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Metallic Glasses (metallic + glasses)
Kinds of Metallic Glasses Selected AbstractsThe Effects of Casting Temperature on the Glass Formation of Zr-Based Metallic Glasses,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Jie Mao Abstract The glass1-forming ability of two alloys, Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8, prepared by arc-melting a mixture of Zr, Cu, Al, Ni and Ag elements is studied as a function of casting temperature. Other processing parameters such as the alloy melt mass, and the vacuum and injection pressures during the copper-mold-casting process are kept constant so just the influence of the casting temperature is considered. The casting temperature determines the characteristics of the liquid melt and the cooling rate. The glass-forming ability is discussed in terms of dissipation of pre-exiting, metastable local-ordering clusters that act as nucleation sites promoting crystallization, the cooling rate at high casting temperatures, and the presence of oxygen in the alloys, which is increased at high casting temperatures. It is found that the glass-forming ranges of alloys shrink as the glass-forming size approaches a critical value. The optimum temperatures are around 1450,K and 1550,K for Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8 alloys respectively. The alloys were studied by XRD, TEM, oxygen-level determination, and DSC. [source] Statistic Analysis of the Mechanical Behavior of Bulk Metallic Glasses,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Hai Bin Yu The Weibull distribution is used to characterize the mechanical behavior of a bulk metallic glass (BMG). The strength of the BMG is quite stable, while the plasticity is much less stable. The reason is attributed to the fraction and distribution of free volumes, which are sensitive to processing conditions. The results demonstrate the close relationship between the distribution and fraction of free volumes and plasticity in BMGs. [source] Designing Ductile Zr-Based Bulk Metallic Glasses with Phase Separated Microstructure,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Xinghao Du Using the thermodynamic computation, the phase-separated Zr-based bulk metallic glasses with a enhanced plasticity up to 20% are developed. The as-cast microstructure is characterized by the macroscopic heterogeneities consisting of the phase-separated regions and glassy matrix regions. The microscaled phase-separated feature is the cause of the remarkable plasticity, and the homogeneous and concurrent formation of multiple shear bands is crucial for the plasticity improvement in metallic glasses. [source] Bulk Metallic Glasses with Functional Physical Properties (Adv. Mater.ADVANCED MATERIALS, Issue 45 200945/2009) [source] Bulk Metallic Glasses with Functional Physical PropertiesADVANCED MATERIALS, Issue 45 2009W. H. Wang Abstract In this review, we report on the formation of a variety of novel, metallic, glassy materials that might well have applications as functional materials. The metallic glasses, with excellent glass-forming ability, display many fascinating properties and features such as excellent wave-absorption ability, exceptionally low glass-transition temperatures (,35,60,°C) approaching room temperature, ultralow elastic moduli comparable to that of human bone, high elasticity and high strength, superplasticity and polymer-like thermoplastic formability near room temperature, an excellent magnetocaloric effect, hard magnetism and tunable magnetic properties, heavy-fermion behavior, superhydrophobicity and superoleophobicity, and polyamorphism, all of which are of interest not only for basic research but also for technological applications. A strategy based on elastic-moduli correlations for fabrication of bulk metallic glasses (BMGs) with controllable properties is presented. The work has implications in the search for novel metallic glasses with unique functional properties, for advancing our understanding of the nature and formation of glasses, and for extending the applications of the materials. [source] Metallic Glasses: Nanoscale Solute Partitioning in Bulk Metallic Glasses (Adv. Mater.ADVANCED MATERIALS, Issue 3 20093/2009) Devitrification of bulk metallic glass leads to novel microstructures with high-density nanoscale crystalline precipitates evenly distributed in a glassy matrix. Xun-Li Wang and co-workers report on p. 305 that significant chemical segregation is revealed in unprecedented detail by atom-probe tomography. This level of detail is crucial for understanding the interference peaks observed in small-angle X-ray and neutron scattering experiments. [source] Nanoscale Solute Partitioning in Bulk Metallic Glasses,ADVANCED MATERIALS, Issue 3 2009Ling Yang Devitrification of bulk metallic glass leads to a novel microstructure, with high-density nanoscale crystalline precipitates evenly distributed in a glassy matrix. Significant chemical segregation is revealed at unprecedented detail by atom-probe tomography. This level of detail is crucial for understanding the interference peaks observed in small-angle X-ray and neutron scattering experiments, an unsolved mistery for over a decade. [source] Correlations for Predicting Plasticity or Brittleness of Metallic Glasses.CHEMINFORM, Issue 25 2007Y. Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Transition of Failure Mode and Enhanced Plastic Deformation of Metallic Glass by Multiaxial Confinement,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Fu-Fa Wu Multiple shear bands are formed in a confined metallic-glass specimen under small-punch loading. The intersecting of shear bands and the formation of profuse secondary shear bands are promoted under this confinement; accordingly, the failure mode changes from catastrophic fracture to stable multiple shear banding. Multiaxial confinement is an effective method to stabilize shear banding and further enhance the mechanical performance, especially the plastic deformation capability of metallic glass. These results present a simple step for making shear banding more stable and exploiting the shear-deformation capability of metallic glasses, leading to the toughening of brittle metallic glasses and potentially broadening their applications. [source] Designing Ductile Zr-Based Bulk Metallic Glasses with Phase Separated Microstructure,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Xinghao Du Using the thermodynamic computation, the phase-separated Zr-based bulk metallic glasses with a enhanced plasticity up to 20% are developed. The as-cast microstructure is characterized by the macroscopic heterogeneities consisting of the phase-separated regions and glassy matrix regions. The microscaled phase-separated feature is the cause of the remarkable plasticity, and the homogeneous and concurrent formation of multiple shear bands is crucial for the plasticity improvement in metallic glasses. [source] Back Cover: TMS Bulk-Metallic Glasses Symposium V (Adv. Eng.ADVANCED ENGINEERING MATERIALS, Issue 11 2008Mater. The backcover shows the nanoindentation of a Zr-based bulk metallic glass with an Al-concentration of 13 at%. Around the indent shear bands are observed indicating some plasticity of that glass. More about the glass-forming ability and ductility of Zr-based and Al-rich bulk metallic glasses can be found in the paper by R. Wunderlich et al. on page 1020. [source] Time,Temperature,Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin FilmsADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Jennifer L. M. Rupp Abstract Time,temperature,transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin films and their specific characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The films crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-film method spray pyrolysis. The crystallization of an amorphous metal oxide thin film generally follows the Lijschitz,Sletow,Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria films to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin films, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin films for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions. [source] Crystallization and Grain Growth Kinetics for Precipitation-Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray PyrolysisADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Jennifer L. M. Rupp Abstract The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum-based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous-nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single-phase metal oxide thin film made by a precipitation-based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non-isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass-ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation-based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices-based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro-solid oxide fuel cells, or oxygen separation membranes on Si-chips. [source] Bulk Metallic Glasses with Functional Physical PropertiesADVANCED MATERIALS, Issue 45 2009W. H. Wang Abstract In this review, we report on the formation of a variety of novel, metallic, glassy materials that might well have applications as functional materials. The metallic glasses, with excellent glass-forming ability, display many fascinating properties and features such as excellent wave-absorption ability, exceptionally low glass-transition temperatures (,35,60,°C) approaching room temperature, ultralow elastic moduli comparable to that of human bone, high elasticity and high strength, superplasticity and polymer-like thermoplastic formability near room temperature, an excellent magnetocaloric effect, hard magnetism and tunable magnetic properties, heavy-fermion behavior, superhydrophobicity and superoleophobicity, and polyamorphism, all of which are of interest not only for basic research but also for technological applications. A strategy based on elastic-moduli correlations for fabrication of bulk metallic glasses (BMGs) with controllable properties is presented. The work has implications in the search for novel metallic glasses with unique functional properties, for advancing our understanding of the nature and formation of glasses, and for extending the applications of the materials. [source] Precursory microstructures in Zr,Cu,Al,Ni bulk metallic glasses examined by anomalous small-angle scattering at the Zr K edgeJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Isao Murase Anomalous small-angle X-ray scattering measurements of Zr,Cu,Al,Ni quaternary alloys have been made at the Zr K absorption edge. In melt-quenched samples, small cluster components without crystallization were found. The contrast change at the edge suggested that compositional fluctuation of Al is incorporated. [source] Crystallization of Lead Niobate Glass by Mechanical ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Junmin Xue Mechanical activation-triggered crystallization in PbNb2O6 -based glass was dependent on the initial presence of nuclei. The crystallization cannot be initiated by mechanical activation in a highly amorphous glass composition quenched from 1350°C where PbNb2O6 nuclei did not exist. The steady growth of nanocrystallites of PbNb2O6 was observed with an increasing degree of mechanical activation in the glass quenched from 1300°C, where a density of PbNb2O6 nuclei existed before mechanical activation. The inability to nucleate in the highly amorphous oxide glass by mechanical activation is consistent with the much higher structural stability as compared with that of metallic glasses, such as Fe-Si-B. The mechanical activation-grown PbNb2O6 nanocrystals were 10,15 nm in size as observed using HRTEM and their crystallinities were further improved by thermal aging at an elevated temperature in the range of 550° to 650°C. [source] Advances in transmission electron microscopy: In situ straining and in situ compression experiments on metallic glassesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2009Jeff Th.M. De Hosson Abstract In the field of transmission electron microscopy (TEM), fundamental and practical reasons still remain that hamper a straightforward correlation between microscopic structural information and deformation mechanisms in materials. In this article, it is argued that one should focus in particular on in situ rather than on postmortem observations of the microstructure. This viewpoint has been exemplified with in situ straining and in situ compression studies on metallic glasses. In situ TEM straining of amorphous metals permits an evaluation of the thickness of the liquid-like layer (LLL) formed because of heat evolution after shear band development. The experimental evaluation confirms that the thickness of a LLL present at the last moment of fracture substantially exceeds the generally accepted thickness of a shear band. In situ TEM and in situ SEM compression experiments on metallic glass pillars lead to the conclusion that smaller sized pillars deform more homogeneously than larger sized pillars. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] Glass forming ability and nanocrystallization kinetics of Fe65Nb10B25 metallic glassesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010J. Torrens-Serra Abstract In this work the mechanisms controlling the nanocrystallization kinetics of the Fe65Nb10B25 metallic glasses have been determined by the combination of the analysis microstructural data from XRD and TEM, and the kinetic analysis performed using the Master Curve method of the continuous heating and isothermal calorimetric curves. The results show that the transformation starts by the nucleation and interface controlled growth of the Fe23B6 -type phase that changes to diffusion controlled growth as the transformation advances until is stopped by the soft-impingement effect. The transformation is modeled in the framework of the Kolmogorov,Johnson,Mehl,Avrami (KJMA) theory using constant activation energy expressions for the nucleation frequency and interface-controlled growth and taking into account the reduction of those quantities with the transformed fraction due to the change in the matrix composition using a mean-field approximation. The parameters of the modeling are determined from the coupling between the isothermal and constant heating rate calorimetric analysis and from the quantitative analysis of microstructural data. This is the outset for the determination of the viscosity, driving force for crystallization, and interfacial energy when replacing the constant activation energy expressions by the classical nucleation and growth ones. Both the glass forming ability in Fe,Nb,B based bulk metallic glasses and the temperature dependence of the interfacial energy are discussed in terms of the influence of the minor alloying elements. [source] Variation of electrical resistance in metallic glasses subjected to 130 MeV 28Si ion irradiationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2004H. Narayan Abstract The change in the electrical resistivity of 2605SC (Fe81B13.5Si3.5C2) and 2705M (Co69B12Si12Fe4Mo2Ni1) metallic glasses (MGs) resulting from 130 MeV 28Si ion irradiation has been investigated. Resistivity as a function of temperature has been measured off-line and in situ before and after irradiation, and on-line as a function of ion fluence. The results show that for the 2605SC MG electrical resistivity increases by 5.2% (fluence = 3.7 × 1014 ions/cm2) and 4.5% (fluence = 1.6 × 1014 ions/cm2). This has been explained on the basis of the ,two-hit model'. For the 2705M MG, however, an unexpected decrease of electrical resistivity of about ,9.6% (fluence = 1.1 × 1016 ions/cm2) and ,8.7% (1.3 × 1014 ions/cm2) is observed, which has been attributed to irradiation-induced structural modification. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transport properties of hydrogen-doped (Zr803d20)1,xHx (3d = Co, Ni) metallic glassesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2004I. Kokanovi Abstract The electrical resistivities of hydrogen-doped (Zr803d20)1,xHx (3d = Ni, Co; x , 0.11) metallic glasses have been measured at temperatures between 2 K and 110 K and in magnetic fields up to 1 T for various dopant concentrations. These systems have a high room-temperature resistivity (, > 160 ,, cm) and become superconducting below 4 K. The increase of the room-temperature resistivity and its temperature coefficient with hydrogen dopant concentration is explained as due to an increase of disorder with hydrogen-doping. The temperature and magnetic field dependence of the resistivity has been analysed using theoretical models of weak-localisation and electron,electron interaction in disordered conductors. The hydrogen dopant is found to reduce the effective electron diffusion constant, D, the spin-orbit scattering rate, ,,1so, the superconducting transition temperature, Tc, and broadens the superconducting transition region. The contribution of the Maki-Thompson interaction to the magnetoresistivity is also reduced. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Atomic structure and positron lifetime in the metallic glass Zr55Cu30Ni5Al10PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2007K. Sugita Abstract Zr-based metallic glasses have superior characteristics such as mechanical strength, corrosion resistance and precision casting ability. From positron lifetime measurements, a negative temperature dependence of the mean positron lifetime above room temperature was reported and ascribed to the presence of shallow traps. However, the trapping sites remain unknown under the present circumstances. To get a further understanding of the experimental positron lifetime value, the positron density distribution and the lifetime in the Zr-based metallic glass Zr55Cu30Ni5Al10 have been calculated. The calculation shows that the positrons are annihilated inhomogeneously and most positrons are annihilated preferentially around Cu/Al. These results indicate that the positron lifetime not exactly reflects the total free volume. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electron-assisted relaxation of tunneling systems in polycrystalline aluminiumPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004G. Weiss Abstract Vibrating reed measurements are presented of pure poly-crystalline Al with a special sample shape that reduces the influence of the clamping. We find significant differences between the sample being normal conducting or superconducting. The overall behaviour in fact resembles very closely that of metallic glasses and clearly demonstrates that also in Al tunneling systems couple to conduction electrons as expected. As a quantitative result we may state that the density of states of tunneling systems in poly-crystalline Al is considerably smaller than in metallic glasses. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||