Low-Density High-Entropy Alloy Research Articles

Phase Diagrams of Alloys and Their Hydrides via On-Lattice Graph Neural Networks and Limited Training Data.

Efficient prediction of sampling-intensive thermodynamic properties is needed to evaluate material performance and permit high-throughput materials modeling for a diverse array of technology applications. To alleviate the prohibitive computational expense of high-throughput configurational sampling with density functional theory (DFT), surrogate modeling strategies like cluster expansion are many orders of magnitude more efficient but can be difficult to construct in systems with high compositional complexity. We therefore employ minimal-complexity graph neural network models that accurately predict and can even extrapolate to out-of-train distribution formation energies of DFT-relaxed structures from an ideal (unrelaxed) crystallographic representation. This enables the large-scale sampling necessary for various thermodynamic property predictions that may otherwise be intractable and can be achieved with small training data sets. Two exemplars, optimizing the thermodynamic stability of low-density high-entropy alloys and modulating the plateau pressure of hydrogen in metal alloys, demonstrate the power of this approach, which can be extended to a variety of materials discovery and modeling problems.

Gamma-ray, fast neutron and ion shielding characteristics of low-density and high-entropy Mg–Al–Ti–V–Cr–Fe–Zr–Nb alloy systems using Phy-X/PSD and SRIM programs

This study aimed to assess the radiation shielding properties of ten low-density high-entropy alloys (LWHEAs) using Phy-X/PSD software to analyze various shielding parameters, such as attenuation coefficients (μm and μ), mean free path (λ), effective atomic number (Zeff), and removal cross-section (ΣR), in the energy range of ▪ to ▪. A comprehensive evaluation was performed to compare the attenuation outcomes provided by HEAs with a range of shielding materials documented in the literature. The study also calculated the build-up factors (BUFs) of the alloys by using the GP-fitting interpolation method. The stopping power of the alloys against H1/He+2 ions was analyzed using the SRIM Monte Carlo code, considering total stopping power (TSP) and projected range (PR). The results indicated that HEA8 (Al3.88Cr14.95Mo27.58Nb26.71Ti13.76Zr13.11) had the best performance in terms of shielding against γ-rays, fast neutrons, and H1/He+2 ions, as it achieved the highest values of parameters such as μm, μ, Zeff, and ΣR, along with the lowest values of HVL, TVL, λ, BUFs (▪▪), TSP, and PR. On the other hand, HEA10 (Mg10.77Al11.96Mn24.35Fe24.75Cu28.17) had the lowest BUFs in both lower (▪▪) and higher (▪▪) energy regions. The order of μm for the alloys was found to be HEA5<HEA6<HEA9<HEA7<HEA10<HEA4<HEA2<HEA3<HEA1<HEA8. The study concluded that LWHEAs possess superior radiation shielding properties compared to conventional materials, making them a promising new class of materials for radiation shielding applications.

Single-phase lightweight high-entropy alloys with enhanced mechanical properties

To develop single-phase lightweight high-entropy alloys (LWHEAs), we perform massive screening over a vast material space containing more than 560,000 possible compounds by employing thermodynamic principles and examine the mechanical properties of the resulting alloys based on density functional theory (DFT) calculations. Considering LWHEAs composed of five principal elements including light atoms such as Li, Mg and Al, we identify 40 optimal atomic compositions for single-phase solid solutions in body-centered-cubic structure. Combined with DFT calculations, it is demonstrated that the valence electron concentration plays an important role in determining elastic moduli and that the identified LWHEAs are ductile as is evidenced by the satisfied Pugh criteria and positive Cauchy pressure. In cases of shear modulus and yield strength, pd-hybridization between Al and transition metal atoms is shown to make a significant contribution through forming strong directional bonds. Together with an observation that the inclusion of Li and Mg atoms is instrumental in reducing the overall density, the present results provide a valuable guidance to develop novel, low-density high-entropy alloys.

Phase stability and compressive properties of low-density (Zr50Ti35Nb15)100-xAlx high entropy alloys

In the present study, phase stability and compressive mechanical properties of the (Zr50Ti35Nb15)100-xAlx (x = 0 to 30 at.%) high-entropy alloys were investigated. It was found that the crystalline structure of cast alloys changed from the initial disordered body-centered cubic (BCC) structure to an ordered body-centered cubic (B2) structure as the Al concentration was increased. Their microstructure and phase evolution after long-term annealing up to 1000 h at temperature ranging from 900 °C to 1100 °C were analyzed. Annealing has no obvious influence on the matrix phase of Zr50Ti35Nb15, which keeps BCC structure during all the annealing processes. For the alloys (Zr50Ti35Nb15)80Al20 and (Zr50Ti35Nb15)70Al30 with higher Al content, secondary phase (Al3Zr5) precipitates after annealing at 900 °C. With the increasing annealing temperature to 1000 °C or 1100 °C，there is a tendency that the amount of the Al3Zr5 phase decreases slightly, indicating that Al3Zr5 phase is unstable at high temperature. Accompanied by the phase change, there were also corresponding variations in compressive properties. The secondary phase precipitated in the (Zr50Ti35Nb15)80Al20 and (Zr50Ti35Nb15)70Al30 decreases the compressive plasticity, but has little influence on the yield strength. Meanwhile, the compressive properties of as-cast (Zr50Ti35Nb15)90Al10 and (Zr50Ti35Nb15)85Al15 were also tested to investigate the effect of Al content on the yield strength. Our findings provide a new insight in developing low-density high entropy alloys containing Al.

Fabrication of MgAlSiCrFe Low-Density High-Entropy Alloy by Mechanical Alloying and Spark Plasma Sintering

Fabrication of MgAlSiCrFe Low-Density High-Entropy Alloy by Mechanical Alloying and Spark Plasma Sintering

MgAlSiCrFeNi low-density high entropy alloy processed by mechanical alloying and spark plasma sintering: Effect on phase evolution and thermal stability

Equiatomic MgAlSiCrFeNi low-density high-entropy alloy (LDHEA) was prepared by mechanical alloying followed by spark plasma sintering (SPS). The phase evolution, chemical composition, and thermal stability of the alloy were analyzed by X-Ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques. Formation of a BCC phase having a lattice parameter of 0.2876±0.03 nm and undissolved Si (~3 at%) was observed after milling of 60 h. DSC experiment up to 1200 °C (1473 K) shows five exothermic heating events corresponding to various phase transformations, which were matched with the results obtained from XRD experiments. It has been found that the alloy after high temperature annealing led to the evolution of a major B2 phase (a=0.289 nm) and also BCC phase along with small amounts of FCC Al-Mg solid solution phase, FCC 1 (a= 0.4082 nm) and FCC 2 (a= 0.4215 nm), monoclinic Al13Fe4 (a= 1.549 nm, b= 0.808 nm, c= 1.248 nm, α = β = 90˚), Mg2Si (a= 0.6351 nm), Cr5Si3 (a=b= 0.9165 nm, c= 0.4638 nm). The spark plasma sintered (SPS) sample also exhibited BCC and B2 phases coexisting with minor amounts of other phases observed for 800 °C (1073 K) annealed sample. The co-exsistence of minor phases with parent BCC phase in SPSed alloy (having relative density of ~99.40%) has led to significantly high hardness and modulus of elasticity of ~9.98 ± 0.3 GPa and 229 ± 0.3 GPa respectively. Various thermodynamics parameters were calculated in order to correlate with the experimental findings of phase evolution and stability of the annealed powder and spark plasma sintered alloy.

Synthesis, Characterization and Thermal Stability of Nanocrystalline MgAlMnFeCu Low-Density High-Entropy Alloy

An equiatomic quinary MgAlMnFeCu high-entropy alloy (HEA) has been synthesized successfully by mechanical alloying (MA). Phase evolution of MgAlMnFeCu HEA has been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS/XEDS). Milling up to 60 h leads to the formation of a mixture of two phases consisting of a BCC phase (a = 2.87 ± 0.02 A) and ϒ-brass-type phase (a = 8.92 ± 0.03 A), with ~ 2 μm powder particle size. The as-milled alloy after spark plasma sintering (SPS) at 900 °C exhibits an experimental density of 4.946 ± 0.13 g cc−1, which is 99.80% of the theoretical density. SPS leads to the formation of C15 Laves phase (MgCu2-type; a = 7.034 ± 0.02 A) and B2 (AlFe-type; (a = 2.89 ± 0.02 A) intermetallic along with the ϒ-brass-type phase. The SPSed sample has exceptional hardness value (~ 5.06 GPa), high compressive strength (~ 1612 MPa) and appreciable failure strain (~ 6.4%) coupled with relatively low density. Various thermodynamic parameters have been considered for understanding the phase evolution and their stability during MA.

Combinatorial development of the low-density high-entropy alloy Al10Cr20Mo20Nb20Ti20Zr10 having gigapascal strength at 1000 °C

A pseudo-ternary combinatorial approach to AlxTayVzCr20Mo20Nb20Ti20Zr10 revealed the composition of refractory high-entropy alloys characterized by outstanding high-temperature yield strength. Compression testing of Al10Cr20Mo20Nb20Ti20Zr10 disclosed yield strengths of 1206 MPa at 1000 °C, one of the highest values reported for refractory high-entropy alloys. Ta-containing AlxTayVzCr20Mo20Nb20Ti20Zr10 presented a lower high-temperature strength, while characterization of Al10Cr20Mo20Nb20Ti20Zr10 showed C14 Al2Zr- and NbCr2-type hexagonal Laves intermetallics, with a hardness of ∼10.5 GPa (higher than that of the body centered cubic phase, at ∼9 GPa). The stronger bonds between Al and transition metals appear to give rise to extraordinary load-bearing capabilities in Al10Cr20Mo20Nb20Ti20Zr10, at high temperatures. Owing to this rare combination of relatively low density (6.96 g/cm3) and remarkable high-temperature strength, Al10Cr20Mo20Nb20Ti20Zr10 has emerged as a potential material for high-temperature structural applications.

Temperature dependent deformation behavior and strengthening mechanisms in a low density refractory high entropy alloy Al10Nb15Ta5Ti30Zr40

A low-density high entropy alloy Al10Nb15Ta5Ti30Zr40 has been developed which exhibits excellent compressive room temperature ductility, despite the presence of Al. Microstructure, room temperature and elevated temperature mechanical properties of this newly-designed alloy have been reported in as cast and heat-treated conditions. The homogenized and continuously cooled (water quenching or air cooling) conditions of this alloy consist of a nanoscale mixture of a disordered BCC and an ordered B2 phases, while subsequent low temperature annealing treatment leads to the formation of additional phases. In the homogenized condition, the yield stress of the alloy is 1050 MPa at 23 °C, 852 MPa at 400 °C and 1059 MPa at 600 °C. Above 600 °C, the yield stress decreases rapidly with increasing temperature becoming 250 MPa at 800 °C and less than 50 MPa at 1000 °C and 1200 °C. Correlations between the mechanical properties and microstructure, as well as temperature-dependent operating strengthening mechanisms, are also discussed in this paper.

Nanocrystalline high-entropy alloys

Abstract

The Phase Composition and Microstructure of AlxCoCrFeNiTi Alloys for the Development of High-Entropy Alloy Systems

Alloying aluminum offers the possibility of creating low-density high-entropy alloys (HEAs). Several studies that focus on the system AlCoCrFeNiTi differ in their phase determination. The effect of aluminum on the phase composition and microstructure of the compositionally complex alloy (CCA) system AlxCoCrFeNiTi was studied with variation in aluminum content (molar ratios x = 0.2, 0.8, and 1.5). The chemical composition and elemental segregation was measured for the different domains in the microstructure. The crystal structure was determined using X-ray diffraction (XRD) analysis. To identify the spatial distribution of the phases found with XRD, phase mapping with associated orientation distribution was performed using electron backscatter diffraction. This made it possible to correlate the chemical and structural conditions of the phases. The phase formation strongly depends on the aluminum content. Two different body-centered cubic (bcc) phases were found. Texture analysis proved the presence of a face-centered cubic (fcc) phase for all aluminum amounts. The hard η-(Ni, Co)3Ti phase in the x = 0.2 alloy was detected via metallographic investigation and confirmed via electron backscatter diffraction. Additionally, a centered cluster (cc) with the A12 structure type was detected in the x = 0.2 and 0.8 alloys. The correlation of structural and chemical properties as well as microstructure formation contribute to a better understanding of the alloying effects concerning the aluminum content in CCAs. Especially in the context of current developments in lightweight high-entropy alloys (HEAs), the presented results provide an approach to the development of new alloy systems.

Physical properties of the multifunctional Mg80Ni10Gd10 alloy

The focus of this work is on exploring the effect of cooling rate on the microstructure and hardness of the Mg80Ni10Gd10 alloy which is known for its potential hydrogen storage capability. A series of chart is displayed to compare the mechanical and transport properties with commercial Mg-based alloys, Mg-based metallic glasses and low density high entropy alloys. We outline the interest of this alloy composition for the development of new light metal high entropy alloy with multifunctionality.

Phase formations in low density high entropy alloys

Phase formations in high entropy alloys (HEAs) with at least two light elements in literature are predicted by CALPHAD (CALculation of PHAse Diagrams) thermodynamic calculations and the results are compared with experimental observations. The comparison suggests that the applicability of traditional CALPHAD calculations depends on the manufacturing processes of HEAs. Factors such as solute trapping, energies of defects need to be considered while predicting phases in HEAs prepared by non-equilibrium processes. The effects of light elements (Al, Ti, Si, alkali and alkaline earth metals) on the phase formations in HEAs are discussed. Especially, intermetallics predicted for Si-containing HEAs by traditional CALPHAD calculation can be suppressed in rapid solidification process, due to the solute trapping effect. Mg or other alkali and alkaline earth metals can lead to the formations of various intermetallics in HEAs prepared by conventional casting, but could be dissolved into solid solutions by non-equilibrium processes such as mechanical alloying. It is proposed that non-equilibrium processes may be an effective way to introduce light elements Si, alkali and alkaline earth metals into HEAs.

Equal-Channel Angular Extrusion of a Low-Density High-Entropy Alloy Produced by High-Energy Cryogenic Mechanical Alloying

In this study, we demonstrate the feasibility of forming a bulk consolidated, low-density high-entropy alloy, namely AlFeMgTiZn, which shows reasonable mechanical properties and high hardness. The fabrication of the high-entropy alloy from powdered precursors via high-energy mechanical alloying as a function of milling time is presented. In turn, the evolution of the alloy microstructure with postmilling anneal treatment is elucidated. Last, the severe plastic deformation processing methodology, i.e., equal-channel angular extrusion, chosen for consolidation, is described and shown to result in a bulk product with good results.