Inherent Shear-Dilatation Coexistence in Metallic Glass

Shear deformation can induce normal stress or hydrostatic stress in metallic glasses [Nature Mater. 2 （2003） 449, Intermetallics 14 （2006） 1033]. We perform the bulk deformation of three-dimensional Cu46Zr54 metallic glass （MG） and Cu single crystal model systems using molecular dynamics simulation. The results indicate that hydrostatic stress can incur shear stress in MG, but not in crystal. The resultant pronounced asymmetry between tension and compression originates from this inherent shear-dilatation coexistence in MG.     

Dynamic Crossover in Metallic Glass Nanoparticles

We report the dynamic crossover behavior in metallic glass nanoparticles(MGNs)with the size reduction based on the extensive molecular dynamics(MD)simulations combined with the activation-relaxation technique(ART).The fragile-to-strong transition of dynamics can be achieved by just modulating the characteristic size of MGNs.It can be attributed to the abnormal fast surface dynamics enhanced by the surface curvature.By determining the potential energy surface,we reveal the hierarchy-to-flat transition of potential energy landscape(PEL)in MGNs,and demonstrate the intrinsic flat potential landscape feature of the MGN with size smaller than a critical size.Our results provide an important piece of the puzzle about the size-modulated potential energy landscape and shed some lights on the unique properties of MGs in nanoscale.     

On the Nano/Micro-Mechanics of Metallic Glass

Metallic glass (MG) is amorphous and has some outstanding properties such as ultrahigh strength, superior elasticity, and excellent thermo-plasticity. However, as MG is relatively new to the metal family, the relationship between its physical properties and amorphous structure is still unclear. This article aims to provide an insightful discussion through a comprehensive review about the investigations in the past few decades on the scientific mechanisms of this class of material. The discussion of the paper will include the following key aspects: (1) the formation mechanism of an amorphous structure through glass transition, (2) the structural characterization and models, (3) the micromechanics of plastic event and shear band, and (4) the correlation between the amorphous structure and its mechanical properties.     

Phonon Dispersion in Ca70Mg30 Metallic Glass

The phonon dispersion curves （PDC） of Ca70Mg30 metallic glass has been studied at room temperature in terms of phonon eigen frequencies of longitudinal and transverse modes employing three different approaches proposed by Hubbard and Beeby （J. Phys. C： Solid State Phys. 13 （1969） 556）, Takeno and Goda （Prog. Theor. Phys. 45 （1971） 331; 47 （1972） 790） and Bhatia and Singh （Phys. Rev. B 31 （1985） 4751）. The well recognized model potential of Gajjar et al. is employed successfully to explain electron-ion interaction in the metallic glass. The effective pair potential is used to generate the pair correlation function g（r）. The local field correction function （Int. J. Mod. Phys. B 17 （2003） 6001） is used for the first time to introduce the exchange and correlation effects on the aforesaid properties. The present findings of PDCs are found to be in agreement with the available theoretical as well as experimental data. The thermodynamic and elastic properties, i.e. longitudinal and transverse sound velocities, isothermal bulk modulus, modulus of rigidity, Poisson＇s ratio, Young＇s modulus and Debye temperature, are also investigated successfully.     

Low-Temperature Physical Mechanism of Inelastic Strain of Metallic Glass

Russian Physics Journal - The paper deals with the low-temperature physical mechanism of inelastic strain of metallic glass, which is the quantum atomic tunneling in a double well potential or...     

A Free-Volume Model for Thermal Expansion of Metallic Glass

Many mechanical,thermal and transport behaviors of polymers and metallic glasses are interpreted by the freevolume model,whereas their applications on thermal expansion behaviors of glasses is rarely seen.Metallic glass has a range of glassy states depending on cooling rate,making their coefficients of thermal expansion vary with the glassy states.Anharmonicity in the interatomic potential is often used to explain different coefficients of thermal expansion in crystalline metals or in different ...     

Ferromagnetic to Paramagnetic Transition in Spherical Spin Glass

Journal of Statistical Physics - We consider the spherical spin glass model defined by a combination of the pure 2-spin spherical Sherrington–Kirkpatrick Hamiltonian and the ferromagnetic...     

Enhanced Laser Cooling of Rare-Earth-Ion-Doped Glass Containing Nanometer-Sized Metallic Particles

The enhanced laser cooling performance ofrare-earth-ions-doped glasses containing small particles is predicted. Thisis achieved by the enhancement of local field around rare earth ions, owingto the surface plasmon resonance of small metallic particles. The role ofenergy transfer between ions and the particle is theoretical discussed.Depending on the particle size and the ion emission quantum efficiency, theenhancement of the absorption and the fluorescence is predicted. Moreover,taking Yb³⁺-doped ZBLAN as example, the cooling power and heat-lightconverting efficiency are calculated. It is finally concluded that theabsorption and the fluorescence are greatly enhanced in these compositematerials, the cooling power is increased compared to the bulk material.     

Reconstruction on Trees and Spin Glass Transition

Consider an information source generating a symbol at the root of a tree network whose links correspond to noisy communication channels, and broadcasting it through the network. We study the problem of reconstructing the transmitted symbol from the information received at the leaves. In the large system limit, reconstruction is possible when the channel noise is smaller than a threshold.We show that this threshold coincides with the dynamical (replica symmetry breaking) glass transition for an associated statistical physics problem. Motivated by this correspondence, we derive a variational principle which implies new rigorous bounds on the reconstruction threshold. Finally, we apply a standard numerical procedure used in statistical physics, to predict the reconstruction thresholds in various channels. In particular, we prove a bound on the reconstruction problem for the antiferromagnetic “Potts” channels, which implies, in the noiseless limit, new results on random proper colorings of infinite regular trees.This relation to the reconstruction problem also offers interesting perspective for putting on a clean mathematical basis the theory of glasses on random graphs. PACS: 02.50.−r (Probability theory, stochastic processes, and statistics), 64.70.Pf (Glass transitions), 89.75.Hc (Networks and genealogical trees)     

The One Glass Transition Criterion for Liquids

Doklady Physics - In this communication, a condition based on the deactivation of the trigger mechanism of creep is proposed for the liquid–glass transition of an amorphous substance. This...     

Glass Formation Ability and Kinetics of the Gd55A120Ni25 Bulk Metallic Glass

We report a new bulk glass-forming alloy GdssA12oNi25. The bulk sample of the alloy is prepared in the shape of rods in diameter 2ram by suction casting. The rod exhibits typical amorphous characteristics in the x-ray diffraction pattern, paramagnetic property at 30OK, distinct glass transition and multi-step crystallization behaviour in differential scanning calorimetry traces. The gJass formation ability of the alloy is investigated by using the reduced glass transition temperature Trg and the parameter γ- Kinetics of glass transition and primary crystallization is also studied. The fragility parameter m obtained from the Vogel-Fulcher-Tammann dependence of glass transition temperature Tg on In φ （φ is the heating rate） classifies the bulk metallic glasses into the intermediate category according to Angell＇s classification.     

The Percolation Signature of the Spin Glass Transition

Magnetic ordering at low temperature for Ising ferromagnets manifests itself within the associated Fortuin–Kasteleyn (FK) random cluster representation as the occurrence of a single positive density percolating network. In this paper we investigate the percolation signature for Ising spin glass ordering—both in short-range (EA) and infinite-range (SK) models—within a two-replica FK representation and also within the different Chayes–Machta–Redner two-replica graphical representation. Based on numerical studies of the ±J EA model in three dimensions and on rigorous results for the SK model, we conclude that the spin glass transition corresponds to the appearance of two percolating clusters of unequal densities.     

A New Cu-Based Metallic Glass Composite with Excellent Mechanical Properties

A new Cu-based bulk metallic glass composite of nominal composition(at.%) Cu_(41)Ni_(27)Ti_(25)Al_7 with excellent plasticity and a strong work-hardening behavior is fabricated. Strength above 1859 MPa and plasticity more than 11% are achieved under compression and tension modes. The deformation mechanism is proposed to the structural heterogeneities of the composite that promotes multiple shear bands meanwhile inhibits their free propagation,which results in the macroscopically plastic strain and work hardening. The alloy contains relatively cheap metals and has a low cost, which is beneficial to industrial applications.     

Effect of Structural Relaxation on Deformation Behaviour of Zr-Based Metallic Glass

Structural relaxation through isothermal annealing at temperature below glass transition is conducted on Zr46.75 Ti8.25 CU7.5Ni11Be27.5 （Vitreloy-4） bulk metallic glass. Defect concentration is correlated with the annealing time t according to differential scanning calorimetry thermalgrams. The effects of structural relaxation on mechanical properties and deformation behaviour are investigated by using instrumented nanoindentation. It is found that the as-cast alloy exhibits pronounced serration flow during the loading process of nanoindentation, and the size and number of the serrations decrease with the annealing time. The change of the deformation behaviour with structural relaxation is explained using a free volume model.     

FeCuNi金属玻璃中第二峰分裂的结构起源

基于分子动力学模拟,采用双体分布函数(PDF)、最大标准团簇(LSC)、拓扑密堆团簇(TCP LSC)和三维可视化技术等微观结构表征方法,研究了10¹²K/s冷速下六种不同组分的Fe₇₀Cu₍(30-x))Ni_x(x=0、5、10、15、20、30)金属玻璃中的偏PDF特征以及Ni含量对TCP LSCs的影响.研究结果表明:FeCuNi金属玻璃中的ICO LSCs不是PDF第二峰分裂的主要结构起源,而TCP LSCs可以相当完美地解释第二峰的分裂特征.Ni含量对TCP LSCs微观结构产生微妙且复杂的影响.拓扑不变性是TCP LSCs的基本特征.     

Increasing Superplasticity and Strong Dynamic Behaviour of Zr--Cu--Ni--Al Bulk Metallic Glass

The plasticity and the dynamic fragility of bulk metallic glass of a Zr62 CuxsNiloAllo alloy are studied by three- point beam bending methods. We find that the alloy behaves super plastic not only at room temperature, but also at high temperatures. More importantly, it is found that the superplasticity increases with increasing temperature. In addition, the dynamic fragility parameter m for the supercooled liquid of this alloy is measured to be 34.87 and the supercooled liquid of Zr62 CuxsNixoAlxo alloy behaves as a strong liquid.     

Compressive Deformation Induced Nanocrystallization of a Supercooled Zr-Based Bulk Metallic Glass

The nanocrystallization behaviour of a bulk Zr-based metallic glass subjected to compressive stress is investigated in the supercooled liquid region. Compared with annealing treatments without compressive stress, compressive deformation promotes the development of nucleation and suppresses the coarsening of nanocrystallites at high temperatures.     

Glass Forming Ability of Metallic Glasses Evaluated by a New Criterion

The glass-forming ability （GFA） of Cu-Zr binary alloys is evaluated using the existing criteria based on calorimetric parameters, and poor relations are found. Therefore, another parameter Tτκ defined as Tκ/Tl, in which Tκ is the Kauzmann temperature and Tl the equilibrium liquidus temperature, is proposed. It exhibits good agreements with the experimental data of the Cu-Zr system and other representative bulk metallic glass formers so long as classifying them into strong or fragile category. It is suggested that kinetic effects are irrelevantly incorporated in the GFA analysis in the previous work.