bluuebunny/crossref_metadata_2025 huggingface dataset:
γ-Brass Crystallization in a Simple Monotomic Liquid
Authors: Zetterling Fredrik H.M. , Dzugutov Mikhail , Lidin Sven
Published: April 2011

We present a molecular dynamics simulation investigating the crystallization pattern of a simple monatomic liquid model which utilize an interatomic interaction potential. The shape of the potential imitates effective interionic interaction in metallic systems. The potentials is constructed to favour icosahedral arrangement in the first coordination shell. We observe that, the system forms a thermodynamically stable solid phase exhibiting cubic symmetry. Its diffraction pattern can be identified as that of γ-brass phase, a terahedrally packed crystalline structure with 52 atoms in the unit cell. We conclude that the monatomic version of γ-brass structure generated in this simultion can be regarded as a new archetype for the γ-base structures observed in many intemetllic compounds.
Refinement of d-AlNico Quasicrystal Structures
Authors: Takakura Hiroyuki , Yamamoto Akiji , Tsai An Pang
Published: April 2011

The models of decagonal Al72Ni20Co8quasicrystal with the space group ofP105/mmcwere refined on the basis of single crystal x-ray diffraction data set using the 5D description. The results of a structure model derived from Al13Fe4-type approximant crystal and Burkov model are compared. The former gives ωR=0.045 andR=0.063 for 449 reflections with 103 parameters and a resonable chemical composition of Al71.2TM28.8(TM=transition metals). The projected structure in consistent with high resolution images of this material. On the other hand, the latter gives ωR=0.161 andR=0.193 for 55 parameters and a compositon of Al64.6TM35.1.
Effects of Hydrogen on the Internal Time Scales in Zr-Ti-Ni-Cu-Be Bulk Metallic Glasses
Authors: Suh Daewoong , Dauskardt Reinhold H.
Published: April 2011

The effects of pre-charged hydrogen on various kinetic processes in a Zr-Ti-Ni-Cu-Be bulk metallic glass alloy were investigated. Hydrogen charging induced longer internal time scales for structural relaxation and viscous flow. Crystallization was retarded by hydrogen charging leading to enhanced glass stability. Positron annihilation spectroscopy indicated reduced average free volume size after hydrogen charging. The reduced free volume and higher viscosity caused by hydrogen retard the plastic deformation and are believed to be responsible for hydrogen embrittlement.
Elastic Properties of Three Bulk Metallic Glasses. Evolution Versus Temperature in the Glass Transition Region and Influence of Crystallisation.
Authors: Van De Moortele B. , Pelletier J.M. , Soubeyroux J.L. , Lu I.R.
Published: April 2011

Three bulk metallic glasses, with different resistance against crystallisation, were investigated using DSC experiments, X-ray diffraction, transmission electron microscopy and mechanical spectroscopy. Like in other non-crystalline materials, the elastic modulus exhibits a large decrease above the glass transition temperature. In materials with a large supercooled region (Pd-Ni-Cu-P for instance), this decrease can reach three decades, leading to an attractive glass forming ability. In contrast, in bulk metallic glasses in which onset of crystallisation occurs very rapidly above Tg, this decrease is on less than one decade. A correlation is made with the microstructure evolution revealed by X-Ray diffraction and transmission electron microscopy.
Fracture Mechanisms of Bulk Amorphous Metal under Impact Loading
Authors: Kobayashi Takao , Shockey Donald A.
Published: April 2011

Advanced diagnostic instruments and analyses applied to failure surfaces and cross sections of bulk metallic glasses (BMGs) can provide insight into the deformation and failure of these materials and assist in prototyping new materials with improved failure resistance. Confocal- optics scanning laser microscopic analysis of conjugate fracture surface topographs suggests that the formation and stretching of ligaments are likely keys to the high impact toughness of Vitreloy.
Production of Zr-based Amorphous Wires by Rotating Disk Casting Method
Authors: Zhang Tao , Inoue Akihisa
Published: April 2011

Continuous amorphous wires with high strength and good ductility have been produced for the Zr55Al10Ni5Cu30and Zr55Ti5Al10Ni10Cu20alloys by a rotating disk casting technique. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous wires have a nearly circular cross-section, smooth peripheral surfaces and diameters in the range from 0.5 to 1.5mm. The amorphous alloy wires have good bending ductility. The maximum tensile strength, μf, is 1600 MPa for Zr55Al10Ni5Cu30 amorphous wire and 1900 MPa for Zr55Ti5Al10Ni10Cu20 amorphous wire, respectively. The success of forming amorphous alloy wires in a continuously long form by the present casting method is important for the further extension of application fields of amorphous alloys.
The Glasses Transition and Low Energy Excitations in Supercooled Metallic Liquid and Glasses
Authors: Kanazawa I.
Published: April 2011

We have introduced the theory of three-dimensional supercooled metallic liquids and glasses, which is based on the gauge invariant agrangian with spontaneous breaking, and discussed the viscosity of the three-dimensional supercooled metallic liquids. n the basis of the present theoretical formula, a qualitative picture of low energy excitations (the boson peak) is proposed.
Investigation on the Thermal Stability of Bulk Glass Forming Alloy Pd-Cu-Ni-P
Authors: Lu I.-R. , Görler G. P. , Willnecker R. , Fecht H. J.
Published: April 2011

The metallic glass former Pd-Ni-P is well known for its pronounced stability against crystallization. Samples of this alloy vitrify completely at low cooling rates down to 0.1 K/s. The addition of copper to this alloy system reduces further the crystallization kinetics significantly. Investigations on critical cooling rates were performed on Pd-Cu-Ni-P alloy by means of isothermal nucleation experiments. The results indicate a critical cooling rate in the order of 5.10−3 K/s, which is the lowest one presently known for metallic glass-formers. The high stability against crystallization during cooling allows for simultaneous measurements of its thermodynamic properties within the entire temperature range from the regime of the liquid to the glassy state. Heat capacity measurements were carried out by differential heat-flow calorimetry and the coefficient of thermal expansion was determined by applying sessile drop technique. The results can be described within the free-volume model.
Dynamic Specific Heat of a Metallic Glass-Former
Authors: Wilde Gerhard
Published: April 2011

Modulated 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

The 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

The 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

New 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

Different 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

Thermal 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

High 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

The 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

Intermetallic 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

In 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

Compression 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

A 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

In 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

The 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

First-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

ABSTRUCT

Positron 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

The 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

The 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

The 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

A 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

The 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

Microsample 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

MgO 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.
Ion Beam Enhanced Formation and Luminescence of Si Nanoclusters from a-SiOx
Authors: Sun Yohan , Seo Se-Young , Shin Jung H. , Kim T. G. , Whang C. N. , Song J. H.
Published: April 2011

The effect of ion beams on the formation of Si nanoclusters from a-SiOx films and their luminescence properties is investigated. a-SiOx films with Si content ranging from 33 to 50 at. % were deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) of SiH4 and O2. Prior to anneal, some samples were implanted with 380 keV Si to a dose ranging from 5.7 × 1014 cm−2 to 5.7 × 1016 cm−2. All films were rapid thermal annealed under flowing Ar environment, and hydrogenated after anneals to passivate defects and to enhance the luminescence of Si nanoclusters. For films with Si content less than 40 at. %, ion beam slightly reduces the photoluminescence (PL) intensity and induces a slight blueshift of the luminescence. For films with Si content greater than 40 at. %, ion beam greatly increases the PL intensity. Based on the effect of the ion beams dose and the ion specie, we propose that ion beams damage greatly promotes nucleation of small Si clusters from the a-SiOx matrix.
Coordination structure of implanted manganese ions in silica glass
Authors: Fukumi Kohei , Chayhara Akiyoshi , Kageyama Hiroyuki , Kadono Kohei , Kitamura Naoyuki , Mizoguchi Hirohsi , Horino Yuji , Makihara Masaki
Published: April 2011

180 keV Mn+ ions were implanted in silica glass at doses ranging from 1×1016 to 2×1017 ions/cm2 at room temperature. The coordination structure of implanted Mn atoms was studied by X-ray absorption spectroscopy. It was found that Mn atoms were mainly coordinated by O atoms in silica glasses as-implanted at doses lower than 5×1016Mn+ions/cm2. The Mn-O bond distance was 2.07 Å and the coordination number was 4.3 in average. Mn atoms were mainly coordinated by Mn and O atoms in the glasses as-implanted at doses higher than 1×1017 Mn+ions/cm2. In all the glasses, Mn atoms which are coordinated by O atoms were present as divalent state. After heating at 700 °C in air, Mn atoms were present as trivalent state and tended to form oxide crystals.
Nanoparticles of metallic Cobalt and Nickel prepared by ion implantation into SiO2
Authors: Cíntora-González O. , Estournès C. , Muller D. , Richard-Plouet M. , Traverse A. , Guille J. L. , Grob J.J.
Published: April 2011

The structural and magnetic properties of nano-sized particles of transition metals (Co and Ni) implanted into amorphous SiO2 are investigated. The SiO2 substrates used were as grown on a silicon (100) wafer under wet O2 atmosphere. The metals were implanted as singly charged atoms energized to 30 or 160 keV. Transmission Electron microscopy (TEM) observations and X-ray absorption spectroscopy (XAS) show that M+ implantation results in the formation of metallic nanoparticles at the vicinity of the surface whereas oxide particles (< 1 nm) are formed in a deeper region. After thermal treatment under hydrogen, TEM evidences the disappearance of the oxide region and an increase in the size of the metallic particle. XAS shows that cobalt and nickel are entirely in the metallic form and saturation magnetization becomes close to the theoretical value.
Secondary Ion Mass Spectrometry with Gas Cluster Ion Beams
Authors: Toyoda Noriaki , Matsuo Jiro , Aoki Takaaki , Chiba Shunichi , Yamada Isao , Fenner David B. , Torti Richard
Published: April 2011

Secondary Ion Mass Spectrometry (SIMS) with Gas Cluster Ion Beams (GCIB) was studied with experiments and molecular dynamics (MD) simulations to achieve a high-resolution depth profiling. For this purpose, it is important to prevent both ion-mixing and the surface roughening due to energetic ions. As the Ar cluster ion beam shows surface smoothing effects and high secondary-ion yield in the low-energy regime, the cluster ion beam would be suitable for the primary ion beam of SIMS. From MD simulations of Ar cluster ion impact on a Si substrate, the ion-mixing is heavier than for Ar monomer ions at the same energy per atom, because the energy density at the impact point by clusters is extremely high. However, the sputtering yields with Ar cluster ions are one or two orders of magnitude higher than that with Ar monomer ions at the same energy per atom. Comparing at the ion energy where the ion-mixing depths are the same by both cluster and monomer ion impacts, cluster ions show almost ten times higher sputtering yield than Ar monomer ions. Preliminary experiment was done with a conventional SIMS detector and a mass resolution of several nm was achieved with Ar cluster ions as a primary ion beam.
Buried Oxide Precipitates In A Si Wafer Due to He ION Implantation and High-Temperature Oxidation
Authors: Nakashima Sadao , Nakata Jyoji , Hayashi Junzou , Imai Kazuo
Published: April 2011

A new method of producing a buried oxide is proposed. It involves implanting a silicon wafer with helium rather than oxygen ions and then subjecting it to high- temperature oxidation. The voids formed by helium ion implantation and subsequent annealing enhance the diffusion of oxygen atoms into the silicon. The oxygen atoms cause thermal oxide to grow at the void/silicon interface and transform the voids into buried oxide precipitates. Auger electron spectroscopy revealed that the total number of oxygen atoms in the precipitates was 9.3 × 1016 cm−2 and that the peak value of oxygen atom concentration in the wafer was approximately 25%.
Cu gettering in Si cavities observed by Positron Annihilation Doppler Broadening
Authors: Schut H. , van Veen A. , Eijt S.W.H.
Published: April 2011

In this study we present the results of Positron Beam Annihilation (PBA) experiments on the gettering of copper in Cz-Si implanted with 33 keV He+ ions with doses ranging from 0.5 to 3× 1016cm−2 followed by an anneal treatment at 1100 K under N2 ambient. For the higher doses this yields a sub-surface layer containing nanometer sized cavities. Copper is introduced into these cavities by diffusing from the backside of the wafer at 1000 K, again under N2 ambient. Mapping of the S and W Doppler broadening parameters, with the implantation dose as running parameter, shows the formation of cavities. After the Cu in-diffusion the change in the values of the characteristic S-W cluster points clearly demonstrates the arrival of Cu at the internal surface of the cavities.
Relating Nanostructures to Mechanical Properties in Ion-Implanted Materials
Authors: Follstaedt David M. , Knapp James A. , Myers Samuel M. , Petersen Gary A.
Published: April 2011

Ion implantation was used to form high densities (~1019 /cm3) of small oxide precipitates in Ni in order to investigate the strength mechanism produced by such highly refined structures. Nanometer-size precipitates of Al2O3 and NiO are found to block dislocation motion in the Ni matrix, producing yield strengths up to 4.6 GPa, more than twice that of hardened bearing steel. Dispersion strengthening theory, developed for micrometer-size precipitates and spacings, was found to account quantitatively for the yield strengths produced by nanometer-size oxides as well. Nanoindentation plus finite-element modeling was used to quantify the mechanical properties of implanted metal layers, and was extended to examination of amorphous Si layers formed by self-ion implantation. The amorphous phase was found to have a yield strength of 4.45 ± 0.20 GPa, Young's modulus of 144 ± 7 GPa, and hardness of 10.3 ± 0.4 GPa. The modulus and hardness are reduced by 10% and 15%, respectively, from those of crystalline Si.
Ar Cluster Ion Bombardment Effects on Semiconductor Surfaces
Authors: Seki Toshio , Tsumura Kazumichi , Aoki Takaaki , Matsuo Jiro , Takaoka Gikan H. , Yamada Isao
Published: April 2011

New surface modification processes have been demonstrated using gas cluster ion irradiations because of their unique interaction between cluster ions and surface atoms. For example, high quality ITO films could be obtained by O2 cluster ion assisted deposition at room temperature. It is necessary to understand the role of cluster ion bombardment during film formation for the further developments of this technology. Variable Temperature Scanning Tunneling Microscope (VT-STM) in Ultra High Vacuum (UHV) allows us to study ion bombardment effects on surfaces and nucleation growth at various temperatures.

The irradiation effects between Ar cluster ion and Xe monomer ion were compared. When a Si(111) surface with Ge deposited to a few Å was annealed to 400°C, it was observed that many islands of Ge were formed. The surface with the Ge islands was irradiated by these ions. In the STM image of cluster-irradiated surface, large craters with diameter of about 100 Å were observed, while only small traces with diameter of about 20 Å were observed in monomer-irradiated surface. The number of Ge atoms displaced by one Ar cluster ion impact was much larger than that by one Xe ion impact. This result indicates that Ar cluster ion impacts can enhance the physical modification of Ge islands. When the sample irradiated with Ar cluster was annealed at 600°C, the hole remained, but the outer rim of the crater disappeared and the surface structure was reconstructed at the site of the rim. The depth of damage region in the target became shallower with decrease of the impact energy. These results indicate that low damage and useful surface modification can be realized using the cluster ion beam.
Finite Element Modeling of Nanoindentation Measurements of Crystalline and Amorphous Si
Authors: Knapp J. A. , Follstaedt D. M. , Myers S. M. , Petersen G. A.
Published: April 2011

Nanoindentation testing of amorphous Si layers, formed by self-ion implantation, has been performed, and their mechanical properties compared to crystalline Si. The data was analyzed using finite element modeling of the indentation measurement, allowing the properties of the thin amorphous layers to be separated from those of the underlying material. By modeling the materials as isotropic, elastic-plastic solids with the Mises yield criterion, the amorphous Si is shown to have a hardness about 15% lower than crystalline Si and an elastic modulus about 10% lower. Electron and atomic force microscopies of the indents indicate that the amorphous Si does not undergo phase changes during indentation, and that it may be somewhat more ductile than crystalline Si.
Thermomechanical Formation an Thermal Sensing of Nanometer-Scal Indenatations in PMMA Thin Films for Parallel and Dense AFM Data Storage
Authors: Cross Graham L.W. , Despont Michel , Drechsler Ute , Dürig Urs T. , Rothuizen Hugo , Binnig Gerd K. , Vettiger Petr , King William P. , Goodson Kenneth E.
Published: April 2011

Thermomechanical writing occurs as Joule-heated, cantilevered tips imprint nanometer-scale inden (bits) in a 50-nm-thick polymer (PMMA) film. Thermal data reading incorporates the same cantilevers operated in a mode to detect a temperature change when a tip follows the contour of a previously written bit. Binnig et.al [1] demonstrated single-cantilever writing and rading density at 400 Gbit/in2. A micromachined 32 × 32 cantilever array has been fabricated [2] and has demonstrated parallel read/write operation at 150 Gbi/in in2 [3]. Although much progress has been made to develop a thermomechanical data storage device [4], the fundamental process of thermomechanical storage processes by applying atomic force microscope (AFM)-based force detection during thermal operation. We examined the thermomechanics of polymer indentation with respect to time and temperature of interaction. This work impacts the operation of AFM cantilevens for combined thermal writing and reading and understnding of fundamental polymer mesoscopic transport.
Modulus Determination of Polymer Matrix Composites: Comparison of Nanoindentation and Dynamic Mechanical Analysis
Authors: Grunlan Jaime C. , Rowenhorst David , Francis Lorraine F. , Gerberich William W.
Published: April 2011

The results of modulus measurements, on carbon black-filled poly(N-vinylpyrrolidone), using dynamic mechanical analysis and nanoindentation were compared. It was shown that beyond the critical pigment volume concentration for this composite system (∼ 25 vol% carbon black), the storage modulus, obtained with dynamic mechanical analysis, decreased with increasing filler concentration. This dropping modulus was due to porosity that developed in the composite films when the critical pigment volume concentration had been exceeded. Elastic modulus obtained with nanoindentation showed the opposite trend, with modulus increasing with additional carbon black loading. An analysis of the method used to calculate modulus based upon indentation data was performed and a mechanism was proposed to explain the disparity between the moduli obtained using these two different methods of measurement.
Microstructure and Mechanical Properties of Electroplated Cu Thin Films
Authors: Volinsky A.A. , Vella J. , Adhihetty I.S. , Sarihan V. , Mercado L. , Yeung B.H. , Gerberich W.W.
Published: April 2011

Copper films of different thicknesses of 0.2, 0.5, 1 and 2 microns were electroplated on top of the adhesion-promoting barrier layers on <100> single crystal silicon wafers. Controlled Cu grain growth was achieved by annealing films in vacuum.

The Cu film microstructure was characterized using Atomic Force Microscopy and Focused Ion Beam Microscopy. Elastic modulus of 110 to 130 GPa and hardness of 1 to 1.6 GPa were measured using the continuous stiffness option (CSM) of the Nanoindenter XP. Thicker films appeared to be softer in terms of the lower modulus and hardness, exhibiting a classical Hall-Petch relationship between the yield stress and grain size. Lower elastic modulus of thicker films is due to the higher porosity and partially due to the surface roughness. Comparison between the mechanical properties of films on the substrates obtained by nanoindentation and tensile tests of the freestanding Cu films is made.
Adhesive Failure of a Thin Epoxy Film on an Aluminized Substrate
Authors: Moody N. R. , Bahr D. F. , Kent M. S. , Emerson J. A. , Reedy E. D.
Published: April 2011

In this study we used nanoindentation to determine mechanical properties and combined nanoindentation with stressed overlayers to determine interfacial fracture energy of a 164 nm thick film of Epon 828/T403 on an aluminized glass substrate. The combination of nanoindentation and a tungsten overlayer was required to trigger delamination of the epoxy film from the aluminized substrate. Mechanics-based models for circular blister formation were then used to determine residual stresses and interfacial fracture energies. This approach showed that the tungsten overlayer had a compressive residual stress of 1.9 GPa which drove blister formation at a fracture energy of 1.9 J/m2 with a phase angle of loading equal to –62°.
Nanoindentation of Pressure Quenched Fullerenes and Zirconium Metal from a Diamond Anvil Cell
Authors: Catledge Shane A. , Spencer Philemon T. , Patterson Jeremy R. , Vohra Yogesh K.
Published: April 2011

The sample size employed in high pressure diamond anvil cells is limited to a diameter of typically 25 to 150 microns. While this size is often sufficient for diagnostics using synchrotron x-ray diffraction and Raman scattering, ex-situ measurements of mechanical properties using conventional microhardness indentation techniques is not feasible. For some materials, the high pressure phase(s) can be quenched to ambient pressure allowing further characterization by other techniques. We make use of the very small probe volume allowed by nanoindentation to investigate the pressure-quenched structures of both C70 fullerene and zirconium. For the case of C70, we show that the amorphous phase established above 35 GPa can be quenched to ambient, and that it shows a largely elastic indentation loading behavior with a hardness of 30 GPa. We establish that this hard carbon phase contains a mixture of sp2- and sp3-bonded carbon and that it can be produced from C70 fullerene by application of pressure at room temperature. With regard to zirconium metal, we confirm the irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal Ω-phase (AlB2 structure) and document an 80% increase in hardness that may be attributed to the presence of covalent bonding based on sd2-hybridized orbitals forming graphite-like nets in the (0001) plane of the AlB2 structure.
Nanoindentation Evaluation of Brittle Films on Metals Natalia
Authors: Tymiak I. , Daugela Antanas , Page Trevor F. , Gerberich William W.
Published: April 2011

The present study addresses two cases of brittle ceramic films on metals. With the assistance of AE as a supplementary technique, yield initiation phenomena have been evaluated for W single crystal surfaces under several nm thick native oxide film. An AE sensor coupled to an indenter tip allowed an increasing sensitivity to localized fracture and plasticity events in the vicinity of an indentation contact. A good correlation between AE signals and indentation induced plasticity and fracture has been accomplished for contacts below 100 μN. Second, mechanical behavior of porous nanocrystalline SiC films on Mo substrates was examined. An analysis was based on the P-δ2 approach. With this method, both loading and unloading parts of indentation curves obtained with sharp pyramidal indenters may be represented as P=Kδ2 where P, and δ denote indentation load and displacement respectively. The parameter K includes a material's hardness/modulus ratio and indenter geometry.