Structure Of Metallic Glasses Research Articles

Stable Operation and Enhanced Sensitivity via Composite Structure Design for Efficient Photoplethysmography and Motion Sensors

Healthcare sensors have attracted lots of interests owing to saving a patient's life by continuously monitoring the patient's health via early diagnosis of the symptoms by using healthcare sensors. Many health-care sensors are available in wearable application that can monitor continuously patient health. There are some common parameters such as a heart rate and human motion that are used to monitor human activity.In order to realize stable operation of health-care sensors, material designs are required considering human-body compatibility. In this research, light-sensors fabricated from low-toxicity organic materials by introducing neutral poly(3,4-ethylenedioxythiophene)-(polystyrene sulfonate) (PEDOT-(PSS)) to improve human-body compatibility as well as to strengthen photoplethysmography (PPG) signal. [1] Neutral PEDOT-(PSS) with heterocyclic 1,3-diazole (HDZ) enhances the polymerization degree, carrier mobility, and other physicochemical properties. Consequently, the presented OPD-based PPG sensor has the ability to diagnose blood circulation status and cardiovascular diseases.Second, we fabricate motion sensors by utilizing metallic glass, i.e., amorphous metallic alloy, which is an alloy composition without grain boundaries and long-range ordering. The unique structure of metallic glass results in excellent tensile strength and strain-resistivity as well as chemical stability to those of conventional metals. The Al-Sm MG-based sensors results in enhanced sensitivity and considerable device stability, because of its amorphous phase. [2][1] Adv. Funct. Mater. 2023, 10.1002/adfm.202309271[2] Electrochimica Acta, 2023, 446, 142053

Mechanical and structural properties of monatomic zirconium metallic glass under pressure variations and annealing processes: A molecular dynamics study

The aim of this study is to investigate how different pressure levels and annealing times affect the local atomic structure and mechanical properties of pure zirconium metallic glasses. Using molecular dynamics simulations with the embedded atom method, we explored how these changes influence the material's inherent characteristics. Analysis of the radial distribution function, coordination number, and Voronoi tessellation revealed a spectrum of structural arrangements in metallic glass formed across a pressure range of 0–70 GPa. Additionally, the glass transition temperature increased with increasing pressure, accompanied by reduced free volume. The annealing process, ranging from 0 to 5 ns on metallic glass synthesized under 0 GPa pressure, showed the coordination number's significance in achieving a glassy state. Regarding mechanical behavior, both elastic constants and moduli showed a progressive increase with rising pressure, while Young's modulus and hardness displayed enhanced values with longer annealing times.

Enhancing the reliability of Reverse Monte Carlo simulations of metallic glass structure by imposing strict constraints from partial pair correlation functions

Reverse Monte Carlo (RMC) simulations are widely used to reconstruct 3-dimensional (3D) metallic glass (MG) structure from neutron/X-ray diffraction data, but their reliability is debated. Here, we employ RMC to simulate a Zr50Cu50 MG’s structure using two types of “experimental” inputs as constraints, one with a total pair correlation function (TPCF) and the other with 3 partial PCFs (PPCFs), all of which were generated from a 3D glass structure obtained from molecular dynamics (MD) simulations of the same alloy. This MD-generated structure is then used as a benchmark to evaluate RMC’s accuracy. Notably, both methods can replicate the MG’s TPCFs, and total bond-angle/bond-length distributions. However, only the PPCFs-constrained RMC is able to re-produce the local structure, as manifested by nearly replicated partial bond-length/bond-angle distributions, partial coordination numbers, atomic volume, etc. This work demonstrates that PPCFs can impose stricter constraints than a TPCF does, significantly improving the reliability of RMC simulations.

Surface Modification of Zr48Cu36Al8Ag8 Bulk Metallic Glass through Glow Discharge Plasma Nitriding

Bulk metallic glasses are modern engineering materials with unique functional properties. Zr-based alloys are particularly attractive as they exhibit high glass forming ability as well as good mechanical properties. Due to their relatively high thermal stability, reaching as much as 400 °C, they can be surface-treated in low-temperature plasma to further improve their mechanical properties. The subject of this study was to determine the influence of the technological parameters of nitriding in low-temperature plasma on the structure and mechanical properties of Zr48Cu36Al8Ag8 bulk metallic glass. In the course of this study, the influence of the ion accelerating voltage on the structure and micromechanical properties of the bulk metallic glass was analyzed. The produced samples were characterized in terms of nanohardness, layer adhesion by using the scratch test, and wear resistance by using the ball-on-disc method. As a result of low-temperature plasma nitriding, a significant increase in the surface nanohardness of the Zr48Cu36Al8Ag8 bulk metallic glass was obtained. The produced layers exhibited high adhesion to the substrate and they improved the wear resistance of the glass. The present study indicates the possibility of modifying the surface properties of bulk metallic glasses by using diffusion processes in low-temperature plasma without substrate crystallization.

Thermal cycling-induced evolution of structure and local mechanical properties in metallic glass

The influence of thermal treatment on the long-term mechanical properties of two different kinds of metallic glasses was investigated in this study. As model systems, bulk metallic glasses (BMGs) with the composition of Pd43Cu27Ni10P20 cycled 60, 200, and 500 times between 77 K and room temperature and Zr44Ti11Cu10Ni10Be25 cycled 300, 500, and 700 times have been employed. To ensure that meaningful steady-state properties have been reached, experiments have been performed three years after sample preparation. It was found that the thermal cycling of the Pd-based BMGs had induced rejuvenation when compared to the non-cycled sample, including a higher relaxation enthalpy, lower modulus, hardness, activation volume, and shear transformation zone volume. However, for Zr-BMGs, a rejuvenation to relaxation behavior is observed. Also, while Zr-BMGs showed significantly changes in yielding behavior upon thermal cycling, fluctuations in Pd-BMGs were negligible. We speculate that the observed substantial differences between these two samples might originate because Pd-BMG has a denser structure and higher fragility, making it more difficult to induce excess free volumes.

Effect of laser power on the structure and wear performance of laser additively manufactured Cu45Zr45Al6Ti4 metallic glass coating

Laser powder bed fusion (LPBF) technology presents significant potential for the production of metallic glass (MG) coatings. This work investigated the influence of laser power on the structure and wear performance of a CuZr-based metallic glass coating with composition of Cu45Zr45Al6Ti4 on Ti substrate. It was observed that the melt pool, which serves as the fundamental building block for constructing MG coatings in LPBF, undergoes a transition from conduction mode to keyhole mode, and subsequently to extended mode with increasing laser power. The MG coatings prepared using low power laser (140 W) and medium power laser (240 W) both exhibited a nearly fully amorphous state. However, at a laser power of 360 W, noticeable crystallization occurred in the coating, as evidenced by SEM observation. The wear rate of Cu45Zr45Al6Ti4 MG coating was measured to be 4.67 × 10−6 mm3·N−1·m−1, which is significantly lower than that of the Ti substrate (6.38 × 10−4 mm3·N−1·m−1). This study reveals the relationship between the laser power and morphology of the melt pool, as well as the structure and wear performance of the LPBF-fabricated MG coatings, offering guidance for optimizing the laser additive manufacturing process of wear-resistant MG coatings.

Medium-range order structure analysis of metallic glasses based on reverse Monte Carlo modeling

The elucidation of amorphous alloy characteristics presents a formidable challenge due to the absence of crystalline arrangements and enigmatic imperfections. This study aimed to tackle this challenge through a comprehensive investigation utilizing synchrotron X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), ab initio molecular dynamics (AIMD) simulations, and reverse Monte Carlo (RMC) modeling. The primary objective was to delve into the medium range order (MRO) structure of metallic glasses (MGs) containing CuXZr100-X, wherein X represents values of 50, 56, 60, and 64. The results obtained from this research demonstrate that an increase in the Cu atom concentration within Cu-Zr MGs leads to the formation of complete icosahedral clusters and high-coordination polyhedral connections, thereby bolstering the stability and heterogeneity of local structures. Examination of the stiff full icosahedral bones shows that defects exist in the network connections on the MRO, resulting in a lack of connectivity in the positive icosahedron. Conversely, the density of defects decreases with an increase in Cu content. The observation suggests that the observed low MRO defects in Cu64Zr36 MGs may be accountable for their excellent glass-forming ability and kinetic stability.

Comprehensive characterization of the structure of Zr-based metallic glasses

Structure of metallic glasses fascinates as the generic amorphous structural template for ubiquitous systems. Its specification necessitates determination of the complete hierarchical structure, starting from short-range-order (SRO) → medium-range-order (MRO) → bulk structure and free volume (FV) distribution. This link has largely remained elusive since previous investigations adopted one-technique-at-a-time approach, focusing on limited aspects of any one domain. Reconstruction of structure from experimental data inversion is non-unique for many of these techniques. As a result, complete and precise structural understanding of glass has not emerged yet. In this work, we demonstrate the first experimental pathway for reconstruction of the integrated structure, for Zr67Ni33\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Zr}}_{{{67}}} {\ ext{Ni}}_{{{33}}}$$\\end{document} and Zr52Ti6Al10Cu18Ni14\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{Zr}}_{{{52}}} {\ ext{Ti}}_{{6}} {\ ext{Al}}_{{{10}}} {\ ext{Cu}}_{{{18}}} {\ ext{Ni}}_{{{14}}}$$\\end{document} glasses. Our strategy engages diverse (× 7) multi-scale techniques [XAFS, 3D-APT, ABED/NBED, FEM, XRD, PAS, FHREM] on the same glass. This strategy complemented mutual limitations of techniques and corroborated common parameters to generate complete, self-consistent and precise parameters. Further, MRO domain size and inter-void separation were correlated to identify the presence of FV at MRO boundaries. This enabled the first experimental reconstruction of hierarchical subset: SRO → MRO → FV → bulk structure. The first ever image of intermediate region between MRO domains emerged from this link. We clarify that determination of all subsets is not our objective; the essence and novelty of this work lies in directing the pathway towards finite solution, in the most logical and unambiguous way.

Structural behavior of copper monatomic metallic glass under various cooling conditions investigated by molecular dynamics simulations

The present research explores the structural characteristics of pure copper (Cu) metallic glass using the embedded atom method (EAM) potential in molecular dynamics simulations. Numerous techniques were used, such as coordination number analysis, Voronoi tessellation, and the radial distribution function (RDF). The findings demonstrate that at a cooling rate of 1012 K/s, crystallization begins. However, the separation of the second RDF peak indicates that under 0 GPa, copper metallic glass forms at cooling rates between 5 × 10¹² K/s and 1014 K/s, with the glass transition temperature (Tg) rising with faster cooling. Voronoi tessellation revealed a rise in icosahedral clusters with quicker cooling, while coordination number analysis indicated changes in the local structure and topology of copper metallic glass during the cooling process.

Special glass structures for first principles studies of bulk metallic glasses

The atomic-level structure of bulk metallic glasses is a key determinant of their properties. An accurate representation of amorphous systems in computational studies has traditionally required large supercells that are unfortunately computationally demanding to handle using the most accurate ab initio calculations. To address this, we propose to specifically design small-cell structures that best reproduce the local geometric descriptors (e.g., pairwise distances or bond angle distributions) of a large-cell simulation. We rely on molecular dynamics (MD) driven by empirical potentials to generate the target descriptors, while we use reverse Monte Carlo (RMC) methods to optimize the small-cell structure. The latter can then be used to determine mechanical and electronic properties using more accurate electronic structure calculations. The method is implemented in the Metallic Amorphous Structures Toolkit (MAST) software package.

Mechanical cycling-induced evolution of structure and local mechanical properties in a PdCuNiP bulk metallic glass

To improve the ductility of bulk metallic glasses (BMGs), external mechanical stimulations can be applied. Thereby, cyclically loading the samples at stress levels below the macroscopic elastic limit leads to permanent structural changes, which can alter the plasticity in bulk metallic glasses. Here, the effect of systematic variations of Pd43Cu27Ni10P20 BMG's structural state, achieved through cyclically loading the material to 70, 80, and 90% of the yield strength, on a range of mechanical properties like modulus, hardness, yield strength, strain rate sensitivity, activation volume, maximum shear stress and stiffness at different probing volume is studied. It is observed that samples rejuvenated from the non-cycled state to the 70% of yield stress state, relaxed when cycled up to 80% of yield stress, and finally rejuvenated again when cycled up to 90% of yield stress. This rejuvenation to relaxation transition might be due to the random atomic rearrangement during the cycling.

Effect of deep cryogenic cycling treatment on structure and properties of metallic glass: A review

Recent researches have shown that metallic glasses (MGs) can be rejuvenated to a more metastable energy state by thermal or mechanical approaches, which causes a looser atomic packing. This process can effectively improve the overall plasticity of MGs. The present work started with the concept of ageing and rejuvenation of MGs, briefly introducing the probable methods to rejuvenate the MGs, then the advantages and disadvantages of various methods were summarized, and the effects of deep cryogenic cycling method (a non-destructive method to sample morphology and feasible to conduct) were investigated in detail. The effects of treating parameters on the degree of rejuvenation and the effects of rejuvenation on the mechanical and magnetic properties of MGs were also summarized. Finally, some conclusions in this field are drawn and some important questions that deserve further study are put forward.

Nanoscale Oxygenous Heterogeneity in FePC Glass for Highly Efficient and Reusable Catalytic Performance.

Metallic glass, with its unique disordered atomic structure and high density of low-coordination sites, is regarded as the most competitive new catalyst for environmental catalysis. However, the efficiency and stability of metallic glass catalysts are often affected by their atomic configuration. Thus, the design and regulation of the nanoscale structure of metallic glasses to improve their catalytic efficiency and stability remains a challenge. Herein, a non-noble component, Fe75 P15 C10 amorphous ribbon, is used as a precursor to fabricate a hierarchical gradient catalyst with nanoscale heterogeneous and oxygenous amorphous structure by simple annealing and acid-immersing. The resulting catalyst offers an ultrahigh catalytic ability of kSA• C0 = 3101mgm-2 min-1 and excellent reusability of 39 times without efficiency decay in dye wastewater degradation. Theoretical calculations indicate that the excellent catalytic performance of the catalyst can be attributed to its unique heterogeneous nanoglass structure, which induces oxygen atoms. Compared to the FePC structure, the FeP/FePCO structure exhibits strong charge transferability, and the energy barrier of the rate-determining steps of the conversion of S2 O8 2- to SO4 -• is reduced from 2.52 to 0.97eV. This study reveals that a heterogeneous nanoglass structure is a new strategy for obtaining high catalytic performance.

Application of lever law in dual-cluster formulas model to interpret eutectic and bulk metallic glass

It is well known that the structure of bulk metallic glass has a close relationship with that of its crystalline eutectic phase, but how this is manifested on the atomic scale is not yet clear. The present paper further develops and optimizes dual-cluster formulas model to describe the eutectic and bulk metallic glass, as C1[(principal cluster)1(glue atom)1 or 3] + C2[(principal cluster)2(glue atom)1 or 3]. C1, C2 are the proportions governed by the lever law, and the two principal clusters which have the highest atomic close-packing efficiency and large degree of isolation are derived from the eutectic-related phases. Cu-Zr binary system are studied using this model and the results match well with the experiments. According to dual-cluster formulas and valence electrons, the correlation between deep eutectic and bulk metallic glass may be disclosed, and a detailed step towards composition design of bulk metallic glass is established as well.

Structure and physical properties of Mg-based metallic glasses prepared by a melt spinning technique

Structure and physical properties of Mg-based metallic glasses prepared by a melt spinning technique

Thick film MEMS process using reverse lift-off

The lift-off process is a microfabrication technique that has the capability of forming thin film structures. However, several issues, such as structural shape and burr formation, arise when applying this method to the formation of thick film structures. Thick film structures formed through the lift-off process exhibit a mountainous cross-sectional shape and non-uniform film thickness due to variations in the width of the structure. These challenges make it difficult to apply the method to MEMS. While the reverse lift-off process addresses some of the structural shape problems, its initial development using metal molds makes it challenging to directly apply to MEMS without modification. Therefore, this paper proposes an adaptation to the Si process and presents a method to reduce burrs. The microfabrication characteristics are evaluated by comparing the cross-sectional shapes of thick metallic glass structures formed through both the lift-off and reverse lift-off processes. The structures formed through the reverse lift-off process exhibit a rectangular cross-sectional shape, and the film thickness remains consistent regardless of the structure's width. However, burrs persist on the backside edge of the structure, which hinders its application to MEMS. This paper confirms that pre-etching the underlying Si substrate into an inverse tapered shape effectively reduces burrs. As an illustration of the improved reverse lift-off process applied to MEMS, MEMS mirror structures are fabricated, and their resonance frequency closely aligns with the design value.

Mechanical properties and thermal stability of ZrCuAlx thin film metallic glasses: Experiments and first-principle calculations

In this work, we provide a holistic picture about the relationship between atomic structure, mechanical properties, and thermal stability of ZrCuAlx thin film metallic glasses (TFMGs) varying the Al content from 0 to 12 at.%, carrying out a broad characterization involving experiments and ab initio molecular dynamic simulations (AIMD). We show that the addition of Al resulted in a change of average interatomic distances by ∼10 pm with the formation of shorter bonds (Al-Zr and Al-Cu), influencing the mechanical response (shear/elastic moduli and hardness) which increases by ∼15% for 12 at.% Al. Moreover, tensile tests on polymer substrate revealed a maximum value for the crack initiation strain of 2.1% for ZrCuAl9, while the strain-to-failure rapidly decreases at higher Al contents. The observed reduction in damage tolerance is correlated to a transition in atomic configuration. Specifically, a maximum in density of full and defective icosahedral cluster population is observed at 9 at.% Al, inducing a more shear-resistant behavior to the material. Thermal stability is investigated by high-energy and conventional x-ray diffraction and electrical resistivity measurements as a function of the temperature. Glass transition (Tg) and crystallization (Tx) temperature increase by Al addition reaching 450 and 500 °C, respectively for ZrCuAl12. The increase in thermal stability is related to the reduction in atomic mobility due to the formation of shorter chemical bonds, inhibiting atomic reconfiguration during crystallization. In conclusion, we provide guidelines to the design of compositional-tailored ZrCuAlx TFMGs with tuned mechanical properties and thermal stability with potential impact on industrial applications.

Depicting Defects in Metallic Glasses by Atomic Vibrational Entropy.

Due to the chaotic structure of amorphous materials, it is challenging to identify defects in metallic glasses. Here we tackle this problem from a thermodynamic point of view using atomic vibrational entropy, which represents the inhomogeneity of atomic contributions to vibrational modes. We find that the atomic vibrational entropy is correlated to the vibrational mean-square displacement and polyhedral volume of atoms, revealing the critical role of vibrational entropy in bridging dynamics, thermodynamics, and structure. On this method, the local vibrational entropy obtained by coarse-graining the atomic vibrational entropy in space can distinguish more effectively between liquid-like and solid-like atoms in metallic glasses and establish the correlation between the local vibrational entropy and the structure of metallic glasses, offering a route to predict the plastic events from local vibrational entropy. The local vibration entropy is a good indicator of thermally activated and stress-driven plastic events, and its predictive ability is better than that of the structural indicators.

Uncovering metallic glasses hidden vacancy-like motifs using machine learning

Vacancies are a ubiquitous type of defect in crystalline materials that can affect their properties and behavior, including atomic diffusivity, deformation processes, thermal conductivity, and electrical conductivity. While well-defined in crystals, it is challenging to identify such topological footprints in the amorphous structure of metallic glasses (MGs). Here, we uncover an unforeseen vacancy-like structural motif named Q7, which refers to an atomic Voronoi polyhedron with seven quadrangular faces, by investigating MG local atomic configurations with the help of machine learning. The Q7 motif exhibits characteristics similar to crystalline vacancies and plays a significant role in short-range structural disorder in MGs. The atoms at the center of the Q7 motif display larger local entropy, atomic volume, and local tension. Additionally, its concentration follows an Arrhenius-like relationship with temperature, accurately indicating the glass transition temperature, and is strongly correlated with the yield and failure of MGs during mechanical deformation. The discovery of the Q7 motif provides new insights into understanding the intricate relationship between local disorder and structural relaxation in MGs, offering a remarkable ability to predict their thermal and mechanical behavior. This potentially paves the way for enhancements in the design and manufacturing processes of MGs and other amorphous materials.

Achieving strength-ductility synergy in metallic glasses via electric current-enhanced structural fluctuations

Structural applications of metallic glasses are limited by their room-temperature brittleness and strain-softening, associated with the extreme localization of plastic flow in shear bands. Herein, we alleviate this dilemma by the structural fluctuation induced by electric currents, achieving simultaneous improvement of strengths, compression plasticity, and strain hardening capacity. The electric current enhances the structural fluctuations at the atomic scale, introducing more soft zones while densifying their surroundings, which differs from previously reported rejuvenation strategies. This unique structural pattern featuring soft zones surrounded by hard zones leads to extensive sprouts and interactions of shear bands, capturing substantial atoms to participate in the deformation. The plausible mechanism behind the electric current-influenced dynamic evolution of amorphous clusters is proposed. Electric current introduces interatomic electrostatic forces between shell atoms of amorphous clusters through charge transfer. This force decreases the coordination of Zr- and Cu-centered clusters and increases the Al-centered icosahedra in the glassy matrix. Differential evolution of clusters under electric currents enhances atomic structural fluctuations and originates from the cohesion mechanism determined by electron distribution. These findings are suggestive of vanishing room-temperature brittleness and shed atomic-scale light on modulations of the structure and properties of metallic glasses by electric currents.