bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Temperature Fatigue Crack Propagation in P/M Ni3Al-B Alloys
Authors: Chang K.-M. , Huang S.C. , Taub A.I. 
Published: March 2011

AbstractDuctile Ni3Al-B type intermetallic alloys show a unique fatigue crack growth behavior at elevated temperatures. A crack propagation mechanism has been investigated in an experimental P/M alloy by testing the alloys with different fatigue frequencies at 400°C. The Ni3Al-B intermetallic alloy shows a substantial time-dependence of fatigue cracl growth rate when tested in air. Under a given cyclic stress intensity, an order of magnitude difference of crack growth rate was observed by decreasing the fatigue frequency. However, such a time-dependence did not occur when the alloy was tested in vacuum. It is concluded that “dynamic” embrittlement in an oxidation environment is the major factor controlling the fatigue crack growth in ordered Ni3Al-B alloys at elevated temperatures.
Structure and Properties of Powder Metallurgy Ni3Al Alloys
Authors: Krueger D.D. , Marquardt B.J. , Field R.D. 
Published: March 2011

AbstractA Ni3AI + B base composition and derivatives containing Hf, Zr, Nb, or Nb + Hf substitutions for Al were processed by powder metallurgy, consolidated by compaction + extrusion, and evaluated for mechanical properties. The mechanical property evaluation consisted of tensile tests performed in air and vacuum, and fatigue crack growth tests performed in air. Microstructures, test specimen fracture morphologies, and tensile and fatigue deformation features were also studied. Some of the substitutions improved certain properties, but none improved ductility. The discussion considers property-fracture morphology-deformation structure relationships.
Effect of Aluminum Addition on Ductility and Yield Strength of Fe3Al Alloys with 0.5 wt % TiB2
Authors: McKamey C. G. , Horton J. A. , Liu C. T. 
Published: March 2011

AbstractStudies have been conducted of the mechanical properties of Fe3Al alloys containing 24 to 30 at.% Al, to which 0.5 wt% TiB2 was added for grain refinement. In tensile tests conducted at room temperature, it has been found that, as the aluminum content is increased, the yield strength decreases sharply from 760 to 310 MPa. The decrease in yield strength is accompanied by a four-fold increase in room-temperature ductility. Ordered iron aluminides (containing no disordered α phase) showed a clear increase in yield strength with temperature above 300°C. Their strength reached a maximum around 600°C, above which it decreased sharply. All these results will be discussed and correlated with stability of superlattice dislocations as a function of aluminum content.
Dispersoids in Intermetallic Alloys: a Review
Authors: Koch Carl C. 
Published: March 2011

AbstractThe existing work on structure and mechanical behavior of intermetallic alloys containing dispersed second phases — dispersoids — is reviewed. The dispersoids considered in the review are those given the conventional definition as inert, stable, insoluble phases in the matrix, such as oxides. The only detailed mechanistic studies of dispersoids in intermetallics have been carried out on the model material Cu3Au, and these did not include elevated temperature, eg. creep, mechanical behavior. A number of investigations on dispersoids in the potentially important elevated temperature materials — the aluminides — are reviewed. The materials discussed include FeAI, Fe3AI, NiAI, Ni3AI, and Ti3Al. Many of these studies are preliminary in nature and much more research anddevelopment is needed to allow for the design of intermetallic-dispersoid materials with improved fabricability and elevated temperature performance.
Selection of Intermetallic Compounds for High-Temperature Mechanical Use
Authors: Fleischer Robert L. 
Published: March 2011

AbstractIn the widespread search for structural materials for high temperatures, it is useful to first apply basic physical considerations to eliminate the least promising candidates. Certain basic quantities are indicators of some of the several properties that are demanded of hightemperature materials. Those properties are high strength and specific strength, high stiffness and specific stiffness, and low creep and thermal expansion coefficient. The basic quantities (structure-insensitive in that they vary little with processing history and consequent microstructural changes) which are chosen to measure these properties are melting temperature Tm, specific gravity ρ, and elastic moduli Cij. Fortunately the most readily available of these structure-insensitive properties, Tm and ρ, are the most useful. As Tm increases, the general trend is for stiffness and strength to increase and thermal expansion and creep to decrease. For space and aircraft applications, knowledge of ρ allows relative values of specific stiffness and specific strength to be estimated from the ratio Tm/ρ. Data for more than 280 intermetallic compounds have been collected and subdivided by crystal class so as to allow the most promising compounds and groups of compounds to be selected. The Ll2 structures tend to lie in the least desirable regions of Tm and ρ and therefore are not the first m candidates for maximizing high-strength at elevated temperatures. At present we have no simple structure-independent indicators of ductility and oxidation resistance--two other properties that are needed in hightemperature structural materials.
Grain Boundary and Surface Segregation in Boron Doped Ni3Al
Authors: White Calvin L. , Choudhury Ashok 
Published: March 2011

AbstractGrain boundary segregation, and its effects on strength and ductility, play an especially important role in the performance of intermetallic alloys based on Ni3Al. The effect of a given segregant on grain boundary strength appears to be determined to some extent by its tendency to segregate to free surfaces. In this paper, we briefly review the available information on grain boundary and surface segregation in boron doped Ni3Al.
Processing Technology for Nickel Aluminides
Authors: Sikka Vinod K. 
Published: March 2011

AbstractDuctile ordered intermetallic alloys of nickel aluminum or nickel aluminum chromium have been developed at the Oak Ridge National Laboratory (ORNL) by optimized additions of boron. These alloys show excellent elevated temperature mechanical properties and corrosion properties. However, in order for the alloys to find use in various applications, they should be fabricable by either the well established or innovative processing technologies. The present paper will discuss the details of fabrication technology being pursued at ORNL. The processes being investigated include powder consolidation by extrusion, powder consolidation by capping, isothermal forging of powder compacted material, twin-roller casting to thin sheet followed by cold-rolling, direct casting rod from liquid, extrusion of billets made by argon-induction melting and electroslag remelting processes, injection molding of powders, and hot isostatic pressing of powders. Relative merits of each process will be discussed. Mechanical properties data on products made by various processes will also be presented and compared.
Room Temperature Tensile Ductility in Powder Processed B2 FeAi Alloys
Authors: Crimp M. A. , Vedula K. M. , Gaydosh D. J. 
Published: March 2011

AbstractIt has been shown that it is possible to obtain significant room temperature tensile ductility in FeAl alloys using iron-rich deviations from stoichiometry. A comparison of the room temperature tensile and compressive behaviors of Fe−50at% Al and Fe−40at% Al shows that FeAl is brittle at higher Al contents because it fractures along grain boundaries before general yielding. Lower aluminium contents reduce the yield stress substantially and hence some ductility is observed before fracture.Addition of boron results in measurable improvements in ductility of Fe−40at% Al and is accompanied by an increase in transgranular tearing on the fracture surface, suggesting a grain boundary strengthening mechanism.Increasing the cooling rate following annealing at 1273 K results in a large increase in the yield strength and a corresponding decrease in ductility.
High Temperature Mechanical Behavior of Some Advanced Ni3Al
Authors: Hsu S. E. , Hsu N. N. , Tong C. H. , Ma C. Y. , Lee S. Y. 
Published: March 2011

AbstractHigh temperature mechanical properties of various Zr and Cr strengthened single phase Ni3Al are investigated, with emphasis on the ability of each element to elevate Tp, the temperature corresponding to the peak yield strength. It is observed that Zr is a very effective strengthener, more so below Tp than above it, while a combination of Cr and Zr is capable of shifting Tp to a higher temperature. The combination results in an effective improvement of the rupture strength of Ni3Al. The strengthening mechanisms of each element will be discussed in this paper.
Modeling of Antiphase Boundaries in L12Structures
Authors: Sanchez J.M. , Eng S. , Wu Y.P. , Tien J.K. 
Published: March 2011

AbstractThe thermodynamic properties of conservative (111) antiphase boundaries in L12ordered structures are modeled using the tetrahedron approximation of the cluster variation method. The concentration and long-range order parameter profiles are determined as a function of temperature and composition of the bulk alloy. Characteristic wetting transitions, with a macroscopic disordered layer growing from the antiphase boundary as the transition temperature is approached, are found for all cases investigated. The effectof antiphase boundaries on the disordering of ordered alloys and on the gliding of superdislocations are discussed.
Fim/atom Probe Studies of B—doped and Alloyed Ni3Ai
Authors: Sieloff D.D. , Brenner S.S. , Burke M.G. 
Published: March 2011

AbstractField—ion microscopy and atom probe microanalysis have been used to determine thestructure and chemistry of grain boundaries in ductile, recrystallized Ni3Al containing 0.23 at % B (500 wt.ppm). The results indicate that the boron concentration fluctuates along the boundary plane and that the boron enriched zone is wider than expected from equilibrium—type adsorption. It was also found that boron lowers the aluminum concentration of some of the boundary regions.
Improving Signal-to-Noise Limits in High Resolution Transmission Electron Microscopy
Authors: Gibson J.M. , McDonald M.L. 
Published: March 2011

ABSTRACTSignal-to-noise ratios for Si <110> lattice images are measured for a variety of different specimen preparation techniques, including ion-milling, chemical polishing, cleavage and in-situ surface cleaning by heating. The noise levels are significantly lower in the latter, possibly permitting new classes of experiments in image quantitation and impurity imaging.
Annealing Effects in Ion Bombarded GaAs: Raman Measurements
Authors: Burns Gerald , Dacol F. H. , Baglin J. E. E. , Wie C. R. , Burstein E. , Cardona M. 
Published: March 2011

ABSTRACTThe surface layer of single crystal GaAs that has been bombarded with high energy (2-15 MeV) ions is strained and contains many defects, but it remains crystalline. We have studied the isochronal annealing behavior of this layer using phonon shifts and widths, which were detected by Raman measurements. We do not find any sharp annealing stages to 500 C, at which temperature the phonons have returned to their positions in the unbombarded crystals. These results are consistent with the idea that the phonon shifts are primarily due to antisites and their complexes with other primary defects. However, other extended defects may still be present, and the Raman data show some evidence for this.
The Temperature Dependence of Ion Beam Mixing of Zr on A12O3
Authors: Farlow G. C. , Withrow S. P. , Easton D. S. 
Published: March 2011

ABSTRACTThree hundred angstrom Zr films were deposited on A12O3 substrates and irradiated with 300 keV Xe ions to a dose of 1 × 1016 /cm2. The irradiation was carried out at 77 K, 300 K (ambient temperature), and 800 K. Changes in the deposited film and the Zr-A12O3 interface were examined by comparing Rutherford backscattering spectra from irradiated and unirradiated regions of the samples. Ion beam induced reactions were observed at all three temperatures. The systematics of the temperature dependence of ion beam mixing are discussed.
Atomic Displacements Around Nitrogen Interstitial Impurities in Ta and Nb
Authors: Rao S. , Savino E. J. , Houska C. R. 
Published: March 2011

ABSTRACTThe core as well as the long range elastic displacements around N octahedral interstitial atoms in Ta and Nb are modelled using the Green Function – Kanzaki force method. The theoretical calculations are compared with experimental attenuation factor and diffuse scattering data, reported in the literature, for both N in Nb and N in Ta [1,2,3]. It is shown that a third neighbor radial Kanzaki force model is needed to explain the experimental findings, and the long range elastic displacement field is non-spherical.
X-Ray Topographic Methods for Stress-Strain Tensor Analyses of Crystals
Authors: Weissmann S. , Mayo W.E. , Kalman Z.H. 
Published: March 2011

ABSTRACTTwo methods for the strain tensor analysis of crystals will be presented. One of them is based on a modified x-ray back-reflection divergent (BDB) method. By the interposition of a wire grid between crystal and film, a computer-aided ray tracing technique was developed resulting in simultaneous precision measurements of d-spacings of several (hkl) planes. The strain input data for the tensor analysis are = (dn-dn°)/dn°, where dn° is the d value of the corresponding unstrained (hkl) planes, the precision of the strain measurements being ± 0.02%. The strain tensor εij obtained from the strain components, referred to the cubic coordinate system, is calculated by a least square method and the principal strains and their directions are determined. From the principal strains and known elastic constants the complete stress-strain configuration as well as the stored elastic energy are determined. An example of application to the elucidation of strains in premartensitic Al Ni crystals will be given. The other x-ray method presented is based on a computer-aided rocking curve analysis (CARCA) method, which is particularly well suited for the tensor analysis of non-uniform strain distribution in epitaxially grown microelectronic materials. This method determines not only the full elastic strain tensor, but also its distribution about a strain center with a resolution of approximately 60 Pm. As an example the strain distribution in an InGaAsP epitaxial film on an InP substrate is presented.
The Structural and Electrical Characterization of Copper Decorated Boundaries in Silicon Bicrystals
Authors: Miller F.S. , Betrabet H.S. , Clark W.A.T. 
Published: March 2011

ABSTRACTSilicon bicrystals have been fabricated by sintering together single crystal {001} and {111} wafers with low angle misorientations In the range of 0.5 to 3.0 degrees. The interfaces in these bicrystals contain regular arrays of screw dislocations with observed spacings of 10 to 40 nm. The dislocations were decorated with copper which was first sputter-deposited on an external surface, then diffused into the interface by annealing the bicrystal at 400°C for 15 minutes. Analytical electron microscopy was used to characterize the spacing, orientation, and copper concentration of these dislocation arrays. The electrical properties of both decorated and undecorated bicrystals were determined using a two-probe step I-V method, and the behavior of both types of bicrystals compared.
Multimodal Time Delays in the Photoplasticity of Mercury Cadmium Telluride
Authors: Pellegrino Joseph , Partridge Julian P. , Son Yo Ho 
Published: March 2011

ABSTRACTThe plastic response of deforming crystals of mercury cadmium telluride to light occurs with a time delay that depends on wavelength, temperature, and bias voltage. The time delay exhibits a temperature dependence which increases as the temperature is lowered, andis approximately 60 seconds at 20°C. A detailed examination of a number of measurements of the time delay at constant temperature reveals that the time delay falls into one of four separate peaks. These peaks shift with temperature with an overall activation energy of approximately 0.2 eV. Furthermore, the photoplastic responses of a given crystal indicate that softening is observed roughly 40% of the time and hardening the remaining 60%. It has also been observed that the relative positions of the time delay peaks can be markedly affected by a static bias voltage.A model which explains these observations involves the coulombic interaction of charged point defects with jogs on dislocations. The model predicts four separate time delay peaks as well as the correct ratio of hardening to softening.
Structure Determination of Tilt Boundaries in Gold by High Resolution Electron Microscopy
Authors: Krakow William , Smith David A. 
Published: March 2011

ABSTRACTA number of tilt grain boundaries prepared from evaporated gold thin films have been investigated by high resolution transmission microscopy. When the grain boundary is parallel to the electron beam and the beam is parallel to a low index rotation axis such as [110] or [001]it is possible to identify atomic positions at the cores of these boundaries as demonstrated here by a Σ = 3 70.5°/[110], (112) growth twin. In many cases it is not possible to make a full atomistic structure determination because the specimen does not have translational periodicity in the beam direction. This may be because the boundary plane is not parallel to the beam or the specimen contains dislocations which have a component of Burgers vector parallel to the beam. Examples are given of various low angle boundary structures in goldwhere there are complications because of the three dimensional nature of their structure.
Interaction between Domain Walls and Point Defects in Tetragonal BaTiO3
Authors: Boser O. , Beshers D. N. 
Published: March 2011

ABSTRACTDopants in ferroelectric materials affect the dielectric constant and the shape of the hysteresis loop. To understand and quantify these effects it is necessary to calculate the interaction between dopant and domain wall. In the following the dopant ion is modelled as an elastic dipole. The stresses surrounding a 180° domain wall are calculated in analogy to calculations in the magnetic case for Bloch walls. It is assumed that electrostrictive effects control the strains and that the spontaneous polarization does not rotate but decreases to zero at the center of the domain wall and increases in the opposite direction on the other side of the domain wall. The calculations are made assumingisotropic elastic constants. It is found that only elastic dipoles oriented in the planeof the domain wall interact with it. The interaction forces as a function of perpendicular distance between wall and dipole show an antisymmetric characteristic.
Surface Dynamics of Small Particles
Authors: Ajayan P.M , Marks L.D , Dundurs J. 
Published: March 2011

ABSTRACTWe investigate the energetics of structure changes in small particles, a phenomena recently observed by high resolution electron microscopy. The energy variations during transformations from a single crystal to symmetric and asymmetric decahedral multiply twinned particle (MTP) structures are evaluated. We examine briefly a few possible energy gain mechanisms during the particle-beam interaction which enable the particles to cross the activation energy barriers and fluctuate between various local energy minima of the morphological potential energy surface.
Surface Faceting of (110) GaAs: Analysis and Elimination
Authors: Parechanian-Allen L. , Weber E.R. , Washburn J. , Pao Y.C. 
Published: March 2011

ABSTRACTA systematic study has been made on (110) GaAs grown by molecular beam epitaxy. This work represents the first systematic investigation of commonly observed faceting on the (110) GaAs surface which has led to the consistent elimination of the defects. This study involved the analysis of facet geometry, a kinetic model of initial facet formation, and the electrical and optical analysis of facet free (110) GaAs. The latter was obtained with proper growth conditions and a Ga rich surface exposure from a GaAs substrate angled 6° toward (111)Ga.
Nuclear Reaction Spectroscopy of Vibrational Modes of Solids
Authors: Zinke-Allmang M. , Kalbitzer S. , Weiser M. 
Published: March 2011

ABSTRACTThe effects of target-atom vibrations on nuclear reaction kinetics have been examined. In particular, Doppler broadening of resonance-type and elastic- scattering reactions has been considered in detail. Depending on the specific process parameters, the resulting energy widths can be many orders of magnitude larger than the energies of the vibrational states of the target solid. Comparison of experimental results on a hydrogen-bearing thin target with the theoretical predictions shows excellent agreement. We will show the importance of this effect in hydrogen profiling measurements and point out the feasibility of vibrational spectroscopy on hydrogen in solids.
Investigation of the Resonant Vibration Modes of Self Interstitial Atoms in Al by Diffuse Inelastic Neutron Scattering
Authors: Urban R. , Ehrhart P. , Chilling W. , Schober H.R. , Lauter H. 
Published: March 2011

ABSTRACTSingle crystals of Al were irradiated up to 480 ppm of Frenkel defects using a specially developed irradiation facility for high dose electron irradiation of large samples below 20 K. Diffuse inelastic neutron scattering measurements have been performed at these samples to study the dynamics of single self interstitial atoms. The measurements were made at 6 K on the sample before annealing and after annealing at 46 K (above stage I) and at 300 K (after complete recovery). The irradiated samples showed a significant increase of the inelastic scattering intensity at transferred energies between 0.7 and 2 THz. By comparison with the results of computer calculations the different frequencies of the energy loss spectrum could be attributed to the different vibration modes of interstitial atoms. The frequencies of the most significant modes of the self interstitial atom are determined to be υ = 0.75 THz and υ = 1.35 THz for the translation-(A2u) and libration-(Eg) mode, respectively.
Analysis of Oxide Surfaces by High Resolution Transmission Electron Microscopy
Authors: Krakow W. , Castano V. 
Published: March 2011

ABSTRACTWe have investigated the surface structure of oxides with low atomic number metallic components (Cu and Al) using two different high resolution electron microscopy techniques. First, using flat-on microscopy normal to the surface, we have studied the epitaxy of vapor deposited Cu on single crystal (110) and (111) surfaces of Au and the subsequent oxidation of the Cu under ambient conditions. Three structural variants of (110) oriented Cu2O were found relative to the underlying ( 11I) Au film and the oxide surface has a shifted, 1/2[110], (1 × 1) surface reconstruction. A (211) Cu2O structure was found for the (110) Au film orientation. This case has two structural variants at 90° to each other where one of these variants exhibits surface roughness of ∼5Å. The second structure has atomic step heights of ∼6Å, and a rectangular surface supercell structure of ∼3.0Å × 7.39Å due to (211) bulk lattice layers.