bluuebunny/crossref_metadata_2025_split huggingface dataset:
Residual Stress Distribution in Feal Weld Overlay on Steel
Authors: Wang X.-L. , Spooner S. , Hubbard C. R. , Maziasz P. J. , Goodwin G. M. , Feng Z. , Zacharia T. 
Published: April 2011

AbstractNeutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay on steel. It was found that the residual stresses accumulated during welding were essentially removed by the post-weld heat treatment that was applied to the specimen; most residual stresses in the specimen developed during cooling following the post-weld heat treatment. The experimental data were compared with a plasto-elastic finite element analysis. While some disagreement exists in absolute strain values, there is satisfactory agreement in strain spatial distribution between the experimental data and the finite element analysis.
Initial Survey on Fracture Toughness of Commerical Nd2Fe14B
Authors: Horton J.A. , Schneibel J.H. 
Published: April 2011

AbstractNd2Fe14B is currently the best (highest energy product) hard magnet available. Like most magnetic materials, it is rather brittle. The fracture toughness of specimens of commercially available Nd2Fe14B magnets were measured using a chevron notch three point bend test. Values ranged from nearly 2 to 5.5 MPa√m. Consistent differences were found between the five different types of materials tested. In this initial survey, insufficient tests were done for good statistics to be obtained. However, it appears that this test will allow differences in fracture toughness between alloys with different compositions and fabricated by different production methods to be measured and tracked as improvements are made.
Mechanical Properties and Structure of Cubic (Al,Cr)3 Ti Alloys
Authors: Nic J. P. , Mikkola D. E. 
Published: April 2011

AbstractSingle phase LI2 (Al,Cr)3Ti alloys show no anomalous strengthening at intermediate temperatures, but the strength rises rapidly at low temperatures. It is likely that a transition from SISF to APB superdislocation dissociation occurs with increasing temperature based on the more rapid decrease in APB energy compared to SISF energy because of entropy considerations. High strain hardening rates are suggested to arise in large part from the formation of large numbers of dipoles. Calculations of interaction forces illustrate the complexity of superdislocation interactions and provide a reasonable mechanism for initiating cross slip.
Understanding The Nb-Ti-A1 System: First Principles Calculations
Authors: Mehl Michael J. 
Published: April 2011

AbstractThe discovery of ductile cubic phases in the Nb-Ti-Al system has led to increased study of these high-temperature intermetallics. I have performed first-principles calculations for ordered crystal structures in this system, paying particular attention to the Nb7Ti7Al2 structure. Somewhat surprisingly, the electronic density of states, lattice constant, and bulk modulus are nearly independent of the ordering of these materials, even though the changes in the total energy are significant.
Abrasive Wear Of Intermetallics
Authors: Hawk J. A. , Alman D. E. , Wilson R. D. 
Published: April 2011

AbstractThe U.S. Bureau of Mines is investigating the wear behavior of a variety of advanced materials. Among the many materials under evaluation are intermetallic alloys based on the compounds: Fe3Al, Ti3Al, TiAl, Al3Ti, NiAl and MoSi2. The high hardness, high modulus, low density, and superior environmental stability of these compounds make them attractive for wear materials. This paper reports on the abrasive wear of alloys and composites based on the above compounds. The abrasive wear behavior of these alloys and composites are compared to other engineering materials used in wear applications.
Estimation of Defect Structure and Site Preference of Additional Elements in B2-Type Nial, Coal and Feal at Offstoichiometry
Authors: Hosoda Hideki , Inoue Kanryu , Mishima Yoshinao 
Published: April 2011

AbstractDefect structures induced by deviation of composition from stoichiometry and site preference of additional elements are predicted for B2-type aluminides (NiAl, CoAl and FeAI) consisting of 8A-group elements by comparing formation energies of particular atomic configurations under the pseudo-ground state. Interaction energies between atoms and vacancies are estimated using a modification of Doyama’s relationship. The results show that vacancy-type defects are formed in NiAl and CoAl only when the total composition of Al and additional elements occupying the Al-site is more than the stoichiometry, whilst with less than the stoichiometry, substitutional defects are formed. In FeAI, only substitutional defects are formed in either case of deviation. Similar to Al, Si occupies only the Al-site, although elements in 1A- and 8A-groups of the periodic table mostly occupy only the Ni-, Co- and Fe-site. The other elements occupy either Al-site or the site of 8A-group elements, or both, depending on the composition.
Solution of the Atomic Structure of the Σ=5 (310) [001] Grain Boundary in Nial by Hrem and Atomistic Simulations
Authors: Fonda R. W. , Yan M. , Luzzi D. E. 
Published: April 2011

AbstractThe atomic structure of the Σ = 5 (310) [001] grain boundary in NiAl has been determined by a synergistic approach combining high resolution electron microscopy (HREM) and atomistic structure calculations. A bicrystal of controlled orientation was produced by diffusion bonding and imaged with the electron beam parallel to the [001] tilt axis. The results showed that the material remains chemically ordered up to the boundary plane. Atomistic structure calculations employed N-body empirical potentials developed for the NiAl phase to examine the changes in interfacial energy due to the incorporation of various point defects at the grain boundary. A self-consistent model structure was determined which was of lowest energy and produced calculated images which matched experimental images of the boundary. Monte Carlo simulations confirm the stability of this structure at finite temperatures.
The Observations on Faulted Dipoles in Deformed Tial—Based Alloys
Authors: Gao Y. , Zhu J. , Cai Q. G. 
Published: April 2011

AbstractThe deformation structure of polycrystalline TiAl-based alloys after uniaxial compression at temperature range from 77K to 1073K has been examined using transmission electron microscopy. It was observed that a large number of faulted dipoles are commonly present in deformation structure of the alloys compressed at low temperature 77K and room temperature. The nature of the faulted dipoles has been determined to be intrinsic stacking fault lying on {111} plane, bounded by 1/6<112] partial dislocations. A possible mechanism for the formation of the faulted dipoles was suggested. The results of the statistic observation shows that faulted dipoles in deformed Ti-48A1 and Ti-(47–48) Al-X (X = V,Cr,Mn) alloys are less than those in single phase Ti-52A1 alloy, and the number of the faulted dipoles decreases with increasing deformation temperature. The effect of the faulted dipoles on plastic deformation of the alloy was discussed.
Temperature-Dependent Structure of a<101> Superdislocations in Ni3Al
Authors: Chrzan D. C. , Foiles S. M. , Daw M. S. , Mills M. J. 
Published: April 2011

AbstractThe dissociated structure of the a〈101〉 superdislocations in Ni3Al is predicted as a function of temperature. The temperature dependence of the relevant fault Helmholtz free energies and elastic constants are calculated within the quasiharmonic approximation using the embedded atom method. The results of these calculations are then incorporated into anisotropic elasticity theory-based calculations of the dissociation distances. The cross-slip activation enthalpy is estimated and found to decrease by 24% at 600 K when compared with its 0 K value. The calculations point to the need to perform experiments to address this temperature dependence.
The Effects of Notches on the Deformation of Ductile Intermetallics
Authors: Schulson Erland M. , Xu Yixin 
Published: April 2011

AbstractThe notch-sensitivity of the ductile L12 aluminides Ni-rich Ni3A1 doped with boron and Zr3A1 is attributed to the triaxial tensile state of stress induced by a notch.
Study of the Effects of Al, Ta, W Additions on the Microstructure and Properties of Mosi2 Base Alloys
Authors: Stergiou A. , Tsakiropoulos P. 
Published: April 2011

AbstractSolidification microstructures and phase selection in ingots and melt-spun ribbons of MoSi2, MoSi2-W-Ta and MoSi2-Al alloys were studied. Rapid quenching from the melt refined the grain size of all alloys by two orders of magnitude compared to the ingots. Zone A microstructures were formed in the wheel side of all alloy ribbons. Addition of W and Ta and of Al suppressed the formation of Mo5Si3 in the ingots and ribbons. Tungsten exhibited complete solid solubility in MoSi2. In the ribbons the solubility of Ta in MoSi2 was extended to 2 at% in Zone A, and in the ingots and zone B of the ribbons hexagonal (C40) TaSi2 and tetragonal (C11b) MoSi2 structures were formed. A fine lamellar microstructure between the Cllb and C40 phases was formed at 1350°C after 48h. Addition of Al changed dramatically the solidification microstructure which consisted of two phases C40 Mo(Al0.5Si0.5)2 and C54 MoAl1.3Si0.7. In the ingots the room temperature hardness decreased with addition of W and Ta and of Al. Addition of Al increased the thermal stability of the MoSi2-Al alloy.
Incipient Melting and Oxidation of Grain Boundary in a Two-Phase Ni3Al Alloy Containing Zr
Authors: Li Huaxin , Chaki T.K. 
Published: April 2011

AbstractIncipient melting and oxidation of grain boundaries at elevated temperatures have been investigated in the investment cast billet of a two-phase (γ + γ′) nickel aluminide alloy (Ni74.48Al16.98Cr8.02Zr0.51B0.10), designated as IC-218. Due to enrichment of Zr, which can form eutectic alloys with Ni, the inter-dendritic regions and grain boundaries melted incipiently at 1150°C. During quenching the molten layers often opened up producing cracks at the boundaries. Annealing at 1200°C in air for 570 min produced elongated ZrO2 precipitates at the grain boundaries. There was Zr depletion inside the grains in the vicinity of the precipitates. Such precipitates were scarcely observed in the specimens annealed in air at 1100°C for 23 h. Thus, the molten Ni-Zr alloy at the boundaries promoted internal oxidation.
Nondestructive Characterization of Woven Fabric Ceramic Composites
Authors: Hsu D. K. , Liaw P. K. , Yu N. , Saini V. , Miriyala N. , Snead L. L. , Lowden R. A. , Mchargue C. J. 
Published: April 2011

ABSTRACTWoven fabric ceramic composites fabricated by the chemical vapor infiltration method are susceptible to high void content and inhomogeneity. The condition of such materials may be characterized nondestructively with ultrasonic methods. In this work, longitudinal and shear waves were used in the quantitative determination of elastic constants of NicalonTM/SiC composites as a function of volume percent of porosity. Elastic stiffness constants were obtained for both the inplane and out-of-plane directions with respect to fiber fabric. The effect of porosity on the modulus of woven fabric composites was also modelled and compared to the measured results. Scan images based on the amplitude and time-of-flight of radio frequency (RF) ultrasonic pulses were used for evaluating the material homogeneity for the purpose of optimizing the manufacturing process and for correlation with the mechanical testing results.
Burner Rig Thermal Fatigue Failure of SiC Continuous Fiber/Si3N4 Ceramic Composites
Authors: Ertürk T. , Park K. , Sung C. 
Published: April 2011

ABSTRACTThe burner rig thermal fatigue properties of SiC continuous fiber/Si3N4 ceramic composites were examined under impinged jet fuel flame, a constant applied tensile stress and thermal cycling in the temperature range 500-1350 °C. The SCS-9 SiC fiber/Si3N4 composites failed within the flame impinged zone, whereas the SCS-6 fiber/Si3N4 composites failed outside the flame impinged zone due to the high thermal stresses resulting from high-temperature gradients. Analytical transmission electron microscopy was used to investigate the microstructure and chemistry of the fiber, matrix and fiber/matrix interface in the failed SCS-9 SiC fiber/Si3N4 composites. The partial degradation of columnar structure of the fiber was interpreted as the dominant mechanism of burner rig thermal fatigue failure of SCS-9 SiC fiber/Si3N4 composites.
Molecular Dynamics Simulations of High Energy Cascades in Iron
Authors: Stoller Roger E. 
Published: April 2011

AbstractA series of high-energy, up to 20 keV, displacement cascades in iron have been investigated for times up to 200 ps at 100 K using the method of molecular dynamics simulation. Thesimulations were carried out using the MOLDY code and a modified version of the many-bodyinteratomic potential developed by Finnis and Sinclair. The paper focuses on those results obtained at the highest energies, 10 and 20 keV. The results indicate that the fraction of the Frenkel pairs surviving in-cascade recombination remains fairly high in iron and that the fraction of the surviving point defects that cluster is lower than in materials such as copper. In particular, vacancy clustering appears to be inhibited in iron. Some of the interstitial clusters were observed to exhibit an unexpectedly complex, three-dimensional morphology. The observations are discussed in terms of their relevance to microstructural evolution and mechanical property changes in irradiated iron-based alloys.
A Phenomenological Model for the Effect of Nanocrystalline Microstructure on Irradiation-Induced Amorphization In U3Si
Authors: Rest J. 
Published: April 2011

AbstractA rate theory model is formulated wherein amorphous clusters are formed by a damage event. These clusters are considered centers of expansion (CEs), or excess-free-volume zones. Simultaneously, centers of compression (CCs) are created in the material. The CCs are local regions of increased density that travel through the material as an elastic (e.g., acoustic) shock wave. The CEs can be annihilated upon contact with a sufficient number of CCs, to form either a crystallized region indistinguishable from the host material, or a region with a slight disorientation (recrystallized grain). Recrystallized grains grow by the accumulation of additional CCs.Preirradiation of U3Si above the critical temperature for amorphization results in the formation of nanometer-size grains. In addition, subsequent reirradiation of these samples in the same ion flux at temperatures below the critical temperature shows that the material has developed a resistance to radiation-induced amorphization (i.e., a higher dose is needed to amorphize preirradiated samples than those that have not been preirradiated). In the model, it is assumed that grain boundaries act as effective sinks for defects, and that enhanced defect annihilation is responsible for retarding amorphization below the critical temperature by, for example, preventing a buildup of vacancies adjacent to the grain boundaries. The calculations have been validated against data from ion-irradiation experiments with U3Si. For appropriate values of the activation energy of thermal crystallization, the model predicts the evolution of a two phase microstructure consisting of nanocrystalline grains and amorphous clusters.
Neutron Diffraction Study of Radiation Damage in U3Si at 30°C and 350°C
Authors: Birtcher R. C. , Richardson J. W. , Mueller M. H. 
Published: April 2011

AbstractWe compare damage evolution in U3Si produced by neutron irradiation at 30°C and 350°C and measured by neutron diffraction. Initial studies found that increasing neutron irradiation dose at 30°C results in monotonic expansion of the a-axis and contraction of the c-axis that transforms the crystal structure from tetragonal to cubic [1]. Additional irradiation results in amorphization. Neutron irradiation at 350°C results in little change to the a-axis and expansion of the caxis.The complete alteration in lattice dilatation during irradiation is interpreted as due to modification of surviving defect configurations at the higher temperature. The high temperature lattice dilations can be explained by defect loop formation in the a-b plane. Confinement of lattice strain to the c-axis during irradiation at 350°C may be the mechanism that prevents the total lattice dilatation from exceeding the critical level required for amorphization.
Effect of Irradiation Spectrum on the Microstructure of Ion-Irradiated A120O3
Authors: Zinkle S. J. 
Published: April 2011

AbstractPolycrystalline samples of alpha-alumina have been irradiated with various ions ranging from 3.6 MeV Fe+ to 1 MeV H+ ions at 650°C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructure of the irradiated specimens. The microstructure following irradiation was observed to be dependent on the irradiation spectrum. In particular, defect cluster nucleation was effectively suppressed in specimens irradiated with light ions such as I MeV H+ ions. On the other hand, light ion irradiation tended to accelerate the growth rate of dislocation loops. The microstructural observations are discussed in terms of ionization enhanced diffusion processes.
Quantitative Hrem of Electron-Irradiated Quartz
Authors: Qin L.C. , Hobbs L.W. 
Published: April 2011

AbstractThe progress of heterogeneous amorphization of electron-irradiated quartz was studied in situ by high-resolution electron microscopy (HREM). The transformation front appears surprisingly sharp when viewed close to edge-on, but the apparent morphological evolution when aperiodic and periodic material overlap in projection is one in which gradual changes in image regularity are observed. Electron-microscopical contrast obtained in HREM irradiations was interpreted quantitatively, through the use of image contrast simulations. When the amorphized portion occupies less than about two-thirds of the total thickness, the HREM images continue to appear crystalline. Only when the amorphized thickness fraction exceeds about two-thirds does the resultant image contrast show mainly non-crystalline features.
Evidence for Electronic Energy Loss Processes Stimulating Solid Phase Epitaxial Regrowth of Spatially Isolated Amorphous Regions in Semiconductor Systems
Authors: Jencic I. , Bench M. W. , Robertson I. M. , Kirk M. A. 
Published: April 2011

AbstractSolid phase epitaxial regrowth of spatially isolated amorphous regions in Si, Ge and GaP has been stimulated by using an electron beam with energies in the range of 50 to 300 keV. In all materials, the rate at which the amorphous zones disappear decreases as the energy of the electron beam increases from 50 keV reaching a minimum below the threshold displacement voltage before it again increases with increasing electron energy. The experimental results are interpreted in terms of creation and motion of defects (dangling bonds, charged defects) along the amorphouscrystalline interface.
Preparation of Thin Film Phthalocyanine Glasses for Optical Limiting
Authors: George R. D. , Snow A. W. , Shirk J. S. , Flom S. R. , Pong R. G. S. 
Published: April 2011

AbstractTo explore the use of phthalocyanine materials as a solid-state component in an optical limiter, the issues of morphology, film processing and optical limiter activity/stability are investigated. Metal-free and lead phthalocyanine films with glassy morphologies are obtained by chemically functionalizing the ring periphery with an amine-epoxy substitution. Uniform films were obtained by a shearing technique. Comparative optical measurements are made on the amine-epoxy lead phthalocyanine compound as a concentrated solution and as a glassy thin film. Both the solution and film are reverse saturable absorbers at 590 nm. The concentrated solution is a very effective optical limiter. The glassy thin film is susceptible to damage (cavitation caused by the incident beam) and performs comparably only at low incident energies. A liquid matrix may have the benefit of self-healing such damage.
Optical Bandwidth Determinants for Excited State Absorptive Limiters
Authors: Miles Perry A. 
Published: April 2011

AbstractThe performance of optical limiters depends on the ratio of the absorptive cross section for the transition from an excited state, σe, to that for transition from the ground state, σg. Both these factors depend on wavelength. It is appropriate to define two bandwidths, one for high energy pulse suppression, depending on σe, and the other for linear transmission, depending on σg. These bandwidths are affected differently by the use of molecular mixtures.
Local and Long-Range Hydrogen Motion in a-Si:H
Authors: Hari P. , Taylor P. C. , Street R. A. 
Published: April 2011

ABSTRACTNuclear magnetic resonance (NMR) measurements of 1H dipolar echoes in a-Si:H indicate that the dipolar spin-lattice relaxation time, T1D, can be used as a measure of local hydrogen motion. In general, the microscopic hydrogen motion is orders of magnitude faster, and the microscopic activation energies are much smaller, than those measured macroscopically using secondary ion mass spectroscopy (SIMS). Although no detailed model exists to explain these apparently divergent results, these discrepancies can be understood phenomenologically by assuming a very broad distribution of rates. In this case the measured activation energies can be shown to scale roughly as the logarithm of the time over which the measurement is made.
Photoelectric-Yield Studies of c-Si/a-Si:H Interfaces
Authors: Sebastiani M. , Di Gaspare L. , Bittencourt C. , Evangelisti F. 
Published: April 2011

ABSTRACTWe report the first yield spectroscopy study on well characterized c-Si/a-Si:H heterojunctions grown in situ under UHV conditions. We find that this spectroscopy, when operated in the constant final state mode, allows a direct and precise determination of the valence-band discontinuity at the interface. A value of δEv = 0.44 ± 0.02 eV was found for the discontinuity.
Bonding of Hydrogen and Deuterium in Silicon Nitride Films Prepared by Remote Plasma Enhanced Chemical Vapor Deposition
Authors: Stevens G. , Santos-Filho P. , Habermehl S. , Lucovsky G. 
Published: April 2011

ABSTRACTWe have deposited Si-nitride thin films by remote plasma-enhanced chemical-vapor deposition using different combinations of hydrogen and deuterium source gases. In one set of experiments, NH3 and SiH4 were injected downstream from a He plasma and the ratio of NH3 to SiH4 was adjusted so that deposited films contained IR-detectable bonded-H in SiN-H arrangements, but not in Si-H arrangements. Similar results were obtained using the same ND3 to SiD4 flow ratio; these films contained only SiN-D groups. However, films prepared from ND3 and SiH4 displayed both SiN-D and SiN-H groups in essentially equal concentrations establishing that H and D atoms bonded to N are derived from both source gases SiH (D) 4 and NH (D) 3, and further that inter-mixing of H and/or D atoms occurs at the growth surface. This reaction pathway is supported by additional studies in which films were grown from SD4 and ND3 with either i) He or ii) He/H2 mixtures being plasma excited. The films grown from the deuterated source gases without H2, displayed only SiN-D bands, whereas the films grown using the He/H2 mixture displayed both SiN-H and SiN-D bands. The total concentration of N-H and N-D bonds in the films grown from the He/H2 excitation was the same as the concentration of N-D, supporting the surface reaction model. In-situ mass spectrometry provides additional insights in the film deposition reactions.