Structure Of Amorphous Alloys Research Articles

Effect of Y element on atomic structure, glass forming ability and magnetic properties of FeBC alloy

Abstract The atomic structure of amorphous alloys plays a crucial role in determining both their glassforming ability and magnetic properties. In this study, we investigate the influence of adding the Y element on the glass-forming ability and magnetic properties of Fe86-xYxB7C7 (x=0, 5, 10 at.%) amorphous alloys via both experiments and ab initio molecular dynamics simulations. Furthermore, we explore the correlation between local atomic structures and properties. Our results demonstrate that an increased Y content in the alloys leads to a higher proportion of icosahedral clusters, which can potentially enhance both glass-forming ability and thermal stability. These findings have been experimentally validated. The analysis of the electron energy density and magnetic moment of the alloy reveals that the addition of Y leads to hybridization between Y-4d and Fe-3d orbitals, resulting in a reduction in ferromagnetic coupling between Fe atoms. This subsequently reduces the magnetic moment of Fe atoms as well as the total magnetic moment of the system, which is consistent with experimental results. The results could help understand the relationship between atomic structure and magnetic property, and providing valuable insights for enhancing the performance of metallic glasses in industrial applications.

Probing microstructural heterogeneity of La-based amorphous alloy under versatile mechanical stimuli

The intrinsic structural heterogeneity of amorphous alloy is closely related to the thermodynamics and dynamical behavior, such as relaxation/crystallization, glass transition and plastic deformation. However, the structural information is submerged into the meta-stable disordered long-range structure, which makes it very difficult to explore the structural heterogeneity of amorphous alloy. A mechanical excitation factor is insufficient to effectively describe the heterogeneity of the microstructure in amorphous alloy, particularly the correlation between structure and dynamics. To explore the essence of the structure in amorphous alloy, it is necessary to consider the different mechanical stimuli. La<sub>62</sub>Cu<sub>12</sub>Ni<sub>12</sub>Al<sub>14</sub> amorphous alloy is selected as the model system, dynamic mechanical process is probed by dynamic mechanical analyzer (DMA). The contributions of <i>α</i> relaxation process and <i>β</i> relaxation process are described in the framework of the quasi-point defect theory. Based on the quasi-point defect theory, the <i>α</i>-relaxation and <i>β</i>-relaxation in the La-based amorphous alloy are separated. Tensile strain rate jump measurements are conducted to study the high temperature rheological behavior of amorphous alloy. The contributions of elasticity, anelasticity, and plastic deformation during the homogeneous flow of amorphous alloy are determined within the framework of quasi-point defect theory. The present work aims to reveal the structural heterogeneities of amorphous alloys under the action of dynamics on various temporal scales. The physical background of the activation, propagation and coalescence of defects in amorphous alloy under different mechanical stimuli are reviewed.

Relationship between relaxation embrittlement and atomic cluster structure in amorphous alloys

Relationship between relaxation embrittlement and atomic cluster structure was explored by simulation and experimental methods for two amorphous alloys: Zr60Cu30Al10 and Zr50Cu40Al10 (referred to as Zr60 and Zr50, respectively). Simulation results from large-scale molecular dynamics revealed that the Zr50 alloy exhibited a higher content of icosahedral clusters, which increased more obvious during the quenching process compared to the Zr60 alloy. As icosahedral clusters exhibit brittleness similar to quasicrystalline structures, we predicted that the Zr50 alloy would have a higher glass transition temperature Tg and more pronounced relaxation-induced brittleness than the Zr60 alloy based on this observation. To validate the predictions, experimental results confirmed the occurrence of relaxation brittleness in Zr50 and relaxation non-brittleness in Zr60, consistent with the XRD analysis and electron microscope-based three-dimensional reconstruction in terms of icosahedral clusters. The agreement between the simulation calculations and the experimental data provides a reference for understanding the mechanism of relaxation embrittlement in amorphous alloys.

Effect of hyperfine structure on crystallization, microstructure and magnetic properties of amorphous Nd9Fe85B6 alloy

Crystallization of amorphous alloy is a commonly used method to fabricate nanocomposite permanent magnets. However, the effect of the hyperfine structures of amorphous alloy on microstructure evolution and magnetic properties of the obtained nanocomposites is far from understood. Here, amorphous Nd9Fe85B6 alloys with different hyperfine structures, i.e., different short-range orders (Rs = 0.80–0.91 nm), were prepared via melt spinning. The effects of the hyperfine structure on crystallization behavior, microstructure, and magnetic properties of the material upon thermal annealing were investigated in depth. Crystallization kinetics calculations show that a larger Rs leads to a smaller apparent crystallization activation energy, which leads to higher volume fractions of α-Fe and Nd2Fe14B. At the same time, a crystallizaition process dependent stage crystallization activation energy of Nd2Fe14B has been obtained, which is low at nucleation stage and increases with crystallization process, i.e. easy for nucleation but hard for growth, which leads to a smaller grain size of Nd2Fe14B. As a result, optimized magnetic properties were obtained in the sample with Rs = 0.91 nm.

Relationship among intrinsic magnetic parameters and structure and crucial effect of metastable Fe3B phase in Fe-metalloid amorphous alloys

The intrinsic heterogeneity of an amorphous structure originates from composition, and the structure determines the magnetic properties and crystallization models of amorphous magnets. Based on classical Fe–B binary magnetic amorphous alloys, the relationship between the structure and magnetic properties was extensively studied. The stacking structure of Fe–B binary amorphous alloys exhibit discontinuous changes within the range of 74–87 at.% Fe. The structural feature can be expressed as Amor. Fe3B matrix + Fe atoms are transforming into Amor. Fe matrix + B atoms with the increase of Fe content. The solute atoms are uniformly distributed in the amorphous matrix holes, similar to a single-phase solid solution structure. The transition point corresponds to the eutectic crystallization model composition (Fe82B18 to Fe83B17). A high Fe content will amplify magnetic moment sensitivity to temperature. Under a given service temperature, the disturbance effect of magnetic moment self-spinning will offset the beneficial effect of increasing Fe content and induce the saturation magnetization (Ms) value to decrease. Binary amorphous Fe–B alloys obtain the maximum Curie temperature near 75 at.% Fe, which is slightly smaller than that of the corresponding metastable Fe3B phase, i.e., the amorphous short-range order structure maintains the highest similarity to the Fe3B phase. The chemical short-range ordering (SRO) structure of amorphous alloys exhibits heredity to corresponding (meta)stable crystal phases. The unique spatial orientation structure of the metastable Fe3B phase is the structural origin of the amorphous nature. This study can guide the composition design of Fe-metalloid magnetic amorphous alloys. The design of materials with excellent magnetic properties originates from a deep understanding of precise composition control and temperature disturbance mechanism.

Effects of a small amount of B addition on the geometric structure, electronic structure and magnetic properties of FePC amorphous alloys

The saturation magnetization of Fe-based amorphous alloys can be effectively increased by adding a small amount of metalloid B. In this paper, the influence mechanism of a small amount of B on the geometric structure, electronic structure and magnetic properties of Fe80P12-xC8Bx (x = 0, 1, 2, 3, 4) amorphous alloys was investigated by using first-principles molecular dynamics simulations. The addition of B does not significantly change the distribution of Voronoi polyhedra with Fe as the center but increases the number of Fe atoms in the vicinity of Fe. The B atom with a small radius easily diffuses to the space between atoms, which increases the density of the Fe-based amorphous alloy and the aggregation among Fe atoms, thus enhancing the interaction between Fe atoms and finally increasing the saturation magnetization of the amorphous alloy. This provides an effective way to develop amorphous alloys with excellent magnetic properties.

Mesoporous Ru(Co, Ni)B bimetallic amorphous alloy for CO2 hydrogenation to formic acid

Amorphous metal alloy catalysts have attracted even-increasing attention owing to their high activity and selectivity. However, they are mainly prepared in ultrafine nanoparticles, which are easily gathered and challenging to separate. In this work, mesoporous Ru(Co, Ni)B bimetallic amorphous alloy catalysts with magnetic properties that can be easily recovered were synthesized via surfactant self-assembly. The as-prepared Ru1%CoB catalyst exhibited 578 μmol/g/h production rate and 99% selectivity to HCOOH during liquid phase CO2 hydrogenation owing to the unique amorphous alloy structure corresponding to the well-distributed, coordination-unsaturated, electron-enriched and synergistic active sites, which promoted the adsorption, activation, dissociation, and surface reaction of CO2 and H2. Moreover, the mesoporous channels also promoted the diffusion and adsorption of CO2 and H2. Besides, the Ru1%CoB catalyst also displayed good durability in CO2 hydrogenation owing to the robust stability against the crystallization of amorphous alloy, the collapse of mesopores, and the leaching of active sites.

Change in the Radius of the First Coordination Sphere in Amorphous Alloys during Deformation

Changes in the structure of amorphous alloys under deformation by high-pressure torsion, multiple-pass rolling, and pressure treatment have been studied using X-ray diffraction and scanning electron microscopy. It has been shown that under all types of deformation, shear bands are formed in amorphous alloys, which are regions of lower density compared to a surrounding undeformed amorphous matrix. Shear bands are regions of an increased free volume; the formation of bands results in steps occurring on the surface of samples. The number of shear bands and the surface morphology of deformed amorphous alloys are determined by the deformation type and physical properties of a material.

Structure and physical properties changes of Fe-based amorphous alloy induced by Joule-heating

Structure and physical properties changes of Fe-based amorphous alloy induced by Joule-heating

Local atomic configurations in mechanically alloyed amorphous (FeCoNi)70Ti10B20 powders

The atomic structure of amorphous (FeCoNi)70Ti10B20 alloy synthesized by mechanical alloying was investigated using high energy synchrotron X-ray diffraction and inverse Monte Carlo simulations of pair distribution functions. Empirical potential structure refinement indicates a chemical short-range order at the length scales of 2.1–2.5 Å via local atomic arrangements forming deformed bcc-like clusters. The structural model obtained was described by bond lengths, coordination numbers, and bond angle distribution functions determined for the first neighbor atoms by x-ray scattering supplemented with 3D Monte Carlo simulations.

Dynamic relaxation behavior and its effect on mechanical properties of FePBCCu amorphous alloy

The correlation between the dynamic relaxation behavior and micro-inhomogeneous structure of amorphous alloy is of significance for exploring the mechanical deformation. In this work, we report the pronounced secondary (β) relaxation process in FeP(B)CCu amorphous alloys with different microstructures, which reveals the local heterogeneity at atomic scale. With the help of thermodynamic analysis, it was found that compared to the partially crystallized alloy, the more local structural heterogeneities were activated in the amorphous matrix due to the low activation energy of β relaxation and the high activation energy of crystallization. Physical aging far below the crystallization temperature demonstrated that atomic rearrangement supported the weakening of β relaxation amplitude as well as the increment of storage modulus, especially for FePBCCu amorphous alloy, which was consistent well with the increases of the reduced modulus and hardness by nanoindentation tests. Moreover, the fitted results from the Maxwell-Voigt model on creep curves revealed that the diffusion and rearrangement of atoms in loosely packed zones corresponding to the β relaxation were more active during aging. Our findings provide new insight into understanding the dynamic relaxation behavior in FePBCCu amorphous alloy and render it an ideal system to probe the correlation between relaxation and mechanical deformation.

Changes in the Structure of Amorphous Alloys under Deformation by High-Pressure Torsion and Multiple Rolling.

X-ray diffraction and scanning electron microscopy were used to study changes in the structure of amorphous alloys under deformation by high-pressure torsion and multiple rolling. The change in mean nearest neighbor distance (the radius of the first coordination sphere) under deformation was determined. During deformation, shear bands are formed in amorphous alloys, which are regions of lower density compared to the surrounding undeformed amorphous matrix. Shear bands are zones of increased free volume, in which crystallization processes are facilitated. The change in the proportion of free volume under deformation of various types was estimated. The formation of shear bands leads to the appearance of steps on the surface of the samples. The number of shear bands and the surface morphology of deformed amorphous alloys were determined by the type of deformation and the physical properties of the material. The results obtained are discussed within the concept of free volume in the amorphous phase.

Advanced structure research methods of amorphous Co69Fe4Cr4Si12B11 microwires with giant magnetoimpedance effect: Part 2 – Microstructural evolution and electrical resistivity change during DC Joule heating

This Part 2 focuses on the processes of atomic regions ordering of the amorphous material and continues study of the processes occurring in Part 1. The formation of pre-crystals / clusters and nanocrystallization of Co-based amorphous microwires during DC Joule heating were investigated, as well as the influence of these processes on the electrical resistance of the samples and the effect of giant magnetoimpedance (GMI). In this paper we investigated the dependence of the change in the maximum response of the GMI diagonal component at different temperatures and holding times in the DC Joule heating process, and discuss the effect of the ductile-brittle transition on the electrical resistance and the GMI effect. Using high-resolution transmission electron microscopy (HR-TEM) and the inverse Fourier transform technique, it was shown that at long exposure during the DC Joule heating, significantly below the crystallization temperature (~ 400 °C), the formation and growth of pre-crystals / clusters occur in various sizes (1 – 8 nm) and shapes. At the initial stage of crystallization, the microwire has three distinct regions of the clusters and nanocrystals formation (surface, pre-surface, and bulk). Moreover, pre-crystals / clusters growth and further bulk formation of nanocrystals (of 10 nm and more) leads to a sharp drop in the electrical resistance and degradation of the GMI microwire diagonal component response. The approach of controlled long-term holding during the DC Joule heating applied in the study allows for creation of various nanoscale structures in an amorphous matrix and provides an opportunity to grow of a given structure in amorphous alloys.

Production conditions and fine structure parameters of metallic glasses based on light rare-earth elements

Thermal regimes of formation and parameters of the fine structure of amorphous alloys based on light rare-earth elements (E-La, Ce, Pr) with normal metals (M-Al, Cu, Ag) obtained by rapid cooling of melt layers on the inner surface of a rotating cylindrical heat receiver are studied. It has been shown that the alloys under study belong to materials with an average level of glass-forming ability (GFA), whichsolidify without crystallization in cross sections from 35 to 65 μm during quenching from a liquid state. Based on the correlation between the sizes of coherent scattering regions and the shortest interatomic distances found by X-ray diffraction for E-M amorphous alloys with the corresponding characteristics of metallic glasses of other classes, a conclusion was made about a close analogy of the atomic structure of noncrystalline phases fixed by quenching metallic melts.

Effects of B substitution for P on structure and magnetic properties of FePB amorphous alloys by first-principle investigation

Effects of the substitution of B for P on structure and magnetic properties of FePB amorphous alloys are investigated by first-principle molecular dynamics. Our analysis shows that Fe-centered polyhedra are mainly distorted icosahedral structures, and P- or B-centered polyhedra are mainly icosahedrons and triangular prisms. It is found that Fe80P5B15 amorphous alloy has the most 15xx bond pairs and higher local five-fold symmetry. With the increase of B atoms, magnetic moment of the amorphous alloy gradually increases, which is in good agreement with the experiments. Due to higher local symmetry, Fe80P5B15 amorphous alloy produces a larger splitting exchange energy and hence a higher magnetic moment. Fe atoms are easy to lose electrons to be positively charged, but B or P atoms are easily to gain electrons and are negatively charged. In addition, on account of the small radius of B atoms, more Fe atoms are aggregated locally in Fe80P5B15 amorphous alloy. The more the number of neighboring Fe atoms, the largrer the magnetic moment of Fe atoms is, which makes magnetic moment in amorphous alloys gradually increases. These findings provide intentional guidance for the development of new soft magnetic materials.

The influence of annealing treatment on the electrocatalytic oxidation performance of Cu46Zr44·5Al7.5Gd2 amorphous alloy

The influences of annealing on the microstructure and the performance of electrocatalytic oxidation of Cu46Zr44·5Al7.5Gd2 amorphous alloy were investigated by operating heat treatment in the vacuum annealing furnace. It is found that structural relaxation occurred in the internal structure of amorphous alloy after annealing treatment, which will cause a significant effect on the relative electrochemical performance. Choosing annealing temperature of 300 °C and holding time of 20 min, hydrofluoric acid corrosion treatment was applied on the relaxation structural stage ribbons. According to cyclic voltammetry and chronoamperometry curve graphs, it is found that it has a high oxidation peak as an electrode, whose corresponding electric potential is −0.11 V and current density is 0.0187 A cm−2. After reusing the experimental samples for 20 cycles, the electrocatalytic oxidation property on methyl alcohol is found to gradually decline and then stabilize. At 1-5 experiment cycles, the effect of electrocatalyst is relatively good, which proves that the sample ribbons can be recycled.

Nanocrystallization and magnetic property improvement of Fe78Si9B13 amorphous alloys induced by magnetic field assisted nanosecond pulsed laser

The influence of the magnetic field (514 and 1642 Gauss) assisted nanosecond pulsed laser processing on the structure and magnetic property of Fe78Si9B13 amorphous alloy is analyzed in this paper. The magnetic field causes the surface to splash obviously, which is related to the Lorentz force generated by the applied magnetic field and current. The magnetic field assisted nanosecond pulsed laser does not cause the Fe78Si9B13 amorphous alloy to crystallize significantly, and the XRD pattern still shows a typical amorphous diffuse scattering peak. However, the magnetic field can enhance the crystallization sensitivity of the Fe78Si9B13 amorphous alloy, and make more nanocrystals formed in the heat affected zone based on the SAXS and TEM data. Moreover, the magnetic property of the Fe78Si9B13 amorphous alloy is improved when the magnetic field is 514 Gauss. The main reason is that the transition from fcc structure units to bcc structure units occurs in the amorphous alloy. When the applied magnetic field intensity is larger (1642 Gauss), the saturation magnetization decreases. It can be explained by the B content in the residual amorphous matrix is too high with the precipitation of α-Fe(Si) nanocrystals, which is not conducive to the increase of the saturation magnetization.

Structure and magnetic properties of amorphous and nanocrystalline Co-Fe-B-(Nb, Ti) alloys

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X=Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Ti8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy. Keywords: amorphous phase, crystallization, nanocrystals, magnetic properties.

Структура и магнитные свойства аморфных и нанокристаллических сплавов Co-Fe-B-(Nb, Ti)

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X = Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Nb8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy.

Effects of annealing time on nanoscale structural heterogeneity and magnetic properties of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy

The evolution of nanoscale structural heterogeneity and its effect on magnetic properties of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy during structural relaxation after being annealed for different times are investigated in this work. The nanoscale structural heterogeneity is found to degenerate gradually with relaxation by using the small-angle X-ray scattering and atomic force microscope. Combined with Mössbauer spectroscopy analysis results, the enhanced comprehensive soft magnetic properties of the relaxed alloys can be attributed to the degeneration of nanoscale structural heterogeneity. From the flow unit model, the volume fraction of flow units decreases with relaxation proceeding, and some of the flow units annihilate and transform into the ideal elastic matrix. On the one hand, the relaxed sample with greater packing density has stronger magnetic exchange interaction and higher saturation magnetic flux intensity. On the other hand, the number density of quasi-dislocation dipoles decreases with the annihilation of flow units in the relaxation process, leading the pinning effect of the domain wall to be weakened. Consequently, the magnetic anisotropy decreases after relaxation, which results in the reduction of coercivity. In this work, the structural mechanism of the evolution of magnetic properties in the relaxation process of Fe<sub>80</sub>Si<sub>9</sub>B<sub>10</sub>Cu<sub>1</sub> amorphous alloy is investigated from the perspective of structural heterogeneity, which is helpful in establishing the correlation between the structure and magnetic properties of Fe-based amorphous alloys.