bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Ductility of Stoichiometric and Ni-Rich Polycrystals of Ni3Al: The Effect of Strain Rate
Authors: Schulson E. M. , Xu Y. 
Published: April 2011

ABSTRACTPolycrystals of stoichiometric Ni3Ai are brittle in air at room temperature, at least at strain rates from 10-4 s-1 to 7 s-1. This is indicative of intrinsic brittle behavior. Nickel-rich (Ni24A1) polycrystals, on the other hand, undergo a brittle-to-ductile transition upon raising the strain rate to above about 10-2 s-1. It is argued that the transition reflects the suppression of environmental embrittlement, not of the intermetallic per se but of a Ni-rich solid solution that decorates the grain boundaries of the off-stoichiometric alloy.
Orientation Dependence of High Temperature Creep Strength and Internal Stress in Ni3Al Alloy Single Crystals
Authors: Miura Seiji , Peng Zhi-Lun , Mishima Yoshinao 
Published: April 2011

ABSTRACTHigh temperature creep behavior of a nickel-rich Ni3(Al,Ta) with the L12 structure is investigated in order to clarify the influence of crystallographic orientation with respect to the stress axis. The single crystals with four different orientations are deformed in compressive creep at temperatures ranging from ‘M 23 to 1273 K under a constant load, initial shear stress being 35 to 120 MPa for (111)[101] slip system. The results show a distinct orientation dependence of creep strength, although shape of creep curves, stress exponent and the activation energy seem to be independent of the orientation. It is shown, however, the internal stress, being measured by strain transient dip tests, is found to be orientation dependent and the creep behavior is independent on orientation if it is interpreted using the effective stress instead of the applied shear stress.
Lattice Defects Affecting Moisture-Induced Embrittlement of Ni-based L12 Ordered Intermetallics
Authors: Takasugi T. , Hanada S. 
Published: April 2011

ABSTRACTMoisture-induced embrittlement of Ll2 alloys (such as Ni3(Si,Ti) and Ni3AI) is observed by tensile test and SEM fractography. A variety of microstructures were prepared by selecting pre-deformation and heat treatment conditions. It is shown that tensile ductility and the associated fractography depend on structure as well as test atmosphere. Well-annealed specimens are susceptible to moisture-induced embrittlement while pre-deformed specimens are resistive to moisture-induced embrittlement. Also, this embrittlement is generally sensitive to the heat treatment scheme preceded by the pre-deformation. Results indicate that the embrittlement occurs when hydrogen is enriched on grain boundaries. On the other hand, the embrittlement can be suppressed when hydrogen is trapped at lattice defects such as dislocations and vacancies. These results are discussed in association with the kinetics of hydrogen in the pre-deformed microstructure.
Effect of Microstructure on the Properties of MoSi2 and its Composites
Authors: Newman A. , Jewett T. , Sampath S. , Herman H. 
Published: April 2011

ABSTRACTThe effects of processing on the microstructure and properties of MoSi2 are examined. A diverse array of samples, processed through a variety of means, were investigated for their microstructural features and indentation fracture behavior. Results from this study indicate that a finely dispersed secondary phase enhances tortuous crack paths, crack branching, and microcracking, thereby improving fracture toughness. The effects of substitutional alloying (Re, Al) and composite additions (SiC) have also been investigated.
Comparison of NbCr2 and HfV2 C15 Laves Phases
Authors: Thoma D. J. , Chu F. , Wills J. M. , Mitchell T. E. 
Published: April 2011

ABSTRACTThe elastic properties, phase stability, and alloying behavior of NbCr2 and HfV2 C15 Laves phases have been investigated with a combined experimental and theoretical approach. Experimental results indicate that HfV2 has anomalous elastic properties as well as a structural instability, but NbCr2 does not. In addition, ternary phase fields of NbCr2 with V and HfV2 with Nb were examined experimentally, and they have substantially different alloying behavior. In order to understand these experimental phenomena, the total energy and electronic structure of C15 NbCr2 and HfV2 were calculated using the linear muffin-tin orbital method with the atomic sphere approximation. Calculation results suggest that the phase instability of HfV2 is induced by phonon softening, and the anomalous elastic properties of HfV2 appear to be attributed to a doubly degenerate electronic energy level with a linear dispersion relation very close to the Fermi level. Finally, density of states plots indicate that for HfV2, some bonding d-states are unoccupied while for NbCr2, all bonding and some anti-bonding d-states are occupied. The bonding difference may be responsible for the alloying behavior in the two Laves phase alloys. As a result, alloy design schemes are suggested for enhanced deformability in Laves phases.
Ti-Modified Niobium-Silicide Based Directionally Solidified in-situ Composites
Authors: Bewlay B. P. , Jackson M. R. , Lipsitt H. A. 
Published: April 2011

ABSTRACTThis paper examines microstructure-property relationships in high-temperature directionally solidified (DS) in-situ composites based on Nb silicides, such as Nb3Si and Nb5Si3. These in-situ composites are based on the Nb3Si-Nb binary eutectic, and are alloyed with Ti. They were prepared using cold crucible Czochralski crystal growth. Ternary Nb-Ti-Si alloys with Ti concentrations from 9 to 45%, and Si concentrations from 10 to 25%, were directionally solidified to generate aligned two- and three-phase composites containing a Nb solid solution with Nb3Si and Nb5Si3 silicides. Fracture toughness values generally greater than 10 MPa√m were measured in these composites. For a given Si concentration, the fracture toughness of the Ti-containing composites was increased ∼ 6 MPa√m over that of the binary alloy composites. The effects of Si concentration, and a range of Nb:Ti ratios, on microstructure, phase equilibria, and fracture toughness were examined.
Determining the Morphology and the Interaction Between Terminally-Anchored Polymer Layers
Authors: Balazs A. C. , Singh C. 
Published: April 2011

ABSTRACTUsing a two dimensional self-consistent field theory, we investigate the interactions between two planar surfaces that are coated with terminally-anchored homopolymers. One surface is coated with A chains and the other is covered with B homopolymers. The chains are grafted at low densities and the B polymers are chosen to be solvophobic, while the A chains are relatively solvophilic. We determine the morphology of the layers and the energy of interaction asthe surfaces are compressed. Our results provide guidelines for controlling the interaction between polymer-coated colloidal particles.
The Effect of Chemical Functionality on Adhesion Hysteresis: A Study using the JKR Method
Authors: Kim Soojin , Young Choi Gun , Nezaj Jeff , Ulman Abraham , Fleischer Cathy 
Published: April 2011

ABSTRACTThe adhesion of crosslinked PDMS surfaces to self-assembled monolayers with different chemical functionality was investigated using the JKR method, the contact mechanics of solids spreading their interfacial area under load. Interfacial H-bonding was shown to be an important chemical interaction causing significant adhesion hysteresis. The number of H-bonds between PDMS and silanol groups on SiO2/Si surfaces increased with time of the contact under a constant load, indicating pressure-induced reorganization of the PDMS network near the interface. The interaction between PDMS and carboxylic acid groups showed somewhat smaller hysteresis which suggests weaker H-bonding strength. The interaction between PDMS and functionalized biphenyl groups exhibited small hysteresis which is believed to be caused by dipolar interaction. whereas that between PDMS and nonpolar perfluorocarbon groups showed negligible hysteresis. The distinction in the behavior of the unloading data between H-bonding related interaction and dipolar interaction seems to indicate the difference in the nature between non-specific (van der Waals, dipolar) and specific (donor-acceptor, H-bond, acid-base) interactions.
Phase Separation Kinetics During Drying
Authors: Saraf R. F. , Ostrander S. , Feenstra R. M. 
Published: April 2011

AbstractKinetics of phase separation at air/polymer interface in a binary polymer mixture on evaporation of common solvent is studied. The lateral dimension of the highly anisotropie, pancake-like, minority phase increases with a growth exponent of 2/3 identical to ‘late-stage’ growth under (classical) thermal-quench at interface. In contrast to the thermal-quench, during drying the kinetics depends on the initial condition (i.e., initial concentration, Co) that is rescaled to obtain a master-curve.
Ancient Medical Instruments: An Overview and Case Study
Authors: Notis M. R. , Jakielski K. E. 
Published: April 2011

ABSTRACTAn overview of the development of the materials used for surgical knives is presented. Because early surgical tools are hard to recognize in terms of specific function, unless they are found in context they are difficult to identify. A rare exception is the collection of Roman surgical implements found in Pompeii. In order to demonstrate the level of technology typical ofthat time, metallographic study has been performed on an object identified as a Roman surgical probe similar to those found in Pompeii. The composition, microstructure, and fabrication technology for this object is discussed in relation to its functional use.
The Design of a Monitoring Program for Iron Alloys on Underwater Historic Shipwrecks in Fathom Five National Marine Park, Ontario, Canada
Authors: Stewart John , Murdock Lome D. , Binnie Nancy 
Published: April 2011

ABSTRACTIn order to design a scheme to monitor the state of preservation of iron alloys that are found on historic shipwrecks sunk in fresh water, it was first necessary to identify the predominant form of corrosion found on the wrecks. This was done by visual observation, in situ surface pH measurements, and X-ray powder diffraction of the corrosion layers. Once the form of corrosion was identified as pitting corrosion, a monitoring scheme based on photographic recording of the rust-red tubercles was designed. This scheme is simple and nondestructive, both necessary characteristics for the monitoring of submerged historic resources.
Examination of Silk Fibers from a Deep Ocean Site: SEM, EDS, & DSC
Authors: Srjnivasan R. , Jakes K. A. 
Published: April 2011

ABSTRACTThe research reported herein is directed toward the determination of the microstructure of silk fibers recovered from the shipwreck site of the S.S. Central America. The structural data obtained from examination of these silk materials using SEM, EDS, and DSC was compared to data obtained from the examination of historic silk fibers (ca. 1860–1880) not exposed to the deep-ocean and of modern silk fibers. Marine silks appear more degraded than historic and modern silk when viewed under the SEM and the fiber surfaces are partially obscured by inorganic deposits. The melting endotherm of marine, historic, and modern silk fibers are comparable to each other, but the glass transition observed in the modern silk is not apparent in the DSC trace of any of the marine silks.
Fracture Surface Topography of Energetic Materials using Atomic Force Microscopy
Authors: Lanzerotti M. Y. D. , Meisel L. V. , Johnson M. A. , Wolfe A. , Thomson D. J. 
Published: April 2011

ABSTRACTHeight profiles spaced 0.008 μm apart across the fracture surface of TNT melt-cast in polycarbonate sleeves have been obtained with an atomic force microscope (AFM). Spatial power spectra (wavelengths of 0.016 μm to 4.0 μm) have been calculated using both a prolate spheroidal data window and a Kaiser window in the horizontal space domain prior to using a fast Fourier transform algorithm. Results based on topographical profiles across the surface include the following. The power spectral density of the individual fracture surface profiles is found to decrease with increasing spatial frequency over the dimensional region examined, ≈ 1.0 μm−1 to ≈ 10.0 μm−1. The spectral amplitudes are found to have a frequency dependence proportional to f s. The determined values of s in the dimensional region 1–10 μm−1 scatter in the range -1 < s < -4. Those values of s outside the range -3 < s < -2 indicate non-fractal fracture. There is significant structure in the spectra even for those with slopes within the range of a fractal dependence. Both observations are consistent with the appearance of numerous peaks in the spectra that indicate that a substantial amount of the fracture occurs at grain boundaries in the form of large clusters of TNT. Such a fracture process is deterministic.
Atomic Structure of Interfaces in Mazed Au Bicrystals
Authors: Hetherington C.J.D. , Dahmen U. , Penisson J-M. 
Published: April 2011

ABSTRACTThin films of {111} Au have been grown on {111} Ge substrates. The film grows epitaxially in two crystallographically equivalent orientations, (111) and (111). After annealing, the film is removed from the substrate and the resulting bicrystal appears as a maze of domains with faceted boundaries mainly of type {112}. The high density of edge-on interfaces in the films makes them well suited to electron microscopy. In the <111> orientation, the 1.44Å spacing of the {220} lattice planes tests the high resolution capabilities of the latest microscopes.The nature of the Au {111} film contrasts with that of films grown using different materials or different substrates and was found to have a three-dimensional character with the occurrence of extensive twinning on (111) in the plane of the film. Areas were found to thin considerably in the high voltage electron microscope and interfaces in these regions were analyzed and rigid body translations across the facets measured. The existence of distinct rigid body translations across neighboring facets is of particular interest.
Read-Shockley Boundaries in Thin Films
Authors: King Alexander H. 
Published: April 2011

ABSTRACTWhen a grain boundary is terminated by a free surface, its behavior may be significantly different than for the same boundary either in an infinite bicrystal, or terminated by triple junctions. In this paper we describe some phenomena related to the free-surface interactions of interfacial dislocations, in thin films. We show that surface relaxation stresses can exert a powerful destabilizing influence upon the dislocation structure of many grain boundaries, and that they can only be made stable if a large lattice friction stress, or other pinning force, resists the motion of the dislocations. Finally, we will show that the only intrinsically stable grain boundary in a thin film is a tilt boundary with its rotation axis parallel to the normal of the film.
Structure and Chemistry of Ti Overlayers on α-Αl2O3(0001)
Authors: Bernath S. , Wagner T. , Hofmann S. , Rühle M. 
Published: April 2011

ABSTRACTTi thin films were grown by molecular-beam epitaxy (MBE) on α-Al2O3(0001) substrates. During room temperature deposition, in the very initial growth stage, AES investigations revealed a chemical reaction between the Ti and the α-Al2O3substrate. An analysis of the AES data based on simple assumptions showed that ∼ 2 monolayers of Ti are oxidized. However, HRTEM analysis indicated an atomically smooth, incoherent interface, without a reaction layer. Reflection high-energy electron diffraction (RHEED) analysis revealed an epitaxial orientation relationship (0001)<2110> Ti ∥ (0001)<1010>Al2O3between Ti and α-Al2O3(0001).
Collective Modes Of Misfit Dislocations in Lattice - Mismatched Thin Films
Authors: Hovakimian L. B. , Tanaka Shun-Ichiro 
Published: April 2011

ABSTRACTWe study the nature and spectrum of fundamental vibrational excitations in the assembly of misfit accomodating dislocations. The physical system considered is a Lomer array of equispaced dislocations in a lattice-mismatched interface between a substrate and a thin film with similar elastic properties. Within the framework of the isotropie elasticity theory we calculate the effective force constants of harmonic springs that establish the dynamical correlations between the oscillating dislocations. Our interest is concentrated on the case where the thickness of the overlay er is much less than the separation between the nearest-neighbor dislocations. We show how in this situation the free surface of the film exerts a profound screening influence on the dislocation-dislocation correlations; it is demonstrated that the force constants exhibit sensitive dependence not only on the lattice mismatch, but also on the film thickness. We then deduce the dispersion of collective dislocation excitations and find that the latter propagate along the interface much more slowly than the ordinary sound waves. Our results reveal the manner in which the thickness of the film controls the magnitude of the vibrational quantum that characterizes the natural oscillations of arrayed dislocations. It is shown that this anomalous energy quantum manifests itself in the low-temperature heat capacity of the misfit array.
A Thermodynamic Model for Solid State Amorphization: Application to Ni-Ti Multilayers of Different Microstructures
Authors: Böttger A. , Benedictas R. , Mittemeijer E.J. 
Published: April 2011

ABSTRACTOn the basis of an assessment of both the phase-formation energies and the energies of interfaces and grain boundaries the driving force for solid state amorphization (SSA) in crystalline Ni- crystalline Ti and amorphous Ni- crystalline Ti multilayers was calculated. It followed that the structure of the interfaces and grain boundaries, and thus their energies is of crucial importance for the occurrence (or not) of SSA. The SSA behaviour of the two types of Ni-Ti multilayers upon annealing was investigated using X-ray diffraction and (high resolution) transmission electron microscopy. The crystalline Ni- crystalline Ti multilayers showed SSA at both the Ni-Ti interfaces and the Ti grain boundaries. The amorphous Ni- crystalline Ti multilayers exhibited SSA at the Ti grain boundaries only. These observations agree with the predictions from the thermodynamic model.
Ab Initio Electronic Structure Calculations of the Σ 5 (210) [001] Tilt Grain Boundary in Ni3Al
Authors: Lu Gang , Kioussis Nicholas 
Published: April 2011

ABSTRACTThe atomic and the electronic structure of the Σ 5 (210) [001] tilt grain boundary in Ni3Al have been calculated using the full potential linearized-augmented plane-wave method. The strain field normal to the boundary plane and the excess grain boundary volume are calculated and compared with the results obtained using the embedded-atom method (EAM). The interlayer strain normal to the grain boundary oscillates with increasing distance from the grain boundary. The bonding charge distributions suggest that bonding in the boundary region is significantly different from that in the bulk. The grain boundary energy and the Griffith cohesive energy are calculated and compared with the EAM results.
Stress in Ag/Ni Multilayers: A Comparison of Specimen-Curvature and X-Ray Diffraction Methods
Authors: Gergaud P. , Labat S. , Yang H. , Bottger A. , SandstrÖm P. , Svedberg Erik , Mittemeijer E.J. , Sundgren J.E. , Thomas O. 
Published: April 2011

ABSTRACTMultilayers and superlattices are of great industrial interest because of their specific properties (magnetic, electronic, tribological…). Multilayers stacking are often in a very high state of intrinsic stress (some GPa) and for reliable integrated devices to be made it is capital to control and understand these intrinsic as well as extrinsic stresses. The objective of the present work is therefore the understanding of the origin of stresses and strains in multilayered metallic materials. Of course, a comparison of the different techniques which can be used for stress determination is a necessary first step of this study. In this aim, we have studied Ag/Ni multilayers, Ag and Ni thin films and Ag/Ni bilayers obtained by sputtering. The stresses have been determined via curvature measurement using both a laser scanning method and X-ray diffraction rocking curves technique, and via X-ray diffraction measurement of several d-spacings which act as in-situ strain gauges (also called the sin2ψ method and related methods). The obtained results from these different techniques are discussed in terms of accuracy, reproducibility and advantages / drawbacks. The obtained stresses from these methods cannot be directly compared and a specific discussion is developed around the relation between the measured strains and stresses and the microstructure of the materials.
Compositional Effects on the Degradation of PVD-Tisin
Authors: McArthur W.F. , Deng F. , Ring K. , Pattison P.M. , Kavanagh K.L. 
Published: April 2011

ABSTRACTPVD-TixSiyNzfilms formed by reactive RF-magnetron co-sputtering of Ti and Si in Ar/N2are evaluated as a diffusion barrier between Cu and Si. A complete range of compositions are obtained by Ti targets inlaid with Si. Film composition is controlled by the target ratio of titanium to silicon and N2partial pressure. Electrical results versus thermal history for films of∼6–18% Si as well as the composition and microstructure as determined by Rutherford back scattering (RBS), TEM and electron diffraction are reported. These films are an amorphous matrix with imbedded nanocrystals of titanium nitride as-deposited and undergo phase separation to yield titanium nitride and silicon nitride after a 1000°C anneal. As-deposited compositions which lie above the TiN-Si3N4phase line yield crystals of TiN. Compositions below the TiN-Si3N4phase line yield crystals of Ti2N. Bulk resistivity as-deposited (<400μΩ2-cm) is acceptable for use as a contact liner/berrier material and improves with annealing. Si pn-diodes metallized with 20nm Ti40Si15N45 and Cu show no significant increase in reverse leakage current at anneal temperatures below 700°C.
Effects of Nitrogen on Preventing the Crystallization of Amorphous Ta-Si-N Diffusion Barrier
Authors: Kim Dong Joon , Jeong Soon Pil , Kim Yong Tae , Park Jong-Wan 
Published: April 2011

ABSTRACTAmorphous Ta-Si-N thin film was deposited by dc sputterring of Ta5Si3 target in (Ar+N2) atmosphere. The crystal structure and the thermal stability of Ta-Si-N thin films were investigated by XRD, RBS, AES, Nomarski microscope, and TEM. When the concentration of nitrogen in Ta-Si-N thin film was higher than 40 at.%, the Ta-Si-N thin film remained the amorphous state after the annealing at 1100°C for 60 min. In this case, the Cu diffusion was prevented by the amorphous Ta-Si-N thin film even if the annealing temperature increased up to 900°C for 30 min. Whereas, the Ta-Si-N thin film with nitrogen concentration less than 40 at. % was transformed from the amorphous to the polycrystalline TaSi2 phases after the annealing at 900°C for 60 min and failed to prevent the Cu diffusion after the annealing at 700°C for 30 min.