High Entropy Research Articles

Novel high entropy alloy/NiAl2O4 photocatalysts for the degradation of tetracycline hydrochloride: Heterojunction construction, performance evaluation and mechanistic insights

Novel NiAl2O4 (NAO)/high entropy alloy (HEA) (Ti), NAO/HEA (Mn) and NAO/HEA (Mo) heterojunction photocatalysts with high photocatalytic activity for the degradation of tetracycline hydrochloride (TC) under simulated sunlight irradiation were synthesized by the polyacrylamide gel method combined with a low temperature sintering technique. The effects of environmental parameters, including drug concentration, catalyst content and pH value, on the photocatalytic activity of NAO/HEA photocatalysts were investigated in detail on the basis of the response surface methodology (RSM) and experimental results. The optimal initial TC concentration, catalyst content, and pH were 100 mg/L, 1 g/L, and 5, respectively. The photocatalytic activity of NAO/HEA photocatalyst (84.6 %) was significantly improved compared to the degradation percentage of HEA (Ti) photocatalyst (36.5 %). The roles of active free radicals including h+, •O2−, •OH and oxygen vacancy in photocatalysis were verified using multiple characterization methods. In-depth analysis was conducted on the degradation pathway of TC, the safety of degradation intermediates, and the photocatalytic mechanism of NAO/HEA (Ti) photocatalyst. The Z - scheme heterojunction can significantly improve the transport efficiency of photogenerated carriers and inhibit the recombination rate of electron hole pairs in the system, which provides a new idea for exploring the application of new HEA - based heterojunction photocatalysts in the field of photocatalysis.

Synthesis of a novel textured high entropy M4AlC3 (M = Ti, V, Mo, Nb, Ta) composites with improved mechanical properties via spark plasma sintering

A novel high-entropy M4AlC3 phase ceramic (M=Ti, V, Mo, Nb, Ta) was synthesized by three-step solid phase sintering, and the textured high-entropy M4AlC3 composites were prepared for the first time by SPS uniaxial pressing of nano flakes generated via reactive ball milling. The microstructure were characterized in detail and Maud software was used for Rietveld refinement analysis of phase composition content. The results showed that Ti, V, Mo, Nb, Ta were successfully dissolved in M4AlC3. On this basis, the density, hardness and mechanical properties before and after texture were tested. The results showed that the textured composite achieved 12.1 GPa Vickers hardness (//C-axis), 2.2 GPa compressive strength (//C-axis), 8.8 fracture toughness of MPa m1/2 (//C-axis) and 726 MPa bending strength (//C-axis). Dispersively distributed nano-Al2O3 and texturization played a key role in strengthening and toughening. This work can provide an important reference for the subsequent preparation and texturing of high-entropy MAX ceramics.

Study of high-entropy oxide diffusion barrier and diffusion resistance mechanism in high-temperature protective coatings

In order to obtain high temperature protective coatings with low diffusivity, high entropy (HEA) as well as high entropy oxide (HEO) diffusion barriers were deposited between the NiCrAlY coating and the substrate by magnetron sputtering. These two coatings were subjected to constant temperature oxidation tests at 1050 °C. These results show that the two coatings containing diffusion barriers have better high-temperature oxidation properties compared to the NiCrAlY coating. Both HEA and HEO diffusion barriers have the desired performance in hindering the diffusion of elements between the coating and the substrate. The evolution of these two diffusion barriers and the mechanism of diffusion resistance during the oxidation process have been investigated.

Structural insights, synthesis, and electrocatalysis of high entropy nanoparticles for fuel cell, metal-air battery, and water-splitting applications

High-entropy alloy nanoparticles (HEA-NPs) have recently sparked great interest in materials science. Their solid-solution states, derived from distinct HEA configurations, make them promising candidates for catalysts with exceptional activity, stability, and tunable performance. However, a comprehensive understanding of the underlying mechanisms governing their electrocatalytic behavior is still lacking, hindering the rational design of HEA electrocatalysts. This review summarizes the fundamental knowledge of HEA-NPs, including the structure-activity correlations of HEA-NPs, diverse synthesis strategies, and applications in electrochemical catalysis. The design strategies for guiding improvements in tunable performance were highlighted. The article concludes with insights, perspectives, and future directions, encapsulating the state-of-the-art knowledge and paving the way for further exploration in this dynamic field.

Effect of Cr content on microstructure, mechanical, and corrosion properties of CoCrxFeMnNi high-entropy alloys fabricated by selective laser melting

The method of using mixed powder for SLM in-situ alloying to prepare high entropy alloys has been verified to be feasible. In this investigation, the effect of Cr addition on microstructure uniformity, mechanical properties, and corrosion resistance of CoCrxFeMnNi High-entropy alloy (with x = 0.4, 0.7, 1.0, 1.3 at. %) prepared by the SLM in-situ alloying technique has been thoroughly investigated. X-ray diffraction and scanning electron microscopy suggest that all CoCrxFeMnNi HEAs samples are composed of a FCC matrix and little residual Cr particles, and all elements of the FCC matrix are evenly distributed, accompanied by a very small amount of Mn evaporation. Electrochemical corrosion tests have shown that with an increase in Cr content, the corrosion resistance of the alloy is significantly improved. The CoCr1.3FeMnNi HEAs possess the best corrosion resistance against the attack of the Cl ion, with a corrosion rate 0.671 × 10−3 mm / year. Furthermore, the Cr element can significantly improve the microhardness, tensile strength, and plasticity of CoCrxFeMnNi HEAs. The CoCr1.3FeMnNi HEAs possess the best mechanical properties, with microhardness 217.8 HV0.5, tensile strength 691 MPa and elongation rate 18.9%, respectively.

A review of flame aerosol synthesis technology for the synthesis of nanoparticles and functional energy materials

The outstanding performance of nanomaterials in chemical, magnetic, electrical, catalytic, and mechanical properties has paved the way for the huge market in material fabrication, energy storage, electronics, and many other industries. Traditional synthesis methods are relatively stunted in industrial applicability and scalability due to complex manufacturing processes and long preparation times, hampering the development and commercialisation of nanomaterials. On the other hand, the flame synthesis method emerges as an inexpensive, efficient, and easily scalable method for the commercial production of nanoparticles. The present review aims to highlight the research status and applications of the nanomaterials synthesised by the flame aerosol method. The advancement of flame aerosol synthesis technologies is reviewed, with emphasis on the state-of-the-art flame reactor configuration and design. Critical flame parameters that govern the formation of nanoparticles in the flame are reviewed to provide an understanding of the formation criteria and growth of nanomaterials in the flame environment. The properties and characteristics of carbon-based, platinum group metal, metal oxide, bimetallic nanoparticles, perovskite and high entropy oxide nanomaterials produced by flame synthesis are extensively reviewed. In addition, commercial manufacturing of flame-synthesised materials along with applications of the nanomaterials in the field of thermal or photocatalytic energy storage, fuel cells, and gas sensing are presented.

Significantly improved bonding strength of Al/Mg bimetallic interface by compound casting via FeCoNiCrCu high entropy alloy coating

FeCoNiCrCu high entropy alloy (HEA) coating was introduced into the interface of Al/Mg bimetal prepared by a compound casting in order to improve the bonding strength of the Al/Mg bimetal. With the application of the FeCoNiCrCu HEA coating, the HEA coating greatly inhibited the diffusion between Al and Mg, and the Al and HEA tended to form a new solid solution structure. The brittle Al–Mg intermetallic compounds were significantly reduced, leading to a remarkable decrease in interface thickness, only 9.86 % of the original interface. The Al/Mg bimetal formed a complex interface of Al3Mg2+Mg2Si/AlxFeCoNiCrCu + FeCoNiCrCu + Mg2Ni mixed phases/δ-Mg + Al12Mg17 eutectic structure. Molecular dynamics simulations further confirmed that adding FeCoNiCrCu HEA coating effectively hindered the diffusion between Al and Mg and prevented the formation of the Al–Mg intermetallic compounds. The shear strength increased from 30.62 MPa to 50.47 MPa, increasing by 64.83%, owing to the remarkable decrease of the Al–Mg intermetallic compounds and the generation of the Mg2Ni mixed phases in the interface. The fracture of the bimetal with the HEA coating occurred between the HEA coating and δ-Mg + Al12Mg17 eutectic with a certain plastic deformation, while the fracture of the bimetal without HEA coating was located in Al3Mg2 layer, showing an obvious brittle fracture.

Dynamic shear resistance and its dependence on geometrical imperfection of high entropy Cantor alloy and BJAM 316L stainless steel

This paper examines the adiabatic shear resistance of recently popular Cantor alloy and Binder Jetting Additive Manufacturing (BJAM) 316L, with emphasis on their dependence on geometrical imperfection. A series of shear tests were conducted by using the Split Hopkinson bar and shear compression specimen (SCS). Both alloys present strain rate dependent shear behaviour with the large dynamic shear failure strain of about 104 %-132 %. Microstructural characterizations reveal that both Cantor and BJAM 316L alloys fail by adiabatic shear band. Introduced by the varying notch root radius, the sharpness significantly affects the dynamic shear resistance of the Cantor and BJAM 316L alloys. The linear functions are proposed to describe the drop of critical strain and energy density with the designed inverse root radius.

Enhancing the adiabatic shear resistance of Ti-Zr-Nb-Al high entropy alloy via metastability engineering

Dual-phase Ti-Zr based high entropy alloys are lightweight structural materials with high specific strength, which are promising for the application in warheads and munitions. However, they usually experience adiabatic shear under impact, resulting in early failure. Here, we demonstrate an effective method to enhance the adiabatic shear resistance, benefiting from the transformation-induced plasticity (TRIP) effect. The composition of Ti-Zr-Nb-Al is designed based on a combination of lattice distortion enthalpy, mixing enthalpy, and Bo¯-Md¯ criteria, to enable a metastable solution structure. The alloy is directly water quenched from 900 ℃ to maximally keep the metastable BCC phase (MA), while an annealed alloy with the BCC+HCP dual-phase structure (PA) is also fabricated for comparison. The metastable MA alloy exhibits a doubled fracture strain and 79% enhancement of impact energy compared with the dual-phase PA alloy, while its dynamic ultimate strength remains almost unchanged. Microstructural analyses at different dynamic stain levels reveal a BCC-α" phase transformation in MA alloy, which delays the generation of phase boundaries, avoids the premature stress concentration, and thereby delays the occurrence of adiabatic shear.

The role of the preparation route on microstructure and mechanical properties of AlCoCrFeNi high entropy alloy

Nearly equiatomic AlCoCrFeNi alloy samples were prepared by induction melting and mechanical alloying (MA) combined with spark plasma sintering (SPS). The cast sample showed a dendritic microstructure composed of spinodally decomposed nanometric constituents of the B2 and BCC phases. The spark plasma sintered sample exhibited an ultrafine-grained microstructure of B2 phase and FCC solid solution and Cr23C6 carbides. The MA+SPS sample was strengthened by compressive stress-strain test up to a yield strength of 2029 ± 5 MPa, resulting significantly higher compared to 1366 ± 32 MPa of the cast sample. In addition to the higher compressive yield strength, the sintered sample exhibited a hardness of more than 130 HV higher compared to the cast alloy. On the other hand, the cast alloy showed high plastic deformation (29%) and significantly high ultimate compressive strength of 3072 ± 122 MPa. Together with these mechanical characteristics, the MA+SPS sample showed good thermal stability while preserving the mechanical properties even after annealing at 800 °C. This was not the case with the cast sample, in which ductility and ultimate strength significantly decreased upon annealing at 800 °C. A substantial yield strength reduction of both MA+SPS and cast samples was recorded when tested at 800 °C. Nevertheless, stress-strain curve trends were observed to be quite different between the two samples, thus suggesting dissimilar deformation mechanisms under high-temperature compression.

Surface nanoprecipitation induced by severe plastic deformation in the Fe49.3Co23Ni23C0.85Mn1Si2.85 biphasic multicomponent alloy

Precipitation strengthening plays a vital role in enhancing the mechanical properties of metallic materials, typically achieved through heat treatment. However, deformation-induced precipitation (DIP) in multicomponent alloys (MAs) without the assistance of annealing is rarely reported, owing to their inherent high entropy and sluggish diffusion effects. This work reveals the significant formation of nanoscale and microscale precipitates in dual-phase Fe49.3Co23Ni23C0.85Mn1Si2.85 MA triggered by surface severe plastic deformation (SSPD) through industrial shot blasting. The SSPD process leads to the formation of ultrafine gradient structures comprising nanocrystalline and submicron-crystalline zones. Submicron SiO2 precipitates emerge at the interfaces of both these zones, while various Mn5Si3 and Si nanoparticles precipitate within the nanocrystalline zone. This phenomenon can be ascribed to the high density of generated substructures, the accelerated diffusion of atoms, and the reduction in solid solubility limits in the SPD-driven non-equilibrium state.

Designing gadolinium-transition metals-based perovskite type high entropy oxides with good cryogenic magnetocaloric performances

Cryogenic magnetic cooling based on the principle of the magnetocaloric effects (MCEs) of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits. Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications. In this study, three gadolinium-transition metal-based high entropy oxides (HEOs) of Gd(Fe1/4Ni1/4Al1/4Cr1/4)O3, Gd(Fe1/5Ni1/5Al1/5Cr1/5Co1/5)O3, and Gd(Fe1/6Ni1/6Al1/6Cr1/6Co1/6Mn1/6)O3 were designed and systematically characterized regarding their structural and cryogenic magnetic properties. These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure, reveal a second-order magnetic transition at low temperatures, and exhibit significant cryogenic MCEs. The magnetocaloric performances of the present HEOs, identified by magnetic entropy changes, relative cooling power, and temperature-averaged entropy changes, were comparable with recently reported candidate materials. The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.

Cooperative roles of twinning, transformation and strain partitioning on the excellent cryogenic strength-toughness synergy of dual-heterogeneous metastable high entropy alloys

In a metastable Fe50Mn30Co10Cr10 high entropy alloy (HEA), a dual-heterogeneous structure, encompassing both grain size and dislocation heterogeneity, has been constructed to obtain excellent cryogenic mechanical performance by varying the annealing temperature (630 and 740 °C) following severe deformation. The HS-630 sample, consisting of recovered coarse-grains (CG), recrystallized fine-grains (FGs) and un-recrystallized ultrafine-grains (UFGs), possesses higher yield strength (YS) of ∼965 MPa, ultimate tensile strength (UTS) of ∼1680 MPa and uniform elongation (UEL) of ∼45% when compared to the fully-recrystallized HS-740 sample at liquid nitrogen temperature (LNT). The difference in YS is primarily caused by the grain boundary and dislocation strengthening of UFGs, whereas the higher ductility of the HS-630 sample is associated with the hierarchical activation of transformation- and twinning-induced plasticity (TRIP and TWIP) effects, and compatible strain partitioning between heterogeneous domains. The dual-heterogeneity results in different critical stresses of ε-phase nucleation in heterogeneous domains, and promotes sustainable TRIP effect in CGs and the emergence of TWIP effect in UFGs with strain progressing. Moreover, the strain of the ductile transformed ε-phase is mainly accommodated by non-basal slip, which contributes to the strain hardening in the later deformation stage. Furthermore, the higher cryogenic impact toughness of the HS-630 sample can be attributed to the synergistic effects of the fracture mode, the transformation characteristics, and the heterogeneous strain partitioning.

Optimized deep learning regression assisted wear rate analysis of Cu–AlCoCrCuFe HEA composite

At present, composites have brought materials to a new era with superior characteristics. The proper selection of materials with optimal processing conditions is one of the prime factors in determining the efficiency of composites. This article introduces a new composite by fabricating a copper matrix with reinforced AlCoCrCuFe High Entropy Alloy (HEA). The ultimate theme of this research is to forecast the wear rate of the Cu–AlCoCrCuFe HEA composite. Using the pin on the disk, the wear test is carried out on varying combinations of parameters. Then Taguchi analysis is carried out to get the precise fit parameters. The wear rate mainly depends on the percentage of HEA, sliding distance, sliding velocity, and the load applied. Correlation analysis is performed to determine the exact parameter determining the optimal wear rate and the coefficient of friction. After feature extraction, the parameters are optimized, and the neural network regression is given the optimized parameters. The network has been trained, and predictions are made using it. The model successfully predicts the wear rate, as evidenced by the declining RMSE of 0.28 and rising R2 values up to 92%. The analysis shows a significant decline in the wear rate with HEA additions. In addition, the wear rate increases with a rise in load, sliding velocity, and sliding distance.

A strong and ductile biocompatible Ti40Zr25Nb25Ta5Mo5 high entropy alloy

A non-equiatomic high entropy alloy (HEA) Ti40Nb25Zr25Ta5Mo5 (at.%) was designed by replacing 5% Ta with 5% Mo in a precursor Ti40Nb25Zr25Ta10 HEA for improved mechanical properties and reduced density. The Ti40Nb25Zr25Ta5Mo5 HEA from copper mould casting exhibited a nearly equiaxed grain structure (grain size: 96 ± 16 μm), but within each equiaxed grain, dendritic structures are discernible in the backscattered electron imaging mode. These dendrites are enriched in Ta, Nb and Mo, while the inter-dendritic regions contain higher Zr and Ti. The as-cast HEA achieved tensile yield strength (σ0.2) of 976 ± 8 MPa and strain to fracture (εf) of 16.80 ± 1.86%, well above the minimum requirements of σ0.2 and εf for medical-grade titanium alloy Ti-6Al-4V (759 MPa and 10%). The formation of microscale and nanoscale shear bands and the presence of significant dislocations in the shear band boundary region played a key role in allowing this as-cast new HEA to achieve the excellent combination of tensile strength and ductility. Furthermore, it exhibited a lower wear rate, lower coefficient of friction and much higher corrosion resistance in Hank’s solution (electrochemical assessments) than Ti-6Al-4V, making it a promising alternative biomedical alloy.

Constructing high entropy alloy/MoC heterostructure as efficient and stable catalysts for oxygen evolution reaction

Due to the expensive cost of precious metals, there is an urgent need to develop cheap and efficient catalysts for the oxygen evolution reaction (OER). As a novel catalyst, high-entropy alloy (HEA) has found widespread application in the field of hydrogen production through water electrolysis. However, a significant portion of HEA catalysts prepared by traditional solvothermal methods are challenging due to their high cost, extended compound cycle, and relatively difficult electronic structure adjustment in the catalytic center. In this study, a heterostructure catalyst composed of MoC and FeCoNiMo HEA alloy (denoted as FeCoNiMo-M) was synthesized by the microwave method. Catalysts produced via the microwave method typically exhibit MoC encloses the spherical heterostructure of the internal high entropy alloy, MoC not only protects the true active center NiOOH, but even further regulates the electronic structure of the catalyst. Notably, the FeCoNiMo-M sample synthesized using microwave demonstrates an overpotential of merely 232 mV (@10 mA cm−2) in 1 M KOH, nearly 20 mV lower compared to the traditional hydrothermally-synthesized FeCoNiMo-H HEA catalyst. Furthermore, the FeCoNiMo-M catalyst demonstrates impressive durability in OER with a significant current density of 100 mA cm−2 for a duration of 240 hours. The in-situ Raman results indicate that the FeCoNiMo-M catalyst undergoes the conversion of the actual reaction intermediate NiOOH and accelerates the OER with only a very low overpotential. These findings suggest that our approach could open up possibilities for the advancement of OER catalysts that are both more convenient and efficient.

Effect of Si concentration and substrate temperature on the microstructure and magnetic properties of FeCoNiCu0.5Six high entropy alloy films

It has been known that Si has the effect to increase the resistivity, permeability, and to decrease the magnetostriction coefficient in Si-containing steel as soft magnetic material. On the other hand, high-entropy alloys are intensively studied as soft magnetic materials in recent years, especially as thin films. In the present work, Si-containing (FeCoNiCu0.5Six) high entropy alloy films (HEAFs) have been prepared by magnetron co-sputtering under different deposition conditions. The microstructure and magnetic properties of FeCoNiCu0.5Six HEAFs have been investigated to clarify the effects of Si concentration on microstructure formation and magnetic properties. It has been found that Si addition strongly affects the magnetic properties of FeCoNiCu0.5Six HEAFs of FCC phase by decreasing the coercivity of the films, but hardly affects the phase formation in the films. On the other hand, it has been found that deposition of the films at moderate high substrate temperatures greatly improve the magnetic properties by increasing the saturation magnetization while keeping low coercivity.

Aluminium matrix composites reinforced with high entropy alloys: A comprehensive review on interfacial reactions, mechanical, corrosion, and tribological characteristics

Aluminium matrix composites (AMCs) reinforced with high entropy alloy particulates (HEAp) represent an innovative category of metal-matrix composites with considerable potential for fulfilling the stringent demands of emerging technological applications. Their appeal lies in the advantageous combination of toughness, strength, ductility, and enhanced workability, addressing acknowledged limitations associated with ceramic-reinforced AMCs. The heightened performance of these composites is attributed to improved wettability between the aluminium matrix and HEAp reinforcement, alongside the intrinsic ductility and hardness of HEAp. This review explores the suitability of high entropy alloys as substitutes for ceramic materials in reinforcing aluminium matrix composites. The mechanical, corrosion, thermal and wear properties of AMCs reinforced with HEAp are thoroughly examined, encompassing fabrication characteristics and interfacial reactions. The incorporation of HEAp is found to notably enhance the strength-ductility ratio of AMCs. Remarkably, HEAp bring about significant improvements in the wear and corrosion resistance of AMCs. The report accentuates the performance benefits and certain challenges associated with the application of HEAp reinforcement in AMCs. Ultimately, this review proposes potential avenues for future research in this domain, outlining directions for further exploration and development.

Numerical study on natural convection in a saturated non Darcian porous medium under radiation and entropy generation effects

This work focuses on analyzing fluid flow, generation of entropy, and heat transfer during natural convection in a cavity enclosed with a non-Darcian saturated porous medium. The influence of viscous dissipation and thermal radiation are considered. The Lattice Boltzmann method is adopted to simulate the governing equations. The study discusses the genersl effect of dimensionless parameters on the fluid structure interaction properties, entropy generation and the thermal field. The parameters investigated include the Grashof number, Eckert number, Rayleigh number, Forchheimer Resistance, inverse Darcy, radiation parameter, and Prandtl number. The combination of studying dimensionless parameters on non-Darcian porous medium, along with the consideration of thermal radiation, viscous dissipation, and entropy analysis, has made this research valuable and worth pursuing. The findings reveal that the areas of high entropy generation are primarily located along the walls (vertical) of the cavity. Moreover, it is observed that as the inverse Darcy and Forchheimer resistance increase, their effect on the average Nusselt number diminishes for varying parameters of radiation. As the Prandtl number increases, the isotherms cluster along the walls (vertical) of the porous cavity. With high Grashof values, convection becomes turbulent, and the temperature distribution becomes non-uniform. Additionally, the entropy caused by heat and fluid friction decreases as the Forchheimer resistance increases.

AlNbTiVZr refractory high entropy alloy combining exceptional high-temperature performance and excellent ductility fabricated by laser direct energy deposition

In this study, a new refractory high entropy alloy (RHEA) Al-Nb-Ti-V-Zr is fabricated by laser direct energy deposition (LDED), and an investigation is conducted to explore the hot deformation. The body-centered cubic (BCC) phase structure and a small number of densely arranged hexagonal lave intermetallic phases of RHEA are predicted by combining XRD with the calculation of empirical parameters. Compression tests are carried out at different temperatures, and the results show that no fracture occurs when the strain reaches 50% at any of the temperatures tested while exhibiting a high yield stress. The dynamic softening effect is enhanced as the temperature increases and the yield stress decreases significantly. A slight hardening trend is observed during the steady-state flow stage of the stress-strain curve. The softening of RHEA is mainly caused by dynamic reversion (DRV) and assisted dynamic recrystallization (DRX), where the atomic mobility at the grain boundaries increases with temperature, promoting the creation of recrystallized grains.