bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of Microstructure in Mechanically Alloyed NiAl
Authors: Pyo Sung G. , Kim Nack J. 
Published: April 2011

AbstractNiAl intermetallic powder has been synthesized by mechanical alloying of elemental powders in an attritor mill using controlled atmosphere. The mechanically alloyed (MA) powders were consolidated by vacuum hot pressing (VHP), resulting in a material which was fully dense. Analytical transmission electron microscopy has been used to understand the development of microstructure with processing. The dispersoid particles present are mostly A12O3 with small amount of A1N. It has been shown that morphology of the dispersoid particles are not uniform and the larger dispersoid particles are located mostly along the grain boundaries with the dispersoid-free zones near them. Coarsening behavior of the dispersoid particles is different depending on their locations, i.e., within the grain or along the grain boundaries. The accelerated coarsening of dispersoids along the grain boundaries occurs concurrently with that of the grains and the formation of dispersoid-free zones (DFZs) are observed along the grain boundaries. It is suggested that this abnormal dispersoid coarsening and the formation of DFZ are due to the coupled migration of dispersoids and grain boundaries.
Interfacial Structure and Lattice Mismatch in Lamellar TiAl Alloys
Authors: Dimiduk Dennis M. , Sun Yongqian , Hazzledine Peter M. 
Published: April 2011

AbstractThe gamma lamellae in TiAI alloys are rotated relative to each other approximately by multiples of 60˚ so that close packed planes and directions nearly align. However, the deviations caused by the tetragonality of the lattice are important in determining the structure of the interfaces and the internal stresses in the lamellae. These, in turn, strongly affect the mechanical properties of the alloys. In this paper two new electron optical techniques are used to quantify the deviations from pure twist boundaries (1) selected area diffraction from two adjacent twin-related lamellae permits c/a to be measured with high precision, (2) convergent beam diffraction is used to measure tilt components of lamellar boundaries and also rotations of vectors within the lamellar boundaries. The results are discussed in connection with the weak beam observations of interface dislocation structures.
Complex Anti Phase Domain Boundaries In A Gamma TiAl Alloy
Authors: Zhang X. D. , Loretto M.H. 
Published: April 2011

AbstractRecent work has shown that antiphase domains are observed in alloys based around TiAl if they are quenched from the alpha field. The present work has shown that the anti phase domain boundaries (APDBs) are in fact not simple APDBs but are composed of very thin (about 2 nm) 90° domains. Although the contrast is dominated by the fact there is a 1/2<101> displacement between the domains either side of this thin 90° domain, there is somewhat more complex contrast associated with the APDBs than the hard sphere model would predict.
Annealing studies of the complex APDBs in a Ti49Al alloy have shown that the originally irregular APDBs in the quenched material facet on {111} planes. The significance of these observations is discussed in terms of mechanisms by which the APDBs are formed in TiAl and in terms of the planar fault energies in the Llo structure.
Phase Stability, Microstructure and Mechanical Properties in the Multi-Phse Alloys Based on the L12-Ni3(Al,Be)
Authors: Matsuo Takahiro , Hosoda Hideki , Miura Seiji , Mishima Yoshinao 
Published: April 2011

AbstractIntermetallic alloys based on the Ll2 Ni3(Al,Be) phase in the ternary Ni-Al-Bc system are prepared so that the alloys are multi-phase with the B2 intermetallic compound NiBe and a Ni primary solid solution denoted as (Ni). Such three-phase alloys, Ni-16 to 20 at%Al-10 at%Be, exhibit good room temperature ductility as measured by four-point bending. In order to examine the phase stabilities and relations among constituent phases, a vertical section of the ternary system is constructed at a constant 10 at%Bc mainly by differential thermal analysis. It is found that improvement in room temperature ductility can be achieved by the formation of a fine mixture of constituent phases during invariant reactions during solidification, which is further enhanced by the co-existence of the Ll2 phase formed as the primary solidification phase.
Creep and Fracture Mechanisms in an Oxide-Dispersion Strengthened Ni3Al-Based Alloy Between 649°C and 982°C
Authors: Mason Ralph P. , Grant Nicholas J. 
Published: April 2011

AbstractAn oxide-dispersion strengthened (ODS) Ni3Al-based alloy has been fabricated and creep tested. Previously reported data for minimum creep rate as a function of stress indicated that two creep mechanisms operate at intermediate temperatures of 732 and 816°C [1]. This paper reports the results of recent interrupted creep tests and fractographic studies which serve to identify the two creep mechanisms. Creep at low stresses or low creep-rates occurs by constrained growth of cavities on transverse grain boundaries. In this low stress region an apparent stress exponent of 5.1 is observed. Creep at high stresses or high creep-rates results from the bulk deformation of grains by power law creep with a much smaller contribution due to grain boundary cavitation. The stress exponents of 13 and 22 observed in this high stress region are typical of ODS alloys. In both regions fracture is observed to be mixed mode with a large transgranular component due to the high grain aspect ratio developed in this material. Limited data at 982°C indicate the occurrence of only one mechanism which can be described by a stress exponent of 9.1. It was not possible, based on fractographic studies, to associate the creep mechanism at 982°C with either of those observed at the intermediate temperatures. No fractographic studies were performed at 649°C due to lack of valid specimens; however, the stress exponent of 13.5 observed at 649°C suggests that creep occurs by deformation of the grains.
Effect of Zirconium On Mechanical Properties and Grain Boundary Chemistry in Ni3Al Alloys
Authors: Lin Dongliang , Gu Yuefeng , Guo Jianting 
Published: April 2011

AbstractThe effects of zirconium addition on tensile properties and grain boundary (GB) chemistry in the Ni3Al alloys were studied. The results showed that with the increasing amount of Zr, the yield and ultimate strength increase, the elongation increases below 0.7 at. % Zr content and decreases above that content. Zirconium segregation to grain boundaries (GBs) is found by Auger electron spectroscopy (AES) study and the amount of Zr at GB is three times greater than that in the bulk. In situ transmission electron microscopy (TEM)/ scanning electron microscopy (SEM) investigation showed that slip can transfer across the GB to the adjacent grain in Zr-doped Ni3Al alloys. These results indicate that the effect of Zr on improving ductility of Ni3Al alloys had a strong relationship with the segregation of Zr on the GBs.
The Cyclic Oxidation behavior of Oxide-Dispersed β-NiAl
Authors: Pint B. A. , Hobbs L. W. 
Published: April 2011

AbstractShort-term cyclic oxidation tests were performed at 1200°C and 1500°C on ²-NiAl with 1 vol% oxide dispersions of Y2O3, La2O3 and Al2O3. The Y2O3 addition resulted in a very adherent ±-Al2O3 scale at 1200°C, with some improvement in the scale adhesion at 1500°C, compared to an undoped ²-NiAl alloy. The La2O3 and Al2O3 additions resulted in more severe oxidation than the undoped ²-NiAl at 1200°C. Both Y and La ions are found to segregate to ±-Al2O3 scale grain boundaries using scanning transmission electron microscopy/energy dispersive x-ray analysis. However, at both 1200°C and 1500°C, the La addition appears to cause a rapid increase in the isothermal oxidation rate, leading to excessive scale spallation.
Improved Dispersion of Silicon Nitride Whiskers
Authors: Shih Wei-Heng , Buchta Michael 
Published: April 2011

ABSTRACTTo improve the dispersion of silicon nitride whiskers in aqueous suspensions, a standard dispersant used in glass fiber industry, 3-aminopropyltriethoxysilane (APS) is added. It was found that the viscosity of the whisker suspensions is lowered and the centrifuged density of the suspensions is increased with the addition of the APS. The pH values of suspensions before and after the addition of APS indicate that APS extracts H+ ions from the solutions and the adsorption of APS on silicon nitride is saturated in our experiment. Our results indicate a colloidal route to the processing of ceramic composites with silicon nitride whiskers as reinforcements.
Enhanced Thermal Conductivity of CVD SiC via Beryllium and Boron Dopings
Authors: Kowbel W. , Gao F. , Withers J. C. 
Published: April 2011

ABSTRACTSiC-SiC composites exhibit excellent mechanical and corrosion properties, which are desired for a variety of advanced applications including fusion reactors, heat exchangers and advanced turbine engines. However, SiC-SiC composites fabricated by the CVI methods have unacceptably low through-the-thickness thermal conductivity, which limits their use in these applications. CVD SiC co-deposition with either beryllium or boron compounds significantly enhanced the thermal conductivity of CVD SiC at temperatures up to 1000°C. Results pertinent to the doping processes and the measured thermal conductivity of doped CVD SiC are reported. Mechanisms for the enhanced thermal conductivity of the CVD SiC are discussed based on the microstructural characteristics of the doped specimens.
Interfacial Properties of As-Received and Coated SiC (SCS-6) Fiber Reinforced Reaction-Formed SiC Matrix Composites
Authors: Gaeta Paula J. , Sisson Richard D. , Singh M. , Eldridge Jeffrey I. 
Published: April 2011

ABSTRACTThe possibility of improving the interfacial shear strength of the SiC fiber reinforced SiC matrix composite system was examined. A ceramic fiber coating was chosen based on availability and chemical stability with the fiber and matrix. Fiber push-out tests conducted on as-received and coated fiber reinforced composite samples allowed characterization of the interfacial shear strength. Average debond shear and frictional sliding stresses were calculated. The effects of sample thickness and second phase addition in the matrix were also evaluated. Tested samples were examined by SEM to determine the location of the interfacial failure and to determine if any interface reactions had occurred. The coating was then evaluated based on the resulting interfacial shear strength, failure location, and integrity of the interface as compared to those properties of samples reinforced with as-received fibers.
“Chemically Bonded Ceramic Matrix Composites: Densification and Conversion to Diffusion Bonding”
Authors: Johnson Bradley R. , Gülgün Mehmet A. , Kriven Waltraud M. 
Published: April 2011

ABSTRACTChemically bonded ceramics appear to be a promising alternative route for near-net shape fabrication of multi-phase ceramic matrix composites (CMC's). The hydraulic (and refractory) properties of fine mono-calcium aluminate (CaAl2O4) powders were used as the chemically bonding matrix phase, while calcia stabilized zirconia powders were the second phase material. Samples containing up to 70 wt% (55 vol%) zirconia have been successfully compacted and sintered.Various processing techniques were evaluated. Processing was optimized based on material properties, dilatometry and simultaneous thermal analysis (DTA'TGA ). The physical characteristics of this novel CMC were characterized by hardness, density, and fracture toughness testing. Microstructures were evaluated by SEM and phase identification was verified using XRD.
The Effect of Migration Energies on Reducing Overprediction in Radiation-Induced Segregation Models
Authors: Allen T. R. , Was G. S. 
Published: April 2011

AbstractModels for calculating radiation-induced segregation (RIS) in concentrated alloys based solely on differences in the magnitude of the vacancy driven flux typically overpredict the amount of grain boundary segregation. A simple sensitivity analysis is used to show that the overprediction may be linked to the choice of input parameters. By varying the Cr-vacancy migration energy from 1.300eV to 1.320 eV and the Fe-vacancy migration energy from1.300eV to 1.305 eV, well within their experimental uncertainty, RIS model calculations are brought into better agreement with AES and STEM-EDS measurements of grain boundary segregation in Fe-Cr-Ni alloys irradiated with protons at 7x 10−6 dpa/s at various temperatures and doses.
Microstructural and Mechanical Property Changes in Model Fe-Cu Alloys
Authors: Rice Philip M. , Stoller Roger E. , Lucas Barry N. , Oliver Warren C. 
Published: April 2011

AbstractThis paper describes a technique developed to determine values for the dislocation barrier strength of the defects believed to be responsible for the embrittlement of light water reactor (LWR) pressure vessel steels. Microstructures consisting of a single defect type were introduced by ion irradiation or thermal annealing, and the defect distributions were determined by TEM. Hardness changes were measured using a nano indenter and the dislocation barrier strengths for the defects involved were computed based on a dispersed barrier hardening model.
Modelling the Structure of Ion Bombarded Binary Alloys
Authors: Ossi Paolo M. 
Published: April 2011

AbstractAn atomistic model of phase formation in ion bombarded thin binary metallic films is discussed. Compositional changes occur at the interface between collision cascades and crystal matrix. Relaxation arises via elementary charge transfer reactions, with formation of dimers of an effective compound. Comparing surface and thermochemical properties of initial and effective alloys, a set of conditions specific to vitrification and respectively tocrystal formation under ion bombardment is obtained.
Microstructure of A12O3 Irradiated with an Applied Electric Field
Authors: Zinkle S. J. , Hunn J.D. , Stoller R.E. 
Published: April 2011

AbstractA thin amorphous film of alumina was irradiated with 2-MeV He+ ions at ~400°C up to a damage level of about 0.01 displacements per atom (dpa). The alumina films were sufficiently thin (~1.8 μm) to allow the ion beam to be completely transmitted through the specimen. An electric field of μ280 V/;mm (dc) was applied continuously during the irradiation. Radiation induced electrical degradation (RIED), i.e. a permanent increase in the conductance of the film, was observed in specimens irradiated at temperatures near 400 to 450°C but did not occur in a specimen irradiated above 500°C. An investigation by transmission electron microscopy found no evidence for colloid formation. The observed increase in the conductance of the alumina film may be due to radiation-induced microcracking.
Photoplastic Effect on Ice
Authors: Khusnatdinov Niyaz N. , Petrenko Victor F. 
Published: April 2011

AbstractThe study of the photoplastic effect (PPE) on ice is essential for both fundamental and applied reasons. It is important for an understanding of dislocation motion as well as the flow of glaciers in cold regions that occurs under intensive solar radiation. It was found that the illumination of ice with UV light (λ < 300 nm) leads to its irreversible hardening1. A prolonged irradiation with a total light exposure of about 8.10−5 J/cm2 at λ= 260 nm can change the creep rate up to 60 percent. Even more pronounced PPE was found in HCI-doped ice with the concentration, n= 1018 cm−3. It is suggested that PPE is caused by the excitation of “autoionization” reaction which was found responsible for the photoconductivity of ice.
Ion-Beam and Electron-Beam Induced Amorphization of Berlinite (AIPO4)
Authors: Bordes N. , Ewing R.C. 
Published: April 2011

AbstractBerlinite (AIPO4) is isostructural with α-quartz. Like α-quartz, berlinite undergoes a pressure-induced amorphization at 15 ±3 GPa; however, upon release of the pressure, unlike α-quartz which remains amorphous, berlinite returns to the original crystalline structure of the single crystal. Berlinite was irradiated with 1.5 MeV Kr+ at temperatures ranging from 20 to 600K. The onset of amorphization was examined by monitoring the electron diffraction pattern by in situ transmission electron microscopy (TEM) at the HVEM-Tandem Facility at Argonne National Laboratory. The berlinite was easily amorphized at 20K at a relatively low dose of 4x1013 ions/cm2 or 0.05 dpa (displacements per atom). The critical amorphization dose increases with the sample temperature. These experiments also showed that the focused electron beam can locally amorphize the berlinite. After these irradiations, berlinite remained amorphous. At 500 °C, berlinite began to recrystallize: small areas of crystalline material appear in the aperiodic matrix. These results suggest that pressure-induced amorphization and ion-beam induced amorphization, in the case of berlinite, are different processes that result in two different aperiodic structural states.
Ion Damage Production in GaAs/Al0.6Ga0.4As Heterostructures
Authors: Turkot B.A. , Robertson I.M. , Kirk M.A. , Rehn L.E. , Baldo P.M. , Forbes D.V. , Coleman J.J. 
Published: April 2011

AbstractThe non-uniform distribution of damage with depth and the onset of amorphization produced in Al0.6Ga0.4As/GaAs heterostructures by 1.5 MeV Kr+ ion implantation at 77K have been investigated by using a combination of RBS channeling and cross-sectional high-resolution TEM techniques. The extent of damage increases with increasing depth in the Al0.6Ga0.4As layer. This depth dependence of the damage can be correlated with an increase in the number of recoil events with an energy between 30 and 50 keV. We propose that the amorphization of Al0.6Ga0.4As requires the superposition of cascade-type damage on a background population of point defects which is created by implantation with high energy ions.
Radiation-Resistant Properties of Inp-Related Materials
Authors: Yamaguchi Masafumi , Ando Koshi , Kamada Hidehiko 
Published: April 2011

AbstractIrradiation effects of high-energy electrons and protons, and 60Co gamma-rays on InP-related materials have been examined in comparison with those of GaAs and Si. Superior radiation-resistance of InP-related materials and their devices compared to GaAs and Si has been found by using deep-level transient spectroscopy (DLTS), photoluminescence (PL) and properties of devices such as solar cells and lightemitting devices. Moreover, minority-carrier injection enhanced annealing phenomena of radiation-induced defects in InP-related materials have also been observed even at low temperature of around 150K.
Two-Photon Absorption in Polybenzidine
Authors: Aranda F. J. , Cheng C. F. , Rao D. V. G. L. N. , Akkara J. A. , Kaplan D. L. , Roach J. F. 
Published: April 2011

AbstractPolymers of Benzidine were synthesized by hydrogen peroxide reaction catalyzed by horseradish peroxidase enzyme. The polymerization reaction was carried out at room temperature in a monophasic organic solvent with a small amount of water at pH 7.5.The technique of degenerate four-wave mixing (DFWM) with nanosecond and picosecond pulses was employed to measure the third-order nonlinear optical susceptibility χ. The samples were studied in solution in Dimethyl sulfoxide:Methanol in volume ratio 4:1. The observed values are of order 10−9 to 10−8esu. Measurements on a thin film agree approximately with the extrapolated values fron solution measurements. Picosecond time resolved measurements indicate a pulse-width limited response followed by a small slow component. Investigation of the total energy transmission as a function of the incident intensity and fluence at 532 nm for pico- and nanosecond pulses indicates reverse saturable absorption. As we observe the nanosecond and picosecond curves to be superimposed for the intensity plot but not for fluence, we conclude that the nonlinearity is predominantly due to two-photon absorption. Numerical analysis of the data yields a value of 12.25 cm/GW for the two-photon absorption coefficient β. The imaginary component of χ obtained is 5 × 10−9esu. The material appears to be a good candidate for applications in optical power limiting and switching.
Optical Limiting in Solutions of Polycyclic Aromatic Hydrocarbon Diones.
Authors: Natarajan L. V. , Sutherland R. L. , McLean D. , Brant M. , Brandelik D. M. , Cooper T. M. , Crane R. L. 
Published: April 2011

AbstractOptical limiting in toluene solutions of substituted benzanthracene- 3,4 diones and three other quinones, namely, benzpyrene-7,8-dione, benzphenanthrene-3,4-dione and chrysene-5,6-dione was investigated at laser wavelengths 532 nm and 694 nm. Low limiting threshold values of the order of 0.01J/cm2 were obtained for some of the quinones at 532nm. Strong triplet-triplet absorption at the excitation laser wavelengths may explain the optical limiting behavior.
Complex Formations in C60 Solutions
Authors: Brandelik D. M. , McLean D. G. , Brant M. C. , Sutherland R. L. , Frock L. R. , Crane R. L. 
Published: April 2011

AbstractComplex formations in C60 solutions have previously been observed in diethylaniline. In a wide survey of solvents conducted in our laboratory, several additional solvents exhibited complexing behavior with C60 when analyzed with UV-Vis and fluorescence spectroscopy. All solvents with complexing behavior contained nitrogen. They are benzonitrile, N-methylpyrrolidone, and triphenylamine. A careful study was done to characterize the formation of the complexes formed in C60/toluene solutions when each complexing agent was added. Diethylaniline was added to the study as a reference complexing system. Formation of the complexes was followed with UV-Vis and fluorescense spectroscopy. Nash plots of the complexes were done to determine the equilibrium constant and the isosbestic point for each system. Nonlinear optical characterization of the complexing solvents was analyzed.
Quantum Chemical Methods for the Design of Molecular Non-Linear Optical Materials
Authors: Till Stephen , Till Jennifer 
Published: April 2011

AbstractThe quantum chemical design of new molecular materials for non-linear applications requires a fundamental understanding of electronic structure and properties. Targeted synthesis of candidates greatly reduces the costs and timescales of an empirical search and this is aided by prior calculation of excited state energies, energy relaxation and transfer rates, molecule-environment interactions and excited state chemistry.Essentially, the problems encountered in the routine application of standard quantum chemical methods are caused by the large size of the molecules of interest. This necessitates either the design of ultra-fast computers or numerical methods which facilitate the application of ‘exact’ techniques or the development of less resource intensive approximate methods with proven accuracy.We shall outline the theories used in the calculation of optical properties and review their computational implementation. Calculations on annellated tetraazaporphyrazines will be presented in illustration.