Stability Of Metallic Glasses Research Articles

Stability of metallic glasses under simulated space conditions

Metallic glasses (MGs), due to their exceptional properties resulting from the amorphous structures, may be potential candidates for space applications. However, the effect of space conditions on the stability of MGs is not clear, which should be taken into account for practical use. The present work assessed the thermal stabilities of MGs in the simulated space thermal fields under vacuum condition, with a specific focus on the cryogenic thermal cycling with a high ratio of the non-isothermal to isothermal durations and the cryogenic treatment for a long-duration. The dynamics and thermal properties of MGs under the simulated space conditions were found to be different than those in laboratory-based conditions. MGs with lower fragility values were also determined to show greater thermal stability. On this basis, rules for the selection of MGs to ensure thermal stability during future space applications were proposed.

Crystallization Mechanism in Spark Plasma Sintered Bulk Metallic Glass Analyzed using Small Angle Neutron Scattering

Understanding the thermal stability of metallic glasses is critical to determining their safe temperatures of service. In this paper, the crystallization mechanism in spark plasma sintered Fe48Cr15Mo14Y2C15B6 metallic glass is established by analyzing the crystal size distribution using x-ray diffraction, transmission electron microscopy and in-situ small angle neutron scattering. Isothermal annealing at 700 °C and 725 °C for 100 min resulted in the formation of (Fe,Cr)23C6 crystals, measured from transmission electron micrographs, to be from 10 to 30 nm. The small angle neutron scattering intensity measured in-situ, over a Q-range of 0.02 to 0.3 Å−1, during isothermal annealing of the sintered samples, confirmed the presence of (Fe,Cr)23C6 crystals. The measured scattering intensity, fitted by the maximum entropy model, over the Q-range of 0.02 to 0.06 Å−1, revealed that the crystals had radii ranging from 3 to 18 nm. The total volume fraction of crystals were estimated to be 0.13 and 0.22 upon isothermal annealing at 700 °C and 725 °C for 100 min respectively. The mechanism of crystallization in this spark plasma sintered iron based metallic glass was established to be from pre-existing nuclei as confirmed by Avrami exponents of 0.25 ± 0.01 and 0.39 ± 0.01 at the aforesaid temperatures.

Hidden amorphous phase and reentrant supercooled liquid in Pd-Ni-P metallic glasses

An anomaly in differential scanning calorimetry has been reported in a number of metallic glass materials in which a broad exothermal peak was observed between the glass and crystallization temperatures. The mystery surrounding this calorimetric anomaly is epitomized by four decades long studies of Pd-Ni-P metallic glasses, arguably the best glass-forming alloys. Here we show, using a suite of in situ experimental techniques, that Pd-Ni-P alloys have a hidden amorphous phase in the supercooled liquid region. The anomalous exothermal peak is the consequence of a polyamorphous phase transition between two supercooled liquids, involving a change in the packing of atomic clusters over medium-range length scales as large as 18 Å. With further temperature increase, the alloy reenters the supercooled liquid phase, which forms the room-temperature glass phase on quenching. The outcome of this study raises a possibility to manipulate the structure and hence the stability of metallic glasses through heat treatment.

Growth of icosahedral medium-range order in liquid TiAl alloy during rapid solidification

The formation and evolution of icosahedral medium-range order structures of TiAl alloy during the rapid solidification are investigated based on molecular dynamics simulations. The icosahedral medium-range order structural evolutions are described in detail by coordination number and icosahedral connectivity parameters. Simultaneously, the evolution of the medium-range order icosahedral clusters is analyzed by nano-clusters tracing method. The results reveal that the full growths of icosahedral medium-range order structures improve the glass forming ability and stability of metallic glass. Meanwhile, the hexagonal connected icosahedral clusters which link via volume-sharing have excellent structural stability, and the dendritic icosahedral clusters based on the hexagonal formation keep continuous growth below the Tg. The junctions which consist of the hexagonal formations enhance the compactness of icosahedral medium-range order structure. Moreover, the icosahedral medium-range order is an appropriate structural characterization which accurately defines the characteristics of amorphous TiAl alloy during the rapid solidification.

Stability of Metallic Glasses: Criteria and Prediction of Ductile-Brittle Transition and Crystallization

Abstract A close correlation between the mechanical behavior changes of metal-metalloid glasses and their relaxation spectrum heat emissions has been found. The criteria of crystallization and ductile-brittle transition for these kinds of metallic glasses (MGs) have been established. They correspond to the heat emission balance between the low- and high-temperature parts of the relaxation spectrum. The model of MGs as a system constituting an additive sum of elementary two-level transitions with continuously distributed activation energies is proposed for the analytical description of the relaxation spectrum and its parameters. The methods developed in the approximation of the model permit the determination of the current state of MG materials at an arbitrary temperature, as well as forecasting of their ductile-brittle transition and crystallization according to heat emission alterations of the relaxation spectrum.

805 分子動力学法による金属ガラスの冷却速度と熱力学安定性の検討(OS8.電子・原子・マルチシミュレーションに基づく材料特性評価(2),OS・一般セッション講演)

805 分子動力学法による金属ガラスの冷却速度と熱力学安定性の検討(OS8.電子・原子・マルチシミュレーションに基づく材料特性評価(2),OS・一般セッション講演)

Stabilization of metallic glass by isochronal and isothermal annealing treatments

The internal friction (IF) of a Zr–Ti–Cu–Ni–Be metallic glass was measured using aninverted torsion pendulum with the free decay method. A single-roller melt-spinningapparatus was used for preparing the specimens. In the isochronal annealing experiment,specimens in different states were prepared by annealing, and the temperature dependenceof the IF was measured from room temperature up to the crystallization temperatureTx. Theglass attained a stabilized state under a long-time annealing near and below the glass transition temperatureTg. IF peaks alwaysappeared near and below Tx, while an anomaly was observed clearly nearTg only in the stabilized state. A differential scanning calorimetry experiment was carried outfor the same specimens, and the results showed the same characteristics. The isothermalannealing experiment revealed that the stabilization was a relaxation process, and how longa time was required for reaching the stabilized state. The essential features of glass-formingmaterials could be clearly observed when the specimens were in the stabilized state.

Thermal de-vitrification and formation of single phase nano-crystalline structure in Fe-based metallic glass alloys

The crystallization temperature obtained in a thermal analyzer has become a conventional means for characterizing the thermal stability of metallic glasses and less importance has been attached to the intermediate crystalline phases until recently that nano-structured alloys can now be prepared by careful heat treatment of metallic glass precursors. This has brought attention to studying in detail, the process of de-vitrification and the formation of intermediate crystalline phases. The de-vitrification of a number of Fe-based metallic glass alloys have been followed with differential scanning calorimeter (DSC). De-vitrification is generally accompanied by two exothermic peaks that signify a two step crystallization reaction. Small additions of transition metallic elements, Cu, Cr, Ta, Nb and Mo alter this shape either leading to complete separation or merging of the two thermal events. Crystallization temperatures characterized by the primary peak temperature varied from 450 °C to 600 °C. The separation between the peaks varied from 0 (for single peak) to more than 100 °C depending on alloy composition. It is found that for alloy compositions where peak separation is less than 20 °C, it was not possible to anneal to single phase nano-structure.

Deformation bands in metallic glasses induced by swift heavy ions

We present a direct experimental evidence that shear bands in metallic glasses can be induced by swift heavy ion irradiation. Transmission electron microscopy micrographs show that shear bands nucleate in the vicinity of the ion paths. Finally, we state that swift heavy-ion irradiation can be used as a nanometer-size probe to test the structural stability of metallic glasses under high local stresses.

Candidate Atomic Cluster Configurations in Metallic Glass Structures

A growing body of evidence supports the importance of solute-centered atomic clusters in the structure and stability of metallic glasses. Beyond a few simple cases, a broad account of these clusters has not been provided elsewhere. Detailed characteristics of a canonical collection of efficiently packed hard sphere clusters are presented here as idealized structural elements in metallic glasses. The nomenclature, topology, geometry and packing efficiency of these clusters are provided and their relevance to the structure of metallic glasses is discussed.

Precipitation of Zr2Cu Stable Crystalline Phase from Zr70Cu27.5Rh2.5 Amorphous Alloy

AbstractThe crystallization process of Zr70Cu27.5Rh2.5 metallic glass was studied with Transmission Electron Microscopy (TEM). In contrast to previous studies where the precipitation of metastable icosahedral quasicrystalline (IQC) particles is of the interest, we designed the present work to focus on the nucleation process of the stable Zr2Cu crystalline phase. It has been found that the alloy consists of IQC particles distributed in amorphous matrix prior to the precipitation of the Zr2Cu stable crystalline phase and Zr2Cu nucleates from the amorphous matrix. The encounter of the IQC phase with Zr2Cu transforms the former into the latter so quickly that no interface between them was found in the present experiment. These insights provide the basis for a discussion of the stability of metallic glasses and the IQC particles.

The roles of thermodynamics and transformation kinetics on phase selection in the non-equilibrium processing of materials

The interplay between thermodynamics and transformation kinetics dictates phase selection during non-equilibrium materials processing. Computing thermodynamics is now a well-recognised technique for the development of multi-component materials, where a thorough experimental study is nearly impossible. Indeed, thermodynamics plays an important role for microstructural engineering, unless kinetics exerts major barriers for phase transformation. The latter plays a dominant role for microstructural development under non-equilibrium processing conditions. This paper demonstrates the importance of both thermodynamics and kinetics on phase selection in far-from-equilibrium conditions, using examples such as the stability of metallic glasses, phase selection during sputter deposition, and phase transformation in energetic ion beam synthesised materials.

Calculations of Crystallization Temperature of Multicomponent Metallic Glasses

A model for calculating crystallization temperature (T x ) of multicomponent metallic glasses is proposed by modifying the Miedema's model which is used for calculating T x of binary systems. The calculations were carried out for nearly 900 metallic glasses including 470 binary and 398 ternary alloys. In the present model, the cavity formation energy (ΔH for cavity ) for multicomponent metallic glasses was theoretically derived on the basis of the Miedema's model. The equation for expressing the relation between experimental T x and theoretical ΔH for cavity was statistically analyzed by the least-squares method, yielding T x = 4.16 x ΔH for cavity + 318. The binary and ternary systems tend to show different equations between Tx and ΔH for cavity . The inherent equation in each system was analyzed as simultaneous achievement of the increase in stability of metallic glasses and decrease in ΔH for cavity due to multicomponent alloying. Furthermore, the glass-forming ability was predicted by reduced crystallization temperature instead of reduced glass transition temperature. As a result, it was found that reduced crystallization temperature can be calculated close to reduced glass transition temperature except for Pt-, Pd- and La-based systems. It is of great importance that T x can be calculated for multicomponent metallic glasses by semi-empirical method.

Glass formation in metallic systems

AbstractThe aim of the present paper is to analyse the formation and stability of metallic glasses. Attention is focused to the history of the progress on new glassy alloys with specific applications: from soft magnetic Fe‐based ribbons obtained by melt spinning or planar flow casting, through metallic glasses acting as precursors of nanocrystalline precipitates embedded in an amorphous matrix, towards the finding of new multicomponent metallic alloys with large glass‐forming ability that open a new area of development and applications of bulk metallic glasses. The glass formation process is discussed in terms of the structure of the resultant material and in terms of the thermodynamics and kinetics of the process. The development of structural criteria for glass formation is based upon the notion that the free energy of particularly stable glassy structures will be low enough to make the driving force for crystallization negligible. Both structural and energetic criteria point to an enhanced glass‐forming ability in multicomponent alloys. Kinetic criteria allow to differentiate between the ease of glass formation from an undercooled melt (or from a mixture of crystalline grains, as in solid state amorphization) and the stability of the glassy state versus devitrification or crystallization. Key kinetic parameters are viscosity and, more specifically in multicomponent systems, diffusivities of the different elements in the crystalline, glassy and metastable liquid state, respectively. The formation of nanostructured materials from controlled thermal treatment and their temperature stability is discussed in terms of the concentration gradients developing at the interface between the nanocrystals and the amorphous matrix. The qualitative influence of several parameters in the glass‐forming ability and glass‐stability as well as their link to the empirical criteria that have been successfully employed to predict the glass‐forming ability are presented.

Stability of three-dimensional metallic glass Ni68B21Si11

Under isothermal and linear heating conditions, the thermal stability of the three-dimensional metallic glass Ni68B21Si11, produced by rapid quenching of the denucleated melt (RQDM), has been systematically studied using PE DSC7 differential scanning calorimetry in relation to denucleation of liquid alloy prior to rapid quenching, pre-anneal treatment of amorphous specimens, and cooling rate. The following results were observed. First, the thermal stability of metallic glass prepared by RQDM is obviously enhanced because of the removal of pre-existing nuclei in advance. This is substantiated by the experimental data showing that the projected life of three-dimensional metallic glass Ni68B21Si11 is increased by an order of magnitude at 400 K. Secondly, pre-anneal treatment of the amorphous alloy leads to a reduction of temperature for the onset of crystallization,Tx, and crystallization heat, ΔH. Finally, quenching rates have little effect on the thermal stability of amorphous alloys.

Formation and stability of metallic glass Cu90?x Ni10P x

In the work reported here we investigated the effects of variations in the concentration of the metalloid element phosphorus on the formation and the thermal stability of Cu-Ni-P ternary glassy alloys prepared by melt-spinning

A tight-binding determination of the glass-forming concentration range in the Ni-Ti system

The stability of metallic glasses in the Ni-Ti system and the relationship between the constitution diagram and glass formation is discussed within a tight-binding scheme. The theory is based on the calculation of the enthalpies of formation of the solid solutions using the coherent potential approximation, whereas the heats of formation of the different compounds are calculated by the recursion method. For the amorphous phases, the model tightbinding Hamiltonian is coupling with a thermodynamic variational technique founded on the Gibbs-Bogolyubov inequality and a hard-sphere Yukawa fluid as a reference system. The theory clearly shows the key role of chemical short-range order in amorphous phases and of the elastic effect which arises from atomic size mismatch in solid solutions.

Formation and stability of aluminum-based metallic glasses in Al-Fe-Gd alloys

Metallic glasses, a class of amorphous alloys made by rapid solidification, have been studied quite extensively for almost thirty years. It has been recognized for a long time that metallic glasses are usually very strong and ductile, and exhibit high corrosion resistance relative to crystalline alloys with the same compositions. Recently, metallic glasses containing as much as 90 atomic percent aluminum have been discovered independently by two groups. This discovery has both scientific and technological implications. The formability of these new glasses has been found to be unusual. Studies of mechanical properties in these new metallic glasses show that many of them have tensile strengths over 800 MPa, greatly exceeding the strongest commercial aluminum alloys. The high strengths of aluminum-rich metallic glasses can be of significant importance in obtaining high strength low density materials. Therefore, from both scientific and technological standpoints, it is important to understand the formation and thermal stability of these metallic glasses. Al-Fe-Gd alloys were chosen for a more-detailed study since they exhibit high tensile strengths.

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.

Influence of Short Range Order, Electron Concentration and Size Misfit on the Structure and Thermal Stability of Metallic Glasses

ABSTRACTThe influence of short range order, electron concentration and size misfit on the thermal stability of (Fe100-xMx)83B17 metallic glasses has been investigated (M = Cr, Mn, Co, Ni, Mo, W). The results are discussed together with Curie-temperature measurements and Mößbauer spectroscopy data. The concentration range in which the various stable and metastable phases form is given.