Constructing Nanoporous Ir/Ta2 O5 Interfaces on Metallic Glass for Durable Acidic Water Oxidation.

Although proton exchange membrane water electrolyzers (PEMWE) are considered as a promising technique for green hydrogen production, it remains crucial to develop intrinsically effective oxygen evolution reaction (OER) electrocatalysts with high activity and durability. Here, a flexible self-supporting electrode with nanoporous Ir/Ta2O5 electroactive surface is reported for acidic OER via dealloying IrTaCoB metallic glass ribbons. The catalyst exhibits excellent electrocatalytic OER performance with an overpotential of 218 mV for a current density of 10 mA cm-2 and a small Tafel slope of 46.1 mV dec-1 in acidic media, superior to most electrocatalysts. More impressively, the assembled PEMWE with nanoporous Ir/Ta2 O5 as an anode shows exceptional performance of electrocatalytic hydrogen production and can operate steadily for 260 h at 100 mA cm-2 . In situ spectroscopy characterizations and density functional theory calculations reveal that the modest adsorption of OOH* intermediates to active Ir sites lower the OER energy barrier, while the electron donation behavior of Ta2 O5 to stabilize the high-valence states of Ir during the OER process extended catalyst's durability.

High-pressure X-ray photon correlation spectroscopy at fourth-generation synchrotron sources.

A new experimental setup combining X-ray photon correlation spectroscopy (XPCS) in the hard X-ray regime and a high-pressure sample environment has been developed to monitor the pressure dependence of the internal motion of complex systems down to the atomic scale in the multi-gigapascal range, from room temperature to 600 K. The high flux of coherent high-energy X-rays at fourth-generation synchrotron sources solves the problems caused by the absorption of diamond anvil cells used to generate high pressure, enabling the measurement of the intermediate scattering function over six orders of magnitude in time, from 10-3 s to 103 s. The constraints posed by the high-pressure generation such as the preservation of X-ray coherence, as well as the sample, pressure and temperature stability, are discussed, and the feasibility of high-pressure XPCS is demonstrated through results obtained on metallic glasses.

The microstructure and thermal stability of the two-phase amorphous melt-spun alloys ejected from a double-chamber crucible.

This work presents the microstructure and properties of two-phase amorphous melt-spun alloys ejected from the crucible with partition between liquids. The microstructure was studied by scanning electron microscopy and transmission electron microscopy and the phase composition was studied by X-ray diffraction. The thermal stability of the alloys was determined using differential scanning calorimetry. The microstructure study proves that the composite alloys are heterogeneous because of the existence of the two amorphous phases obtained due to the use of a partition between the liquids. This microstructure correlates with complex thermal characteristics not found in homogeneous alloys of the same nominal composition. The layered structure of these composites influences the formation of fractures during tensile tests.

Nanoscale-to-Mesoscale Heterogeneity and Percolating Favored Clusters Govern Ultrastability of Metallic Glasses.

Comprehending and controlling the stability of glasses is one of the most challenging issues in glass science. Here we explore the microscopic origin of the ultrastability of a Cu-Zr-Al metallic glass (MG). It is revealed that the ultrastable window (0.7-0.8 Tg) of MGs correlates with the enhanced degree of nanoscale-to-mesoscale structural/mechanical heterogeneity and the connection of stability-favored clusters. On one side, the increased fraction of stability-favored clusters promotes the formation of a stable percolating network through a critical percolation transition, which is essential to form ultrastable MG. On the other side, the enhanced heterogeneity arising from an increased distribution in local clusters may promote synergistically a more efficient and frustrated packing of amorphous structure, contributing to the ultrastability. The present work sheds new light on the stability of MGs and provides a step toward next-generation MGs with superior stability and performances.

Toughening materials: enhancing resistance to fracture.

It has been said that 'God invented plasticity, but the Devil invented fracture!' Both mechanisms represent the two prime modes of structural failure, respectively, plastic collapse and the rupture/breaking of a component, but the concept of developing materials with enhanced resistance to fracture can be difficult. This is because fracture resistance invariably involves a compromise-between strength and ductility, between strength and toughness-fundamentally leading to a 'conflict' between nano-/micro-structural damage and the mechanisms of toughening. Here, we examine the two major classes of such toughening: (i) intrinsic toughening, which occurs ahead of a crack tip and is motivated by plasticity-this is the principal mode of fracture resistance in ductile materials, and (ii) extrinsic toughening, which occurs at, or in the wake of, a crack tip and is associated with crack-tip shielding-this is generally the sole mode of fracture resistance in brittle materials. We briefly examine how these distinct mechanistic processes have been used to toughen synthetic materials-intrinsically in gradient materials and in multiple principal-element metallic alloys with the example of metallic glasses and high-entropy alloys, and extrinsically in ceramics with the example of ceramic-matrix composites-in comparison to Nature which has been especially adept in creating biological/natural materials which are toughened by one or both mechanistic classes, despite often consisting of constituents with meagre mechanical properties. The success of Nature has been driven by its ability to cultivate the development of materials with multiple length-scale hierarchical structures that display ingenious gradients and structural adaptability, a philosophy which we need to emulate and more importantly learn to synthesize to make structural materials of the future with unprecedented combinations of mechanical properties. This article is part of a discussion meeting issue 'A cracking approach to inventing new tough materials: fracture stranger than friction'.

Mapping the Viscoelastic Heterogeneity at the Nanoscale in Metallic Glasses by Static Force Spectroscopy.

Nanoscale viscoelastic heterogeneity is an important concept for understanding the relationship between the microscopic atomic structure and the macroscopic mechanical behaviors in metallic glasses. However, the direct measurement of viscoelastic behavior at the nanoscale is still missing. Here we report a new measurement method based on static force microscopy to directly measure the viscoelastic properties at the nanoscale. The observed adhesive force and elastic modulus maps clearly display a typical hierarchical viscoelastic microstructure consisting of local hard and soft regions. Moreover, the adhesive force is more sensitive than the elastic modulus to viscoelastic heterogeneity and exhibits a bimodal distribution. In addition, we found that the structural relaxation and the rejuvenation effects induce the transition between the solid-like and liquid-like modes. The new measurement technique provides a powerful and quantative tool to investigate the nanoscale heterogeneity and build a connection between the microscopic structure and macroscopic mechanical behaviors in amorphous materials.

Integration of Transparent Supercapacitors and Electrodes Using Nanostructured Metallic Glass Films for Wirelessly Rechargeable, Skin Heat Patches.

Here we demonstrate an unconventional fabrication of highly transparent supercapacitors and electrodes using random networks of nanostructured metallic glass nanotroughs for their integrations as wirelessly rechargeable and invisible, skin heat patches. Transparent supercapacitors with fine conductive patterns were printed using an electrohydrodynamic jet-printing. Also, transparent and stretchable electrodes, for wireless antennas, heaters and interconnects, were formed using random network based on nanostructured CuZr nanotroughs and Ag nanowires with superb optoelectronic properties (sheet resistance of 3.0 Ω/sq at transmittance of 91.1%). Their full integrations, as an invisible heat patch on skin, enabled the wireless recharge of supercapacitors and the functions of heaters for thermal therapy of skin tissue. The demonstration of this transparent thermotherapy patch to control the blood perfusion level and hydration rate of skin suggests a promising strategy toward next-generation wearable electronics.

Facile Electrochemical Method for the Fabrication of Stable Corrosion-Resistant Superhydrophobic Surfaces on Zr-Based Bulk Metallic Glasses.

Both surface microstructure and low surface energy modification play a vital role in the preparation of superhydrophobic surfaces. In this study, a safe and simple electrochemical method was developed to fabricate superhydrophobic surfaces of Zr-based metallic glasses with high corrosion resistance. First, micro-nano composite structures were generated on the surface of Zr-based metallic glasses by electrochemical etching in NaCl solution. Next, stearic acid was used to decrease surface energy. The effects of electrochemical etching time on surface morphology and wettability were also investigated through scanning electron microscopy and contact angle measurements. Furthermore, the influence of micro-nano composite structures and roughness on the wettability of Zr-based metallic glasses was analysed on the basis of the Cassie-Baxter model. The water contact angle of the surface was 154.3° ± 2.2°, and the sliding angle was <5°, indicating good superhydrophobicity. Moreover, the potentiodynamic polarisation test and electrochemical impedance spectroscopy suggested excellent corrosion resistance performance, and the inhibition efficiency of the superhydrophobic surface reached 99.6%. Finally, the prepared superhydrophobic surface revealed excellent temperature-resistant and self-cleaning properties.

Excellent dye degradation performance of FeSiBP amorphous alloys by Fenton-like process.

Amorphous alloys are being newly applied in wastewater treatment because of their unique atomic packing structure. They possess excellent degradation efficiency, stability and reusability. In this work, Fe80Si10B10 and Fe83Si5B8P4 amorphous ribbons exhibited advanced catalytic performance for the degradation of Methyl Blue (MB) and Rhodamine B (RhB) dyes, and the color removal reach nearly 100% within 11 min for both the dyes. Compared with the Fe80Si10B10 amorphous ribbon, the Fe83Si5B8P4 ribbon showed higher degradation efficiency due to its lower reaction activation energy, higher electron transfer ability and higher Fe content, and the formation of the galvanic cell between the strong Fe-P bonds and the weak Fe-B bonds. It also exhibited high stability and reusability. The degradation efficiency was improved when the appropriate concentration of H2O2 is added. As regards the pH, high degradation efficiency was observed in acidic MB solution, but it decreased as the pH increased up to pH 7. The application of the electro-Fenton-like process is discussed, which can effectively improve the degradation performance in a nearly natural solution. This study presents a high efficiency low-cost catalyst for synthetic dye degradation and expands the functional applications of Fe-based amorphous alloys.

Exploring the Phase Space of Multi-Principal-Element Alloys and Predicting the Formation of Bulk Metallic Glasses.

Multi-principal-element alloys share a set of thermodynamic and structural parameters that, in their range of adopted values, correlate to the tendency of the alloys to assume a solid solution, whether as a crystalline or an amorphous phase. Based on empirical correlations, this work presents a computational method for the prediction of possible glass-forming compositions for a chosen alloys system as well as the calculation of their critical cooling rates. The obtained results compare well to experimental data for Pd-Ni-P, micro-alloyed Pd-Ni-P, Cu-Mg-Ca, and Cu-Zr-Ti. Furthermore, a random-number-generator-based algorithm is employed to explore glass-forming candidate alloys with a minimum critical cooling rate, reducing the number of datapoints necessary to find suitable glass-forming compositions. A comparison with experimental results for the quaternary Ti-Zr-Cu-Ni system shows a promising overlap of calculation and experiment, implying that it is a reasonable method to find candidates for glass-forming alloys with a sufficiently low critical cooling rate to allow the formation of bulk metallic glasses.

Identification of spatial magnetic inhomogeneities by nuclear forward scattering of synchrotron radiation.

Spatially confined magnetic inhomogeneities were revealed by measuring nuclear forward scattering time spectra on the same sample in two different geometric arrangements. They differ by 180° rotation of the sample around one of the polarization axes. A basic theoretical description of this phenomenon and its relation to a spatial distribution of nuclei featuring different magnetic moments is provided. From an experimental point of view, the violation of rotational invariance was observed for an inhomogeneous Fe81Mo8Cu1B10 metallic glass. The development of magnetic inhomogeneities and their relation to the evolution of time spectra was studied during thermal annealing.

Nanoscale Structural Evolution and Anomalous Mechanical Response of Nanoglasses by Cryogenic Thermal Cycling.

One of the central themes in the amorphous materials research is to understand the nanoscale structural responses to mechanical and thermal agitations, the decoding of which is expected to provide new insights into the complex amorphous structural-property relationship. For common metallic glasses, their inherent atomic structural inhomogeneities can be rejuvenated and amplified by cryogenic thermal cycling, thus can be decoded from their responses to mechanical and thermal agitations. Here, we reported an anomalous mechanical response of a new kind of metallic glass (nanoglass) with nanoscale interface structures to cryogenic thermal cycling. As compared to those metallic glasses by liquid quenching, the Sc75Fe25 (at. %) nanoglass exhibits a decrease in the Young's modulus but a significant increase in the yield strength after cryogenic cycling treatments. The abnormal mechanical property change can be attributed to the complex atomic rearrangements at the short- and medium- range orders due to the intrinsic nonuniformity of the nanoglass architecture. The present work gives a new route for designing high-performance metallic glassy materials by manipulating their atomic structures and helps for understanding the complex atomic structure-property relationship in amorphous materials.

Strain Distribution Across an Individual Shear Band in Real and Simulated Metallic Glasses.

Because of the fast dynamics of shear band formation and propagation along with the small size and transient character of the shear transformation zones (STZs), the elementary units of plasticity in metallic glasses, the description of the nanoscale mechanism of shear banding often relies on molecular dynamics (MD) simulations. However, the unrealistic parameters used in the simulations related to time constraints may raise questions about whether quantitative comparison between results from experimental and computational analyses is possible. Here, we have experimentally analyzed the strain field arising across an individual shear band by nanobeam X-ray diffraction and compared the results with the strain characterizing a shear band generated by MD simulations. Despite their largely different spatiotemporal scales, the characteristic features of real and simulated shear bands are strikingly similar: the magnitude of the strain across the shear band is discontinuous in both cases and the direction of the principal strain axes exhibits the same antisymmetric profile. This behavior can be explained by considering the mechanism of STZ activation and percolation at the nanoscale, indicating that the nanoscale effects of shear banding are not limited to the area within the band but they extend well into the surrounding elastic matrix. These findings not only demonstrate the reliability of MD simulations for explaining (also quantitatively) experimental observations of shear banding but also suggest that designed experiments can be used the other way around to verify numerical predictions of the atomic rearrangements occurring within a band.

Interatomic repulsion softness directly controls the fragility of supercooled metallic melts.

We present an analytic scheme to connect the fragility and viscoelasticity of metallic glasses to the effective ion-ion interaction in the metal. This is achieved by an approximation of the short-range repulsive part of the interaction, combined with nonaffine lattice dynamics to obtain analytical expressions for the shear modulus, viscosity, and fragility in terms of the ion-ion interaction. By fitting the theoretical model to experimental data, we are able to link the steepness of the interionic repulsion to the Thomas-Fermi screened Coulomb repulsion and to the Born-Mayer valence electron overlap repulsion for various alloys. The result is a simple closed-form expression for the fragility of the supercooled liquid metal in terms of few crucial atomic-scale interaction and anharmonicity parameters. In particular, a linear relationship is found between the fragility and the energy scales of both the screened Coulomb and the electron overlap repulsions. This relationship opens up opportunities to fabricate alloys with tailored thermoelasticity and fragility by rationally tuning the chemical composition of the alloy according to general principles. The analysis presented here brings a new way of looking at the link between the outer shell electronic structure of metals and metalloids and the viscoelasticity and fragility thereof.

Brittle-to-Ductile Transition in Metallic Glass Nanowires.

When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure.

Stretchable, Transparent Electrodes as Wearable Heaters Using Nanotrough Networks of Metallic Glasses with Superior Mechanical Properties and Thermal Stability.

Mechanical robustness, electrical and chemical reliabilities of devices against large deformations such as bending and stretching have become the key metrics for rapidly emerging wearable electronics. Metallic glasses (MGs) have high elastic limit, electrical conductivity, and corrosion resistance, which can be promising for applications in wearable electronics. However, their applications in wearable electronics or transparent electrodes have not been extensively explored so far. Here, we demonstrate stretchable and transparent electrodes using CuZr MGs in the form of nanotrough networks. MG nanotroughs are prepared by electrospinning and cosputtering process, and they can be transferred to various desired substrates, including stretchable elastomeric substrates. The resulting MG nanotrough network is first utilized as a stretchable transparent electrode, presenting outstanding optoelectronic (sheet resistance of 3.8 Ω/sq at transmittance of 90%) and mechanical robustness (resistance change less than 30% up to a tensile strain of 70%) as well as excellent chemical stability against hot and humid environments (negligible degradation in performance for 240 h in 85% relative humidity and 85 °C). A stretchable and transparent heater based on the MG nanotrough network is also demonstrated with a wide operating temperature range (up to 180 °C) and excellent stretchability (up to 70% in the strain). The excellent mechanical robustness of these stretchable transparent electrode and heater is ascribed to the structural configuration (i.e., a nanotrough network) and inherent high elastic limit of MGs, as supported by experimental results and numerical analysis. We demonstrate their real-time operations on human skin as a wearable, transparent thermotherapy patch controlled wirelessly using a smartphone as well as a transparent defroster for an automobile side-view mirror, suggesting a promising strategy toward next-generation wearable electronics or automobile applications.

Crystallization of Metallic Glasses and Supercooled Liquids.

This is an overview of recent findings on the structural changes observed upon heating, including crystallization processes in conventional metallic glasses, bulk metallic glasses, and their corresponding supercooled liquids. This paper encapsulates the various crystallization behaviors in metallic glasses by primary, eutectic, and polymorphous mechanisms, highlighting the complexity and diversity of the nucleation and growth mechanisms involved. Mechanically induced room-temperature crystallization is also discussed.

A Review of the Development of Titanium-Based and Magnesium-Based Metallic Glasses in the Field of Biomedical Materials.

This article reviews the research and development focus of metallic glasses in the field of biomedical applications. Metallic glasses exhibit a short-range ordered and long-range disordered glassy structure at the microscopic level, devoid of structural defects such as dislocations and grain boundaries. Therefore, they possess advantages such as high strength, toughness, and corrosion resistance, combining characteristics of both metals and glasses. This novel alloy system has found applications in the field of biomedical materials due to its excellent comprehensive performance. This review discusses the applications of Ti-based bulk metallic glasses in load-bearing implants such as bone plates and screws for long-term implantation. On the other hand, Mg-based metallic glasses, owing to their degradability, are primarily used in degradable bone nails, plates, and vascular stents. However, metallic glasses as biomaterials still face certain challenges. The Young's modulus value of Ti-based metallic glasses is higher than that of human bones, leading to stress-shielding effects. Meanwhile, Mg-based metallic glasses degrade too quickly, resulting in the premature loss of mechanical properties and the formation of numerous bubbles, which hinder tissue healing. To address these issues, we propose the following development directions: (1) Introducing porous structures into titanium-based metallic glasses is an important research direction for reducing Young's modulus; (2) To enhance the bioactivity of implant material surfaces, the surface modification of titanium-based metallic glasses is essential. (3) Developing antibacterial coatings and incorporating antibacterial metal elements into the alloys is essential to maintain the long-term effective antibacterial properties of metallic biomaterials. (4) Corrosion resistance must be further improved through the preparation of composite materials, while ensuring biocompatibility and safety, to achieve controllable degradation rates and degradation modes.

Anticorrosion and Antimicrobial Tannic Acid-Functionalized Ti-Metallic Glass Ribbons for Dental Abutment.

In this study, a recently reported Ti-based metallic glass (MG), without any toxic element, but with a significant amount of metalloid (Si-Ge-B, 18 atom %) and minor soft element (Sn, 2 atom %), was produced in ribbon form using conventional single-roller melt-spinning. The produced Ti60Zr20Si8Ge7B3Sn2 ribbons were investigated by differential scanning calorimetry and X-ray diffraction to confirm their amorphous structure, and their corrosion properties were further investigated by open-circuit potential and cyclic polarization tests. The ribbon's surface was functionalized by tannic acid, a natural plant-based polyphenol, to enhance its performance in terms of corrosion prevention and antimicrobial efficacy. These properties can potentially be exploited in the premucosal parts of dental implants (abutments). The Folin and Ciocalteu test was used for the quantification of tannic acid (TA) grafted on the ribbon surface and of its redox activity. Fluorescent microscopy and ζ-potential measurements were used to confirm the presence of TA on the surfaces of the ribbons. The cytocompatibility evaluation (indirect and direct) of TA-functionalized Ti60Zr20Si8Ge7B3Sn2 MG ribbons toward primary human gingival fibroblast demonstrated that no significant differences in cell viability were detected between the functionalized and as-produced (control) MG ribbons. Finally, the antibacterial investigation of TA-functionalized samples against Staphylococcus aureus demonstrated the specimens' antimicrobial properties, shown by scanning electron microscopy images after 24 h, presenting a few single colonies remaining on their surfaces. The thickness of bacterial aggregations (biofilm-like) that were formed on the surface of the as-produced samples reduced from 3.5 to 1.5 µm.

Machine learning-guided exploration and experimental assessment of unreported compositions in the quaternary Ti-Zr-Cu-Pd biocompatible metallic glass system.

Due to their outstanding elastic limit, biocompatible Ti-based bulk metallic glasses (BMGs) are candidate materials to decrease the size of medical implants and therefore reduce their invasiveness. However, the practical use of classical Ti-BMGs in medical applications is in part hindered by their high copper content: more effort is thus required to design low-copper Ti-BMGs. In this work, in line with current rise in AI-driven tools, machine learning (ML) approaches, a neural-network ML model is used to explore the glass-forming ability (GFA) of unreported low-copper compositions within the biocompatible Ti-Zr-Cu-Pd system. Two types of models are trained and compared: one based on the alloy composition only, and a second based on various features derived from the alloying elements. Contrary to expectation, the predictive power of both models in evaluating GFA is similar. The compositional space identified by ML as promising is experimentally assessed, finding unfortunately low GFA. These results indicate that the ML approach may be premature for specific composition tuning of amorphous metallic materials. We emphasise that the development of ML tools in GFA prediction requires an improvement of the dataset, in terms of homogeneity, size and GFA descriptors, which must be supported by increased reporting of high-quality experimental GFA measurements, both positive and negative. STATEMENT OF SIGNIFICANCE: Biocompatible Ti-based bulk metallic glasses (BMGs) are candidate materials for use in the next generation of minimally invasive dental implants where improved mechanical properties, such as high strength are required. Despite promising in vitro/vivo evaluations, implementation of alloys for practical applications is partly hindered by the presence of copper as the main alloying element. Recent studies have presented AI-guided and machine learning strategies as appealing approaches to understand and describe the glass forming ability (GFA) of BMG-forming compositions. In this work, we employ and evaluate the capacity of a machine-learning model to explore low-copper compositional spaces in the biocompatible Ti-Zr-Cu-Pd system. Our results highlight the limits of such a computational approach and suggest improvements for future designing routes.