bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Microstructure and Tensile Properties of Extruded Melt-Spun Ribbons of Iron-Rich B2 FeAl
Authors: Baker I. , Gaydosh D.J. 
Published: March 2011

AbstractThe microstructure of extruded rods of iron-rich FeAl (B2-structure), as characterized by TEM, SEM, optical microscopy and x-ray diffractometry, consisted of elongated grains with a <111> fibre texture containing a high dislocation density. Numerous oxide particles were found, mostly in lines which reflected the matrix flow during extrusion. In addition, some large inclusions were present. Tensile testing of annealed, relatively dislocation-free specimens as a function of increasing temperature found increasing ductility up to 900K, above which a ductility drop occurred accompanied by a change in fracture mode, from transgranular cleavage to intergranular fracture. The yield strength, which was independent of temperature up to 800K (at ∼500MPa), also decreased rapidly as diffusion became more important. The predominant slip vector changed from <111> to <100> around 700K
High Temperature Strength of Ordered and Disordered Ni4Mo
Authors: Kao H. P. , Brooks C. R. , Vasudevan K. 
Published: March 2011

AbstractThe alloy Ni−20 at. % Mo is FCC and disordered at high temperatures, but below 868°C forms a superlattice of the D1a type. The disordered structure can be retained by quenching, and subsequent aging below 868°C can develop a variety of ordered domain structures. In the disordered condition, the yield stength at 25°C is typically 140– The tensile properties were measured for two ordered domain sizes: 24 nm and 3,000 nm. For the 24 nm domain size, the yield strength at 25°C was 862 MPa (125,000 psi). This decreased with increasing test temperature to about 690 MPa (100,000 psi) at 800°C, then decreased greatly to about 210 MPa (30,000 psi) at 1000°C. In the ordered condition, the alloy had a very low ductility (1% elongation or less) from 25°C to the disordering temperature of 868°C, above which it increased considerably (e.g., 30% elongation). The alloy with the 3,000 nm domain size showed similar behavior, although the strength was less. (The ordered alloy with 24 nm domain size had a yield strength-temperature curve similar to that of Waspaloy.) These results are correlated with fractography of the tensile samples.
Grain Boundary Chemistry and Ductility in Ni-Base LI2 Intermetallic Compounds
Authors: Taub A. I. , Briant C. L. 
Published: March 2011

AbstractThe available experimental data for the Ni3X, LI2 intermetallics indicate a strong effect of chemistry on the tendency for brittle intergranular fracture. Combining the data for the binary compounds with the effects of macroalloying with × substituents and microalloying with boron, the resistance to intergranular fracture varies as Fe ~ Mn > Al ~ Ga > Si > Ge. Two models have been proposed to explain these chemistry effects. The basis for both models is that electronic charge localization is responsible for the brittle behavior of the ordered intermetallics. The models differ in the measure of charge redistribution; one uses valency differences whereas the other uses electronegativity differences.
Ductility and Fracture Behavior of Polycrystalline Ni3Al Alloys
Authors: Liu C. T. 
Published: March 2011

AbstractThis paper provides a comprehensive review of the recent work on tensile ductility and fracture behavior of Ni3AI alloys tested at ambient and elevated temperatures. Polycrystalline Ni3Al is intrinsically brittle along grain boundaries, and the brittleness has been attributed to the large difference in valency, electronegativity, and atom size between nickel and aluminum atoms. Alloying with B, Mn, Fe, and Be significantly increases the ductility and reduces the propensity for intergranular fracture in Ni3Al alloys. Boron is found to be most effective in improving room-temperature ductility of Ni3Al with <24.5 at. % Al.The tensile ductility of Ni3Al alloys depends strongly on test environments at elevated temperatures, with much lower ductilities observed in air than in vacuum. The loss in ductility is accompanied by a change in fracture mode from transgranular to intergranular. This embrittlement is due to a dynamic effect involving simultaneously high localized stress, elevated temperature, and gaseous oxygen. The embrittlement can be alleviated by control of grain shape or alloying with chromium additions. All the results are discussed in terms of localized stress concentration and grain-boundary cohesive strength.
A Review of Recent Developments in Iron Aluminides
Authors: Mendiratta Madan G. , Ehlers Sandra K. , Dimiduk Dennis M. , Kerr William R. , Mazdiyasni Siamack , Lipsitt Harry A. 
Published: March 2011

AbstractThis paper presents a review of recent research conducted at the Air Force Wright Aeronautical Laboratories (AFWAL)/Materials Laboratory to develop iron-aluminides as elevated temperature structural materials. The research consisted of investigations on the microstructure, tensile behavior, deformation, and fracture mechanisms of the DO3 and B2 ironaluminides. Binary Fe-Al alloys with a wide range of Al contents, solidsolution ternary alloys and precipitation- and dispersion-strengthened two-phase alloys have been investigated. It is shown that iron-aluminides have a potential to be structural materials at least up to 650°C.
Atomistic Simulations of [001] Symmetric Tilt Boundaries in Ni3Al
Authors: Chen S. P. , Voter A. F. , Srolovitz D. J. 
Published: March 2011

AbstractWe report a systematic atomistic simulation study of [001] symmetric tilt grain boundaries (GB) in Ni3Al, Ni, and Al. We found that the grain boundary energies and cohesive energies of Ni3Al and pure fcc Ni are approximately thesame. Grain boundary energies aid cohesive energies in Ni3Al depends stronglyon the grain boundary composition. The Al-rich boundaries have highest grain boundary energies and lowest cohesive energies. This offers an explanation for the stoichiometric effect on the boron ductilization
Kinetics of Oxidation of Ni Aluminide Exposed to Oxygen-Sulfur Atmospheres
Authors: Natesan K. 
Published: March 2011

AbstractAs part of a development effort on nickel aluminides based on Ni3Al as structural materials for fossil energy applications, oxidation/sulfidation studies are being conducted at Argonne National Laboratory on materials that are being developed at Oak Ridge National Laboratory. Sheet samples of nickel aluminide, containing 23.5 at, % Al, 0.5 at. % Hf, and 0.2 at. % B were tested in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made at 875°C by a thermogravimetric technique in exposure atmospheres of air, a low-p02 gas mixture, and low-p02 gas mixtures with several levels of sulfur. getailed analyses of the corhosion product scale layers were conducted using a scanning electron microscope equipped with an energy dispersive x-ray analyzer and an electron microprobe. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low-p02 environment developed an aluminum oxide scale. As the sulfur content of the gas mixture increased, the alumina scale exhibited spallation and the alloy tended to form nickel sulfide as the reaction phase. The results indicated that the sulfidation reaction in nickel aluminide specimens (both bare and preoxidized) was determined by the rate of transport of nickel from the substrate through the scale to the gas/alumina scale interface, mechanical integrity of the scale, and the H2S concentration in the exposure environment.
Temperature and Orientation Dependence of Surface Film Effects in Single Crystal Nial
Authors: Noebe R.D. , Kim J.T. , Gibala R. 
Published: March 2011

AbstractDuring deformation of bcc metals and bcc-based ordered alloys, conditions of elastic and plastic constraint associated with the presence of thin adherent surface films can be responsible for introducing increased densities of mobile dislocations in the metal, resulting in enhanced ductility and reduced yield and flow stresses of the film-coated materials. In the present paper, surface film effects were investigated as a function of temperature and crystallographic orientation for single crystal β-NiAl. Appreciable temperature-dependent and orientation-dependent surface film effects were observed, as were significant effects of film adherence on the observation of surface film softening.
Dislocation Reactions at Grain Boundaries in Li2Ordered Alloys
Authors: King A.H. , Yoo M.H. 
Published: March 2011

AbstractThe characteristics of perfect grain boundary dislocations in ordered alloys are discussed, and consideration is given to the possible formation of perfect and imperfect grain boundary dislocations by the impingement of crystal lattice dislocations. It is shown that many dislocation reactions at grain boundaries in ordered alloys are made unfavorableif chemical co—ordination must be maintained in the structure of the grain boundary. This leads to a suggestion that the effect of boron in the grain boundaries of Ni3AI is to reduce the importance of chemical ordering, and thus to promote deformation by allowing greater freedom for dislocation reactions to occur.
Observation of Damage Structures in Proton-Implanted Gallium Arsenide by Cross-Sectional Tem
Authors: Loretto D , Brown G. T. , Jones I. P. 
Published: March 2011

ABSTRACTSemi-insulating and SI-doped <100> GaAs have been irradiated to a dose of 1016 protons cm−2. Samples have been annealed for 20 minutes at 400,500 and 600°C. Cross-sectional TEN has shown the as-implanted and 400°C annealed GaAs to contain no visible damage. After 500 and 600°C anneals a heterogeneous distribution of planar raft-like defects apears on {(11} and {110}. The density of these defects is much lower in the Si-doped material.
A Model for the Application of Dlts on Normally-on Hemt Structures
Authors: Huang Y. J. , Ioannou D. E. 
Published: March 2011

ABSTRACTThis paper presents an analytical model for the application of capacitance DLTS on the normally-on HEMT structure. Based on the charge conservation law, the DLTS signal is derived by taking into account both the Schottky gate and the heterojunction depletion layer capacitances. It is shown that the anomalous features observed by using the conventional DLTS technique on a HEMT structure can be reasonably explained with this model. Some results obtained by simulation of typical measurements are presented, which confirm our conclusions.
Combined Atom-Probe and Electron Microscopy Characterization of Fine Scale Structures in Aged Primary Coolant Pipe Stainless Steel
Authors: Bentley J. , Miller M. K. 
Published: March 2011

ABSTRACTThe capabilities and complementary nature of atom probe field-ion microscopy (APFIM) and analytical electron microscopy (AEM) for the characterization of finescale microstructures are illustrated by examination of the changes that occur after long term thermal aging of cast CF 8 and CF 8M duplex stainless steels. In material aged at 300 or 400°C for up to 70,000 h, the ferrite had spinodally decomposed into a modulated fine-scaled interconnected network consisting of an iron-rich α′ phase and a chromium-enriched α phase with periodicities of between 2 and 9 nm. G-phase precipitates 2 to 10 nm in diameter were also observed in the ferrite at concentrations of more than 1021 m−3. The reported degradation in mechanical properties is most likely a consequence of the spinodal decomposition in the ferrite.
The Contrast of Dislocations in X-Ray Topographs of Homogeneously Bent Silicon Crystals
Authors: Loxley Neil , Tanner Brian K. 
Published: March 2011

ABSTRACTThe contrast of dislocations in X-ray transmission topographs has been studied as a function of specimen curvature. It has been shown that in the symmetric Laue geometry, contrast differences between Lang and Hirst Curved Crystal topographs are attributable to inhomogeneous bending of the specimen wafers.
Digital X-Ray Rocking Curve Topography
Authors: Ananthanarayanan T. S. , Rosemeier R. G. , Mayo W. E. , Dinan J. H. 
Published: March 2011

SUMMARYThere is a considerable body of work available illustrating the significance of X-ray rocking curve measurements in micro-electronic applications. For the first time a high resolution (100-150µm) 2-dimensional technique called DARC (Digital Autcmated Rocking Curve) topography has been implemented. This method is an enhancement of the conventional double crystal diffractometer using a real time 2-dimensional X-ray detector.Several materials have been successfully examined using DARC topography. Same of these include: Si, GaAs, AlGaAs, InGaAs, HgMnTe, Al, Inconel, steels, etc. By choosing the appropriate Bragg reflection multi-layered micro-electronic structures have been analyzed nondestructively. Several epitaxial films, including HgCdTe and ZnCdTe, grown by molecular beam epitaxy, have also been characterized using iARC topography. The rocking curve half width maps can be translated to dislocation density maps with relative ease. This technique also allows the deconvolution of the micro-plastic lattice strain ccaponent from the total strain tensor.
Infrared Cathodoluminescence Studies from Dislocations in Silicon in tem, a Fourier Transform Spectrometer for Cl in Tem and Els/cl Coincidence Measurements of Lifetimes in Semiconductors
Authors: Graham R. J. , Spence J.C.H. , Alexander H. 
Published: March 2011

ABSTRACTIn this paper we report the first observations by cathodoluminescence in TEM of radiative infrared emission from dislocations in silicon. These results were obtained at 23-25K in a Philips EM400 electron microscope. Our results are interpreted in the light of earlier photoluminescence work, and the prospects for obtaining spectra from a small number of well characterized dislocations with high spatial resolution are reviewed. Preliminary results are also reported showing the infrared band-gap emission spectrum of GaInAs at 90K recorded using a small Fourier Transform Spectrometer fitted to the same electron microscope. Finally, we describe timing coincidence experiments from samples in which only those visible CL photons are counted which arrive at the detector at the same time as the corresponding transmitted electron energy loss event. We describe the use of this technique for life-time mapping in semiconductors.
Partial Dislocation Mobility in GaAS
Authors: Cooman B. C. De , Carter C.B. 
Published: March 2011

ABSTRACTThe dislocation loop shape in high stress deformed GaAs can be used to obtain information on the relative velocity of individual dislocation segments. It is shown that 30/90 β-dislocations and 90/30 β-dislocations have different velocities. A variety of loop shapes observed can be modelled by focussing on differences in mobility of individual kinks. It is shown that the observation of faulted dipoles is only possible in high stress p-type GaAs in which the screw dislocation segments have appreciable velocity at the low temperatures used during the deformation.
Dislocation-Solute Interactions at Twin Boundaries in Dendritic Web Silicon
Authors: Jayaram R. , Spitznagel J. A. , Meier D. L. , Greggi J. , Burke M. 
Published: March 2011

ABSTRACTDLTS, TEM and APFIM techniques have been used to study impurity-defect interactions responsible for reducing minority carrier diffusion lengths in solar cells of dendritic web silicon. Fine scale precipitates of SiOx, which decorate dislocations piled up at the twin planes in low eff clency cells, appear to be the dominant recombination centers.
Nondestructive Evaluation of Dislocation Subgrain Structures in Silicon Using Thermal Wave Imaging Techniques
Authors: Regnault William F. 
Published: March 2011

ABSTRACTChemical sensors are being developed for in-dwelling biomedical applications. As sensor technologies progress, there is a tendency to fabricate more complex devices in a smaller area, thus enabling multiple sensors to be placed within a single in-dwelling catheter. As the active area of the detector is decreased, the defect structure of both the substrate and the various layers that make up the device plays an increasingly significant role in determining the ultimate sensitivity and reliability. A simple screening test to evaluate the viability of the substrate and the interfaces would aid in the initial evaluation of the fabricated device. To this end, thermal-wave imaging techniques have been applied to the study of a dislocation subgrain structure in a polycrystalline silicon wafer. Comparisons have been made between the results obtained using thermal-wave imaging, defect etching studies, and EBIC measurements.
Photoluminescence Investigation of Dislocation-Related Defects in High Purity Silicon
Authors: Hunter A. T. , Schumacher Kimberly L. 
Published: March 2011

ABSTRACTWe conducted a luminescence investigation of the D1-D4 luminescence lines (0.8 to 1.0 eV) in three samples of high-purity, float-zone silicon. We conclude that the D3 line is a transverse-optical-phonon replica of the D4 line. In the samples studied, all of the defects were formed in the bulk of the crystals by high temperature thermal stress. The free-exciton lifetimes are short, varying between ∼20 nsec at a dislocation density of 1 × 106 cm−2 to ∼200 nsec at a density of 7 × 104 cm−2. The D4 decay shows a small temperature dependence, and varies between samples.
Dislocation Dynamics Investigated by Means of Nuclear Magnetic Resonance a Complementarynew Technique
Authors: De Hosson J. Th. M. , Kanert O. 
Published: March 2011

ABSTRACTPulsed nuclear magnetic resonance proved to be a new complementary technique for the study of moving dislocations in Al—base alloys. Spin—lattice relaxation measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in Al—base alloys are different compared to those in ultra—pure Al. From the motion induced part of the spin—lattice relaxation rate the mean jump distance of mobile dislocations has been determined as a function of strain. Measurements have been performed on Al—Cu, Al—Li and Al—Zn binary alloys. Asa typical illustration of the strength of this technique, this paper reports the resultsobtained of Al—(1—2 at%) Zn solid solution.
Dislocation—like Defects in an Amorphous Lennard—jones Solid
Authors: Shi L. T. , Chaudhari P. 
Published: March 2011

ABSTRACTIt has been found, using computer simulation techniques, that both edge and screw dislocations can be stably introduced into an amorphous Lennard-Jones solid, and can be moved through the model under an applied shear stress.
Cathodoluminescence of Ingaas-GaAs Single Heterostructures
Authors: Fitzgerald E.A. , Kavanagh K.L. , Ast D.G , Kirchner P.D. , Pettit G.D. , Woodall J.M. 
Published: March 2011

ABSTRACTMismatched InGaAs-GaAs epitaxial layers were grown by molecular beam epitaxy (MBE) on substrates containing 9800 or <100 dislocations/cm2. Cathodoluminescence (CL), transmission electron microscopy (TEM), Rutherford backscattering spectroscopy (RBS), and energy dispersive x-ray analysis (EDX) were used to analyze the effect of mismatch and substrate dislocation density on interface morphology. Surface ridges in scanning electron microscopy (SEM) images were found to correlate with areas of high recombination in CL. The spacing of dark recombination lines seen in CL was found to be an order of magnitude larger than the spacing of misfit dislocations seen in TEM. CL/IEM correlation reveals that some areas of the misfit array act more strongly as recombination centers than others. CL of step etched samples show that interface defects propagate into the GaAs buffer layer to depths of 4000 Å below the interface. The substrate dislocation density does not have a major effect on the number or spacing of the dark recombination lines.
Interfacial Particles in Mbe Sillicon Homoepitaxy Growth
Authors: Chrenko R.M. , Hall E.L. , Lewis N. , Smith G.A. 
Published: March 2011

ABSTRACTParticles are observed at the epitaxial layer-substrate Interface of silicon MBE layers when Improper pre—deposition cleaning methods are used. HRTEM shows that the particles In our material are 5 nm to 10 nm In size, and Molre fringe patterns suggest the material Is crystal line. Using a combination of SIMS, HRTEM, and x-ray microanalysis methods, It Is concluded that the Interfacial particles In our material contain carbon and not oxygen, and are beta-SiC growing epitaxially with the silicon.
Tm Analysis of Interfaces Beiween Nb and Al2O3 Precipitates
Authors: Mader W. 
Published: March 2011

ABSTRACTA Nb—Al alloy has been internally oxidized to produce A12O3precipitates. The interface between plate—like AI2O3 precipitates and the Nb matrix has been investigated by diffraction, CTEM, and HREM techniques. Periodic arrays of misfit dislocations were observed which acted as diffraction gratings for the electrons. The location of misfit dislocation cores could be determined from HREM images within an accuracy of a few lattice spacings. It can be concluded that the misfit dislocations lead to a good matching of atomic rows across the interface. The dislocation arrangement at this partially coherent interface is in accordance with theoretical expectations from dislocation theory.
Solute-Atom Segregation and Two-Dimensional Phases at Internal Interfaces: Atomic Resolution Observations
Authors: Herschitz Roman , Seidman David N. , Brokman Avner 
Published: March 2011

ABSTRACTSolute-atom segregation effects to individual stacking faults (SFs) in Co-0.96 at.% Nb and Co-0.98 at.% Fe alloys were studied employing the atom-probe field-ion microscope (FIM) and transmission electron diffraction techniques. The mean composition of individual SFs was measured for bulk specimens which had been equilibrated in the range 450-575°C. In addition, the composition was measured with a spatial resolution, within the plane of the SFs, of ~1 Å and with a spatial resolution of <4 Å perpendicular to the SFs. These measurements demonstrated the following: (a) The meancompostion of the SFs increased with decreasing temperature according to an Arrhenius-like expression; (b) The Nb or Fe concentrations fall off very quickly with distance--within <4 Å from the plane of the SF the bulk concentation is achieved; (c) The SFs equilibrated above 4500 C contained solute-atom fluctuations (≈5 to 20 \ diameter) which correspond to compositions with stoichiometries of ≈Co2Nb or ≈Co3Fe. In the case of the Co(Nb) alloy, a transmission electron diffraction pattern was obtained ofa SF--with the electron beam normal to the SF--which exhibited superlattice reflections with six-fold symmetry around the hcp matrix reflections. This latter result is consistent with a two-dimensional phase in the SF plane with the composition Co2 Nb. Both the atom-probe FIM and the electron diffraction studies are consistent with two dimensional (2D) ordered phases in the SFs.
Structure Imaging and Defects in Crystallized Oxynitride Glasses
Authors: Rai R.S. , O'Keefe M.A. , Thomas G. 
Published: March 2011

ABSTRACTHigh resolution electron microscopy has been employed to elucidate fault defects and structural details of the δ1 and δ2-Y2Si2O7 crystalline phases. From this study δ1 and δ2-Y2Si2O7 have been found to be orthorhombic having the same cell parameters but different atomic arrangements due to a change in their space groups. Computer simulations were necessary for interpreting details from the high resolution electron micrographs.
Interlayer Spacing of Sputter Deposited Vanadium Pentoxide
Authors: Aita Carolyn Rubin , Kwok Chee-Kin , Kao Mei Lee 
Published: March 2011

ABSTRACTVanadium pentoxide films were grown by sputtering a V target in O2-bearing atmospheres containing 0 to 98% Ar. The interlayer spacing was siudied as a function of sputtering gas 02content. The results are discussed in terms of defects in thevanadyl 0 layir and correlated with target surface oxidation.