bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ transmission electron microscopy of nano-sized metal clusters
Authors: De Hosson Jeff Th. M. , Palasantzas George , Vystavel Tomas , Koch Siete 
Published: April 2011

ABSTRACTThe paper concentrates on in situ transmission electron microscopy of nano-sized Mo and Nb clusters. In particular, this contribution presents challenges to control the microstructure in nano-structured materials via a relatively new approach, i.e. using a so-called nanocluster source. An important aspect is that the cluster size distribution is monodisperse and that the kinetic energy of the clusters during deposition can be varied. The deposited Mo clusters with sizes 5 nm or larger show a body-centered crystal (bcc) structure. The cubic clusters are self-assembled from smaller ones and forming distorted cubes of typical size 7.8 nm or larger. With reducing cluster size to ≤3 nm, the face centered crystal (fcc) structure appears due to dominance of surface energy minimization, while self-assembly into large cubes with sizes up to 20 nm is still observed. In situ TEM annealing leads to cluster coalescence at temperatures ∼800 °C, with the crystal habit changing to rhombic dodecahedron for isolated clusters, while large cubes change to faceted polyhedra. In situ TEM annealing studies on Nb clusters showed that cluster coalescence events were not observed even at rather elevated temperatures because of the formation of oxides.
Neutron Spectroscopy of Carbon nano-Materials
Authors: Kolesnikov Alexander I. , Loong Chun-K. , Moravsky Alexander P. , Loutfy Raouf O. , Burnham Christian J. 
Published: April 2011

ABSTRACTVibrational spectra for single wall carbon nanotubes, double wall carbon nanotubes, single wall carbon nanohorns and C60-peapods have been measured with inelastic neutron scattering in a wide range of energy transfer, 5–220 meV. A decrease in intensity around 75–100 meV and the appearance of two peaks around 120–125 meV and 150 meV in the double wall nanotubes and C60-peapods spectra compared to single wall carbon nanotubes and nanohorns were observed. These findings indicate the possibility of strong interaction between the walls of the double wall carbon nanotube, and between C60 molecules and carbon nanotube of the peapod. Alternatively, a possible contamination of the samples by hydrogen (even in microscopic quantities) covalently bonded to the carbon also can account for the observed phenomena.
An Experimental Evaluation of the Constant β Relating the Contact Stiffness to the Contact Area in Nanoindentation
Authors: Strader Jeremy H. , Shim Sanghoon , Bei Hongbin , Oliver W. C. , Pharr G. M. 
Published: April 2011

ABSTRACTMeasurements of mechanical properties by nanoindentation with triangular pyramidal indenters like the Berkovich rely heavily upon the relationship between the contact stiffness, S, the contact area, A, and the reduced elastic modulus, Er. This relationship is often written in the form S = 2βEr(A/π)1/2, where β is a constant that depends on the geometry of the indenter. Although the most common values for β used in experimental measurements are 1.000 and 1.034, various theoretical analyses have yielded values as small as 1.00 or as large as 1.2, depending on the assumptions made to model the deformation. Here, we explore the most appropriate value of β by performing careful experiments in fused quartz with thin gold coatings applied to the surface to reveal the actual contact area when observed in the scanning electron microscope. Experiments were performed not only with the Berkovich indenter, but with five other three-sided pyramidal indenters with centerline-to-face angles ranging from 35.3° (cube corner) to 85°. Results are discussed as they apply to obtaining accurate measurements of mechanical properties by nanoindentation.
Mechanisms Underlying Hardness Numbers
Authors: Gilman John J. 
Published: April 2011

ABSTRACTRelationships of indentation hardness numbers to to other physical properties are demonstrated. They differ depending on the type of chemical bonding; metals, alloys ionic, covalent, and metal-metalloid. The properties are: shear modulus; ionic charge; band-gap density; polarizability; and formation energy, respectively. In each case the rationale is provided. The concept of a “bonding Modulus” is introduced. It is concluded that the conventional wisdom that hardness is a purely empirical property does not hold. Phase transformations and indentation hardness are connected broadly.
Dislocation Nucleation at a Surface Step by a Multiscale Approach
Authors: Li Chengzhi , Segall Darren , Xu Guanshui 
Published: April 2011

ABSTRACTNucleation of a <111> screw dislocation at a step from a {112} surface of tantalum has been studied by a multiscale approach. The profile of the dislocation, represented by the relative displacement between two adjacent atomic layers along the slip plane, is solved based on the variational boundary integral formulation of the Peierls-Nabarro dislocation model, in which the interatomic potential is incorporated based on atomic calculations of generalized stacking fault energies. The results show that the atomic scale step significantly facilitates dislocation nucleation from the surface. The results from all atom calculations are also presented to corroborate the results obtained by this multiscale approach.
Determination of Plastic Properties of Polycrystalline Metallic Materials by Nanoindentation – Experiments and Finite Element Simulations
Authors: Durst Karsten , Backes Björn , Göken Mathias 
Published: April 2011

ABSTRACTThe determination of plastic properties of metallic materials by nanoindentation requires the analysis of the indentation process and the evaluation methods. Particular effects on the nanoscale, like the indentation size effect or piling up of the material around the indentation, need to be considered. Nanoindentation experiments were performed on conventional grain sized (CG) as well as on ultrafine-grained (UFG) copper and brass. The indentation experiments were complemented with finite element simulations using the monotonic stress-strain curve as input data. All indentation tests were carried out using cube-corner and Berkovich geometry and thus different amount of plastic strain was applied to the material, according to Tabors theory. We find an excellent agreement between simulations and experiments for the UFG materials from which a representative strain of εB ≈ 0.1 and εcc ≈ 0.2 is determined. With these data, the slope of the stress-strain curve is predicted for all materials down to an indentation depth of 800 nm.
Nano-Mechanical Investigation of the Byssal Cuticle, a Protective Coating of a Bio-Elastomer
Authors: Holten-Andersen Niels , Slack Nelle , Zok Frank , Herbert Waite J. 
Published: April 2011

ABSTRACTThe mechanical properties of the mussel byssal thread have been investigated via nano-indentation, with the emphasis on the differences between the cuticle and the fibrous interior. The cuticle hardness was found to be 30–40% higher than that of the underlying fibrous interior. In contrast, the Young's moduli in the two regions were virtually identical to one another. Elemental analysis via energy dispersive spectroscopy indicated surprisingly high levels of Al and Br in the cuticle considering the low amounts found in seawater. A potential role of Al in byssal thread mechanics is discussed in light of the unique capability of the cuticle to accommodate strains of 70% by the underlying fibrils in the core without delamination.
On the Measurement of Creep by Nanoindentation with Continuous Stiffness Techniques
Authors: Rar Andrei , Sohn Sangjoon , Oliver Warren C. , Goldsby David L. , Tullis Terry E. , Pharr George M. 
Published: April 2011

ABSTRACTMeasurement of material creep parameters by means of nanoindentation using continuous stiffness techniques avoids the problems associated with thermal drift that often plague creep measurements based on the time dependence of the indentation depth alone [1, 2]. Problems with thermal drift are negligible from a practical point of view during continuous stiffness measurements because the contact stiffness can be measured over a short time period, typically less than one second, during which time the displacements due to thermal drift are minimal. Determination of the time dependence of the indentation depth from the stiffness data relies on the well-known relation between contact stiffness and the square root of the contact area. For pyramidal indenters, the true indentation contact depth must be proportional to the contact stiffness, leading to the assumption that indentation depth is also proportional to the contact stiffness. In this study, we critically examine this assumption using data obtained from experiments on a relatively soft material, epoxy, and a relatively hard material, fused quartz. The results show that just after initial load application, the change in contact area may be different than that expected from the change in indentation depth. One possible explanation for the observed behavior is examined by finite element modeling.
On the Measurement of Material Creep Parameters by Nanoindentation
Authors: LaManna J. A. , Oliver W. C. , Pharr G. M. 
Published: April 2011

ABSTRACTPrevious studies of how material creep parameters can be measured by nanoindentation testing have focused mostly on measurement of the stress exponent for creep, n, and the activation energy, Qc. However, a more complete characterization requires that the material constant A in the uniaxial creep equation εu =Aσn (where εu is the uniaxial strain rate and σ is the uniaxial stress) also be evaluated. Here, we begin to address this issue by performing simple nanoindentation creep experiments in amorphous selenium at temperatures above and below the glass transition. At 35°C and above, the material exhibits a simple linear viscous creep behavior that is load history independent. This allows the parameter A to be determined from the indentation load-displacement-time data by means of an analytical solution. To examine the validity of the approach, values of the parameter A measured in nanoindentation tests are compared to independent measurements obtained in uniaxial tension creep experiments.
Viscoelastic Characterization of Polymers Using Dynamic Instrumented Indentation
Authors: White C. C. , Drzal P. L. , VanLandingham M. R. 
Published: April 2011

ABSTRACTDynamic nanoindentation was performed on a poly(methyl methacrylate, PMMA), and two different poly(dimethyl siloxane, PDMS) samples having different crosslink densities. Comparison was made between dynamic nanoindentation and rheological instrumentation measurements in the glassy and rubbery plateau regions of polymeric materials. Excellent agreement between bulk rheological data and dynamic nanoindentation data was observed for the two glassy materials and the less compliant of the two PDMS samples. Results were divergent for the more compliant PDMS sample.
Spherical Indentation Creep Following Ramp Loading
Authors: Oyen Michelle L. 
Published: April 2011

ABSTRACTDepth-sensing indentation testing is a common way to characterize the mechanical behavior of stiff, time-independent materials but presents both experimental and analytical challenges for compliant, time-dependent materials. Many of these experimental challenges can be overcome by using a spherical indenter tip with a radius substantially larger than the indentation depth, thus restricting deformation to viscoelastic (and not plastic) modes in glassy polymers and permitting large loads and contact stiffness to be generated in compliant elastomers. Elastic-viscoelastic correspondence was used to generate spherical indenter solutions for a number of indentation testing protocols including creep following loading at a constant rate and a multiple ramp-and-hold protocol to measure creep response at several loads (and depths) within the same test. The ramp-creep solution was recast as a modification to a step-load creep solution with a finite loading rate correction factor that is a dimensionless function of the ratio of experimental ramp time to the material time constant. Creep tests were performed with different loading rates and different peak load levels on glassy and rubbery polymeric materials. Experimental data are fit to the spherical indentation solutions to obtain elastic modulus and time-constants, and good agreement is found between the results and known modulus values. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test the a priori assumption of linear viscoelastic material behavior used in the modeling.
Multiscale Modeling of Two Dimensional Rough Surface Contacts
Authors: Luan Binquan , Hyun Sangil , Robbins Mark O. , Bernstein Noam 
Published: April 2011

ABSTRACTA hybrid simulation method is used to study non-adhesive contact between two-dimensional self-affine rough surfaces. We find strong scale dependence as the contact dimensions decrease to the atomic scale. Both purely elastic and plastic materials are considered, and show different trends with system size. In all cases the contact area rises linearly with applied load, but the slope is substantially different from continuum predictions. We also examine the effect of commensurability between contacting surfaces. Contact area and frictional forces can be very different for commensurate and incommensurate surfaces, particularly for plastic materials.
Friction and Wear Properties of ALD Coated MEMS
Authors: Nistorica Corina , Gory Igor , Skidmore George D. , Mantiziba Fadziso M. , Gnade Bruce E. 
Published: April 2011

ABSTRACTA comparative study of the microtribological properties of native oxide covered single crystal silicon and silicon coated with atomic layer deposited (ALD) alumina films is presented. The dry friction and wear behavior were investigated using a novel microelectromechanical system (MEMS) tribotester. The coefficient of friction for alumina coated surfaces and for silicon uncoated surfaces was monitored before and after wear. The friction versus normal load curves of uncoated silicon can be described by a Johnson-Kendall-Roberts model with pressure dependent shear strength while for the alumina coated surfaces, a linear dependence between the friction force and the normal load was found. Both uncoated silicon surfaces and alumina coated surfaces showed a decrease of the friction force with the number of sliding cycles.
Aspects of Tip Shape Characterization for Nanoindentation of Compliant Materials
Authors: VanLandingham Mark R. , Juliano Thomas F. , Hagon Matthew J. 
Published: April 2011

ABSTRACTThe application of nanoindentation methods to compliant materials, such as polymeric and biological materials, often requires the use of instrumentation designed with enhanced force sensitivity, which limits its maximum force level. Because tip geometry is normally characterized using indentation of fused silica, the maximum contact depths achieved by low-force instruments during this calibration are often less than 300 nm. However, penetration into more compliant materials can be several micrometers or more. Extrapolation of tip shape data from fused silica indentation can lead to significant uncertainties in the indentation measurements for compliant materials. In this paper, atomic force microscopy (AFM) is used to provide tip shape information for a Berkovich tip and a series of conical tips. Use of AFM allows a larger range of depth to be calibrated and provides three-dimensional tip information.
A critical examination of the Berkovich vs. conical indentation based on 3D finite element calculation
Authors: Shim Sanghoon , Oliver Warren C. , Pharr George M. 
Published: April 2011

ABSTRACTMuch of our understanding of the elastic-plastic contact mechanics needed to interpret nanoindentation data comes from two-dimensional, axisymmetric finite element simulations of conical indentation. In many instances, conical results adequately describe real experimental results obtained with the Berkovich triangular pyramidal indenter, particularly if the angle of the cone is chosen to give the same area-to-depth ratio as the pyramid. For example, conical finite element simulations with a cone angle of 70.3° have been found to accurately simulate experimental load-displacement curves obtained with the Berkovich indenter. There are instances, however, where conical simulations fail to capture important behavior. Here, 3D finite element simulations of Berkovich indentation of fused silica are compared to similar simulations with a 70.3° cone. It is shown that a potentially significant difference between the two indenters exists for the contact areas and contact stiffnesses. Implications for the interpretation of nanoindentation data are discussed.
Quantitative Analysis of γ Precipitates in Cyclically Deformed Ni3(Al, Ti) Single Crystals Using Magnetic Technique
Authors: Umakoshi Yukichi , Yasuda Hiroyuki Y. , Yanai Toshifumi 
Published: April 2011

ABSTBACTNi-18at.%Al-4at.%Ti single crystals containing small γ precipitates in γ′ matrix were prepared by aging at 1073K after solution treatment from γ′ single phase region. The size, shape and volume fraction of the γ precipitates were examined during aging and deformation by means of changes in spontaneous magnetization and coercive force. Cyclic deformation behavior of these crystals was discussed through change in the morphology of γ precipitates using magnetic technique.
Transformation Behavior of TiNiPt Thin Films Fabricated Using Melt Spinning Technique
Authors: Inamura Tomonari , Takahashi Yohei , Hosoda Hideki , Wakashima Kenji , Nagase Takeshi , Nakano Takayoshi , Umakoshi Yukichi , Miyazaki Shuichi 
Published: April 2011

ABSTRACTMartensitic transformation behavior of Ti50Ni40Pt10 (TiNiPt) melt-spun ribbons were investigated where the heat treatment temperature was systematically changed from 473K to 773K. A hot-forged bulk TiNiPt material with the similar chemical composition was also tested as a comparison. θ-2θ X-ray diffraction analysis and transmission electron microscopy observation revealed that the as-spun ribbons were fully crystallized. The apparent phases of as-spun ribbons at room temperature are both B19 martensite and B2 parent phase instead of B2 single phase for the hot-forged bulk material. No precipitates were found in as-spun and heat-treated ribbons. It was revealed by differential scanning calorimetry that all the specimens exhibit one-step transformation. The martensitic transformation temperatures of the TiNiPt as-spun ribbons are 100K higher than those of the hot-forged bulk material, and the martensitic transformation temperature decreases with increasing heat treatment temperature.
Sub-nano and Nano-structures of Hydrides of LaNi5and its related Intermetallics
Authors: Akiba Etsuo , Sakaki Kouji , Nakanura Yumiko 
Published: April 2011

ABSTRACTSub-nano and nano-structures of intermetallics such as LaNi5and its related alloys were studied by in-situ X-ray and neutron diffraction methods. From the profile shape analysis, changes in lattice strain and crystalline size during hydrogenation/dehydrogenation were estimated, while the crystal (sub-nano) structures were refined by the Rietveld method using diffraction patterns. The crystallite size of the alloys studied did not change during hydrogenation and dehydrogenation. It was found formation of remarkably dense dislocations and vacancies in the lattice of hydrides of LaNi5and related intermetallics.
Atomic, Electronic, and Magnetic Structure of Iron-Based Sigma-Phases
Authors: Korzhavyi Pavel A. , Sundman Bo , Selleby Malin , Johansson Börje 
Published: April 2011

ABSTRACTA combination of ab initio total energy calculations with Calphad approach is applied to model the site occupancy and thermodynamic properties of the Fe-Cr, Co-Cr, Fe-V, and Fe-Mo binary sigma-phases as a function of composition and temperature. For each binary sigma-phase the parameters of the model are the ab initio calculated total energies of so-called end-member compounds, which represent all the 25=32 variants of complete occupancy of each of the five crystallographically inequivalent sites by one or the other alloy component. The paramagnetic state of the sigma-phases has been taken into account within the disordered local moment approach. The Fe and Co atoms are found to retain high spin moments when they occupy high-coordination-number sites in the structure. Using our model we were able to reproduce the experimentally observed site occupancy in the FeCr sigma-phase. The calculated site occupancies in the Co-Cr, Fe-V, and Fe-Mo sigma-phases are also presented and discussed.
Characterization and Catalytic Properties of Ni3Al for Hydrogen Production from Methanol
Authors: Xu Ya , Kameoka Satoshi , Kishida Kyosuke , Demura Masahiko , Tsai An-pang , Hirano Toshiyuki 
Published: April 2011

ABSTRACTThe stability of catalytic activity and selectivity of Ni3Al for methanol decomposition were studied by life test at 633 K on the alkali-leached powder samples. The characterization of the samples was carried out by X-ray diffraction, inductively coupled plasma (ICP) analysis, SEM observation, and surface area measurement. The life test showed that the alkali-leached Ni3Al exhibits a very stable activity and a high selectivity for methanol decomposition. The surface characterization after reaction suggests that the high selectivity and stable activity may be attributed to the formation of tiny particles and porous structure which increased the surface area significantly during reaction. These results indicate a possibility of Ni3Al as a catalyst for hydrogen production reaction.
Thermomechanical Treatment of a Fe3Al alloy
Authors: Konrad Joachim , Zaefferer Stefan , Schneider André , Frommeyer Georg , Raabe Dierk 
Published: April 2011

ABSTRACTA binary Fe3Al alloy is investigated with respect to hot and warm rolling behavior and microstructural as well as microtextural modifications. Rolling has been performed in the A2 and B2 order regimes. The differences in microstructure are investigated. The performed texture analysis reveals the differences in hot and warm rolling textures depending on the hot rolling temperature. On the basis of microtexture investigations by means of electron backscatter diffraction (EBSD) differences concerning orientation gradients and sub-grain structures are found. A model of combined order-related and non-order related effects is proposed explaining the observed material behavior. The results are used for process modification.
Ab initio calculation of point defect energies and atom migration profiles in varying surroundings in L12-ordered intermetallic compounds
Authors: Vogtenhuber Doris , Houserova Jana , Wolf Walter , Podloucky Raimund , Pfeiler Wolfgang , Püschl Wolfgang 
Published: April 2011

ABSTRACTFormation energies of antisite defects and vacancies were derived for the L12-ordered intermetallics Ni3Al, Ni3Ga, Pt3Ga, and Pt3In by a supercell ab initio approach. A thermodynamic treatment of point-like defects was then used for the calculation of temperature-dependent defect properties. Energy profiles for atom jumps in Ni3Al in systematically varied atomic neighborhoods were calculated by statically displacing the jumping atom or by using a nudged elastic band method. It is discussed how a kinetic Monte-Carlo model can be modified so that the jump barrier height reflects the strongest neighborhood influences.