High-entropy Alloys Research Articles

TiZrHfNb refractory high-entropy alloys with twinning-induced plasticity

The twinning-induced plasticity (TWIP) effect has been widely utilized in austenite steels, β-Ti alloys, and recently developed face-centered-cubic (FCC) high-entropy alloys (HEAs) to simultaneously enhance the tensile strength and ductility. In this study, for the first time, the TWIP effect through hierarchical {332<113> mechanical twinning has been successfully engineered into the TiZrHfNb refractory HEAs by decreasing temperature and tailoring the content of Nb to destabilize the BCC phase. At cryogenic temperature, the comprehensive hierarchical {332}<113> mechanical twins are activated in TiZrHfNb0.5 alloy from micro- to nanoscale and progressively segment the BCC grains into nano-scale islands during deformation, ensuring sustainable strain hardening capability and eventually achieving a substantial 35% uniform tensile elongation. In addition, at 77 K, the tensile strength and uniform elongation of TiZrHfNbx alloys can further be adjusted by a moderate increase of Nb. The results above shed new light on the development of high-performance refractory HEAs with a high and adjustable strength and ductility combination down to the cryogenic temperature.

Microstructure evolution and performance of TiMoCrWxTay refractory high-entropy alloy coatings prepared using laser cladding

Refractory high entropy alloy (RHEA) coatings containing W and Ta elements at the same time usually have excellent performance at high temperature, which are promising candidate materials for high temperature protective coating materials. In this work, the effects of W and Ta on the microstructure and performance evolution of TiMoCrWxTay RHEA coatings have been investigated. Experimentally, TiMoCrWxTay coatings are mainly composed of BCC phase, Laves phase and Ti-rich phase, with W and Ta atoms preferably dissolved in BCC phase. The W atoms promote the formation of dendrites and the growth of rod-like and equiaxed crystals and the Ta atoms promote the formation of cellular crystals and produce the effect of fine crystal strengthening. W and Ta atoms have significant influence on the tribological properties of TiMoCrWxTay coatings. The tribological properties of TiMoCrWxTay coatings at 800 °C are better than those at room temperature. TiMoCrWxTay RHEA coatings follow near-linear oxidation kinetics during the oxidation of 50 h at 800 °C.The oxidation resistance of the coatings first increases and then decreases with the increase of Ta content. Ta2O5, TiO2 and other oxides may have a shielding effect on the oxidation of W. In particular, The W0.3Ta0.5 shows the best tribological properties and oxidation resistance, and the mass gain of W0.3Ta0.5 is only 13.4 mg/cm2 after the oxidation test for 50 h. It indicates that TiMoCrWxTay coatings can obtain good high temperature performance by optimizing the content of W and Ta in RHEA coatings. This work can provide guidance for the research and application of TiMoCrWxTay RHEA coatings.

Different TBS and Grain Numbers on Mechanical Behavior of FeNiCrCoCu High-Entropy Alloys: A Molecular Dynamics Simulation

High-entropy alloy (HEA) is a type of alloy that exhibits high hardness, strength, good wear resistance, corrosion resistance, and versatility. Molecular dynamics simulations were conducted to illustrate the microscopic evolution of FeNiCrCoCu HEAs under varying twin boundary spacing (TBS). Compression revealed dislocation migration, variations in the quantity and radius of nanovoids, as well as grain boundary diffusion. With increasing strain, high-energy regions expand on the surface of the crystal, transitioning from an initially smooth state to uniform deformation accompanied by grain boundary diffusion, while dislocations occur within the crystal. The number and radius of observed nanovoids within the crystal increase. The mechanical characteristics of FeNiCrCoCu HEAs are influenced by the TBS size. The alloy demonstrates better mechanical properties when the TBS is 1.22[Formula: see text]nm. FeNiCrCoCu HEAs with a constant TBS showed improved mechanical characteristics when a greater number of grains ([Formula: see text]) were present.

Atomic insight into nanoindentation response of nanotwinned FeCoCrNiCu high entropy alloys

FeCoCrNiCu high-entropy alloys (HEAs) exhibit extraordinary mechanical properties and have the capability to withstand extreme temperatures and pressures. Their exceptional attributes make them suitable for diverse applications, from aerospace to chemical industry. We employ atomic-scale simulations to explore the effects of twinning boundary and twinning thickness on the mechanical behavior of nanotwinned FeCoCrNiCu during nanoindentation. The findings suggest that as the twinning thickness decreases within the range of 19.3–28.9 Å, both twinning partial slips (TPSs) and horizontal TPSs gradually become dominant in governing the plastic behaviors of the nanotwinned FeCoCrNiCu, thereby resulting in an inverse Hall–Petch effect. Remarkably, when the twinning thickness is compressed below 19.3 Å, a shift in the plastic deformation mechanism emerges, triggering the conventional Hall–Petch relation. The observed Hall–Petch behavior in nanotwinned FeCoCrNiCu is attributed to the strengthening effect imparted by the twinning boundaries. Consequently, the twinning boundary play an instrumental role in steering the plastic deformation mechanism of the nanotwinned FeCoCrNiCu when the twinning thickness descends beneath 19.3 Å. This study contributes significant insights towards the design of next-generation high-performance HEAs, underpinning their potential industrial utilization.

Lattice-Disordered High-Entropy Alloy Engineered by Thermal Dezincification for Improved Catalytic Hydrogen Evolution Reaction.

A disordered crystal structure is an asymmetrical atomic lattice resulting from the missing atoms (vacancies) or the lattice misarrangement in a solid-state material. It has been widely proven to improve the electrocatalytic hydrogen evolution reaction (HER) process. In the present work, due to the special physical properties (the low evaporation temperature of below 900 °C), Zn is utilized as a sacrificial component to create senary PtIrNiCoFeZn high-entropy alloy (HEA) with highly disordered lattices. The structure of the lattice-disordered PtIrNiCoFeZn HEA is characterized by the thermal diffusion scattering (TDS) in TEM. Density functional theory (DFT) calculations reveal that lattice disorder not only accelerates both the Volmer step and Tafel step during the HER process but also optimizes the intensity and distribution of projected density of states (PDOS) near the Fermi energy after the H2O and H adsorption. Anomalously high alkaline HER activity and stability are proven by experimental measurements. This work introduces a novel approach to preparing irregular lattices offering highly efficient HEA and a TDS characterization method to reveal the disordered lattice in materials. It provides a new route towards exploring and developing the catalytic activities of materials with asymmetrically disordered lattices. This article is protected by copyright. All rights reserved.

High-entropy alloy electrocatalysts go to (sub-)nanoscale.

Alloying has proven power to upgrade metallic electrocatalysts, while the traditional alloys encounter limitation for optimizing electronic structures of surface metallic sites in a continuous manner. High-entropy alloys (HEAs) overcome this limitation by manageably tuning the adsorption/desorption energies of reaction intermediates. Recently, the marriage of nanotechnology and HEAs has made considerable progresses for renewable energy technologies, showing two important trends of size diminishment and multidimensionality. This review is dedicated to summarizing recent advances of HEAs that are rationally designed for energy electrocatalysis. We first explain the advantages of HEAs as electrocatalysts from three aspects: high entropy, nanometer, and multidimension. Then, several structural regulation methods are proposed to promote the electrocatalysis of HEAs, involving the thermodynamically nonequilibrium synthesis, regulating the (sub-)nanosize and anisotropic morphologies, as well as engineering the atomic ordering. The general relationship between the electronic structures and electrocatalytic properties of HEAs is further discussed. Finally, we outline remaining challenges of this field, aiming to inspire more sophisticated HEA-based nanocatalysts.

Oxidation resistance and hardness of high entropy alloy composite coating Al70(Cr-Fe-Ni)(30-X)(SiC)X prepared on AISI 1018 substrate by mechanical alloying

ABSTRACT We successfully coated low carbon steel with high entropy alloy (HEA) composite coating Al70(Cr-Fe-Ni)(30-x)(SiC)x to increase its oxidation resistance. The coating was applied using mechanical alloying (MA), and the phase and microstructure, including hardness, were characterised thoroughly. All samples covered the substrate with a thickness of the coating layer ranging from 103.637 ± 10.5 to 222.751 ± 8.5 μm. The sample with 10 at.% of SiC gave optimal results with a better coating layer thickness, fewer nodules formed, the lowest weight gain value, the best oxidation rate constant, and the ability to produce a larger thickness of Al2O3.

Microstructure Evolution and Wear Mechanism of Si-Effected Al0.6CoCrFeNi High-Entropy Alloy Coatings by Laser Cladding

Microstructure Evolution and Wear Mechanism of Si-Effected Al0.6CoCrFeNi High-Entropy Alloy Coatings by Laser Cladding

Development of Ti–V–Cr–Mn–Mo–Ce high-entropy alloys for high-density hydrogen storage in water bath environments

Development of Ti–V–Cr–Mn–Mo–Ce high-entropy alloys for high-density hydrogen storage in water bath environments

Mechanical Properties and Hydrogen Embrittlement Resistance of the High‐Entropy Alloy CrFeMnNiCo and Its Subsystems

The effects of hydrogen on the mechanical properties of CrNiCo and CrFeNiCo medium‐entropy alloys (MEAs) and CrFeMnNiCo high‐entropy alloys (HEAs) are investigated. Although their total elongation is less than that of the commonly used stainless steel (SS) 316L (SS316L), the tensile strengths of HEAs and MEAs are 150–350 MPa higher than that of SS316L. Hydrogen charging up to 1400 appm (nominal concentration) does not affect the tensile strength of SS316L; however, it decreases the elongation by less than 20%. In contrast, hydrogen increases the tensile strength of MEAs and HEA, but has little effect on elongation. Among the MEAs and HEAs, CrNiCo exhibits the highest tensile strength and total elongation. No brittle fracture due to hydrogen is observed on the fracture surfaces of the H‐charged samples. However, nanotwin structures are more common in H‐charged MEAs and HEAs than in H‐uncharged MEAs and HEA. Additionally, the calculation results based on the first‐principles reveal for the first time that single vacancies or tiny vacancy clusters do not trap H in MEAs compared to HEAs, such that cracks due to H are unlikely to occur. Thus, the hydrogen embrittlement resistance of MEAs may be improved.

Accelerated Discovery of (TiZrHf)x(NbTa)1- x High-Entropy Alloys With Superior Thermal Stability and a New Crystallization Mechanism.

Nanocrystalline (nc) metals are generally strong yet thermally unstable, rendering them difficult to process and unsuitable for use, particularly at elevated temperatures. Nc multicomponent and high-entropy alloys (HEAs) are found to offer enhanced thermal stability but only in a few empirically discovered systems out of a vast compositional space. In response, this work develops a combinatorial strategy to accelerate the discovery of nc-(TiZrHf)x(NbTa)1- x alloy library with distinct thermal stability, in terms of phases and grain sizes. Based on synchrotron X-ray diffraction and electron microscopy characterizations, a phase transition is observed from amorphous-crystalline nanocomposites to a body-centered cubic (bcc) phase upon annealing. With increased NbTa content (decreased x value), the system tends to achieve thermally stable dual bcc phases upon annealing; in contrast, alloys with increased TiZrHf content (x > 0.6) maintain a single-composition nanocomposite state, impeding crystallization and grain growth. This investigation not only broadens the understanding of thermal stability but also delves into the onset of crystallization in HEA systems.

Sub-2 nm Microstrained High-Entropy-Alloy Nanoparticles Boost Hydrogen Electrocatalysis.

High-entropy alloys (HEAs) confine multifarious elements into the same lattice, leading to intense lattice distortion effect. The lattice distortion tends to induce local microstrain at atomic level and thus affect surface adsorptions toward different adsorbates in various electrocatalytic reactions, yet remains unexplored. Herein, this work reports a class of sub-2nm IrRuRhMoW HEA nanoparticles (NPs) with distinct local microstrain induced by lattice distortion for boosting alkaline hydrogen oxidation (HOR) and evolution reactions (HER). This work demonstrates that the distortion-rich HEA catalysts with optimized electronic structure can downshift the d-band center and generate uncoordinated oxygen sites to enhance the surface oxophilicity. As a result, the IrRuRhMoW HEA NPs show a remarkable HOR kinetic current density of 8.09mA µg-1 PGM at 50mV versus RHE, 8.89, 22.47 times higher than those of IrRuRh NPs without internal strain and commercial Pt/C, respectively, which is the best value among all the reported non-Pt based catalysts. IrRuRhMoW HEA NPs also display great HER performances with a turnover frequency (TOF) value of 5.93 H2 s-1 at 70mV versus RHE, 4.6-fold higher than that of Pt/C catalyst, exceeding most noble metal-based catalysts. Experimental characterizations and theoretical studies collectively confirm that weakened hydrogen (Had) and enhanced hydroxyl (OHad) adsorption are achieved by simultaneously modulating the hydrogen adsorption binding energy and surface oxophilicity originated from intensified ligand effect and microstrain effect over IrRuRhMoW HEA NPs, which guarantees the remarkable performances toward HOR/HER.

In-situ microstructural evolution during tensile loading of CoCrFeMnNi high entropy alloy welded joint probed by high energy synchrotron X-ray diffraction

The research regarding high entropy alloys (HEAs) has proved them to be suitable for engineering applications. Nevertheless, assessing their processability is key for industrial deployment. Of special relevance in terms of processing techniques arised welding. In this work, Gas Tungsten Arc Welding (GTAW) was chosen as a processing method to attest for the suitability of the equiatomic CoCrFeMnNi HEA for one of the most common real-world mechanical solicitations, tensile loading. We delve into an in-situ synchrotron X-ray diffraction analysis of the mechanical behavior of a high-performing GTAW CoCrFeMnNi HEA joint. Local analysis of the microstructure evolution, considering the base material, heat affected zone and fusion zone, was performed by tracking changes in the diffracted intensity and lattice strain. Orientation-dependent evolution is highlighted by considering partial azimuthal integration detailing texture impact across the joint. Evidence of strain concentration at specific locations is correlated with the microstructure and overall macroscopic mechanical behavior.

Convolutional neural network based methodology for flexible phase prediction of high entropy alloys

ABSTRACT The advent of high entropy alloys has created a design space that is unfeasible to explore solely through experimentation, thus necessitating the use of computational methods, such as artificial neural networks. This study proposes a new architecture utilizing a convolutional layer to extract relevant elemental features from the alloy composition without limiting the model to specific elements by treating the elemental composition of the high entropy alloy in a similar manner to a row of pixels, using relevant elemental properties in lieu of color values. This convolutional model was able to predict the crystal structure of solid solutions in a high entropy alloy composition with an accuracy of 89.3% in a six-way classification and the formation of intermetallics with an accuracy of 91.4% during holdout validation, while being capable of accurately predicting the primary crystal structure of high entropy alloys containing elements the model was not trained on. Significant space still exists for further experimentation and improvement with this methodology, including augmenting the available datasets and implementation of additional convolutional layers. Due to the limited interpretability of the model architecture, care should be taken when inferring trends from the model prior to validation through experimental, or well-established computational methods.

Influence of Zirconium on the Microstructure, Selected Mechanical Properties, and Corrosion Resistance of Ti20Ta20Nb20(HfMo)20-xZrx High-Entropy Alloys.

The presented work considers the influence of the hafnium and molybdenum to zirconium ratio of Ti20Ta20Nb20(HfMo)20-xZrx (where x = 0, 5, 10, 15, 20 at.%) high-entropy alloys in an as-cast state for potential biomedical applications. The current research continues with our previous results of hafnium's and molybdenum's influence on a similar chemical composition. In the presented study, the microstructure, selected mechanical properties, and corrosion resistance were investigated. The phase formation thermodynamical calculations were also applied to predict solid solution formation after solidification. The calculations predicted the presence of multi-phase, body-centred cubic phases, confirmed using X-ray diffraction and scanning electron microscopy. The chemical composition analysis showed the segregation of alloying elements. Microhardness measurements revealed a decrease in microhardness with increased zirconium content in the studied alloys. The corrosion resistance was determined in Ringer's solution to be higher than that of commercially applied biomaterials. The comparison of the obtained results with previously reported data is also presented and discussed in the presented study.

Prediction of the Cohesion Energy, Shear Modulus and Hardness of Single-Phase Metals and High-Entropy Alloys.

In order to facilitate the prediction of some physical properties, we propose several simple formulas based on two parameters only, the metallic valence and metallic atomic radii. Knowing the composition, for single-phase alloys, the average parameters can be calculated by the rule of mixture. The input parameters can be obtained from tabulated databases. Adopting from the literature the results of Coulomb crystal model for metals and single-phase high-entropy alloys, we have derived formulas for the shear modulus (G) and the cohesion energy (Ecoh). Based on these parameters separately, we set up two formulas to estimate the hardness in the case of pure metals. For single-phase (solid-solution) HEAs, by simplifying the Maresca and Curtin model, we obtained a formula for estimating the hardness, which takes into account the atomic misfit in addition to G. The maximal hardness for single-phase HEA is approximately 600 kg/mm2 and is obtained for a composition with a valence electron concentration of approximately 6 ÷ 7.

Microstructural development and mechanical behavior of a near-eutectic high entropy alloy Al1.8CrCuFeNi2 fabricated by hot isostatic pressing

In this study, a near-eutectic high entropy alloy Al1.8CrCuFeNi2 was processed by hot isostatic pressing (HIP). It is shown that the as-HIPed alloy demonstrates excellent formability and shows uniform and refined B2 grains. Large Cr0.7Fe0.3 precipitates were found at the grain boundaries while nano-sized Cu, Cu3Ni and Fe–Cr particles were uniformly distributed within the grain interior. The fine structure and various precipitates lead to high compressive strength of ∼1800 MPa and good hardness of ∼470 HV. B2 matrix and intergranular Cr0.7Fe0.3 deformed mainly via dislocation slipping while intragranular Fe–Cr particles showed complex interaction with dislocations to impede dislocation motion. Moreover, the Fe–Cr nano-precipitates also deformed with the formation of stacking faults, which may further enhance the alloy. The high strength could be due to the activation of multiple deformation and strengthening mechanisms and mainly attributed to the precipitate strengthening.

Obtaining high-entropy alloy coating by laser remelting of metal powder composition: mathematical modelling of the transient thermal state

Obtaining high-entropy alloy coating by laser remelting of metal powder composition: mathematical modelling of the transient thermal state

Interaction of C, N and O interstitial solute atoms with screw dislocations in HfNbTaTiZr high entropy alloy

Using density functional theory (DFT), we characterize the interaction of screw dislocations with interstitial impurities, in particular oxygen, nitrogen and carbon, in the HfNbTaTiZr alloy of body-centered cubic (BCC) structure. Considering different configurations representative of the disordered solid solution alloy, we evidence a noticeable core spreading of the screw dislocation whether with or without solute, associated with a wide range in dislocation-solute interaction energy, which is found to be mainly attractive for the three investigated impurities. This interaction energy is shown to be highly influenced by the type of the metal atoms in the neighbourhood of the solute. Notably the more BCC elements are present around the solute (either Nb or Ta), the more repulsive this interaction is.

Tailoring the Microstructure and Mechanical Properties of Ta-Alloyed AlCoCrFeNi High-Entropy Alloys

Tailoring the Microstructure and Mechanical Properties of Ta-Alloyed AlCoCrFeNi High-Entropy Alloys