Local atomic structures of single-component metallic glasses

In this study we examine the structural properties of single-component metallic glasses of aluminum. We use a molecular dynamics simulation based on semi-empirical many-body potential, derived from the embedded atom method (EAM). The radial distribution function (RDF), common neighbors analysis method (CNA), coordination number analysis (CN) and Voronoi tessellation are used to characterize the metal’s local structure during the heating and cooling (quenching). The simulation results reveal that the melting temperature depends on the heating rate. In addition, atomic visualization shows that the structure of aluminum after fast quenching is in a glassy state, confirmed quantitatively by the splitting of the second peak of the radial distribution function, and by the appearance of icosahedral clusters observed via CNA technique. On the other hand, the Wendt-Abraham parameters are calculated to determine the glass transition temperature (T_g), which depends strongly on the cooling rate; it increases while the cooling rate increases. On the basis of CN analysis and Voronoi tessellation, we demonstrate that the transition from the Al liquid to glassy state is mainly due to the formation of distorted and perfect icosahedral clusters.     

Local atomic structures in Zr-Ni metallic glasses

Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr₆₄Ni₃₆ metallic glass consist of Zr₂Ni-like and ZrNi-like CSROs.     

Correlation between the atomic and electronic structure of metallic glasses

⁵⁷Fe Mössbauer and photoemission measurements were performed on meltquenched amorphous Fe(Zr, B) and (Fe, Ni)B alloys. The atomic and electronic structure of Fe₉₀Zr₁₀ and Fe₈₈B₁₂ glasses were found to be different. Half of the Zr content could be replaced by B in the Fe₉₀Zr₁₀ glass without changing its structure. Mossbauer investigation of the amorphous (Fe_1?xNi_x)_100?yB_y (0<=x<=0.80, 12<=y<=40) system indicates preferential arrangement of Fe and Ni atoms on the transition metal sites. According to the present XPS measurements there is a remarkable shift of 0.5 eV to higher binding energies of the B ls core level energy in the Ni rich glasses compared to Fe₈₈B₁₂ corresponding to a stronger binding between the Ni and the B atoms than that of Fe and B.     

Metallic liquids and glasses: atomic order and global packing

In this Letter, we have revealed the common structural behavior of metallic glasses through scrutinizing the evolution of pair distribution functions from metallic liquids to glasses and statistically analyzing pair distribution functions of 64 metallic glasses. It is found that the complex atomic configuration in metallic glasses can be interpreted globally as a combination of the spherical-periodic order and local translational symmetry. The implications of our study suggest that the glass transition could be visualized mainly as a process involving in local translational symmetry increased from the liquid to glassy states.     

The influence of 3d-impurities on magnetic and transport properties of CoSiB metallic glasses

Temperature dependencies of magnetic susceptibility and electric resistivity of Co-based metallic glasses (MGs) of the general composition _Co(72-x)Mex(Si,B₎₂₈${\mathrm{Co}}_{(72-x)}{\mathrm{Me}}_x(\mathrm{Si},\mathrm{B}{)}_{28}$(Me=Fe,Cr,Si:B=18:10)$(\mathrm{Me}=\mathrm{Fe},\mathrm{Cr},\mathrm{Si}:\mathrm{B}=18:10)$ have been studied up to 950 K. The studied MGs were found to be ferromagnets at the room temperature and their Curie point _TC$T_{\mathrm{C}}$ ranges within 260–560 K depending on the dopant contents. At the temperatures higher than _TC$T_{\mathrm{C}}$, a wide paramagnetic region exists. The regularities of magnetic moment variation upon Cr doping evidence a formation of antiferromagnetic clusters, which determine the anomalous behavior of resistivity.     

Relevance of Fe atomic volumes for the magnetic properties of Fe-rich metallic glasses

The atomic volume V_a-Fe that can be assigned to Fe atoms in Fe–metalloid (Fe–MD) and Fe–early transition metal (Fe–TE) glasses was deduced in a previous paper (I. Bakonyi, Acta Materialia 53 (2005) 2509) from an analysis of available density data for such amorphous alloys. In the present paper, based on a similarity of the amorphous and face-centered cubic (fcc) structures, the distinctly different magnetic behaviors of these two families of amorphous alloys are discussed in terms of the relative position of V_a-Fe and the critical volume V_fcc?-Fe≈11.7 Å³/atom separating the so-called low-spin (LS) and high-spin (HS) state of fcc-Fe. For Fe–MD systems, V_a-Fe is found to be definitely larger than V_fcc*-Fe whereas for Fe-TE systems V_a-Fe is fairly close to V_fcc*-Fe. Since in topologically disordered alloys a distribution of atomic volumes is inherently present, in Fe–MD glasses the Fe atoms can be assumed to exhibit exclusively the HS state whereas in Fe–TE amorphous alloys a comparable fraction of Fe atoms can be either in the LS or the HS state. According to previous theoretical band structure calculations, an antiferromagnetic state can also be stable just around V_fcc*-Fe. The simultaneous presence of Fe atoms with such a rich variety of magnetic states due to the specific position of the average of the atomic volume distribution can well explain the complex magnetic behavior observed in Fe-rich Fe–TE metallic glasses such as, e.g., in amorphous Fe–Zr alloys around 90 at% Fe.     

How does the structural inhomogeneity influence the shear band behaviours of metallic glasses

ABSTRACT

Here we propose a model to understand the influence of structural inhomogeneity on the shear band behaviours of metallic glasses. By considering the inhomogeneous structure and stress concentration, the model predicts that the strain for shear band nucleation in metallic glasses can be variable and far below the theoretical elastic limit. During sliding, the shear band will approach a dynamic equilibrium state of balanced free volume generation and annihilation. By considering the accumulation of irreversible structure change, the shear band will finally develop into fracture. Under fluctuating load, the shear band shows an ‘activate-arrest’ behaviour, which results from a delayed response to the external load change. These results reasonably explain and correlate the physics behind the elastic limit, stick-slip shear band behaviour, implicit shear events, and shear band fracture in metallic glasses. The study can provide another perspective and platform to understand the correlations between structural inhomogeneity and shear band behaviours in metallic glasses, and further explore other shear band related phenomena not only in metallic glasses but also in the class of shear-softened materials.     

金属玻璃的稳定性

玻璃态材料自诞生以来一直受到自身稳定性的困扰。为了保障玻璃的服役安全性,人们一直努力提高玻璃的耐久性和稳定性。玻璃能否经年累月地保持长期稳定？影响其稳定性的物理机制和根源是什么？这些都是非晶态物理领域长期关注的重要难题。根据以往对非晶合金稳定性的研究结果,文章将简单介绍玻璃亚稳性的起源,然后介绍玻璃如何能够保持长期稳定,如何提高玻璃的热力学和动力学稳定性以制备出超稳玻璃,最后介绍影响玻璃稳定性的材料因素,用于指导有效地获得高稳定性玻璃。对玻璃稳定性的认识和理解,既能够保障玻璃材料服役过程中的安全性,又对认识过冷液体和玻璃转变等基本物理问题非常关键。     

Microstructure of fragile metallic glasses inferred from ultrasound-accelerated crystallization in Pd-based metallic glasses

By utilizing ultrasonic annealing at a temperature below (or near) the glass transition temperature Tg, we revealed a microstructural pattern of a partially crystallized Pd-based metallic glass with a high-resolution electron microscopy. On the basis of the observed microstructure, we inferred a plausible microstructural model of fragile metallic glasses composed of strongly bonded regions surrounded by weakly bonded regions (WBRs). The crystallization in WBRs at such a low temperature under the ultrasonic vibrations is caused by accumulation of atomic jumps associated with the beta relaxation being resonant with the ultrasonic strains. This microstructural model successfully illustrates a marked increase of elasticity after crystallization with a small density change and a correlation between the fragility of the liquid and the Poisson ratio of the solid.     

Correlation between atomic size and elastic properties/glass transition temperature in metallic glasses

<正>As a relative newcomer in the glass family,metallic glass challenges our standpoint on crystalline metals and extends our knowledge concerning the nature of glasses[1].Metallic glasses have attracted considerable attention because of their unique mechanical,physical,and chemical properties[2-4].Newly developed bulk metallic glass can combine toughness and strength beyond the benchmark ranges established by the     

The stability of metallic glasses under ion irradiation

Abstract

Metallic glasses of Fe₈₀B₂₀ and Fe₈₀P₁₃C₇ prepared by rapid quenching have been implanted with 40 keV Ar⁺, P⁺ and B⁺ ions at doses up to 2.10¹⁶ ions cm^?2 at 273 K. The structure of the glasses was examined by X-ray diffraction. Crystallites of α-Fe and Fe₃B, present in F₈₀B₂₀ samples, either become highly defective or are amorphised. Implantation also produces structural changes in the amorphous Fe₈₀B₂₀ (a-Fe₈₀B₂₀) phase as revealed by changes in the width β of the principal diffraction halo. Both disordering and relaxation effects are observed, dependent on the initial degree of order within the a-Fe₈₀B₂₀ phase before irradiation. Implantation of F₈₀p₁₃C₇ results in an increase in the content of γ-Fe and Fe₃P crystallites, already present before irradiation, and in the nucleation of α-Fe.     

The electrical conductance growth of a metallic granular packing

We report on measurements of the electrical conductivity on a two-dimensional packing of metallic disks when a stable current of ~1 mA flows through the system. At low applied currents, the conductance σ is found to increase by a pattern σ(t) = σ _∞ ? Δσ E _α [ ? (t/τ) ^α ], where E _α denotes the Mittag-Leffler function of order α ∈ (0,1). By changing the inclination angle θ of the granular bed from horizontal, we have studied the impact of the effective gravitational acceleration g _eff = gsinθ on the relaxation features of the conductance σ(t). The characteristic timescale τ is found to grow when effective gravity g _eff decreases. By changing both the distance between the electrodes and the number of grains in the packing, we have shown that the long term resistance decay observed in the experiment is related to local micro-contacts rearrangements at each disk. By focusing on the electro-mechanical processes that allow both creation and breakdown of micro-contacts between two disks, we present an approach to granular conduction based on subordination of stochastic processes. In order to imitate, in a very simplified way, the conduction dynamics of granular material at low currents, we impose that the micro-contacts at the interface switch stochastically between two possible states, “on” and “off”, characterizing the conductivity of the micro-contact. We assume that the time intervals between the consecutive changes of state are governed by a certain waiting-time distribution. It is demonstrated how the microscopic random dynamics regarding the micro-contacts leads to the macroscopic observation of slow conductance growth, described by an exact fractional kinetic equations.     

Thermopower of iron-boron metallic glasses

The thermopower of Fe-B metallic glasses has been measured from 300 K to 800 K. The thermopower is negative over the entire temperature range and the temperature dependence varies for various boron concentrations. The effects of crystallization processes and of possible spin dependent scattering process on the temperature dependence of the thermopower are discussed.The author expresses her thanks to P. Duhaj for the preparation of the samples and to P. Mrafko for the computer data processing.     

Optical properties of metallic glasses

Optical reflection spectra of metallic glasses (Pd₈₁Si₁₉ and Pd₈₄Si₁₆) were measured in the spectral range 0.03 to 12 eV and the optical constants were determined by Kramers-Kronig analysis. The experimental reflectivity spectra of glassy Pd₁₈Si₁₉ are similar to the one obtained for Au₈₁Si₁₉ prepared by getter sputtering in argon. However, the energy ranges where intra- and interband optical transitions occur are quite different for the two alloys.     

非晶合金的离子辐照效应

非晶合金作为一种快速凝固形成的新型合金材料,引起了材料研究者的极大兴趣.微观结构上长程无序、短程有序的特征使其具有独特的物理、化学和力学性能,在许多领域展现出良好的应用前景,尤其是有望成为核反应堆、航空航天等强辐照环境下的备选结构材料.本文深入探讨非晶合金的辐照效应,主要讨论离子辐照对非晶合金微观结构、宏观力学性能以及其他物理化学性能的影响,可为进一步理解非晶合金的微观结构和宏观力学性能之间的关系提供有效的实验和理论基础,也可为非晶合金在强辐照环境下的服役性能预测提供实验依据,对推进非晶合金这一先进材料的工程化应用具有重要的理论与实际意义.     

纳米结构非晶合金材料研究进展

迄今为止,人类社会新技术的发展主要是基于各种晶体材料(如金属、半导体等)的应用.晶体材料的性能可以通过改变它们的微观缺陷结构和/或微观化学结构来调控,但这对于当前的非晶材料而言却是难以实现的.新型的纳米结构非晶材料可以通过引入大量的非晶/非晶界面来改变非晶材料的微观缺陷结构和/或微观化学结构,从而实现对其性能的调控.本文主要讨论了目前纳米结构非晶合金材料的研究进展,包括其制备方法、结构特征和新性能.通过利用这些新特性,有可能会开启一个基于非晶材料的新技术时代.     

Magnetostriction of ferromagnetic metallic glasses

Linear saturation magnetostrictions (295 K) of Fe_80t-xCo_xB₂₀, 0?x?80, and Fe_80?xNi_xB₂₀, 0?x?60 (at. %) glasses are reported. The saturation magnetostrictions of the Fe-Ni-base glasses vary as the sqaure of their respective saturation magnetizations. The behavior in the Fe-Co-base glasses is strikingly different. The compositional trends suggest a difference in origin of magnetostrictions between Fe-Ni-base and Co-containing glasses. When magnetostrictions for these glasses are compared with those for Fe-Co and Fe-Ni polycrystalline alloys, the most significant discrepancies appear in the Fe-rich compositions. This is probably related to the difference in short range order between the crystalline and non-crystalline Fe-rich alloys: α-Fe is 8-fold coordinated whereas all of the metallic glasses studied show ～ 12-fold metal coordination.     

On the structural stability of metallic glasses

We discuss the various possibilities advanced to account for the structural stability of metallic glasses. Using a formalism based on the pseudopotential theory and the Gibbs-Bogoliubov inequality we calculate the free energies and free energies of formation for the glassy phase of MgCa at various concentrations and compare these results with those for the corresponding solid and liquid phases of the same system. Subsequently, we attempt to explain the stability of the metallic glasses by noting a matching between the positions of the first peakq _m in the relevant structure factor and the maximumq _s in the relevant screened pseudopotential.The major part of this work was done in the H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, England