Structure Of High-entropy Alloys Research Articles

A voting-based ensemble classifier to predict phases and crystal structures of high entropy alloys through thermodynamic, electronic, and configurational parameters

This study aims to predict the various phases present in high entropy alloys (HEAs) and consequently classify their crystal structure employing multiple machine learning (ML) algorithms utilizing five thermodynamic, electronic and configurational parameters which are considered to be essential for the formation of HEA phases. The properties of a high entropy alloy can eventually be traced through accurate phase and crystal structure prediction, which is essential for selecting the ideal elements for designs. Twelve distinct ML algorithms were executed to predict the phases of HEAs, adopting an experimental database of 322 different HEAs, involving 33 amorphous (AM), 31 intermetallics (IM), and 258 solid solutions (SS) phases. Among the twelve ML models, Cat Boost Classifier displayed the optimum accuracy of 98.06 % for phase predictions. Further, crystal structure classification of the SS phase (body-centered cubic- BCC, face-centered cubic- FCC, and mixed body-centered and face-centered cubic- BCC+FCC) has endeavoured for better microstructure evolution using a different database containing of 194 additional HEAs data with 61 FCC, 76 BCC, and 57 BCC+FCC crystal structures and in comparison to the other models tested, the Gradient Boosting Classifier evolved with the highest accuracy of 86.90 %. An ensemble classifier was also introduced to improve the performance of the ML models, resulting in an accuracy increase to 98.70 % and 86.95 % for phase and crystal structure predictions, respectively. Additionally, the influence of parameters on model accuracy was determined independently.

High-Entropy Alloys and Their Affinity with Hydrogen: From Cantor to Platinum Group Elements Alloys.

Properties of high-entropy alloys are currently in the spotlight due to their promising applications. One of the least investigated aspects is the affinity of these alloys to hydrogen, its diffusion, and reactions. In this study, high pressure is applied at ambient temperature and stress-induced diffusion of hydrogen is investigated into the structure of high-entropy alloys (HEA) including the famous Cantor alloy as well as less known, but nevertheless important platinum group (PGM) alloys. By applying X-ray diffraction to samples loaded into diamond anvil cells, a comparative investigation of transition element incorporating HEA alloys in Ne and H2 pressure-transmitting media is performed at ambient temperature. Even under stresses far exceeding conventional industrial processes, both Cantor and PGM alloys show exceptional resistance to hydride formation, on par with widely used industrial grade Cu-Be alloys. The observations inspire optimism for practical HEA applications in hydrogen-relevant industry and technology (e.g., coatings, etc), particularly those related to transport and storage.

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.

Improving the performance of machine learning model predicting phase and crystal structure of high entropy alloys by the synthetic minority oversampling technique

It is critical to select the suitable integration of elements that has an influence on phase formation when selecting the proper High Entropy Alloys (HEAs) with desired qualities. Machine Learning (ML) models were used to predict the phase and crystal structure of HEAs in this study. Trained on extensive experimental datasets, the set of input characteristics includes Atomic size difference, Mixing Enthalpy, Mixing Entropy, Valence Electron concentration, Electronegativity difference, Ω and Average Melting Temperature. The phase is divided into three categories: Solid solution (S), Dual phase (D), and Intermetallic (Im). Crystal structure classifications include BCC, FCC, and FCC+BCC. For phase and crystal structure prediction, five ML algorithms were used: Decision Tree (DT), K Nearest Neighbour (KNN), Random Forest (RF), Gradient Boosting (GB) and eXtreme Gradient Boosting (XG Boosting), The classification of the HEAs phase has been predicted with great accuracy using an XG Boosting (80 %) and Random Forest exhibits the highest accuracy (94 %) for crystal structure prediction when model is trained on an experimental dataset. Even though the ML model predicts the classes with a better degree of accuracy (>80 %), the F1 value of each class varies more dramatically. This issue has arisen as a result of an imbalance in the dataset's class distribution. To boost performance, this work uses an ML model in conjunction with the Synthetic Minority Oversampling Technique (SMOTE). According to this approach, XG boosting identified the crystal structure with 93 % accuracy and predicted the phase of HEAs with 84 % accuracy. Additionally, it has been noted that each class's F1 score improved and the difference between them was reduced after using the SMOTE technique. It is evident that the SMOTE approach has improved the ML model's ability to differentiate between the various classes.

Enhancing the microstructure and mechanical properties of CrCoFeNiAl high-entropy alloy produced by hot press sintering through laser remelting

Herein, laser remelting (LR) and hot press sintering (HPS) were combined to process high-entropy alloy (HEA) and strengthen desirable microstructure. The microstructural changes of HEA before and after LR processing were experimentally investigated. In Scanning Electron Microscope (SEM) and electron backscatter diffraction (EBSD) observations, it was found that the microstructure of the remelting zone was mainly composed of dendritic isometric crystals, and the laser remelting technique can refine the grain structure of HEA. The combined strengthening features of dislocations and twinning were observed by Transmission electron microscopy (TEM), and the phase structure of the grains was analyzed in conjunction with the X-ray diffraction(XRD) analysis, confirming the presence of B2 with BCC solid-solution and FCC phase. Finally, micron-sized scratches, tensile experiments and microhardness experiments were performed, and it was found that the Mechanical properties of the remelting zone were significantly enhanced. It was demonstrated that the strengthening of HEA, sintered by LR and HPS techniques, is due to the synergistic influence of various strengthening mechanisms, such as fine grain strengthening, dislocation strengthening, solid-solution strengthening and twinning strengthening.

Deformation mechanisms in high entropy alloys: a minireview of short-range order effects.

The complex atomic scale structure of high entropy alloys presents new opportunities to expand the deformation theories of mechanical metallurgy. In this regard, solute-defect interactions have emerged as critical piece in elucidating the operation of deformation mechanisms. While notable progress has been made in understanding solute-defect interactions for random solute arrangements, recent interest in high entropy alloys with short-range order adds a new layer of structural complexity for which a cohesive picture has yet to emerge. To this end, this minireview synthesizes the current understanding of short-range order effects on defect behavior through an examination of the key recent literature. This analysis centers on the nanoscale metallurgy of deformation mechanisms, with the order-induced changes to the relevant defect energy landscapes serving as a touchstone for discussion. The topics reviewed include dislocation-mediated strengthening, twinning and phase transformation-based mechanisms, and vacancy-mediated processes. This minireview concludes with remarks on current challenges and opportunities for future efforts.

The application of EET in high-entropy alloy

High-entropy alloy with multi-principal elements is a novel design concept for the field of alloy, which breaks through the traditional alloy development frame based on “one or two major alloy elements”. High entropy alloy composed of different metallic elements (generally ≥ 5) can present different novel properties by changing mole ratios or elements. In this work, the valence electron structure of high entropy alloys with compositions near Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 was studied using the Empirical Electron Theory of Solid and Molecules (EET). The predicted results agree well with the experimental data. Results shows that EET can be used to forecast the HEAs’ properties and design the constituent of HEAs.

Stretchable high-entropy alloy nanoflowers enable enhanced alkaline hydrogen evolution catalysis

High-entropy alloys have received much attention in many fields for their unique physicochemical properties, yet precise control at the atomic level in terms of size and morphology remains a great challenge. Herein, we report a kind of stretchable Pt(Co/Ni)MoPdRh HEAs nanoflowers (NFs) assembled by ultra-thin nanosheets (∼ 1.68 nm) for alkaline hydrogen evolution reaction (HER) via one-step wet chemical strategy. The mass activity of HEA NFs reaches 16.64 A mgHEA−1, which is 6.38 times higher than that of commercial Pt/C. The enhanced HER performance and stability is attributed to the multiple active sites in HEAs for reducing the water dissociation energies barriers as well as favoring H adsorption and the strain effect induced by unique structure. This work not only provides a general method for synthesizing unique structures of high entropy alloys, but also provides a fundamental understanding for the study of catalysis in HEAs.

Uncertainty quantification of predicting stable structures for high-entropy alloys using Bayesian neural networks

High entropy alloys (HEAs) have excellent application prospects in catalysis because of their rich components and configuration space. In this work, we develop a Bayesian neural network (BNN) based on energies calculated with density functional theory to search the configuration space of the CoNiRhRu HEA system. The BNN model was developed by considering six independent features of Co-Ni, Co-Rh, Co-Ru, Ni-Rh, Ni-Ru, and Rh-Ru in different shells and energies of structures as the labels. The root mean squared error of the energy predicted by BNN is 1.37 meV/atom. Moreover, the influence of feature periodicity on the energy of HEA in theoretical calculations is discussed. We found that when the neural network is optimized to a certain extent, only using the accuracy indicator of root mean square error to evaluate model performance is no longer accurate in some scenarios. More importantly, we reveal the importance of uncertainty quantification for neural networks to predict new structures of HEAs with proper confidence based on BNN.

Uniaxial pulling and nano-scratching of a newly synthesized high entropy alloy

Multicomponent alloys possessing nanocrystalline structure, often alluded to as Cantor alloys or high entropy alloys (HEAs), continue to attract the great attention of the research community. It has been suggested that about 64 elements in the periodic table can be mixed in various compositions to synthesize as many as ∼108 different types of HEA alloys. Nanomechanics of HEAs combining experimental and atomic simulations are rather scarce in the literature, which was a major motivation behind this work. In this spirit, a novel high-entropy alloy (Ni25Cu18.75Fe25Co25Al6.25) was synthesized using the arc melting method, which followed a joint simulation and experimental effort to investigate dislocation-mediated plastic mechanisms leading to side flow, pileup, and crystal defects formed in the sub-surface of the HEA during and after the scratch process. The major types of crystal defects associated with the plastic deformation of the crystalline face-centered cubic structure of HEA were 2,3,4-hcp layered such as defect coordination structures, coherent ∑3 twin boundary, and ∑11 fault or tilt boundary, in combination with Stair rods, Hirth locks, Frank partials, and Lomer–Cottrell locks. Moreover, 1/6 <112> Shockley, with exceptionally larger dislocation loops, was seen to be the transporter of stacking faults deeper into the substrate than the location of the applied cutting load. The (100) orientation showed the highest value for the kinetic coefficient of friction but the least amount of cutting stress and cutting temperature during HEA deformation, suggesting that this orientation is better than the other orientations for improved contact-mode manufacturing.

The structural, magnetic and magnetocaloric properties of MnCrNiGeSi high-entropy alloy

The structural, magnetic and magnetocaloric properties of Mn20Cr14Ni33Ge25Si8 and Mn24Cr10Ni33Ge25Si8 high entropy alloys (HEAs) were investigated. The HEAs were prepared by arc melting method. The structural analysis indicates that the structure of HEAs is orthorhombic with Pnma space group. In magnetic measurements, the maximum saturation magnetization was found to be 56.7 A m2kg−1. The Curie temperature of HEAs is 361 and 387 K, respectively. The Curie temperature shifts to the high temperature, when 4% Mn is added, resulting the long-range orientation of the magnetic moments. The magnetic entropy change of Mn24Cr10Ni33Ge25Si8 is 3.6 Jkg−1K−1 at around 387 K. Consequently, Large magnetic entropy change is achieved with low hysteresis and soft magnetic property at high temperature.

Effect of melt superheating treatment on corrosion resistance of Al2CoCrCuFeNi high entropy alloy in 0.5 M HNO3 solution

Al2CoCrCuFeNi high-entropy alloy (HEA) was heated by vacuum arc furnace at different powers (5.26kW, 6.15 kW, 7.28 kW, 8.26 kW) to different temperatures above the liquidus point (labeled as T1, T2, T3 and T4). The structure and corrosion resistance were investigated by means of X-ray diffraction, scanning electron microscopy with spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and electrochemical workstation. It was found that the HEAs with different superheating temperatures were all simple face-centered cubic (FCC) and body-centered cubic (BCC) solid solutions without complex phases. As the superheating temperature increased, the structure of HEAs became dense, the segregation decreased, and some fine-scale precipitations were formed at T4. When the heating temperature reached T3 or higher, the corrosion current density of the alloy decreased by more than 1/2, and the range of the passivation zone also became wider, indicating that the corrosion resistance was significantly improved. It was found that the pitting potential Eb ranked: T1<T2<T4<T3, indicating that the alloys labeled as T3 and T4 had better pitting resistance than those labeled as T1 and T2. The potential range of the stable passivation region △E ranked: T1<T2<T3<T4, which proved that the passivation film on the surface of HEA became more and more stable as the superheating temperature increased.

Regulating electrolytic Fe0.5CoNiCuZn high entropy alloy electrodes for oxygen evolution reactions in alkaline solution

• FeCoNiCuZn x HEAs are prepared by one-step electrochemical reduction of their oxides. • Use of ZnO as the precursor prevents the evaporation of Zn for preparation Zn-containing HEAs. • The composition and structure of HEAs can be easily controlled by adjusting the ingredient of oxide precursors. • Zn enhances the OER activity of FeCoNiCuZn x and the high entropy effect stabilize Zn in the HEAs. • The HEA(Zn0.8) exhibits the best OER activity and a good durability. The properties of high entropy alloys (HEAs) depend on their phase structures and compositions. However, it is difficult to control the composition of the HEAs that contain highly volatile metals by the conventional arc melting method. In this paper, homogeneous powdery face centered cubic (FCC) phase Fe 0.5 CoNiCuZn x HEAs were prepared by the electrolysis of metal oxides in molten Na 2 CO 3 -K 2 CO 3 using a stable Ni11Fe10Cu inert oxygen-evolution anode. The use of oxide precursors and relatively low synthetic temperature are beneficial to efficiently preparing HEAs that contain highly volatile elements such as Zn. Moreover, the microstructures and compositions of the electrolytic HEAs can be easily tailored by adjusting the components of oxide precursors, then further regulating its properties. Thus, the electrocatalytic activity of Fe 0.5 CoNiCuZn x HEAs towards oxygen evolution reactions (OER) was investigated in 1 M KOH. The results show that Zn promotes the OER activity of Fe 0.5 CoNiCuZn x HEAs, i.e., the HEA(Zn 0.8 ) shows the best OER activity exhibiting a low overpotential of 340 mV at 10 mA/cm 2 and excellent stability of 24 h. Hence, molten salt electrolysis not only provides a green approach to prepare Fe 0.5 CoNiCuZn x HEAs but also offers an effective way to regulate the structure of the alloys and thereby optimizes the electrocatalytic activities for water electrolysis.

Method to identify the phase structures of high entropy alloys with modified lattice distortion enthalpy

Severe lattice distortion is one of important characteristics of high entropy alloys (HEAs) and exercises considerable influence over phase structures, and atomic volume V is thought to be the key factor for lattice distortion. In the present work, the calculation of V was modified by taking the stacking density effects into consideration, and the calculation of lattice distortion enthalpy (∆HLD) caused by elastic lattice distortion for HEAs was optimized accordingly. With this method, two phase structure formation rules were proposed: valence electron concentration(VEC)−∆HLD rule for crystal structure of solid solution and chemical enthalpy(∆Hchem)−∆HLD rule for phase composition. The prediction effect of these two rules were verified by analyzing 100 existing HEAs, and the intrinsic effect of lattice elastic distortion on the phase formation of HEAs were discussed. The results of the research would be helpful in the composition design of HEAs.

Обзор исследований сплавов, разработанных на основе энтропийного подхода

This paper provides a review of studies on the development and characterization of high-entropy alloys (HEAs). It is structured in the following way. Alloys’ design strategy based on entropy approach. Expectations and modern perceptions. This section describes the initial principles of multicomponent alloys design which provide stable structure and mechanical properties. It is noted that the role of high mixing entropy in the formation of disordered solid solutions and the suppression of the brittle intermetallic phases formation have been significantly reconsidered over time. Currently, obtaining a single-phase solid solution structure is not the main requirement for HEAs. The composition of HEAs. This section describes some typical multicomponent alloys having different elemental compositions. It is shown, that at present time the most studied alloys are based on 3-d transition elements. Using alloys of this group the possibility of providing both high and low values of strength and ductility is shown. Fabrication methods of HEAs. This section describes the methods for the fabrication of high-entropy alloys. It is noted that the most commonly used methods are based on the melting of the initial materials and its subsequent crystallization. Such methods of HEAs fabrication as powder metallurgy, magnetron sputtering, self-propagating high-temperature synthesis, melt spinning, and diffusion welding are also discussed. Structure of HEAs. This section provides the data on HEAs possessing multiphase structure and containing fine nanosized precipitates. Besides, the studies in which HEAs have been obtained in the form of metallic glasses, carbides, oxides, and borides are reviewed. The factors that can affect the structural state of the multicomponent alloys are discussed. The ambiguity of opinions of different research groups is noted. Properties of HEAs. This section mainly concentrates on the mechanical properties of HEAs. However, some other promising properties of HEAs like high wear resistance and reduced diffusivity are also discussed. Plastic deformation of HEAs. This section describes the evolution of the structure and properties of HEAs caused by thermal and mechanical processing. Characterization methods of HEAs. This section lists the characterization techniques, which are most frequently used to study HEAs. The structure of these alloys is mainly studied by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and optical microscopy. The methods for properties measurements are also briefly reviewed. Application of HEAs. This section describes the promising fields of HEAs application. It can be utilized in the aerospace, aircraft, and nuclear industries as well as for car manufacturing, austoelectronics, and in the design of microwave devices. Russian-language publications on HEAs. This section lists the studies, published in the Russian language as well as the thesis, done in Russian universities.

Microstructure and magnetic behavior of FeCoNi(Mn–Si)x (x = 0.5, 0.75, 1.0) high-entropy alloys

Abstract

Influence of remelting and annealing treatment on corrosion resistance of AlFeNiCoCuCr high entropy alloy in 3.5% NaCl solution

Corrosion resistance of the cast, remelted and annealed AlFeNiCoCuCr high entropy alloys (HEAs) in 3.5% NaCl solution were investigated. The corrosion potentials (mV) of as-cast, annealed and remelted alloys ranked: −237.36 < −215.36 < −189.39, while corrosion current densities (A/cm2) ranked: 2.1632 × 10−4 > 1.3011 × 10−4 > 9.8937 × 10−5. Therefore, combining the results of the immersion tests, it can be concluded that corrosion resistance exhibited the rank: annealed > remelted > as-cast. The structures of HEAs had been researched by X-ray diffraction, optical microscopy, polarization scanning, and scanning electron microscopy. It was found that the dendrine regions grew after remelting and annealing compared with as-cast specimens, but new phases appeared only after annealing. In addition, corrosion formation turned gradually from intercrystalline and pitting corrosion to single pitting corrosion. Pitting corrosives of remelted HEA were much less than that of as-cast HEA and the annealed one had the least pitting corrosives.

The Valence Electron Structure of High-Entropy Alloys

Empirical Electron Theory in Solids and Molecules (EET) was used to analyze the valence electron structure of ZrTiHfVNb, ZrTiHfVTa and ZrTiHfNbMo high-entropy alloys. The parameters characterizing the valence electron structure of high-entropy alloys were calculated, which were used to discuss the hardness and melting temperature of high-entropy alloys. The results show that the hardness of high-entropy alloys is positively correlated to the shared electron pair number in valence electron structure. The theoretical melting temperatures of high-entropy alloys were predicted by the parameters characterizing the valence electron structure.

Tribological behavior of AlCoCrCuFeNi and AlCoCrFeNiTi0.5 high entropy alloys under hydrogen peroxide solution against different counterparts

Tribological properties of AlCoCrCuFeNi and AlCoCrFeNiTi0.5 alloys under 90% H2O2 solution rubbing against 1Cr18Ni9Ti steel, ZrO2 ceramic and SiC ceramic were investigated. The tribological behavior is dependent on the counterparts and the structure of high entropy alloys. The high entropy alloys exhibit significantly lower friction coefficient and wear loss sliding against SiC ceramic than 1Cr18Ni9Ti steel and ZrO2 ceramic, which can be attributed to the lubricating colloidal film formed by tribo-chemical reaction between H2O2 and SiC. Moreover, the AlCoCrFeNiTi0.5/SiC tribo-pair preserves better tribological properties than AlCoCrCuFeNi/SiC tribo-pair, as results of high strength and hardness of AlCoCrFeNiTi0.5 alloy.

Mechanical Properties and Structures of High Entropy Alloys and Bulk Metallic Glasses Composites

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) have unique structures at the length scales of micro- and nano-metre, and exhibit unique properties, which make them potential materials for structural applications. The tensile ductility of dendrite/BMG composites can be greatly improved by Bridgman solidification. The BCC structured HEA with a composition of Ti0.5AlCoCrFeNi exhibits ultrahigh fracture strength which is competitive to most of the BMGs, moreover, the strength can be sustained at high temperatures. The phase changes of HEAs are closely related to the atomic packing efficiency (APE).