000 °C), the HEA was able to maintain excellent performance, which was comparable to the commercial René N5 second-generation Ni-based single crystal superalloy. Finally, the high performance was examined by the model of strengthening contribution, which proved that the high-volume fraction of L12 precipitates in single crystal HEA was the primary reason for their significant precipitation and solid solution strengthening. Additionally, the formation of Lomer-Cottrell locks and stacking faults could enhance the high-temperature properties of the single crystal HEA.

Microstructural study on in-situ high-entropy (NbMoTaWV)C reinforced nanocrystalline NbMoTaWVC refractory high entropy alloys prepared by mechanically alloying

Refractory high-entropy alloys (RHEAs) can be commonly regarded as the best candidates for potentially substituting for the nickel-based superalloys practically used in the areas of aviation and nuclear industry, which can significantly endure in high-temperature and harsh environment. In this work, a nanocrystalline NbMoTaWVC RHEA is successfully produced by mechanical alloying method and X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and spherical aberration corrected transmission electron microscopy (AC-TEM) are employed to systematically characterized the microstructural details of NbMoTaWV and NbMoTaWVC RHEAs mechanically alloyed powders. Our results can support the evidence that the observable minimum nanoparticle sizes of the NbMoTaWV and NbMoTaWVC RHEAs considerably decrease to approximately ∼100 nm. Furthermore, the average grain sizes are gradually refined and thus notably drop to around of 30–50 nm, and five elemental powders can be found to be homogeneously alloyed. The evidence can be confirmed that the order of solid solution may be proposed as follows: Nb → Mo → V → Ta → W. The chemical short-range order occurred at the local nanoscale of NbMoTaWV and NbMoTaWVC RHEAs. Meanwhile, further microstrutural analysis can demonstrate that NbMoTaWV and NbMoTaWVC RHEAs powders with ultrafined grain have a bcc phase structure and bcc + bct matrix phases combined with high-entropy tungsten carbides (NbMoTaWV)C and (NbMoTaWV)2C of nano-precipitated phases, respectively, suggesting that the martensitic transformation probably occurred. The NbMoTaWV and NbMoTaWVC RHEAs powders of locally crystal lattice distortion rates reached approximately 8.07% and 6.33%.

Achieving a Deeply Desodiated Stabilized Cathode Material by the High Entropy Strategy for Sodium-ion Batteries.

Manganese-based layered oxides are currently of significant interest as cathode materials for sodium-ion batteries due to their low toxicity and high specific capacity. However, the practical applications are impeded by sluggish intrinsic Na+ migration and poor structure stability as a result of Jahn-Teller distortion and complicated phase transition. In this study, a high-entropy strategy is proposed to enhance the high-voltage capacity and cycling stability. The designed P2-Na0.67Mn0.6Cu0.08Ni0.09Fe0.18Ti0.05O2 achieves a deeply desodiation and delivers charging capacity of 158.1 mA h g-1 corresponding to 0.61 Na with a high initial Coulombic efficiency of 98.2%. The charge compensation is attributed to the cationic and anionic redox reactions conjunctively. Moreover, the crystal structure is effectively stabilized, leading to a slight variation of lattice parameters. This research carries implications for the expedited development of low-cost, high-energy-density cathode materials for sodium-ion batteries.

Achieving a Deeply Desodiated Stabilized Cathode Material by the High Entropy Strategy for Sodium‐ion Batteries

Manganese‐based layered oxides are currently of significant interest as cathode materials for sodium‐ion batteries due to their low toxicity and high specific capacity. However, the practical applications are impeded by sluggish intrinsic Na+ migration and poor structure stability as a result of Jahn‐Teller distortion and complicated phase transition. In this study, a high‐entropy strategy is proposed to enhance the high‐voltage capacity and cycling stability. The designed P2‐Na0.67Mn0.6Cu0.08Ni0.09Fe0.18Ti0.05O2 achieves a deeply desodiation and delivers charging capacity of 158.1 mA h g‐1 corresponding to 0.61 Na with a high initial Coulombic efficiency of 98.2%. The charge compensation is attributed to the cationic and anionic redox reactions conjunctively. Moreover, the crystal structure is effectively stabilized, leading to a slight variation of lattice parameters. This research carries implications for the expedited development of low‐cost, high‐energy‐density cathode materials for sodium‐ion batteries.

Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content

Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content