bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Specific Heat of a Metallic Glass-Former
Authors: Wilde Gerhard 
Published: April 2011

AbstractModulated temperature calorimetry measurements on the bulk glass forming Pd40Ni40P20 alloy are reported in the frequency range between 1/30 s−1 and 1/1000 s−1. These measurements represent the first experimental assessment of the slow relaxation modes of a metallic liquid over a substantial frequency interval. The results reveal the typical behavior known for dissipative systems. The frequency-dependence of the dynamic specific heat is compared to results of dynamic rheology measurements that have been performed on the same material at similar modulation frequencies to compare the dynamic response of the respective modes.
Phase Equilibria and Glass Forming Ability in the Zr-Cu-Ni-Al System
Authors: Swenson Douglas J. , Bhattiprolu Sreenivas 
Published: April 2011

AbstractThe constitution of the 66.67 at.% Zr isopleth of the Zr-Cu-Ni-Al quaternary system has been studied, utilizing X-ray diffraction and electron probe microanalysis to establish phase equilibria at 800°C, and differential scanning calorimetry to study the liquidus hypersurface. As would be expected in a four-component system, phase equilibria were found to be complex. However, it was determined that the isoplethal subsection Zr2Cu-Zr2Ni is pseudobinary, and subsequently a large portion of the quaternary isopleth is pseudoternary, comprising equilibria involving the phases Zr2Cu, Zr2Ni and Zr6NiAl2. Moreover, these three phases participate in a pseudoternary eutectic reaction: L → Zr2Cu + Zr2Ni + Zr6NiAl2 at 852°C. Utilizing the thermal analysis data, the composition of the eutectic point was estimated to lie very near that of the well-known bulk metallic glass forming alloy Zr65Cu17.5Ni10Al7.5. The compositional proximity of a “deep” eutectic valley to this quaternary alloy thus provides a thermodynamic rationale for its high glass forming ability.
Thermophysical Properties of Bulk Metallic Glasses in the Stable and Undercooled Liquid – A Microgravity Investigation
Authors: Fecht Hans-Jörg , Wunderlich Rainer K. , Glade Stephen C. , Johnson William L. 
Published: April 2011

AbstractThe thermophysical properties in the stable and undercooled liquid phase of a series of Zr- based metallic glass forming alloys have been investigated under the condition of reduced gravity on board spacelab. Properties measured included the specific heat capacity and the enthalpy of fusion, the electrical resistivity, the total hemispherical emissivity, and the thermal transport properties. Results for the bulk metallic glass forming alloys indicate a pronounced change in chemical short range order in the liquid phase as function of temperature.
Quaternary and Quinary Ni-based Amorphous Alloys in the Ni-Zr-Ti-X (X=Al, Si, P) and Ni-Zr-Ti-Si-Y (Y=Sn, Mo, Y) Systems
Authors: Lee M.H. , Yi S. , Park T.G. , Kim W.T. , Kim D.H. 
Published: April 2011

AbstractNew Ni-based bulk amorphous alloys in the alloy system Ni-Zr-Ti-X (X=Al, Si, P) and Ni-Zr- Ti-Si-Y (Y=Sn, Mo, Y) were developed through systematic alloy design based upon the empirical rules for high glass forming ability (GFA). Additions of a small amount of Si and/or Sn to a ternary Ni-Ti-Zr alloy are very effective to increase GFA as well as the undercooled liquid region (ΔTX). Changes in crystallization mode during continuous heating of amorphous phase and lowered liquidus temperature by quaternary and quinary additions are associated with the enhanced GFA and the enlarged ΔTx. Development of new Ni-based amorphous alloys with high GFA and large ΔTx expands structural application of amorphous alloys.
Composition Dependence of Phase Separation and Crystallization in Deeply Undercooled Zr-(Ti-)Cu-Ni-Al Alloys
Authors: Kündig Andreas A. , Löffler Jörg F. , Johnson William L. 
Published: April 2011

AbstractDifferent bulk glass forming alloys in the neighborhood of Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) have been investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and small-angle neutron scattering (SANS). Along the Ti/Al line in composition space, Zr52.5Cu17.9Ni14.6Al10−xTi5+x with – ≤ x ≤ +2.5, the glass transition temperature, Tg, and the undercooled liquid regime (the difference between the first crystallization temperature and the glass transition temperature) continually decrease with increasing x. SANS measurements of annealed alloys show interference maxima, giving evidence for decomposition on the nanometer scale, up to a critical temperature Tc. In contrast to Tg, Tc increases with x and thus intercepts with Tg in the range –2.5 ≤ x ≤ –1.25, depending on the time scale of the experiment. At this composi- tion, significant changes in DSC traces and XRD patterns are observed. Additional isothermal DSC experiments show that the onset times for crystallization are significantly different for temperatures below and above Tc. We conclude that Tc, respectively the relation between Tc and Tg, determines the crystallization behavior and the thermal stability of these bulk metallic glasses.
Modeling Effects of Material Properties and Three-Dimensional Surface Roughness on Thermal Barrier Coatings
Authors: Glynn Michael L. , Ramesh K.T. , Wright P.K. , Hemker K.J. 
Published: April 2011

ABSTRACTThermal barrier coatings (TBCs) are known to spall as a result of the residual stresses that develop during thermal cycling. TBC's are multi-layered coatings comprised of a metallic bond coat, thermally grown oxide and the ceramic top coat, all on top of a Ni-base superalloy substrate. The development of residual stresses is related to the generation of thermal, elastic and plastic strains in each of the layers. The focus of the current study is the development of a finite element analysis (FEA) that will model the development of residual stresses in these layers. Both interfacial roughness and material parameters (e.g., modulus of elasticity, coefficient of thermal expansion and stress relaxation of the bond coat) play a significant role in the development of residual stresses. The FEA developed in this work incorporates both of these effects and will be used to study the consequence of interface roughness, as measured in SEM micrographs, and material properties, that are being measured in a parallel project, on the development of these stresses. In this paper, the effect of an idealized three-dimensional surface roughness is compared to residual stresses resulting from a grooved surface formed by revolving a sinusoidal wave about an axis of symmetry. It is shown that cylindrical and flat button models give similar results, while the 3-D model results in stresses that are significantly larger than the stresses predicted in 2-D.
Post-Exposure Evaluation of Thermal Barrier Coatings by Electrochemical Impedance Spectroscopy
Authors: Zhang Jianqi , Desai Vimal 
Published: April 2011

ABSTRACTHigh temperature behavior of air plasma sprayed (APS) thermal barrier coatings (TBC) was investigated in this study by electrochemical impedance spectroscopy (EIS). Scanning electron microscope (SEM) was used to examine cross-sectional morphology of exposed TBC. It was found that characteristic EIS spectra were obtained effectively to differentiate variant post-exposed TBC such as isothermal oxidation and cyclic oxidation. In addition, the type and length of high temperature exposure were qualitatively discernible from the EIS data. A model of an EIS alternative current (AC) equivalent circuit was proposed quantitatively to relate the EIS parameters to the morphological properties of the exposed TBC and functional relationships have been established between them. From the results, EIS has been identified capable of monitoring the microstructure of post-exposed TBC and evaluating TBC damage.
Strain-Rate Dependence of the Brittle-to-Ductile Transition Temperature in TiAl
Authors: Khantha M. , Vitek V. , Pope D. P. 
Published: April 2011

ABSTRACTThe brittle-to-ductile transition (BDT) and the strain-rate dependence of the brittle-to-ductile transition temperature (BDTT) have been recently investigated in single crystals of TiAl [1]. It was found that the activation energy associated with the BDTT is 1.4 eV when the slip is dominated by ordinary dislocations and 4.9 eV when it is dominated by superdislocations. Despite this difference in the activation energies, the BDTT, while varying with the strain-rate, remains in the same temperature range, viz., between 516–750C and 635–685C for ordinary and superdislocations, respectively. In this paper, we examine how the activation energy of the BDTT can vary with the type of dislocation activity and explain why it can attain values which are clearly much larger than the activation energy for dislocation motion. We describe a strain-rate dependent mechanism of cooperative dislocation generation in loaded solids above a critical temperature and use it to explain the characteristics of the BDT in TiAl. We show that the activation energy associated with the BDTT is a composite value determined by two or more inter-dependent thermally activated processes and its magnitude can be much larger than the activation energy for dislocation motion in certain materials. The predictions of the model are in good agreement with observations in TiAl.
Twinning in Crack Tip Plasticity of Two-Phase Titanium Aluminides
Authors: Appel Fritz 
Published: April 2011

ABSTRACTIntermetallic titanium aluminides based on γ(TiAl) are prone to cleavage fracture on low index lattice planes. Unfavourably oriented grains may therefore provide easy crack paths so that the cracks can rapidly grow to a length which is critical for failure. The effect of crack tip plasticity on crack propagation in γ(TiAl) was investigated by conventional and high-resolution electron microscopy. Crack tip shielding due to mechanical twinning was recognized as toughening mechanism, which occur at the atomic scale and apparently is capable to stabilize fastly growing cracks. The potential of the mechanism will be discussed in the context of novel design concepts for improving the strength properties of γ-base titanium aluminide alloys.
Development of Tough and Strong Cubic Titanium Trialuminides
Authors: Varin Robert A. , Zbroniec Les , Wang Zhi Gang 
Published: April 2011

ABSTRACTIn this work, the recent breakthroughs in the understanding of the fracture behavior and fracture toughness of L12-ordered titanium trialuminides are described and discussed. First, it is shown that, as opposed to many other intermetallics and specifically those with an L12 crystal structure, the fracture toughness of L12 titanium trialuminides is insensitive to testing in various environments such as air, water, argon, oxygen and vacuum (∼1.3×10–5 Pa). Second, it is reported here that by increasing the concentration of Ti combined with boron (B) doping, the room temperature fracture toughness of a Mn-stabilized titanium trialuminide can be improved by 100% from ∼4 MPam1/2 to ∼8 MPam1/2 and by 150–250% at 1000°C to ∼(10–12) MPam1/2 with a simultaneous suppression of intergranular fracture (IGF) to ∼(40–50%). Almost three fold increase in yield strength to ∼550 MPa is attained at room temperature for high Ti, boron-doped trialuminides. Both Vickers microhardness and strength increase linearly with increasing concentration of (Ti+B) indicating a classical solid solution strengthening response.
The Yield Anomaly in CoTi
Authors: Wittmann M. , Baker I. , Evans N.D. 
Published: April 2011

ABSTRACTCompression tests performed on both stoichiometric and cobalt-rich CoTi over a range of temperatures show a positive temperature dependence of the yield stress with increasing temperature, before a decline occurs at high temperatures. In the region of the peak yield stress, serrated yielding and a negative rate sensitivity of the yield stress were observed. Static strain-aging also occurs. These observations are consistent with strong solute-dislocation interactions. Results from quenching experiments and strain rate change tests are presented, together with transmission electron microscope observations of the dislocation structures below, at, and slightly above the peak temperature. The results suggest that the yield anomaly in CoTi can be accounted for by a classical dynamic strain aging mechanism.
Microstructural Evolution and Mechanical Properties of Al3-based Multi-Phase Alloys
Authors: Miura Seiji , Fujinaka Juri , Nino Rikiya , Mohri Tetsuo 
Published: April 2011

ABSTRACTA preliminary study on the phase relations in Al-Mo-Ti-X quaternary systems in the vicinity of Ti-trialuminide phases is carried out with various additives X= Mn, Cr, Fe, Ni and Ag. In the Al-Mo-Ti ternary system, a bcc-phase field extends from the Ti-Mo edge to high Al region at high temperatures and it equilibrates with a DO22-Al3Ti phase containing a large amount of Mo. It is found that, by additions of X= Mn, Cr, Fe or Ni, an L12-(Al, X)3 Ti phase appears near the two-phase region composed of the DO22-Al3 Ti and bcc phases in the Al-Mo-Ti ternary system. By heat treatment at 1223 K, the bcc phase of quaternary alloys decomposes into the A15-Mo3Al, DO22, L12 and/or σ phases, and no voids are observed. The mechanical properties of these alloys are also investigated by Vickers hardness.
Microstructures and Mechanical Properties of the γ / κ Two Phase Fe-Mn-Al-C (-Cr) Alloys
Authors: Handa Kazuyuki , Kimura Yoshisato , Mishima Yoshinao 
Published: April 2011

ABSTRACTIn view of the possibility of the E21-type intermetallic compound as a strengthener in austenitic alloys at high temperatures, mechanical properties and microstructures of the γ / κ two-phase alloys in the Fe-Mn-Al-C system were investigated. Alloy compositions with more than 1.5wt% C were selected in order to stabilize the γ / κ two-phase microstructure in the high temperature regime exceeding 873K. During furnace cooling after the homogenization treatment, κ phase precipitates on the γ grain boundary, which results in the poor tensile ductility. In these alloys, tensile yield strength at 873K and 1073K increases with increasing κ phase volume fraction. Applying ageing treatment at 1073K after the solid solution treatment followed by water quenching causes the formation of a uniform γ / κ lamellar microstructure, and the remarkable improvement of ductility was achieved. The addition of Cr, which is expected to improve the oxidation resistance, reduces the phase stability of κ phase, and leads to the formation of Cr7C3 carbide and β-Mn phase with more than 5.5wt.% Cr addition.
Anomalous Strain Rate Dependence of Tensile Elongation in Moisture-Embrittled L12 Alloys
Authors: Takasugi T. , Kaneno Y. , Inoue H. 
Published: April 2011

ABSTRACTThe effect of strain rate on tensile ductility of moisture-embrittled L12-type Co3Ti and Ni3(Si, Ti) ordered alloys was investigated at ambient temperatures (298K∼423K) by tensile test and SEM fractography. The anomalous increase of tensile elongation and ultimate tensile stress was observed in a low strain rate region and also at high temperatures, accompanied with an increased area fraction in ductile transgranular fracture pattern. The anomalous strain rate dependence of tensile ductility was shown to become more evident with decreasing grain size. As a process counteracting to the hydrogen decomposition from moisture in air, oxidation process on the alloy surface was suggested.
First-Principles Calculations of Electronic Structure and Structural Properties for MoV, MoNb, and MoTa
Authors: de Coss R. , Aguayo A. , Murrieta G. 
Published: April 2011

ABSTRACTFirst-principles total-energy electronic structure calculations based on the full-potential linearized augmented plane wave (LAPW) method have been used to study the electronic and elastic properties of MoV, MoNb, and MoTa with the B2 (CsCl) estructure. From the calculated values for the bulk modulus we have determined the melting temperature using an empirical correlation. The chemical bond and the electronic structure around the Fermi level are analyzed. In particular, we found that MoTa which have the experimental determined highest melting point of the studied materials, present the largest bulk modulus and the highest degree of covalence bonding of these intermetallic compounds.
Low Temperature Positron Lifetime and Doppler Broadening Measurements in B2-type FeAl Alloys
Authors: Haraguchi Tomohide , Hori Fuminobu , Oshima Ryuichiro , Kogachi Mineo 
Published: April 2011

ABSTRUCTPositron lifetime and Doppler broadening measurements were carried out at a low temperature, 100K, for B2-type intermetallic compounds FeAl with composition ranges from 41.2 to 50.7 at%Al systematically in order to clarify the feature of lattice defects of the alloys. Quenching temperature dependences of positron lifetimes ranging from 573 to 1173 K was examined for alloys with 41.2, 49.0 and 50.7 at%Al. Two lifetime component analyses could not be made except for a few spectra, indicating a saturation trapping of positrons at atomic vacancies. The mean positron lifetimes are in a range of 175–195 psec, which are not corresponding to vacancy clusters but to mono and/or di-vacancies. The tendency for S-parameter to increase with increase in Al content was found. This suggests that such an increase of S-parameters is attributed to change in the fraction of atoms around the vacancies, not to increase in vacancy concentration.
Long Term Oxidation of Model and Engineering TiAl Alloys
Authors: Locci Ivan E. , Brady Michael P. , Smialek James L. 
Published: April 2011

ABSTRACTThe purpose of this research was to characterize the oxidation behavior of several model (TiAl, TiAl-Nb, TiAl-Cr, TiAl-Cr-Nb) and engineering alloys (XD, K5, Alloy 7, WMS) after long-term isothermal exposure (∼7000 h) at 704°C, and after shorter time exposure (∼1000 h) at 800°C in air. High-resolution field emission and microprobe scanning electron microscopy were used to characterize the scales formed on these alloys. Similarities and differences observed in the scales are correlated with the various ternary and quaternary microalloying additions.
Transition Metal Impurity-Dislocation Interactions in NiAl: Dislocation Friction and Dislocation Locking
Authors: Kontsevoi O. Yu. , Gornostyrev Yu.N. , Freeman A.J. 
Published: April 2011

ABSTRACTThe energetics of the interaction of the <100>{010} edge dislocation in NiAl with early 3d transition metal (TM) impurities was studied using the ab initio real-space tight-binding LMTO-recursion method with 20,000 atom clusters and up to 1,000 non-equivalent atoms in the dislocation core. The coordinates of the atoms in the core were determined within the Peierls-Nabarro (PN) model with restoring forces determined from full-potential LMTO total energy calculations. TM impurities were then placed in different substitutional positions near the dislocation core. For most positions studied, the interaction between impurities and the dislocation is found to be repulsive (dislocation friction). However, when the impurity is in the position close to the central atom of the dislocation core, the interaction becomes strongly attractive, thus causing dislocation locking. Since the size misfit between the Al atom and the substituting TM atom is very small, this locking cannot be explained by elastic (or size misfit) mechanisms; it has an electronic nature and is caused by the formation of the preferred bonding between the electronic states of the impurity atom and the localized electronic states appearing on the central atom of the dislocation core. The calculated results are then discussed in the scope of experimental data on solid solution hardening in NiAl.
Microhardness Anisotropy and the Indentation Size Effect (ISE) on the (100) of Single Crystal NiAl
Authors: Stevenson M.E. , Weaver M.L. , Bradt R.C. 
Published: April 2011

ABSTRACTThe Knoop microhardness anisotropy of single crystal NiAl, a B2 intermetallic compound, was investigated on the (001) plane at indentation test loads from 25 to 500 g. An energy balance analysis was applied to analyze the indentation size effect (ISE). The load independent, orientation independent Knoop microhardness was determined to be 220 kg/mm2 for the (100) plane of NiAl.
On the Stress Anomaly of γ-TiAl
Authors: Fivel Marc C. , Louchet Francois , Viguier Bernard , Verdier Marc 
Published: April 2011

ABSTRACTA 3D mesoscopic simulation of dislocation behaviour is adapted to the case of γ-TiAl. It shows that, in the temperature range of the stress anomaly, ordinary dislocation motion essentially proceeds through a series of pinning and unzipping processes on screw dislocations. Pinning points are cross-slip generated jogs, whose density increases with temperature. Unzipping of cusps restores the screw character of the dislocation. The balance between pinning and unzipping becomes increasingly difficult as temperature raises, and results in dislocation exhaustion. All these features agree with the so-called “Local Pinning Unzipping” mechanism.
Effects of a pre-anneal on the mechanical properties of γ-TiAl
Authors: Grégori Fabienne , Penhoud Philippe , Veyssière Patrick 
Published: April 2011

ABSTRACTThe temperature, TP, and the stress, σP, at which the yield stress of γ-TiAl alloys peaks are influenced by factors such as alloy composition and load orientation. Available data indicates that in the absence of adequate heat treatments, TP and σP are shifted towards values significantly higher than those of samples pre-annealed in order to precipitate interstitial atoms. Conditions under which precipitation influences the anomalous regime are revealed by dedicated tests. In addition to pointing out the clear effect of interstitials, these tests suggest that further ordering may contribute to the strength of Al-rich γ-TiAl.
Measurement of the Tension/Compression Asymmetry Exhibited by Single Crystalline γ-Ti 55.5at%Al
Authors: Zupan Marc , Hemker K.J. 
Published: April 2011

ABSTRACTMicrosample test specimens of single crystalline γ-Ti 55.5at%Al oriented near the [001], and [-110] crystal axes have been deformed in tension and compression at 973K. From these experiments, measurements of the 0.2% offset flow stress have been made as a function of temperature, crystal orientation and sense of the applied load. A measurable violation of Schmid's law was observed and a significant tension/compression asymmetry has been observed at this temperature for the above listed orientations. Single-cycle loading experiments designed to measure the tension/compression asymmetry of the yield strength on the same sample have been conducted along the ∼[-110] and [001] orientations. The flow strength measurements from the specimens, which underwent the fully reversed cyclic-loading experiment, fall near those of the monotonically loaded microsamples deformed at the same temperature, which suggests that the same deformation mode was active in both tension and compression.
Ion-Plating Deposition of MgO Protective Layer for AC-Plasma Display Panels
Authors: Uetani Kazuo , Kajiyama Hiroshi , Kato Akira , Tokomoto Isao , Koizumi Yasuhiro , Nose Koichi , Ihara Yasushi , Onisawa Ken-ichi , Minemura Tetsuroh 
Published: April 2011

AbstractMgO thin films as a protective layer in plasma display panels (PDPs) were deposited by an advanced ion-plating (AIP) apparatus that we had developed. The AIP method enables plasma operation at low-pressures of 10−3 Pa. The MgO thin films were mainly (111) oriented with a small amount of randomly oriented textures. The preferred orientation of the films was dependent on deposition conditions; oxygen content and substrate temperature. Fine columnar structures grew with sharp apexes at the film surface. Secondary electron emission coefficient from a film deposited by the AIP method was higher than that by a conventional electron beam evaporation method. The MgO protective layer could be expected to improve PDPs by our AIP deposition.