High-entropy Metallic Glasses Research Articles

High Oxygen Reduction Efficiency and Durability of Nano-Honeycomb Pt3(NiFeCo) Replenished by High-Entropy Metallic Glass Support.

Developing low-Pt oxygen reduction reaction (ORR) catalysts with high efficiency and robustness is critical for practical fuel cells. The most advanced ORR catalysts either feature high percentages of Pt (>70 at.%) or exhibit poor durability when reducing Pt loading. Herein, a multicomponent solid-solution Pt3(FeCoNi) honeycomb nano-framework supported by the specially designed high-entropy metallic glass (MG) is reported for efficient ORR. This hybrid catalyst with a low surface Pt loading of 5.79µgcm-2 displays exceptional mass and specific activities of 7.02Amgpt -1 and 8.15mAcmPt -2 at 0.9V, respectively, which are ≈15 and 22 times higher compared with commercial Pt/C. The analyses reveal the weakened chemisorption of oxygenated species, which is induced by the strong strain and ligand effects originating from the synergistic multicomponent alloying. This in turn enhances the intrinsic ORR activity. Moreover, benefiting from a unique replenishment behavior, the hybrid catalyst delivers ultra-high durability with negligible activity decay even after 50 000 potential cycles. This mechanism is achieved by sacrificing the interior MG supplementary support to dynamically compensate for the loss of catalytically active surface. The work provides an alternative way to design more efficient and durable low-Pt electrocatalysts for electrochemical devices.

Bridging the gap between high-entropy alloys and metallic glasses: Control over disorder and mechanical properties of coatings

High-entropy alloys (HEAs) and high-entropy metallic glasses (HEMGs) represent two intensively researched classes of materials with high technological interest for applications as functional coatings with high strength, hardness, toughness, and corrosion resistance. The distinctive structural difference between single-phase crystalline solid solutions for HEAs and liquid-like disorder for HEMGs generates a seemingly insuperable contrast. In this work, we demonstrate that we can deliberately choose between crystalline or glassy properties by introducing structural disorder in HfMoNbTiZr thin films of identical composition. Using pulsed laser deposition (PLD) at different growth conditions, we reproducibly tune the structure of HfMoNbTiZr coatings from crystalline to fully amorphous. We show that the level of disorder has a profound impact on the mechanical properties of the coatings using the hardness derived from nanoindentation measurements as an example. While the hardness of polycrystalline HfMoNbTiZr layers already exceeds the single-phase bulk value, the amorphous HfMoNbTiZr is even clearly harder, demonstrating a distinctive improvement with introducing disorder. Our findings bridge the two seemingly different concepts of HEAs and HEMGs and demonstrate that structural disorder is not a given material property. Instead, disorder can serve as a useful design parameter for customizing the properties of functional coatings.

Low-temperature magnetic refrigeration in Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses

This paper focuses on the magnetocaloric effect (MCE) of Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses (HE-MGs). XRD and TEM results indicate that both HE-MGs are amorphous. Magnetic studies show that both HE-MGs display spin-glass behavior, undergo a second-order phase transition from ferromagnetic to paramagnetic, and exhibit soft magnetic properties at the Curie temperature (TC). Notable large and broad table-like magnetic entropy change characteristics of Gd20Tb20Er20Al20Fe20 (Gd20Tb20Er20Al20Co20) appear near a TC of 92 (51) K. Hence, under 7 T magnetic field, |-∆SMmax|, ∆ TFWHM, and RCP are 7.83 (10.10) J·kg-1·K-1, 120.07 (71.88) K, and 1008.26 (805.70) J·kg-1, respectively. Furthermore, the modulation of the magnetic and magnetocaloric properties of the samples after substitution of Fe for Co was revealed by the intricate 3d-3d and 3d-4f exchange interactions within the system. The magnetic phase transition critical behaviors in both HE-MGs were analyzed using the scaling law to clarify the deviation of amorphous materials from the mean-field theory. Thus, this study not only highlights the potential of this material for low-temperature magnetic refrigeration applications, but also expands our understanding of its physical properties.

Unique Energy‐Storage Behavior Driven by High Entropy in Metallic Glasses

AbstractThe rejuvenation or energy‐storage behavior in metallic glasses (MGs) has been extensively explored for its theoretical and practical significance. However, very limited research focuses on the rejuvenation of high entropy metallic glasses (HEMGs), leaving uncertainties about how configurational entropy influences this process. In this study, cryogenic temperature cycling (CTC) is utilized to unlock the rejuvenation potential of a series of La‐based MGs with different entropy values. Comparative analysis of these MGs reveals that increased entropy boosts the maximum rejuvenation degree from 37% to 65% and widens the range of energy states where rejuvenation occurs. The changed rejuvenation behavior induced by entropy increase, which has never been reported other studies, are related to glass's structures, fragility and coupling degree between β and α relaxations. Besides, a new rejuvenation mechanism is revealed in HEMGs, which differs significantly from unrestricted growth and interconnection of flow units observed in most MGs. The atomic motion in HEMGs is confined within the icosahedral backbone network during CTC. Surprisingly, this local motion can propagate through strong interactions between adjacent atoms, facilitating the activation of α relaxation. These discoveries offer novel approaches to tune energy‐storage behavior of MGs by modulating icosahedral network structures through entropy control.

Impact of annealing on structural and corrosion resistance properties of Ti20Zr20Hf20Be20Ni20 high-entropy metallic glass

Impact of annealing on structural and corrosion resistance properties of Ti20Zr20Hf20Be20Ni20 high-entropy metallic glass

Atomic Structure Amorphization and Electronic Structure Reconstruction of FeCoNiCrMox High-Entropy Alloy Nanoparticles for Highly Efficient Water Oxidation.

The complexity of the multielement interaction in high-entropy alloys (HEAs) may provide more active sites to adapt different catalytic reaction steps in oxygen evolution reaction (OER). Investigating the correlation between structure and performance of HEAs electrocatalysts is both essential and challenging. In this work, FeCoNiCrMox HEAnanoparticles are successfully fabricated utilizing a unique nanofabrication method called inert gas condensation. With the increase of high-valence metal component Mo, the atomic structure amorphization and electronic structure reconstruction are unveiled. According to the X-ray photoelectron spectroscopy valence spectra, the d-band center of FeCoNiCrMox is ascending, and thus enhancing the adsorption energy. Synchrotron pair distribution function analysis reflects the degree of structural disorder and reveals a robust correlation with the intrinsic OER activities of the electrocatalysts. FeCoNiCrMo1.0 high-entropy metallic glass nanoparticles exhibit an outstanding OER performance with an ultralow overpotential of 294.5mV at a high current density of 100mAcm-2. This work brings fundamental and practical insights into the modulation mechanism of metal components of HEAs catalysts for developing OER.

Continuous polyamorphic transition in high-entropy metallic glass

Polyamorphic transition (PT) is a compelling and pivotal physical phenomenon in the field of glass and materials science. Understanding this transition is of scientific and technological significance, as it offers an important pathway for effectively tuning the structure and property of glasses. In contrast to the PT observed in conventional metallic glasses (MGs), which typically exhibit a pronounced first-order nature, herein we report a continuous PT (CPT) without first-order characteristics in high-entropy MGs (HEMGs) upon heating. This CPT behavior is featured by the continuous structural evolution at the atomic level and an increasing chemical concentration gradient with temperature, but no abrupt reduction in volume and energy. The continuous transformation is associated with the absence of local favorable structures and chemical heterogeneity caused by the high configurational entropy, which limits the distance and frequency of atomic diffusion. As a result of the CPT, numerous glass states can be generated, which provides an opportunity to understand the nature, atomic packing, formability, and properties of MGs. Moreover, this discovery highlights the implication of configurational entropy in exploring polyamorphic glasses with an identical composition but highly tunable structures and properties.

A pressure and entropy criterion for glass transition decoupling in high-entropy metallic glasses

Decoupling between calorimetric and dynamical glass transitions has been observed in high-entropy metallic glasses (HEMGs) owing to their complex entropy effects. Pressure is another versatile thermodynamic variable that can be used to control the properties of metallic glasses (MGs) owing to the reduced interatomic distances. However, how can it affect such anomalous decoupling behavior in HEMGs remains unclear. Here, molecular dynamics simulations are performed to investigate the influence of pressure on the decoupling behavior in several prototypical MGs and HEMGs. We find that pressure can enhance the sluggish atomic diffusion and depress structural α-relaxation, thus promoting the decoupling in HEMGs, even with less atomic size mismatch. Finally, incorporating pressure and configurational and mismatch entropies, we propose a general criterion based on an explainable machine-learning method to quantitatively classify MG's decoupling or not. These findings refine our understanding of glass transitions and suggest an avenue for manipulating decoupling behaviors in HEMGs.

Multiphase coupling corrosion mechanism of the AlNiZrYCo high-entropy metallic glass coating prepared by plasma spraying

The AlNiZrYCo high-entropy metallic glass (HEMG) coating with an amorphous content of 60 % was prepared by supersonic plasma spraying, and its multiphase coupling corrosion mechanism was investigated. Due to the presence of amorphous phase and passivation elements, the formation of a passive film that was abundant in Co elements on the surface of the coating efficiently inhibited Cl- erosion. The existence of crystalline and oxide phases in the coating led to galvanic corrosion, accelerating the corrosion process of the coating.

A study of crystallized behavior, microstructure and magnetic properties of new Co28Fe28Ni19Si13B8Cu1Nb1Mo2 high-entropy metallic glass

The crystallized behavior, microstructure and magnetic properties of Co28Fe28Ni19Si13B8Cu1Nb1Mo2 high-entropy metallic glass are studied by DSC, XRD, TEM and VSM. The results show that two crystallization peaks occur with a difference of approximately 129–149 K, but the activation energy is different. The activation energy of the first peak is 175.3 kJ/mol and the second is that of 460.1 kJ/mol. After annealing, the Co7Fe3 phase first precipitates with a feature of three-dimensional growth. When the annealing temperature is higher than the second crystallization temperature, the phases such as (Fe,Ni,Mo)23B6, Co3Mo2Si, Co4B, Fe3Mo precipitate sequentially, meanwhile Cu accumulates into small clusters to provide heterogeneous nucleation centers for the crystalline phase in the early stage of crystallization. Finally, the Hc increase with temperature, and the Ms first increasing and then decreasing with the maximum value of 93.11 emu/g at 893 K.

Influence of Al addition on the microstructure and properties of Fe25Co25Ni25(Si0.3B0.7)25 high entropy metallic glass

This research work was focused on the development of a new series of high entropy metallic glasses (HE-MGs) combined with higher thermal stability, acceptable soft magnetic property, microhardness and good corrosion resistance by adding various Al content (1–8 at.%) on the basis of Fe25Co25Ni25(Si0·3B0.7)25 high entropy metallic glass using single-roller melt-spinning approach. It is found that the proper addition of Al can efficiently improve the anti-corrosion performance of high entropy metallic glasses, in particular, the corrosion current density is decreased from 7.61 μA/cm2 and 9.26 μA/cm2 for the 1 at.% and 2 at.% Al-added alloys to 5.11 μA/cm2 for the 5 at.% Al-added alloy. However, the improvement of Al content could deteriorate the soft magnetic property and thermal stability of HE-MGs. The saturation magnetization flux density and onset crystallization temperature reduce from 0.85 T to 766.15 K for the 1 at.% Al-added alloy to 0.53 T and 736.75 K for the 8 at.% Al-added alloy. Besides, the Vickers’ microhardness of all investigated alloy ribbons can reach 1124 HV0.2 or above. Therefore, this kind of senary new-type HE-MGs can be used as a promising magnetic shielding metal material with high hardness, superior thermal stability and good anti-corrosion performance for the surface protection of key component in harsh marine corrosive environment.

High entropy metallic glasses, what does it mean?

We performed calorimetric measurements on 30 bulk metallic glasses, each differing in their mixing entropies ΔSmix. On this basis, the excess entropies ΔS and excess enthalpies ΔH of glasses with respect to their maternal crystalline states are calculated. It is found that the excess entropy ΔS on the average decreases with increasing mixing entropy ΔSmix. This means that the so-called “high-entropy metallic glasses” (i.e., the glasses having highΔSmix) actually constitute glasses with low excess entropy ΔS. We predict that such glasses should have reduced relaxation ability. We also found that the excess enthalpy ΔH of glass linearly increases with its excess entropy ΔS, in line with a general thermodynamic estimate.

High stability and high corrosion resistance of a class of Co–Cr–Mo–Nb–B high-entropy metallic glasses

In this study, we have developed a class of new Co–Cr–Mo–Nb–B high-entropy metallic glass alloys with high stability and high corrosion resistance. It was found that for Co26Cr26Mo26Nb7B15 metallic glass, the glass transition temperature reached to 1058 K, and the initial crystallization temperature of Co24.5Cr26.5Mo26.5Nb7.5B15 metallic glass was as high as 1132 K. There is a large hardness of 18.1 GPa and Young's modulus of 267 GPa of Co27.5Cr27.5Mo26.5Nb3.5B15 metallic glass. The excellent thermodynamic property and mechanical properties were proved to be related to the covalence bond and hybridization of metal-metalloid bonds. The Co–Cr–Mo–Nb–B metallic glasses exhibited a lower self-corrosion current density and higher self-corrosion voltage compared with 316 in 1 M hydrochloric acid solution, and the high corrosion resistance could be attributed to passive films enriched with Cr3+ and Mo4+. These findings provide a new and effective way to design high-entropy metallic glasses with excellent comprehensive properties and suitable for high stability applications.

Layered High-Entropy Metallic Glasses for Photothermal CO2 Methanation.

High entropy alloys and metallic glasses, as two typical metastable nanomaterials, have attracted tremendous interest in energy conversion catalysis due to their high reactivity in nonequilibrium states. Herein, a novel nanomaterial, layered high entropy metallic glass (HEMG), in a higher energy state than low-entropy alloys and its crystalline counterpart due to both the disordered elemental and structural arrangements, is synthesized. Specifically, the MnNiZrRuCe HEMG exhibits highly enhanced photothermal catalytic activity and long-term stability. An unprecedented CO2 methanation rate of 489mmol g-1 h-1 at 330°C is achieved, which is, to the authors' knowledge, the highest photothermal CO2 methanation rate in flow reactors. The remarkable activity originates from the abundant free volume and high internal energy state of HEMG, which lead to the extraordinary heterolytic H2 dissociation capacity. The high-entropy effect also ensures the excellent stability of HEMG for up to 450 h. This work not only provides a new perspective on the catalytic mechanism of HEMG, but also sheds light on the great catalytic potential in future carbon-negative industry.

Connection between Mechanical Relaxation and Equilibration Kinetics in a High-Entropy Metallic Glass.

The slow transition from an out-of-equilibrium glass towards a supercooled liquid is a complex relaxation phenomenon. In this Letter, we study the correlation between mechanical relaxation and equilibration kinetics in a Pd_{20}Pt_{20}Cu_{20}Ni_{20}P_{20} high-entropy metallic glass. The evolution of stress relaxation with aging time was obtained with an unprecedented detail, allowing us to pinpoint new interesting features. The long structural relaxation towards equilibrium contains a wide distribution of activation energies, instead of being just associated to the β relaxation as commonly accepted. The stress relaxation time can be correlated with the equilibration rate and we observe a decrease of microstructural heterogeneity which contrasts with an increase of dynamic heterogeneity. These results significantly enhance our insight of the interplay between relaxation dynamics and thermodynamics in metallic glasses.

Multi-scale defects activation in Gd18.33Tb18.33Dy18.34Co17.5Al27.5 high-entropy metallic glasses revealed by nanoindentation

Defect activation is of fundamental importance for plastic deformation. However, its mechanism is not yet fully disclosed in metallic glasses (MGs), especially for those with high configurational entropy that demonstrate outstanding physical or chemical properties, more particularly, mechanical characteristics. In this work, multi-scale defects activation of three rare-earth-based MGs with low-, medium-, and high-entropy (LE, ME, and HE) were systematically investigated by tracing their room-temperature nanoindentation behaviors. Among the three alloys, the Gd18.33Tb18.33Dy18.34Co17.5Al27.5 HE MG exhibits the highest hardness and elastic modulus. Unlike the poor deformability of the LE MG, the pronounced nanoindentation displacements under a constant load were observed in HE and ME MGs, especially at high loading rates. To reveal the plastic origin of HE MGs, a generalized physical model (so-called Maxwell-Voigt) was utilized to describe the nanoindentation deformation on the mesoscale. The characteristic relaxation spectra show that the activated defects with longer relaxation time are mainly responsible for the large nanoindentation displacement at high strain rates. Based on the cooperative shearing model, the shear transformation zone (STZ) volume is determined to be around 0.45–2.98 nm3. The statistics of the short-range order indicate that the HE MG possesses a highly ordered configuration, which results in the difficulty of STZ activation for requiring overcoming a high energy barrier, and a high elastic modulus of the HE MG. Our work might provide insight into the underlying plastic deformation mechanism of HE MGs from the characteristics of activated defects as well as their entropy effect.

Structure and entropy control of polyamorphous transition in high-entropy metallic glasses

Recently, a putative phase transition has been discovered in metallic glasses that could lead to two distinct amorphous states. This phenomenon, known as polyamorphism, has garnered significant interest, but its origins are still not fully understood, and predicting which compositions may undergo this transition remains a daunting task. Here, through development and experimental analysis of 62 different high entropy metallic glasses (HEMGs), we have discovered that the polyamorphic transition of HEMGs is closely linked to the complexity of their parent crystalline phase. Specifically, the number of crystal phases observed in x-ray diffraction is consistently higher in compositions capable of exhibiting polyamorphism in HEMGs compared to those that cannot. Furthermore, we have identified a high-entropy effect that enhances the enthalpy of polyamorphous transition. These findings shed light on how the structure and entropy play a crucial role in controlling the polyamorphous transition and offer insights for materials design.

Magnetic and magnetocaloric effect of Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass

Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity (RC) was reported. Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K. In addition, we find that the magnetic entropy change (−ΔS M) originates from the sample undergoing a ferromagnetic (FM) to paramagnetic (PM) transition around 20 K. Under a field change from 0 T to 7 T, the value of maximum magnetic entropy change ( −ΔSMmax ) reaches 12.5 J/kg⋅K, and the corresponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K. The large RC and wide temperature range make the Er20Ho20Dy20Cu20Ni20 high-entropy metallic glass be a promising material for application in magnetic refrigerators.

Effects of rare-earth element Y content on the microstructure and properties of quinary Al–Ni–Zr–Co–Y high entropy metallic glasses

A series of quinary (Al1/4Ni1/4Zr1/4Co1/4)100-xYx (x = 16–28 at.%) high entropy metallic glass ribbons were successfully fabricated through the high-speed single roller melt-spinning method. The effects of rare-earth element yttrium content on the microstructure and performances of alloy ribbons were systematically investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), heat treatment, transmission electronic microscopy (TEM), atomic force microscopy (AFM) and electrochemical experiments. The microhardness of metallic ribbons was measured by Vickers hardness tester. Results show that the microstructure of the as-quenched alloy ribbons maintain the glassy state and the average microhardness value of each specimen can reach 488 HV0.1 or above. The surface morphologies of the as-spun ribbon samples exhibit the smooth surface with small roughness value of Ra = 0.115–0.150 nm. In the meantime, with the increase of Y content, the glass transition temperature can be detected in the DSC traces when Y content is over 22 at.%, and the crystallization onset temperature shifts to the lower temperature region, suggesting that the thermal stability of amorphous state in Al–Ni–Zr–Co–Y alloy ribbons has been weakened. The (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons own the highest crystallization onset temperature (∼742 K). Adding appropriate yttrium element can enlarge the super-cooled liquid region and improve the glass-forming ability. In 3.5 wt% NaCl solution, the prepared alloy ribbons can maintain smaller corrosion current densities (∼10−8 A cm−2) than traditional Al-based amorphous alloys, 6061 Al alloy and other common structural steels. The X-ray photoelectron spectrometer results indicate that the passive film of equiatomic alloy ribbons is rich in oxides of Al, Zr, Co, and Y elements, which has excellent resistance to chloride ion attack. On the basis of all experimental results, (Al1/4Ni1/4Zr1/4Co1/4)84Y16 alloy ribbons can optimally combine outstanding corrosion resistance, superior thermal stability, and acceptable microhardness. The above research results lay a solid foundation for the composition development of high-performance high entropy metallic glasses.

Sluggish atomic dynamics in a Y-Sc-Co-Al high entropy bulk metallic glass

We present how 20 at% Sc addition affects the atomic packing and dynamics in a Y-Co-Al metallic glass (MG) and find that it greatly suppresses the dynamics of Co atoms by reducing the atomic packing difference in their surroundings. The Co atoms tending to be mobile or static depend on their nearest neighbors, i.e., possessing more Y/Y+Sc atoms but fewer Co atoms or vice versa. The X-ray absorption fine structure results confirm that Sc addition mainly changes the local environment around Co atoms, forming more Co-Co and Co-Sc pairs but significantly fewer Co-Y pairs than in the ternary counterpart, which can seriously slow the atomic dynamics and stabilize the competing phases. Our findings shed new light on the understanding of strong glass forming ability of the Sc-added Y-based high entropy MG from its local structure and dynamics and will be helpful in developing new bulk MGs.