bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Pressure Studies of Quasicrystals
Authors: Sadoc Anne , Itié Jean-Paul , Polian Alain , Kelton Kenneth F. 
Published: April 2011

AbstractHigh pressure X-ray diffraction studies of quasicrystals are presented and discussed for icosahedral Al-Cu-Ru and Ti-Zr-Ni alloys. The results in hydrogenated Ti-Zr-Ni show that Ti- Zr-Ni may be more compressible after hydrogenation.
Quasicrystalline Films and their Amorphous Precursors
Authors: Haberkern Roland , Barzola-Quiquia Jose , Madel Caroline , Häussler Peter 
Published: April 2011

AbstractBinary and ternary aluminum based amorphous precursor films have been prepared by the sequential-flash evaporation technique in the case of Al-Mn, Al-Fe, Al-Cu-Fe and Al-Pd-Mn and by co-sputtering in the case of Al-Pd-Re. For well adjusted compositions and an appropriate heat treatment films can be transformed into polycrystalline single phased quasicrystals for all of the systems mentioned above. The transition can be monitored by in situ measurements of electronic transport properties. The structure factors as a function of composition and annealing state has been measured by electron diffraction. They show a unique behavior if the composition is chosen to that of the related quasicrystal. For high annealing states of the amorphous phase the structure factor becomes more intense at the peak positions of the following i-phase. This is interpreted as a unique radial near- and medium-range order of both the i-phase and its amorphous precursor. The final transformation into the quasicrystal is sharp for Al-Cu-Fe and is broad in the case of Al-Pd-Mn and Al-Pd-Re. The transport properties of the resulting single phased films are similar to that of the related bulk samples and allow systematic studies as a function of composition. Some of the i-Al-Pd-Re films are on the insulating side of the metal-insulator transition.
AC Conduction in Quasiperiodic Lattices
Authors: Wangs Chumin , Oviedo-Roa Raúl , Śnchez Vicenta , Pérez Luis A. 
Published: April 2011

AbstractThe electronic transport in Fibonacci lattices at zero temperature is studied by means of the Kubo-Greenwood formula within the tight-binding scheme, where a renormalization process capable to address the electrical conductivity in macroscopic quasiperiodic systems is used. The effects of the Fermi-energy location on the ac conductivity are analyzed in detail for a wide range of the system sizes. Special attention is paid to the transparent states, whose transmission coefficient is unity. The results show a rapid decay of their ac conductivity as the frequency increases in comparison with that of periodic systems, and the spectra scale with the inverse of the system size as occur in periodic ones, where analytical results are obtained. Furthermore, a new low-frequency minimum appears when the inhomogeneity of the Fibonacci lattice grows.
Crystallization Behavior of Zr65−×−yTixAlyCu22Ni13 Bulk Metallic Alloys by in-situ Neutron Diffraction
Authors: Soubeyroux Jean-Louis , Claret Nicolas 
Published: April 2011

AbstractSeveral alloys of the Zr65×−yTixAlyCu22Ni13 system were found to be bulk metallic glasses. They have been investigated by DSC and in-situ neutron diffraction. DSC and neutron studies were performed at the same heating rates in order to correlate the evolution of the characteristic temperatures to the crystallization of phases. The first phase appearing at crystallization is dependant on the titanium content, being Zr2Ni for Ti ≈ 5% and a quasi- crystalline phase for Ti ≈ 2.5%. These phases are metastable and transform to Zr2Cu and other phases.
Structural and Electronic Properties of Zr-Ti-Cu-Ni-Be Alloys
Authors: Löffler Jörg F. , Tang X.-P. , Wu Yue , Johnsona William L. 
Published: April 2011

AbstractWe present crystallization studies on Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) and on other alloys, where the (Zr,Ti) and (Cu,Be) contents, along the line in composition space connecting Vit1 and Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4), were varied. Results from x-ray diffraction (XRD), small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC) are combined to describe the crystallization behavior of these alloys at deep undercooling. SANS gives evidence for decomposition and the formation of nanometer sized crystals below a critical temperature Tc, which varies drastically as a function of composition. When Tc intersects with the glass transition temperature Tg, changes in the crystallization behavior are observed by DSC and XRD. At annealing temperatures near Tg, XRD resolves quasicrystalline phases for all alloy compositions from Vit1 to Vit4. From 9Be nuclear magnetic resonance (NMR) experiments performed on Vit1 upon annealing, we obtain information about the electronic structure and volume fraction of Be containing crystalline and quasicrystalline phases.
Local Atomic Structures and Plastic Deformation Modes in the Supercooled Liquid State of La55Al25Ni20
Authors: Ohkubo Tadakatsu , Hirotsu Yoshihiko , Inoue Akihisa 
Published: April 2011

AbstractAn in-situ electron diffraction structure analysis of La55Al25Ni20in the supercooled liquid temperature range (ΔTx) revealed a gradual structural change with a local phase separation due to strong atomic correlations especially of La-La and Al-Ni. On the basis of the structural data, structure models corresponding to the structures at temperatures between Tg and Tx were constructed using molecular dynamics (MD) simulation technique. These constructed structure models were then utilized for MD simulations to understand plastic deformation in the supercooled liquid state under a constant strain-rate. A larger elongation was obtained for the structure in the middle of the ΔTx range, but for the structure near Tx the elongation was relatively smaller which was supposed to be due to the local phase separation. These simulation results correspond well to the experimental elongation behaviors in the superplastic deformation that the elongation is enhanced in the middle of ΔTx but suppressed as the temperature is increased towards Tx.
Hydrogen-doped Bulk Metallic Glasses as High Damping Material
Authors: Yagi Teruaki , Oguro Rikiya , Tamura Ryuji , Takeuchi Shin 
Published: April 2011

AbstractBulk metallic glasses have extremely high strength and high ductility and are quite useful as the structural material. Many of bulk metallic glasses are based on Zr, Ti and Pd; these elements have a high affinity with hydrogen and hence the bulk metallic glasses can contain a large amount of hydrogen atoms. It is known that hydrogenized amorphous metals, as well as hydrogenized metallic crystals, exhibit Snoek-type relaxation, and hence metallic glasses containing a high density of hydrogen can have a high internal friction.In the present experiments, internal friction measurements have been performed for bulk metallic glasses doped with a variety of hydrogen concentrations. It is shown that the peak value of the internal friction reaches the order of 10-2 in Zr-based bulk metallic glasses which have the fracture strength as high as 1.5 GPa. Thus, hydrogen-doped bulk metallic glasses can be used as the high-strength, high-damping material.
The Shear Modulus of Vit 1 in the Supercooled Liquid and Glassy State
Authors: Bains Alijeet S. , Gordon Craig A. , Granato Andrew V. , Lebedev Alexander B. , LaMadrid Marissa A. , Johnson William L. 
Published: April 2011

AbstractUsing a non-contact electromagnetic-acoustic transformation (EMAT) technique, we have measured the temperature dependence of the infinite frequency shear modulus of Vit 1 at constant heating rate in the glassy and supercooled liquid states. Values of the shear softening fragility parameter -dln(G/Gg/d(T/Tg) are compared with those obtainable from specific heat and viscosity measurements, using the interstitialcy theory of condensed matter states. There is overall agreement found between these independently measured values.
Synthesis and Viscoelasticity of Zr-based Bulk Glassy Alloy Containing ZrC Particles
Authors: Kato Hidemi , Hirano Tomoya , Inoue Akihisa , Kawamura Yoshihito , Chen H. S. 
Published: April 2011

AbstractCylindrical composite Zr55Al10Ni5Cu30 bulk glassy alloys containing up to 17.5 vol.% ZrC particles were prepared with using an in-situ reaction forming ZrC between graphite particles with diameters of ∼10 m and Zr metal in molten alloy during arc-melting followed by copper mold casting. Because the in-situ reaction suppresses an agglomeration and segregation among dispersoids in the glassy matrix, mechanical properties of the composite materials at room temperature, especially toughness and plastic elongation, were significantly improved from the Zr55Al10Ni5Cu30 single glassy phase. In order to demonstrate the influence of the dispersed ZrC particles on workability of the supercooled liquid of the alloy, viscous flow behaviors under constant strain-rates were investigated. Although the Newtonian viscosity becomes larger, the composite material has the same viscoelastic properties, i.e., “shear thinning”, and excellent workability as the single glassy phase in spite of the dispersed particles.
Intermetallic Phases in Ti-Ag-Zr-Ni Alloys
Authors: Nicula Radu C. , Jianu Adrian D. , Bunescu Mihaela C. , Ponkratz Ulrich E. , Stir Manuela E. , Schick Christoph 
Published: April 2011

AbstractTitanium and zirconium based metallic glasses and crystalline intermetallic compounds with improved mechanical properties are presently a field of intense application-oriented research. The formation and stability of nanocrystalline phases in Ag-substituted Ti-Zr-Ni alloys was followed usingin-situhigh-temperature synchrotron radiation diffraction experiments. The substitution of Ti with Ag enhances the formation of amorphous or nanostructured phases during rapid solidification. High-resolution powder diffraction and electron microscopy investigations indicate that the as-quenched alloys are either amorphous or in a mixed nanostructured state. Upon heating, the alloy structure transforms to a fine mixture of icosahedral and crystalline phases depending on the alloy composition and thermal processing parameters. Differential scanning calorimetry studies were performed in order to identify the nature and sequence of the observed structural phase transitions. The experimental results are discussed with respect to the non- equilibrium synthesis and processing of bulk amorphous and bulk nanocrystalline materials in Ti/Zr-based alloys.
Nanometer scale intermixing mechanism in Ag-based nanocomposites
Authors: Jianu Adrian D. , Kuncser Victor E. , Nicula Radu C. , Palade Petre , Stir Manuela E. , Bunescu Mihaela C. , Burkel Eberhard 
Published: April 2011

AbstractA new Ag-Sm-Fe nanocomposite material was obtained by high-energy ball-milling of elemental μ-Fe powder and melt-spun Ag-Sm flakes. Magnetic Fe nanocrystals were thus embedded in a paramagnetic Ag-based matrix. Synchrotron radiation powder diffraction and temperature dependent Mössbauer spectroscopy were used to study the nanometer scale Fe/Ag(Sm) intermixing mechanism. The evolution of the average grain size and microstrains in the Ag-based matrix vs. the milling time were obtained from the analysis of the X-ray diffraction linewidths. For reference Fe powder samples, a bimodal grain size distribution was evidenced by Mössbauer spectroscopy. The magnetic behaviour of the Fe nanocrystals was analysed with respect to the superparamagnetic relaxation effect and collective excitations. The nanometer scale intermixing of Fe nanocrystals in the Ag-based matrix is completed when the Fe and matrix grains have comparable dimensions.
Diffusion in Metallic Glasses and Supercooled Melts
Authors: Faupel F. , Rätzke K. , Ehmler H. , Klugkist P. , Zöllmer V. , Nagel C. , Rehmet A. , Heesemann A. 
Published: April 2011

AbstractDiffusion in metallic glasses and in the supercooled liquid state is of considerable interest not only from the technological point of view but also in terms of fundamental science, particularly in connection with the glass transition. Within the framework of the mode coupling theory the glass transition is a kinetic phenomenon characterized by the arrest of viscous flow at a critical temperatureTcwell above the calorimetric glass transition temperatureTg. BelowTcthe theory predicts cooperative hopping processes. We present results from isotope effect measurements which indeed confirm the highly collective nature of diffusion in metallic glasses and suggest cooperative hopping processes to be closely related to the universal low-frequency excitations as observed in recent molecular dynamic simulations. In accord with the mode coupling scenario these cooperative hopping processes are also observed in the supercooled liquid state of the new bulk metallic glasses well aboveTg. The reported kink in the Arrhenius plot for diffusion of various elements is shown to be related to structural changes aboveTg, e.g., an increase in free volume as probed by positron annihilation, but not to a change in the diffusion mechanism. Measurements of the activation volume of diffusion indicate that, depending on the structure of the glass, cooperative hopping may take place without assistance of thermally generated defects or via delocalized thermal defects. Moreover, we provide evidence of the existence of an opposite Kirkendall effect in interdiffusion between certain amorphous alloys that combine slow diffusion via thermal defects and fast direct diffusion.
Glass-Forming Ability and Crystallization of High Purity Pd-Cu-Ni-P Alloy
Authors: Nishiyama Nobuyuki , Matsushita Mitsuhide , Inoue Akihisa 
Published: April 2011

AbstractGlass-forming ability, thermal stability and nucleation behavior of a Pd40Cu30Ni10P20 alloy prepared using a high purity polycrystalline phosphorus are investigated. The critical cooling rate for glass formation for the high purity alloy is the same as that for the previous result, but the improvement of undercooling reaches about 80 K as compared with the fluxed ordinary alloy. In comparison with the non-fluxed alloy, the solidified structure of the present highly purified alloy is significantly different. The non-fluxed sample shows the characteristic “island-like” structure consisted of acicular fcc-Pd2Ni2P solid solution and Cu3Pd intermetallic compound. These acicular phases appear to be caused by the growth of quenched-in nuclei. In the isothermal experiment, nucleus density exhibits time dependence even at 683 K near the nose temperature. It is assumed that the crystallization behavior for the highly purified alloy is closer to homogeneous nucleation from quenched-in nuclei dominant behavior. In order to investigate the nucleation behavior, in-situ TEM observation was carried out. Spherical Pd15P2 particle with a diameter about 15 nm is observed, and this spherical region repeats generation and annihilation during isothermal annealing. The reason for the high glass-forming ability is discussed on the basis of the obtained results.
Crystallization in Zr-Cu-Ni-Al Metallic Glasses
Authors: Köster U. , Zander D. , Janlewing R. 
Published: April 2011

AbstractZr-Cu-Ni-Al exhibits one of the best glass forming alloys known. In a narrow concentration range, however, annealing leads to the formation of a metastable icosahedral phase. The aim of this paper is to investigate in detail the influence of alloying with Hf or Si, Sn, Y, Cr and Mo on the quasicrystal formation in Zr69.5Cu12Ni11Al7.5 glasses.Whereas Y addition leads to loss in thermal stability and pronounced formation of quasicrystals, the addition of Si, Sn or Mo does not deteriorate thermal stability. Sn and Si were observed even to improve thermal stability significantly, but also to change phase selection during the early stages of crystallization. Si addition results in the formation of the tetragonal Zr2Ni phase and Mo as well as Cr to the formation of the fcc, so-called big-cube phase.Nucleation rates for the quasicrystal formation were measured by means of crystallization statistics. By modeling the obtained nucleation rates in the framework of diffusion controlled classical nucleation the interface energies (between quasicrystals and amorphous matrix) as well as metastable melting temperatures for the quasicrystalline phase could be derived. In all cases nucleation could be described best with a homogeneous model with transient rates.In order to understand the formation of the icosahedral structure also data on the influence of oxygen and hydrogen contamination as well as recent results of other authors on the influence of noble metals such as Ag, Pd, Au and Pt will be discussed in detail. There is some evidence that the quasicrystals are a hybrid of two structural elements, i.e. the tetragonal Zr2Ni (Al2Cu) and the tetragonal Zr2Cu (MoSi2) structure. It is further assumed that an icosahedral short-range order of the melt is stabilized by the addition of elements like Hf, probably Y or by contamination with very small amounts of oxygen, thus leading to a reduced interfacial energy between the quasicrystals and the amorphous matrix and therefore to a lower nucleation barrier.
Core Losses and Soft Magnetic Properties of Nanocrystalline Fe-Zr-Nb-B Alloys with Zero-Magnetostriction
Authors: Makino Akihiro , Inoue Akihisa , Masumoto Tuyoshi 
Published: April 2011

AbstractThe structure, the soft magnetic properties and the core losses for Fe-Zr-Nb-B(-Cu) nanocrystalline alloys were investigated. It has been already reported that the typical ternary nanocrystalline Fe90Zr7B3 and Fe84Nb7B9 alloys exhibit good soft magnetic properties and a small negative and a small positive magnetostriction (λs), respectively. The soft magnetic properties of the nanocrystalline Fe84–90(Zr, Nb)7B3–9 quaternary alloys with mixed compositions of Fe90Zr7B3 and Fe84Nb7B9 cannot be improved whereas very small magnetostrictions are obtained. The quaternary alloys with 7 at% (Zr + Nb) have structures of an amorphous with α-Fe phases on the free and roll-contacted surfaces at an as-quenched state. The crystalline surface layers deteriorate the soft magnetic properties at a crystallized state. The high saturation magnetic induction of 1.64 T, the high permeability of 60,000 at 1 kHz and the very low core loss of 0.9 W/kg at 1.4 T and 50 Hz are obtained for the Fe85.5(Zr1/3Nb2/3)6B8.5 alloy containing 6 at% of (Zr + Nb) content with nearly zero-λs produced by crystallizing the single amorphous phase without the crystalline surface layers. The thermal stability of the core loss of the quaternary alloy is significantly higher than that of the Fe78Si9B13 amorphous alloy. The crystalline surface layers of the Fe84–90(Zr, Nb)7B3–9 quaternary alloys disappear by 1 at% Cu addition, which results in significant improvement of the soft magnetic properties at a crystallized state.
Preparation and Characterization of the Soft Magnetic FeCo-based Amorphous Alloy with Enhanced Magnetic Properties and Thermal Stability
Authors: Hollmark Martin , Tkatch Victor , Khartsev Sergey , Grishin Alex 
Published: April 2011

AbstractA glassy structure was formed in the Fe40Co40P14B6 alloy by melt-spinning technique. The as-quenched 2-8 mm wide and 15-30 [.proportional]m thick ribbons exhibit good soft magnetic properties: the saturation magnetization of 1.45 T, the coercive force of 4 A/m and maximum differential permeability at 60 Hz of about 90000. The FeCo-based glass crystallizes via eutectic reaction into a mixture of an austenite and a b.c. tetragonal Fe3P-like phase similar to that of the well-known Fe40Ni40P14B6metallic glass, but at temperatures about 60 K higher than the latter. The evaluation of the thermodynamic and kinetic parameters of crystallization process brought us to the conclusion that the improved thermal stability of the Fe40Co40P14B6 glass is caused by the enhanced interfacial nucleus-glass energy.
Internal Stresses in Bulk Metallic Glass Matrix Composites
Authors: Üstündag Ersan , Dragoi Danut , Clausen Bjorn , Brown Donald , Bourke Mark A. M. , Balch Dorian K. , Dunand David C. 
Published: April 2011

AbstractComposites consisting of a bulk metallic glass (BMG) matrix and metallic fibers or particulates have been shown to exhibit superior mechanical properties as compared to monolithic BMGs. To understand the role of reinforcements in this improvement, it is necessary to investigate the state of internal stresses in these composites. These stresses arise from the thermal expansion mismatch between the reinforcement and the matrix, as well as the elastic and plastic incompatibilities between the two phases. Neutron diffraction and synchrotron X-ray diffraction were used to measure these mismatch-induced stresses in BMG-matrix composites with various reinforcements: continuous W fibers, W or Ta particles, and dendritic, in-situ formed precipitates. The results are compared to numerical and analytical predictions of internal stresses.
Failure of a Thermal Barrier System Due to a Cyclic Displacement Instability in the Thermally grown Oxide
Authors: Mumm Daniel R. , Evans Anthony G. 
Published: April 2011

ABSTRACTThe mechanism controlling the cyclic failure of a commercial thermal barrier system has been investigated. The system comprises an electron-beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia thermal barrier coating (TBC), deposited on a (Ni Pt) Al bond coating. The thermally grown oxide (TGO) layer that forms between the TBC and bond coat at high temperature is unstable with respect to out of plane displacement, provided initial perturbations are present. With cyclic thermal exposure, the TGO displaces into the bond coat at periodic interfacial sites. The out-of-plane displacements induce strains above the TGO, normal to the interface, that cause cracking. The cracks nucleate either within the TBC layer or at the TBC/TGO interface, and extend laterally until they coalesce with cracks from other sites and coating failure occurs by large scale buckling. The TGO displacements are accommodated by visco-plastic deformation of the underlying bond coat, and are driven by a lateral component of the growth strain in the TGO. The susceptibility of the TGO to out-of-plane displacement depends critically upon the initial morphology of the metal/oxide interface. The observed material responses are compared with predictions of a ‘ratcheting’ model.
Microstructural Characterization of Yttria-Doped Zirconia Coatings with Electron Microprobe Wavelength Dispersive Compositional Mapping
Authors: Marinenko Ryna B. , Verkouteren Jennifer R. , Bright David S. 
Published: April 2011

ABSTRACTThe use of digital electron microprobe x-ray compositional mapping with wavelength dispersive spectrometers to understand the microstructure of yttria stabilized zirconia thermal barrier coatings is described. Data from quantification of element x-ray maps can be utilized to infer what phase or phases are present. Analysis of a plasma-sprayed coating prepared from a fused and crushed feedstock is compared to an annealed specimen of the same material.
The Influence of the Texture on the Creep behavior of γ-TiAl Sheet Material
Authors: Bartels Arno , Schillinger Wolfram , Chatterjee Anita , Clemens Helmut 
Published: April 2011

ABSTRACTIn hot rolled Ti-46.5at%Al-4at%(Cr,Nb,Ta,B) sheets a strong modified cube texture is found. The c-axes of the tetragonal unit cells in the grains are aligned with the transverse direction of the sheets. This texture causes an anisotropy of the creep resistance which is improved in transverse direction. Heat treatments with different subsequent cooling rates were performed in order to obtain lamellar microstructures with a different spacing of lamellae. Creep experiments exhibit an increase of the creep resistance which is highest after fast cooling. The texture measurements show no longer an alignment of c-axes after the heat treatment in the α-phase field, but a weak {110}-fiber texture in rolling direction occurs which causes a small improvement of the creep resistance in rolling direction. However, the creep resistance of the lamellar microstructure is more determined by the morphology than by the texture.