High-entropy Alloys Research Articles

Accelerating high-entropy alloy discovery: efficient exploration via active learning

The exploration of the complex composition space for high entropy alloys (HEAs) is extremely challenging and resource intensive using traditional materials discovery approaches. Here, we apply Bayesian optimization in the form of active learning with a neural network model to efficiently explore the vast composition space of HEAs with a focus on predicting their stable phases. For example, by focusing data acquisition on the uncertain regions, we achieved a testing accuracy of 95% with 27% of an experimental HEA dataset, comparable to the accuracy (94.6%) of a random forest model trained with 80% of the full dataset (2198 quinary HEAs). Similarly, with just ∼2% of a CALPHAD dataset we achieved a testing accuracy for phase predictions above 96%, which is comparable to the accuracy (above 97%) achieved when an XGboost model is trained with nearly the full dataset (664,650 quinary HEAs). Thus, our approach greatly facilitates both computational and experimental exploration of HEA design spaces.

Synthesis and Characterization of WNiFeCo, WNiFeMo, and WNiFeCoMo Compositional Complex Alloys Manufactured by Powder Metallurgy Technique

AbstractThe WNiFeCo, WNiFeMo, and WNiFeCoMo compositional complex alloys (CCAs) were prepared by powder metallurgy technique. The thermodynamic investigations of the CCAs proved that WNiFeCo, and WNiFeMo, are medium entropy alloys (MEAs), whereas WNiFeCoMo is a high entropy alloy (HEA). The density of the prepared specimens was estimated. The sintered CCAs were characterized by investigating their microstructures and elemental distribution using SEM and EDX analysis. The crystal structure of the different phases was identified utilizing X-ray diffraction (XRD). From XRD results, W, Fe7W6, and FeNi were observed in all CCAs, whereas Co7W6, MoNi4, and Co7Mo6 phases were found in WNiFeCoMo HEA. WNiFeCo MEA contained a Co7W6 phase, while the MoNi4 phase was observed in WNiFeCo MEA. The A7B6 phases are formed in the CCAs which have good characteristics. The hardness, Young’s modulus, and corrosion behavior were evaluated. Among the investigated CCAs, WNiFeMo MEA showed the highest relative density percentage (95%), Young’s modulus (190 GPa), hardness (451 HV), and lowest corrosion rate in 3.5% NaCl (0.22 mm/y). The surface morphology of the WNiFeCo, WNiFeMo, and WNiFeCoMo alloys displayed uniform corrosion, galvanic corrosion, and localized corrosion.

Laser Powder Bed Fusion Printing of CoCrFeMnNi High Entropy Alloy: Processing, Microstructure, and Mechanical Properties

AbstractEquiatomic CoCrFeMnNi high entropy alloy (HEA) powder was processed by laser powder bed fusion (LPBF) additive manufacturing (AM). The properties of the spherical pre-alloyed CoCrFeMnNi powder were characterized and its processability using LPBF AM was systematically investigated through the volumetric energy density (VED) based on the surface roughness, defects (micro-cracks and porosity) and densification. After optimization, LPBF processing at a VED of 104 J/mm3 achieved highly dense and crack-free vertical and horizontal test specimens with a porosity fraction lower than 0.01% and micro-pores having a mean size of, respectively, 25.9 μm and 13.4 μm, as determined from X-ray micro-computed tomography (μCT) inspection. Scanning electron microscope (SEM) analysis of the as-built (AB) CoCrFeMnNi processed at a VED of 104 J/mm3 showed a heterogeneous solidification microstructure, consisting of columnar grains with a cellular subgrain structure, and electron backscattered diffraction (EBSD) revealed a crystallographic texture mainly along the < 100 > direction. Post treatment with hot isostatic pressing (HIP) was effective in closing the remnant micro-pores in the bulk volume of the AB CoCrFeMnNi. Also, the cellular sub-grain structure in the AB CoCrFeMnNi completely disappeared after HIP and the resulting microstructure consisted of recrystallized equiaxed grains with annealing twins. The room temperature tensile response was anisotropic for AB CoCrFeMnNi with horizontally built specimens exhibiting higher strength and fracture strains (global and local) compared to vertically built ones; HIP reduced the anisotropy in the tensile properties and led to similar tensile strength with elongation values that were ~ 50% higher than in the AB condition. The HIPed CoCrFeMnNi also displayed higher Charpy impact toughness and absorbed energy at both room and liquid nitrogen temperatures compared to the AB material. Examination of the fracture surfaces after tensile and Charpy impact testing revealed ductile features with characteristic dimpled appearance and pointed to the important role of the remnant micro-pores on failure in the AB CoCrFeMnNi. Tribological assessments pointed to the superior low-stress abrasion resistance of AB and HIPed CoCrFeMnNi compared to 316L stainless steel (SS), which was included in this study to reinforce the analysis. SEM observations revealed that scratching and micro-fracture are the dominant wear mechanisms for the CoCrFeMnNi HEA, whereas ploughing and cutting parallel to the abrasive flow direction are the dominant mechanisms for 316L SS. To the authors’ knowledge, this study is the first to evaluate and report the low-stress abrasion resistance of any high entropy alloy. To understand the corrosion behavior, polarization curves of AB and HIPed CoCrFeMnNi were measured in 3.5 wt% NaCl and 1N H2SO4 solutions, and the results were compared to those of 316L SS. The findings indicate that AB and HIPed CoCrFeMnNi outperform 316L SS in a chloride-containing environment, but not in an acid-containing environment. Additionally, observations of hydrogen permeability revealed that AB CoCrFeMnNi permeates a lower volume of hydrogen atoms (by ~ 5 times) compared to 316L SS, despite its higher (by nearly 3 times) diffusion coefficient. Electrochemical hydrogen permeation data showed that the concentration of atomic hydrogen in the sub-surface of AB and HIPed CoCrFeMnNi was, respectively, about 32 and 26 times lower than in 316L SS. This study provides important material–structure–property data and indicates a promising outlook for LPBF of the CoCrFeMnNi HEA with high-performance.

High-throughput and data-driven machine learning techniques for discovering high-entropy alloys

High-throughput and data-driven machine learning techniques for discovering high-entropy alloys

Enhanced hydrogen storage efficiency with sorbents and machine learning: a review

AbstractHydrogen is viewed as the future carbon–neutral fuel, yet hydrogen storage is a key issue for developing the hydrogen economy because current storage techniques are expensive and potentially unsafe due to pressures reaching up to 700 bar. As a consequence, research has recently designed advanced hydrogen sorbents, such as metal–organic frameworks, covalent organic frameworks, porous carbon-based adsorbents, zeolite, and advanced composites, for safer hydrogen storage. Here, we review hydrogen storage with a focus on hydrogen sources and production, advanced sorbents, and machine learning. Carbon-based sorbents include graphene, fullerene, carbon nanotubes and activated carbon. We observed that storage capacities reach up to 10 wt.% for metal–organic frameworks, 6 wt.% for covalent organic frameworks, and 3–5 wt.% for porous carbon-based adsorbents. High-entropy alloys and advanced composites exhibit improved stability and hydrogen uptake. Machine learning has allowed predicting efficient storage materials.

Process Optimization of CoCrFeMnNi High Entropy Alloy Fabricated by Selective Laser Melting Based on Thermal Mechanism and Molten Pool Behavior Analysis

Process Optimization of CoCrFeMnNi High Entropy Alloy Fabricated by Selective Laser Melting Based on Thermal Mechanism and Molten Pool Behavior Analysis

New strategy in light-weight and ultrastrong Ti40Nb15Mo30(NbC)15 refractory complex concentrated alloy

Traditional refractory high-entropy alloys (RHEAs) generally exhibit a trade-off between high-temperature strength and light weight. In present work, a novel design strategy based on tailoring element distribution is proposed to achieve excellent high-temperature strength at a density lower than 7 g·cm-3. Specifically, a Ti40Nb15Mo30(NbC)15 composite was designed and prepared by powder metallurgy. The composite is found to be composed of two ultrafine-grained (UFG) phases including a body-centered cubic (bcc) solid-solution phase and a face-centered cubic (fcc) ceramic reinforcement phase (Ti, Nb)C. The as-sintered composite shows a uniform and UFG microstructure where two phases are interconnected. Due to this unique microstructure, the Ti40Nb15Mo30(NbC)15 composite displays superb specific yield strengths among surveyed RHEAs, complex concentrated alloys, and metal-matrix composites from 800°C (243 MPa·g-1·cm3) to 1000°C (127 MPa·g-1·cm3). The outstanding high-temperature compressive strength was found to be associated with high resistance to dislocation motion and strong dislocation interactions in both the bcc and fcc phases. The phase interface after hot compression remained semi-coherent, vindicating its high stability. The high-density of stable phase interfaces not only retards the dislocation motion due to the large image force near the phase boundary but also induces a high value of activation energy for diffusion. The high activation energy can further achieve significant microstructure stability even after a long-term annealing (36 h) at 1000°C. This work provides new perspectives for the design and application of light and ultrastrong refractory complex concentrated alloys (RCCAs) by comparison to the insufficient strength of many traditional and light RCCAs.

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.

Design and Development of Ti‐Zr‐Nb‐Ta‐Ag High Entropy Alloy for Bioimplant Applications

A new non‐equiatomic 35Ti‐35Zr‐20Nb‐5Ta‐5Ag at % high entropy alloy (HEA) is designed by combining the HEA concept with the properties required for bioimplants. Mechanical alloying is used to synthesize the HEA, which is then compacted at 550 and 700 MPa and sintered at 1300 oC. The phases, microstructure, and mechanical properties are investigated, and in vitro corrosion properties are studied in a simulated body fluid. After 20 hours of mechanical alloying, a single BCC phase with a nanocrystalline size of 3.6 nm was formed. After sintering, the microstructure is composed of dual‐phase BCC structures: the major BCC 1 phase, the grain boundary BCC 2 phase, and the ultra‐fine equiaxed phase. The results of the micro‐indentation test indicate that the elastic modulus of the HEA is 84.4 ± 8.7 GPa and 113.2 ± 13.36 GPa, and its Vickers microhardness is 3.47 ± 0.1 GPa and 5.35 ± 0.2 GPa when it was compacted at 550 and 700 MPa respectively. The corrosion resistance tests reveal that HEA compacted at 700 MPa has higher corrosion resistance than commercial Ti6Al4V alloy. The developed Ti‐Zr‐Nb‐Ta‐Ag HEA has improved corrosion resistance and a lower elastic modulus, making it a potential candidate for bioimplant applications.This article is protected by copyright. All rights reserved.

Effect of short-range order on lattice distortion, stacking fault energy, and mechanical performance of Co-Fe-Ni-Ti high-entropy alloy at finite temperature

Effect of short-range order on lattice distortion, stacking fault energy, and mechanical performance of Co-Fe-Ni-Ti high-entropy alloy at finite temperature

Compositionally graded titanium to aluminum processed by laser powder bed fusion process: Microstructure evolution and mechanical properties

A compositionally graded Ti–Al alloy with a designed composition range from pure Ti to pure Al was successfully produced by a laser powder bed fusion (L-PBF) system equipped with two powder feeders. The compositionally graded Ti–Al profile is confirmed by scanning electron microscopy, X-ray diffraction analysis, electron backscatter diffraction microscopy, and transmission microscopy. The graded material is free of macro-horizontal cracks, but micro-cracks appear at the center of the sample. Varying the Ti and Al ratio along the build direction induces microstructural changes, transforming α+β-Ti into solid solution, creating intermetallics (Ti and Al), and yielding an Al phase with diverse morphologies. Additionally, the Ti–Al ratio's influence on microstructure formation and phase evolution results in varying mechanical properties among the graded material's layers. The results demonstrate that the L-PBF process can achieve continuous compositional grading of Ti–Al materials in a single run. Moreover, this study hold the potential to facilitate the design and production of numerous compositional variants for high entropy alloys and multi-materials, enabling future investigation into microstructural evolution, phase transformation, and physical and mechanical properties.

Research on Mechanical Properties and Corrosion Behavior of (Co34Fe8Cr29Ni8Si7)100−xBx High Entropy Alloy Coating

Research on Mechanical Properties and Corrosion Behavior of (Co34Fe8Cr29Ni8Si7)100−xBx High Entropy Alloy Coating

Wear resistance optimized by heat treatment of an in-situ TiC strengthened AlCoCrFeNi laser cladding coating

Abstract An AlCoCrFeNi high-entropy alloy coating containing 20 % mass fraction of TiC was prepared using the laser cladding method. The effect of heat treatment on the coating’s microstructure was analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). It was observed that following high-temperature heat treatment, the phase transition of AlCoCrFeNi–20%TiC shifted from BCC to FCC at 750 °C. Through microhardness and wear resistance tests, the increased diffusion of carbon post-heat treatment led to a higher precipitation of TiC-reinforced phases, resulting in exceptional wear resistance with a notable 128.3 % enhancement.

Grain growth kinetics, phase evolution during annealing and strain rate sensitivity of TRIP-assisted, dual-phase, non-equiatomic high entropy alloy

Transformation-induced plasticity-assisted dual-phase high-entropy alloys (TRIP-DP-HEAs) belong to a recently developed class of HEAs. TRIP-DP-HEAs have been reported to exhibit superior strength-ductility combination at room temperature as well as at high temperatures. Small amounts of carbon additions to TRIP-DP-HEAs are known to further improve the strength as a result of interstitial solid solution and nanoprecipitate strengthening effects. Current investigation compares the grain growth kinetics in a metastable, dual-phase (FCC and HCP), Fe49.5Mn30Co10Cr10C0.5, carbon-containing high entropy alloy (C-DP-HEA) with that in the corresponding carbon-free variant, Fe50Mn30Co10Cr10 HEA (DP-HEA). The alloys after being subjected to cold rolling, were annealed at 900 °C, 1000 °C and 1100 °C for 3, 30, 60 and 120 min, followed by water quenching. Slower grain growth kinetics was observed in C-DP-HEA due to Zener pinning by carbide particles. The activation energy for grain growth in C-DP-HEA was determined to be 339.71 kJ/mol, which is larger than that of DP-HEA (282.68 kJ/mol). The microstructures of the C-DP-HEA samples, after annealing at 900 °C for different durations of times and quenching, were investigated. The HCP phase fraction in the microstructure initially decreased with increase in annealing time/grain size and later increased with further increase in annealing time/grain size. This is explained based on the counteracting effect of grain boundary density and back stresses acting in samples having increased grain size. Strain rate sensitivity (SRS) parameter, ‘m’, was evaluated for both C-DP-HEA and DP-HEA. The strain rate jump tests were conducted at two quasi-static strain rates, 1 × 10−3 s−1 and 5 × 10−3 s−1, and at room temperature as well as at higher temperatures, 900 °C, 1000 °C and 1100 °C. The ‘m’ value was found to depend on the grain size, test temperature, and the presence of carbon in the alloy.

Fatigue Behavior of Medium Entropy Alloys AlCrFe<sub>2</sub>Ni<sub>2</sub> and AlCrFe<sub>2</sub>Ni<sub>2</sub>Mo<sub>0.1 </sub>- A Comparison with Super Duplex Steel 1.4517

Fatigue Behavior of Medium Entropy Alloys AlCrFe<sub>2</sub>Ni<sub>2</sub> and AlCrFe<sub>2</sub>Ni<sub>2</sub>Mo<sub>0.1 </sub>- A Comparison with Super Duplex Steel 1.4517

Influence of Solution Alkalinity and Alternating Current Density on Anti-corrosion Property of CoCrFeMnNi High-Entropy Alloy in Simulated Concrete Pore Solution

Influence of Solution Alkalinity and Alternating Current Density on Anti-corrosion Property of CoCrFeMnNi High-Entropy Alloy in Simulated Concrete Pore Solution

The effect of replacing molybdenum with vanadium on the tendency to amorphisation, structure and thermal properties of high-entropy alloys of the Fe–Co–Ni–Cr–(Mo,V)–B system

The effect of replacing molybdenum with vanadium on the tendency to amorphisation, structure and thermal properties of high-entropy alloys of the Fe–Co–Ni–Cr–(Mo,V)–B system

Microstructure and Properties of CoCrFeNiMnTix High-Entropy Alloy Coated by Laser Cladding

Microstructure and Properties of CoCrFeNiMnTix High-Entropy Alloy Coated by Laser Cladding

Unveiling the potential of (CoFeNiMnCr)3O4 high-entropy oxide synthesized from CoFeNiMnCr high-entropy alloy for efficient oxygen-evolution reaction

AbstractElectrochemical water-splitting is a promising green technology for the production of hydrogen. One of the bottlenecks, however, is the oxygen evolution half-reaction (OER), which could be overcome with the development of a suitable electrocatalyst. Recently, non-noble metal, high-entropy oxides (HEO) have been investigated as potential OER electrocatalysts, but complex synthesis approaches that usually produce the material in powder form limit their wider utilization. Here, an innovative synthesis strategy of formulating a nanostructured (CoFeNiMnCr)3O4 HEO thin film on a CoFeNiMnCr high entropy alloy (HEA) using facile electrochemical and thermal treatment methods is presented. The CoFeNiMnCr HEA serves as exceptional support to be electrochemically treated in an ethylene glycol electrolyte with ammonium fluoride to form a rough and microporous structure with nanopits. The electrochemically treated CoFeNiMnCr HEA surface is more prone to oxidation during a low-temperature thermal treatment, leading to the growth of a spinel (CoFeNiMnCr)3O4 HEO thin film. The (CoFeNiMnCr)3O4 HEO exhibits a superior overpotential of 341 mV at 10 mA cm−2 and a Tafel slope of 50 mV dec−1 along with remarkable long-term stability in alkaline media. The excellent catalytic activity and stability for the OER can serve as a promising platform for the practical utilization of (CoFeNiMnCr)3O4 HEO. Graphical abstract

Improving tensile and impact properties of Fe50Mn30Co10Cr10 high entropy alloy via microstructural engineering

This study investigates the Fe50Mn30Co10Cr10 high entropy alloy (HEA), featuring a dual-phase structure with face-centered cubic (FCC) and hexagonal close-packed (HCP) phases, in both cast and forged states. The cast samples exhibited an average tensile strength of 675.9 MPa and an elongation at break of 34 %, while the forged samples showed superior properties with a strength of 821.0 MPa and 50 % elongation. Impact tests at room temperature, 200 K, and 77 K revealed that forged samples consistently had higher impact energy (144 J, 119 J, and 109 J, respectively) compared to cast samples (99 J, 80 J, and 66 J). This research underscores the significant influence of the dual-phase structure and fabrication process on the mechanical and impact properties of the Fe50Mn30Co10Cr10 system HEAs.