Single-phase High-entropy Alloys Research Articles

Enhancing strength-ductility synergy of thermally oxidized dual-phase HEA particles reinforced aluminum matrix composites via heterogeneous interface

This work firstly oxidizes single-phase high entropy alloy (HEA) to form FCC and BCC dual-phase structure, and also introduces multi-component nano-oxides on surface to prepare oxidized HEA (OHEA) reinforcements, followed by preparation of OHEA/Al composites by spark plasma sintering. The introduction of O element accelerates interdiffusion between OHEA and Al matrix. FCC phase inside OHEA evolves into soft phase, and BCC matrix phase evolves into hard phase, forming heterogeneous interface in OHEA/Al composites. During tensile process, cracks preferentially initiated in hard phase due to severe stress concentration, and the soft phase effectively retarded crack propagation. Compared with 2024Al matrix, yield strength, tensile strength, and elongation of OHEA/Al composites increased by 35.31%, 57.34%, and 63.33%, respectively, realizing excellent combination of strength and toughness. Grain refinement, thermal mismatch, Orowan, and load transfer strengthenings synergistically improve the performance. The proposed method provides a promising avenue to optimize the properties of composites by pre-oxidizing HEA particles to construct heterogeneous interfacial structure.

Strength-ductility balance of AlCoCrFeNi2.1 eutectic high-entropy alloy via additive manufacturing

AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA), with its distinctive heterogeneous structure, not only overcomes the drawback of insufficient strength of FCC single-phase high-entropy alloys (HEAs), but also overcomes the drawback of insufficient ductility of BCC single-phase HEAs, making it a promising candidate for engineering application. In addition, EHEAs possessing excellent castability are considered to be suitable for additive manufacturing (AM). The AlCoCrFeNi2.1 EHEA prepared by direct energy deposition (DED) exhibits a dual-phase structure consisting of FCC(L12) and BCC(B2) phases. With the increase of deposition height, its morphology transforms from columnar and dendrite structures to lamellar structure. Furthermore, the tensile strength and yield strength of the DED-ed EHEA samples increase, while the ductility decreases with the increase of deposition height. Especially, the middle region of the DED-ed samples achieves a good strength-ductility balance. The lamellar structure composed of soft FCC(L12) phase and hard BCC(B2) phase produces a hetero deformation induced (HDI) hardening, which improves the strength of the samples and promotes plastic deformation. The FCC(L12)/BCC(B2) phase interfaces not only hinder the movement of a large number of dislocations and cause dislocation pile-up, but also allow some dislocations to slip across, which helps to plastic co-deformation of two phases in the EHEA samples. This work provides useful guidance for the performance improvement of EHEAs using laser additive manufacturing.

Synthesis and characterization of FeAlZnCrCuMg alloy using high energy ball milling

A High entropy alloy of more than four equi-atomic components has been produced by a high energy ball mill. Metallic powders of each component in equi-atomic ratio were milled in wet conditions. The X-ray diffraction (XRD) pattern for the samples, which were collected at regular intervals of time, displayed the process of formation of single phase high entropy alloy. Body centered cubic structure of the FeAlZnCrCuMg alloy was confirmed after 25 h of milling. The lattice parameter of the alloys has been found to be 2.88 Å. Transmission electron microscopy (TEM) analysis of the sample also confirmed the formation of single phase high entropy alloy.

Ultra-strong and ductile precipitation-strengthened high entropy alloy with 0.5 % Nb addition produced by laser additive manufacturing

Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys (HEAs) is challenging. The present work investigates the in-situ synthesis of Fe49.5Mn30Co10Cr10C0.5 interstitial solute-strengthened HEA containing 0.5 wt.% Nb (hereafter referred to as iHEA-Nb) using laser melting deposition (LMD), aiming at simultaneously activating multiple strengthening mechanisms. The effect of Nb addition on the microstructure evolution, mechanical properties, strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated. Multiple levels of heterogeneity were observed in the LMD-deposited microstructure, including different grain sizes, cellular subgrain structures, various carbide precipitates, as well as elemental segregation. The incorporation of Nb atoms with a large radius leads to lattice distortion, reduces the average grain size, and increases the types and fractions of carbides, aiding in promoting solid solution strengthening, grain boundary strengthening, and precipitation strengthening. Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa, respectively, while maintaining the elongation over 30 %. Deformation twins were generated in the tensile deformed samples, contributing to the occurrence of twinning-induced plasticity. This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date, demonstrating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments. In addition, single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA, the micromechanical properties of grains with different orientations were significantly enhanced.

Composition-based phase stability model for multicomponent metal alloys

The vastness of the space of possible multicomponent metal alloys is hoped to provide improved structural materials but also challenges traditional, low-throughput materials design efforts. Computational screening could narrow this search space if models for materials stability and desired properties exist that are sufficiently inexpensive and accurate to efficiently guide experiments. Toward this effort, here we develop a method to rapidly assess the thermodynamic stability of a metal alloy composition of an arbitrary number of elements, stoichiometry, and temperature based on density functional theory (DFT) data. In our model, the Gibbs free energy of the solid solution contains binary enthalpy contributions and ideal configurational entropy, whereas only enthalpy is considered for intermetallic competing phases. Compared to a past model for predicting the formation of single-phase high-entropy alloys [M. C. Troparevsky et al., Phys. Rev. X 5, 011041 (2015)], our method is similarly inexpensive, since it assesses enthalpies based on existing DFT data, but less heuristic, more broadly applicable, and more accurate (70%–75%) compared to experiment.

Synthesis of metallic high-entropy alloy nanoparticles.

The theoretically infinite compositional space of high-entropy alloys (HEAs) and their novel properties and applications have attracted significant attention from a broader research community. The successful synthesis of high-quality single-phase HEA nanoparticles represents a crucial step in fully unlocking the potential of this new class of materials to drive innovations. This review analyzes the various methods reported in the literature to identify their commonalities and dissimilarities, which allows categorizing these methods into five general strategies. Physical minimization of HEA metals into HEA nanoparticles through cryo-milling represents the typical top-down strategy. The counter bottom-up strategy requires the simultaneous generation and precipitation of metal atoms of different elements on growing nanoparticles. Depending on the metal atom generation process, there are four synthesis strategies: vaporization of metals, burst reduction of metal precursors, thermal shock-induced reduction of metal precursors, and solvothermal reduction of metal precursors. Comparisons among the methods within each strategy, along with discussions, provide insights and guidance for achieving the robust synthesis of HEA nanoparticles.

Efficient screening of single phase forming low-activation high entropy alloys

Screening of chemical space constituting a palette of seven low-activation metallic elements (Ti, V, Cr, Mn, Fe, Ta, and W) is performed to find single-phase equiatomic/non-equiatomic body-centered cubic (BCC) quaternary/quinary high entropy alloys (HEA). A high throughput screening using ab-initio computations-assisted thermodynamic modeling strategy is implemented. Benchmarking the accuracies of the empirical models for predicting simple solid solutions HEAs is performed considering experimentally synthesized thirty-six low-activation HEAs from the literature. Based on the most efficient empirical model, compositional ranges of several new HEAs are suggested where the formation of single-phase HEA is most preferable. A thorough comparison of high-throughput screening results with CALPHAD data and experiments establishes the efficiency of the high-throughput screening strategy.

(Invited) The More Elements the Better? Studying Structure-Function Relations in High Entropy Alloy Nanoparticles As Fuel Cell Electrocatalysts

Low-temperature polymer electrolyte membrane fuel cells (PEMFCs), which convert chemical energy into electricity, are widely considered a suitable, sustainable technology to replace conventional combustion engines. However, fundamental issues such as fuel cell efficiency and durability still leave room for improvement, which could be achieved by finding more active and stable fuel cell electrocatalysts.[1] High entropy alloys (HEA) – solid solutions of five or more elements - are an emerging material class in the development of novel electrocatalysts. These multi-metallic compounds provide exciting new possibilities for catalyst design.[2] Recent theoretical analyses predict a great potential for HEAs as fuel cell catalysts due to the almost unlimited number of unique surface sites, which enables a wide distribution of adsorption energies. By changing the composition, the distribution of adsorption energies can be tailored toward the optimal binding energies of the catalytic intermediates.[3] The field of high entropy alloy catalysis enables a new, statistical approach to materials design. From an experimental viewpoint, however, HEAs come with new challenges regarding their synthesis and characterization.While HEA nanoparticles are essential for efficient catalysis to provide sufficiently large surfaces, their synthesis is only in its infancy. For a direct comparison between theoretically predicted properties and the performance of the prepared catalysts, single-phase HEA nanoparticles are essential.[4] Through studies of the synthesis pathways and in-depth structural characterization of the HEA nanoparticles with synchrotron X-ray techniques, it is possible to prepare model single-phase HEA nanoparticle catalysts. These well-mixed, multi-metallic materials allow us to study not only the different structure-activity properties of HEA nanoparticle fuel cell catalysts but to also explore the stability of these novel materials under reaction conditions. Studying the dissolution and degradation behaviour of model HEA catalysts in an acidic environment, the mechanisms that underly the degradation of multi-metallic PEMFC catalysts are explored. By relating structural characterization techniques with electrochemical analyses,[5] we can address the question of which role element mixing can play in the activation and stabilization of new fuel cell catalysts.[1] Schroeder, J.; Pittkowski, R. K.; Du, J.; Kirkensgaard, J. J. K.; Arenz, M. J. Electrochem. Soc. 2022, 169, 104504.[2] Löffler, T., Ludwig, A., Rossmeisl, J, Schuhmann, W. Angew. Chem. Int. Ed. 2021, 60, 2-12.[3] Batchelor, T. A. A, Pedersen, J. K., Winther, S.H., Castelli, I.E., Jacobsen, K. W., Rossmeisl, J. Joule 2019, 3, 834-845.[4] Pittkowski, R.; Clausen, C. M.; Chen, Q.; Stoian, D.; van Beek, W.; Bucher, J.; Welten, R. L.; Schlegel, N.; Mathiesen, J. K.; Nielsen, T. M.; Rosenkranz, A. W.; Bojesen, E. D.; Rossmeisl, J.; Jensen, K. M. Ø.; Arenz, M. ChemRxiv, 2022, https://doi.org/10.26434/chemrxiv-2022-khw4t.[5] Schroeder, J.; Pittkowski, R. K.; Martens, I.; Chattot, R.; Drnec, J.; Quinson, J.; Kirkensgaard, J. J. K.; Arenz, M. ACS Catalysis 2022, 12, 2077–2085

Mechanical Alloying as a Way to Produce Metastable Single-Phase High-Entropy Alloys beyond the Stability Criteria.

Various stability criteria developed for high-entropy alloys are applied to compositions produced by mechanical alloying. While they agree with the annealed samples, these criteria fail to describe the as-milled metastable systems, highlighting the ability of mechanical alloying to overcome the limitations imposed by these criteria. The criteria are based on atomic size (Ω ≥ 1.1 and δr ≤ 6.6%) and/or electronegativity misfit, as well as on mixing enthalpy (Λ>0.95 J mol-1K-1 and -5 kJ mol-1<∆Hmix<0), or purely thermodynamic (ϕYe>20; ϕKing>1; Teff<500 K). These criteria are applied to several compositions found in the literature and to two metastable fcc solid solutions produced by mechanical alloying with compositions Al0.75CoXFeNi with X = Cr and Mn. Single-phase microstructures are stable up to above 600 K, leading to more stable multiphase systems after annealing above this temperature. Mössbauer spectrometry shows that, whereas the alloy with Cr is paramagnetic in the as-milled and annealed state, the alloy with Mn changes from paramagnetic to ferromagnetic behavior (Curie temperature ~700 K) after annealing. Thermomagnetic experiments on annealed samples show for both compositions some hysteretic events at high temperatures (850 to 1000 K), probably ascribed to reversible ordering phenomena.

On the Passive Behavior of the Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) consisting of five or more elements in equimolar or near-equimolar ratios, represent an emerging class of materials showing an exceptional combination of properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. The possibility of high corrosion resistance with single phase HEAs has been demonstrated but the absence of single primary element in the HEA makes the prediction of its corrosion resistance extremely difficult.EIS was originally developed as a tool for corrosion research and is well suited for the identification of complex mechanism involving adsorption intermediates, and 2D and 3D formation of thin films in the nanometer range. Additionally, EIS can be used for a comprehensive description of the passive film properties. This project focus on the well-defined Cantor alloy to studies its passivation in sulfuric acid solution with various chloride ions contents. EIS and linear wseep voltammetry have been used in order to describe the passive film formation as well as the passive film stability (Fig. 1). A specific attention has been paid in order to finely describe the passive film properties as a function of the applied potential and the chloride contents.In parallel, the resistance of the passive film was studied using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM), which allows to generate a single pitting on the alloy and to study its initiation, propagation and repassivation as a function of the potential and the chloride ion concentration. This approach allows in particular to get rid of the stochastic aspect of the localized corrosion and to perform quantitative analysis of the exchanged charge during the single-pit propagation.Figure 1: Current potential curve and EIS diagrams measured at different potential for describing the passive film formation on Cantor alloy in chloride containing sulfuric acid solution. Figure 1

Hard yet tough and self-lubricating (CuNiTiNbCr)Cx high-entropy nanocomposite films: Effects of carbon content on structure and properties

The single-phase high-entropy alloy film is difficult to meet severe friction conditions due to its low hardness and high friction coefficient. Nano-composite structure film is composed of at least two separated phases, showing the properties of strength and toughness integration and excellent wear resistance. The design of nanocomposite structures can effectively improve the mechanical properties and tribological properties of high-entropy alloy films. In this study, the (CuNiTiNbCr)Cx nanocomposite high-entropy films (HEFs) integrated with high hardness, high toughness, and self-lubrication were synthesized by the double-target co-sputtering method. The effect of carbon content on microstructure, mechanical properties, and tribological properties of (CuNiTiNbCr)Cx films was studied. With the increase of carbon content in the HEFs, the carbon atoms preferentially react with Ti, Nb, and Cr to form a (TiNbCr)C ceramic-reinforced phase, and then the excess carbon atoms precipitate in the form of amorphous carbon (a-C) lubricating phase in the HEFs. The structure of the HEFs changes from an amorphous structure to a nanocomposite structure of amorphous (amorphous CuNiTiNbCr phase + a-C phase)/nanocrystalline (TiNbCr)C phase. When the carbon content is about 21.2 at.%, the carbide phase in the film reaches saturation and the hardness and modulus of the films are highest, which are 18 GPa and 228 GPa, respectively. The HEFs with a carbon content of 44.0 at.% show the best toughness and tribological properties with a friction coefficient of 0.16 and a wear rate of 2.4 × 10–6 mm3/(N m), which is mainly attributed to the excellent resistance to fatigue crack growth and the interfacial lubricating layer formed in the friction process. The nanocomposite (CuNiTiNbCr)Cx HEFs show very promising application prospect in the field of friction protection.

Strong yet strain-hardenable equiatomic CoCrFeMnNi high-entropy alloys by dynamic heterostructuring

Heterostructuring gives solutions to achieve better mechanical performance of metallic materials. For instance, partial static recrystallization by short-term annealing induces bimodal grain size distribution. Distinct from the well-studied ‘static heterostructuring’ by cold rolling followed by annealing, this study introduces ‘dynamic heterostructuring’ by hot rolling. Dynamic recrystallization (DRX) during the hot rolling as a softening mechanism leaves room for dislocation accumulation. With the expectations of enhanced strain hardening of the as-rolled materials with the aid of the DRX, we monitored tensile responses of the as-hot-rolled equiatomic CoCrFeMnNi high-entropy alloys (HEAs). Among the hot rolling temperatures from 800 ℃ to 900 ℃ with a thickness reduction ratio of 78.6% for the HEAs, the hot rolling at 850 °C results in a bimodal grain size distribution, i.e., partial DRX. It comprises relatively fine DRXed grains and coarse unrecrystallized grains: the latter is harder than the DRXed ones with relatively low dislocation density. The microstructural heterogeneity results in uniform elongation of ∼13% due to the accumulation of dislocations at the grain boundaries inside the soft DRXed grains. This endows the as-hot-rolled single-phase HEAs with strain hardenability without the aid of phase transformation, deformation twinning, or precipitates. In addition, the hot-rolled HEAs with high dislocation density have doubled yield stresses of those of conventionally cold-rolled and annealed counterparts. Considering the industrial benefits of the simplified thermo-mechanical control processes, this work extends the academic and practical value of DRX by dynamic heterostructuring through annealing-free hot rolling.

Understanding the Structural Evolution of IrFeCoNiCu High-Entropy Alloy Nanoparticles under the Acidic Oxygen Evolution Reaction.

High-entropy alloy (HEA) nanoparticles are promising catalyst candidates for the acidic oxygen evolution reaction (OER). Herein, we report the synthesis of IrFeCoNiCu-HEA nanoparticles on a carbon paper substrate via a microwave-assisted shock synthesis method. Under OER conditions in 0.1 M HClO4, the HEA nanoparticles exhibit excellent activity with an overpotential of ∼302 mV measured at 10 mA cm-2 and improved stability over 12 h of operation compared to the monometallic Ir counterpart. Importantly, an active Ir-rich shell layer with nanodomain features was observed to form on the surface of IrFeCoNiCu-HEA nanoparticles immediately after undergoing electrochemical activation, mainly due to the dissolution of the constituent 3d metals. The core of the particles was able to preserve the characteristic homogeneous single-phase HEA structure without significant phase separation or elemental segregation. This work illustrates that under acidic operating conditions, the near-surface structure of HEA nanoparticles is susceptible to a certain degree of structural dynamics.

Високоентропійний NiFeCrWMo сплав, отриманий в процесі механічного легування

In this work, the evolution of the structure and phase composition of the multicomponent Ni-Fe-Cr-W-Mo system during mechanical alloying (MA) of an equiatomic mixture of elemental metal powders in a planetary mill is investigated. The formation of the phase composition and structure of the powdered equiatomic high-entropy NiFeCrWMo alloy at different stages of mechanical alloying was determined by scanning electron microscopy, X-ray diffraction and X-ray spectral analysis. It was found that during 10 hours of МА, a single-phase high-entropy alloy with the structure of a BCC solid solution in the nanostructural state with a crystallite size of 22 nm and a lattice strain (microstress) of 0.61 % was formed. It was shown that the metal components were completely dissolved in the solid state during mechanical alloying, in contrast to their limited solubility under equilibrium conditions. Moreover, despite the different features of the formation of solid solutions in high-entropy alloys and traditional materials, the order of dissolution of element atoms in the lattice of a solid solution follows general principles and occurs depending on the melting point in the following sequence: Ni→Fe→Cr→Mo→W. The average particle size of the produced powdered NiFeCrWMo high-entropy alloy is 3.8 μm, and their shape is predominantly spherical or close to spherical. The microstructure of the particles of the powdered NiFeCrWMo high-entropy alloy at the early stage (1.5 hours) of mechanical alloying is a layered structure formed in the process of grinding, deformation, and cold welding of particles of elemental metal powders. After 10 hours of МА, the microstructure of the alloy particles becomes homogeneous and contains a small amount of WC inclusions as a result of milling due to wear of grinding bodies in the MА process. The obtained NiFeCrWMo high-entropy alloy can be used in the future as a component/binder for other composite materials, for example, hard alloys based on WC to replace Co. Keywords: high-entropy alloy, mechanical alloying, structure, phase composition, solid solution, nanostructure

Atomistic simulation and experimental verification of tribological behavior of high entropy alloy/graphene composite coatings

Dissatisfactory yield strength and wear have been critical issues in FCC single phase high entropy alloy (HEA) limiting wide applications as advanced engineering materials, in spite of their attractive mechanical and physical properties. Here we show by introducing graphene layer, the tribological properties of Fe20Ni20Cr20Co20Cu20/graphene composite coatings can be noticeably enhanced. In this work, molecular dynamics simulations were performed to probe the tribological mechanisms of HEA/graphene composite coatings. It was revealed that the reasonable choice of single-layer graphene geometry and embedding position play an important part in friction reduction and anti-wear of the coatings. The graphene interface not only cause robust dislocation blockage from HEA, but also reduces the accumulation of atoms at surface during sliding. Besides, the influence of temperature on the tribological behavior of the coatings is explored. The tribological performances of the coatings were also investigated by the experimental nanoscratch test, which are consistent with the simulation results. The present work provides a theoretical and technical support for the design of wear-resistant self-lubricating coatings, promoting the engineering applications of HEA coating materials.

A map of single-phase high-entropy alloys

High-entropy alloys have exhibited unusual materials properties. The stability of equimolar single-phase solid solution of five or more elements is supposedly rare and identifying the existence of such alloys has been challenging because of the vast chemical space of possible combinations. Herein, based on high-throughput density-functional theory calculations, we construct a chemical map of single-phase equimolar high-entropy alloys by investigating over 658,000 equimolar quinary alloys through a binary regular solid-solution model. We identify 30,201 potential single-phase equimolar alloys (5% of the possible combinations) forming mainly in body-centered cubic structures. We unveil the chemistries that are likely to form high-entropy alloys, and identify the complex interplay among mixing enthalpy, intermetallics formation, and melting point that drives the formation of these solid solutions. We demonstrate the power of our method by predicting the existence of two new high-entropy alloys, i.e. the body-centered cubic AlCoMnNiV and the face-centered cubic CoFeMnNiZn, which are successfully synthesized.

In situ analysis of the Portevin-Le Chatelier effect from low to high-entropy alloy in equal HfNbTaTiZr system

The HfNbTaTiZr system is designed from low-entropy to high-entropy by unary, binary, ternary, quaternary, and quinary equal-molar element alloys. At first, the effect of mixing entropy on elevated temperature tensile behaviors ranging from 400 °C to 800 °C and strain rate 1 × 10−4 s–1 in body-centered-cubic (BCC) alloys is systematically discussed, including dynamic strain aging, serration behavior and in-situ deformation behavior of Portevin-Le Chatelier (PLC) band analysis. The results show that in BCC high-entropy alloys (HEAs), with the increase of the alloy elements, the range of the transition temperature of PLC bands expands, and the degree of dynamic strain aging at high temperature also enhances. The theoretical model was verified with the critical strain of unary, binary, and ternary alloys, and it predicts the PLC effect under the specific temperature and strain rate. Apply Applied to quinary alloys, the difference in serration phenomena between face-centered-cubic (FCC) and BCC HEA are investigated, showing that the high melting point of Nb and Ta elements lead to the slower self-adjusting velocity in HfNbTaTiZr alloy. Digital image correlation analysis is in-situ to analyze different types of PLC bands at various strain rates from 1 × 10–2 to 1 × 10−3 s–1 and elevated temperature from 200 °C to 600 °C. The BCC single-phase HEA reveals the transmission properties of the PLC bands and it is consistent with the serration behavior in the tensile stress-strain curve.

Tuning Elinvar effect in severely distorted single-phase high entropy alloys

In this work, we fabricated a series of severely distorted high-entropy Elinvar alloys through micro-alloying of (CoNi)50−x(TiZrHf)50Fex (in atomic percentage). Through carefully designed experiments, we demonstrate a tunable Elinvar effect that is positively correlated with overall lattice distortion in single-phase B2 high entropy alloys. Finally, we propose a simple physical model that captures the general trend of our experimental findings.

Influence of the scanning angle on the grain growth and mechanical properties of Ni10Cr6W1Fe9Ti1 HEA fabricated using the LPBF–AM method

It is difficult to control the microstructure of materials developed following the additive manufacturing (AM) process, and researchers have been trying to address this problem for a long time. Process parameters, such as the scanning strategy, significantly affect microstructural properties. Scanning strategies can be tuned to achieve control over the crystal texture of alloys. However, in-depth studies on the relationship between the scanning strategy and the deflection growth have not been conducted to date. Changes in the scanning angle result in changes in the direction of the temperature gradient associated with the molten pool, and this eventually affects the growth of grains. Herein, a new generalized method has been proposed to control the extent of deflection growth in grains realized. The results help determine the relationship between the scanning angle and the grain deflection growth in space. The LPBF-AM technology was used under conditions of varying scanning angles to fabricate Ni10Cr6W1Fe9Ti1, a single-phase (FCC) high-entropy alloy. The experimental results reveal that the angle corresponding to the deflection growth angle in space is approximately equal to the scanning angle. The extent of epitaxial growth in grains is low, and the amount of low-angle grain boundaries（GB） is high when the scanning angle is 67°. This can be attributed to the presence of small grains. The performance of the alloy was optimized, and it was observed that the performance of the prepared alloy was better than the performance recorded for previously reported alloys. The tensile strength, yield strength, and elongation post fracture were recorded to be 961.65 MPa, 739.77 MPa, and 26.5%, respectively. This report which states that the AM method can be used to fabricate single-phase (FCC) high-entropy alloys characterized by high strength and good ductility. The determination of the relationship between the scanning angle and the deflection growth of grains in space help provide a platform to achieve precise control over the microstructure of materials.

The more the better: on the formation of single-phase high entropy alloy nanoparticles as catalysts for the oxygen reduction reaction.

High entropy alloys (HEAs) are an important new material class with significant application potential in catalysis and electrocatalysis. The entropy-driven formation of HEA materials requires high temperatures and controlled cooling rates. However, catalysts in general also require highly dispersed materials, i.e., nanoparticles. Only then a favorable utilization of the expensive raw materials can be achieved. Several recently reported HEA nanoparticle synthesis strategies, therefore, avoid the high-temperature regime to prevent particle growth. In our work, we investigate a system of five noble metal single-source precursors with superior catalytic activity for the oxygen reduction reaction. Combining in situ X-ray powder diffraction with multi-edge X-ray absorption spectroscopy, we address the fundamental question of how single-phase HEA nanoparticles can form at low temperatures. It is demonstrated that the formation of HEA nanoparticles is governed by stochastic principles and the inhibition of precursor mobility during the formation process favors the formation of a single phase. The proposed formation principle is supported by simulations of the nanoparticle formation in a randomized process, rationalizing the experimentally found differences between two-element and multi-element metal precursor mixtures.