bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical Microsensors for Satellite Applications
Authors: Weiller B. H. , Barrie J. D. , Aitchison K. A. , Chaffee P. D. 
Published: April 2011

AbstractWe have been investigating several chemical microsensor technologies for the detection of chemicals found in propellant and rocket exhaust plumes and as contaminants for satellite components. In this work we have developed a catalytic metal sensor for the detection of H2contamination in electronic device packages. The sensor is based on the resistance of a thin film Pd/Ni alloy. Data have been obtained on its response at room temperature to various levels of H2as well as the effects of H2O and O2on its performance. Hydrogen levels to 10.5 ppm have been detected and the responsivity is about twice that of similar sensors. The sensor is insensitive to H2O but its response to H2is strongly inhibited by O2.
Using Dx Centers to Write Erasable Metallic Patterns in AlGaAs
Authors: Thio Tineke , Linke R.A. , Devlin G.E. , Bennett J.W. , Chadi J.D. , Macdonald R.L. , Mizuta M. 
Published: April 2011

AbstractDX centers are semiconductor dopants which form deep states due to a large lattice relaxation. At low temperature, the DX centers exhibit persistent photoconductivity. When exposed to light in a spatial pattern, the photocarriers are confined to the illuminated regions by Coulomb interaction with the localised DX centers. The resulting spatial modulation of the free carrier density gives rise to a modulation of both the electrical conductivity and the dielectric constant. We demonstrate both effects by measurements of the conductance anisotropy and optical diffraction of samples exposed to excitation in a striped pattern. Erasure is achieved by thermal annealing. The constrast ratio of the conductivity modulation is greater than 108; in our experiment it is limited to ∼100 by light scattering. We estimate that 100nm resolution is feasible. Optical diffraction efficiencies up to 40% have been demonstrated in a stripe-illuminated thick sample. The persistence of the written patterns at low temperature is potentially useful in high-density data storage applications and the fabrication of erasable submicron devices.
First-Principles Studies of γ-Tial Based Ternary Alloys
Authors: Wolf W. , Podloucky R. , Rogl P. 
Published: April 2011

AbstractSelf-consistent total energy calculations were performed to investigate the effects of ternary additions of 3d, 4d and 5d transition metal elements (V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt) to Ll0 ordered γ-TiAl. In general, we studied ordered solids of 4 atoms per unit cell. In the case of Mn additions larger supercells with up to 32 atoms were also treated. Minimizing the total energy with respect to volume and c/a ratio leads to the determination of lattice distortions due to alloying by the ternary elements. These distortions prove to be strongly dependent on whether the alloying element substitutes Al or Ti atoms. Furthermore, the site preference can be derived by comparing the formation energies of Tin-1XAln and TinXAln-i, where X is the substituting element. As a result the change of the geometry of L10 TiAl due to alloying can be estimated and may thereby give insight into the conditions at semicoherent γ/γ′ and α2/γ interfaces, which are associated to be responsible for ductility improvements of γ-TiAl based alloys.
Effects of Hydrogen on Fatigue Crack Growth of Iron Aluminides
Authors: Castagna A. , Stoloff N.S 
Published: April 2011

AbstractThree Fe-Al alloys, FAP-Y, FA-129, and Fe-35a%Al, containing 16, 28, and 35a%Al, respectively, have been subjected to fatigue crack growth testing in moist air, in oxygen, and in gaseous hydrogen. In each case hydrogen and air were embrittling. Crack growth rates increased significantly as frequency decreased. Fatigue crack growth results have been compared with those for other structural iron-base alloys. Surprisingly, FAP-Y displays the highest crack growth rate of any alloy examined, except at very low levels of stress intensity range. The mechanisms for embrittlement by hydrogen and by moisture in air are discussed.
Anomalous Oxidation of Intermetallics
Authors: Berztiss D. A. , Pettit F. S. , Meier G. H. 
Published: April 2011

AbstractMoSi2, (γ-NiAl and TiAl with Cr additions are of interest for high temperature applications in oxidizing environments, where an oxide layer such as SiO2 or Al2O3 should form to protect the base material. At elevated temperatures (600-1700°C), a protective SiO2 layer forms on MoSi2, while near 500°C pesting and/or accelerated oxidation could disintegrate the material to powder as Mo and Si oxidize to form a complex, thick, non-protective oxide layer. Use of γ -TiAl is limited by poor oxidation resistance, whereby layered mixed oxides of TiO2 and Al2O3 form. With the addition of Cr from 4 to 34 at%, results are varied: protective Al2O3 formation, mixed oxide formation as with TiAl or more rapid oxidation than TiAl. NiAl is currently used as a diffusion coating on Ni-based superalloys and is being considered for use as a structural material itself because of its excellent oxidation resistance, i.e. forming α-alumina above 1000°C. Recent work indicates that pure NiAl oxidized under low oxygen partial pressures in a contained atmosphere develops nonprotective oxide scales similar to accelerated oxidation of MoSi2. This study explores the parameters defining protective behavior of these intermetallics and attempts to describe and explain anomalies at low temperatures and pressures.
Core Structure And Mobility Of a <101] Dislocations In L10 TiAl
Authors: Rao S. , Woodward C. , Simmons J. , Dimiduk D. 
Published: April 2011

AbstractAn empirical atomistic potential, fit to the structural and elastic properties of L10 TiAl within the embedded atom method (EAM), is used to simulate the mobility of two possible planar forms of a<101] dislocations in a model L10 compound. The two configurations examined were: the planar SISF-APB-CSF coupled (P core) and the decomposed 1/2<110]-SISF-SESF coupled (D core). Six different line orientations are considered for the P core: 0° (screw), 30°, 60°, 90° (edge), 120° and 150°. The ‘ideal’ friction stress at 0°K of a<101] dislocations in the P form is found to be a function of line orientation, with the close packed line directions, <101] (screw) and <110] (60°), having friction stresses ranging from 0.001–0.002μ. Previously calculated results on the friction stress of a/2<110] dislocations, using an identical potential are consistently higher than the friction stress of a<101] dislocations. Simulations of the interaction of glide strains with the D core for the 60° (line directions < 110]) and 120° (line directions <011]) orientations show that the Shockley partial trailing the SESF in the D core is strongly pinned. The dislocation moves by extension of SESF when glide stresses are applied with SESF as the trailing fault.
The High-Temperature Oxidation of Nb-40Ti-15Al and the Effect of Cr Alloying and Silicide Diffusion Coatings
Authors: Cockeram B. V. , Schmutzler H. J. , Shyue J. , Hoshino K. , Meng S. , Wheeler R. , Fraser H. L. 
Published: April 2011

AbstractThe high-temperature oxidation resistance of Nb-40Ti-15Al-(0 or 5)Cr alloys has been studied. The kinetics and activation energy for the isothermal oxidation of Nb-40Ti-15Al are similar to pure titanium. Detailed TEM analysis of the oxidized Nb-40Ti-15Al alloy reveals that oxygen dissolution has produced a case layer by the decomposition of the matrix B2 phase into oxygen saturated alpha-Ti and an A15 phase. Internal oxidation of the A15 phase to form AlNbO4occurred in the case layer near the scale/metal interface. The phase separated case layer evolved into a segregated oxide layer containing a co-continuous TiO2phase. These morphologies of the oxide scale and case layer correlate well with the kinetic data, and suggest that oxygen dissolution in α-Ti and diffusion through TiO2control the high-temperature oxidation rates. The Cr additions reduced the thickness of the case layer and slowed the oxidation kinetics, but did not change the mechanism. In addition, excellent cyclic oxidation resistant was provided by the silicide diffusion coatings.
Application of Norbury Rule to Thermal Conductivity in Intermetallic Compounds
Authors: Terada Yoshihiro , Mohri Tetsuo , Suzuki Tomoo 
Published: April 2011

AbstractThermal conductivity data at room temperature, which are measured by laser-flash method, are presented in B2 aluminides and titanides, and in nickel based L12 compounds. The thermal conductivity λ is changed in the following order of the compounds. λ(NiAl) >λ(CoAl)>λ(FeAl), λ(NiTi)<λ(CoTi)<λ(FeTi), λ(Ni3Al)>λ(Ni3Si) and λ(Ni3Ga)>λ(Ni3Ge). According to Norbury rule originally proposed for the concentration dependence of electrical resistivity, the increasing rate is greater in the solid solution, where the position of solute elements is more remote in horizontal distance from a host metal in the periodic table. It is found that this rule holds for the thermal conductivity measured for the intermetallic compounds with the combination of a series of guest constituents and a fixed host constituent both in the B2 and Ll2 intermetallic compounds.
The Mechanical Properties of Fe-36.5Al and its Cr or ti Containing Alloys at Elevated Temperature
Authors: Li Dingqiang , Liu Yi , Shan Aidang , Lin Dongliang 
Published: April 2011

AbstractThe mechanical properties of B2 structural FeAl alloys, prepared by hot rolling, at elevated temperatures have been measured by tensile tests. The alloys of Fe-36.5at.%A1, Fe-36.5at.%A1-5at.%Cr and Fe-36.5at.%Al-2at.%Ti were taken for tensile tests at a temperature range from room temperature to 1000°C. The fracture surfaces of these alloys were observed by SEM. The results showed that elongations of these alloys increased with increasing temperature when the testing temperatures were above 600°C. All the maximum elongations of these alloys appeared at 1000°C and those of Fe-36.5A1, Fe-36.5Al-5Cr, and Fe-36.5Al-2Ti alloys were 120%, 183% and 208% respectively. Fracture surfaces showed that failure of these alloys was by a combination of intergranular fracture and transgranular cleavage below 700°C. but showed a ductile fracture above 700°C. The ductility and strength of ternary alloys were higher than that of binary FeAl alloy at elevated temperatures, especially at high temperature. The <111> dislocations and helices have been observed in Fe-36.5A1 alloy by TEM. The large elongation of FeAl alloy at high temperature resulted from <111> dislocations slipping and <111> helices climbing.
<111> Slip in Nial Single Crystals Between 4.2K and 100K
Authors: Sun Y. Q. , Taylor G. , Darolia R. , Hazzledine P. M. 
Published: April 2011

AbstractSlip in <111> directions is a deformation mode found in many intermetallic compounds ordered into the B2 (CsCl) structure, but in NiAl it is active only under the limiting conditions of uniaxial loading along <100> and low testing temperatures. This paper investigates the deformation characteristics of <100> oriented NiAl tested between 4.2K and 300K. Compression tests have shown that below about 100K, deformation takes place by slip in <111> directions without kinking, whereas between 100K and 300K kinking in the form of shearing on {100} becomes the dominant mode of plastic deformation, occurring usually near one or both ends of the compression samples. The yield stress has been found to exhibit a normal decrease with temperature, but at a rate that is smaller than most bcc metals. The sensitivity of the flow stress to strain-rate changes is also characteristically small, giving activation volumes around b3, b being the Burgers vector of a<111> superdislocation. Both slip line observations and transmission electron microscopy have shown slip mainly on {110} near 80K, but with increasing activity on {112} and cross-slip between {110} and {112} with the lowering of temperature to 4.2K.
Site Preference of Ternary Additions in Ni3A1
Authors: Sluiter M. , Takahashi M. , Kawazoe Y. 
Published: April 2011

AbstractThe site preference of a large number of alloying elements in Ni3AI (γ′) was studied in a systematic way by using electronic structure calculations based on the local density approximation. Alloying elements in this intermetallic may occupy exclusively the Ni or Al sublattices, or may exhibit no particular site preference. By performing the calculations both for spin-polarized and non-spin-polarized cases, it was found that magnetism strongly affects the computed site substitution behavior of Mn, Fe, and Co in Ni3Al. In the case of Fe, for example, a preference for the Ni sublattice is computed when magnetic effects are ignored, but when magnetic effects are accounted for it is found that Fe has no significant site preference, in much better agreement with a large number of experimental determinations. Some trends regarding the site preference across the periodic table are shown and discussed.
Quantitative Evaluation of Crack Bridging in Fully Lamellar Ti-48A1-2Cr-2Nb
Authors: Wissuchek D. J. , Lucas G. E. , Evans A. G. 
Published: April 2011

AbstractThe toughening effect of ligaments in a fully lamellar Ti-48Al-2Cr-2Nb alloy has been determined by evaluation of J integrals of the crack tip and crack wake regions from surface strain maps. The crack tip fracture toughness KtiP was found to vary with lamellae orientation and ranged from Ktip = 13 MPa√m for inter-lamellar fracture to Ktip = 19.5 MPa√m for translamellar fracture The bridging contribution to fracture toughness was found to arise from a bimodal distribution of ligament sizes. Fracture surface reconstructions showed a distribution of large hinges that initiated at grain or subcolony boundaries and smaller ligaments associated with delaminations within a grain. The stress-displacement functions for these two ligament populations have been determined from a large scale bridging analysis of the resistance curves along with fractographic information. The small ligamerts appear to account for the initial rapid rise in crack growth resistance; and the large hinges, for the slow continued rise in toughness at large crack extensions.
Experimental Tem and Image Simulation of <A> Dislocations in Ti3A1
Authors: Wiezorek JÖrg M.K. , Court S. A. , Humphreys C.J. 
Published: April 2011

AbstractThe fine structure and the character of a dislocations on prism planes have been determined for room-temperature deformed polycrystalline Ti3Al using a combination of experimental and computational techniques of transmission electron microscopy (TEM). Within the resolution limits of the weak-beam technique the fine structure of prism plane a dislocations in Ti3Al is found to be planar and to comprise only a single ribbon of antiphase boundary and no experimentally observable stacking faults.
Fatigue Crack Growth Characteristics and Fracture Toughness of γ-Tial Base Alloy Sheet Material
Authors: Behr R. , Wanner A. , Clemens H. , Glatz W. 
Published: April 2011

AbstractRoom temperature tension-tension fatigue crack growth experiments were perfomed on single edge notch specimens of Ti-48Al-2Cr sheet materials produced on industrial scale with different microstructures ranging from near gamma to fully lamellar. Crack extension was monitored using a travelling optical microscope and a DC potential method. Crack paths and fracture surfaces were investigated by SEM. Fracture toughness data were determined by monotonic loading of previously fatigued samples.
Microstructures in Rapidly Solidified Gamma Titanium-Aluminum Alloys with Erbium Additions
Authors: Kral M. V. , Bassler B. T. , Hofmeister W. H. , Wittig J. E. 
Published: April 2011

AbstractErbium additions of 0.25, 0.5, 1.0 and 2.0 atomic percent were incorporated into base alloys of 40 at.% titanium - 60 at.% aluminum by arc melting. Samples of 0.30g were electromagnetically levitated and melted and then rapidly solidified by double anvil splat quenching with liquid temperatures ranging from the liquidus temperature to near the maximum undercooling temperature for each alloy. Microstructures of TiAl with 0.25 and 0.5 at.% Er showed the presence of small erbium rich particles within γ grains as well as antiphase domain boundaries, while TiAl with 1.0 and 2.0 at.% Er showed no evidence of these features. These observations were correlated with solidification velocity measurements on levitated samples. Evidence for disordered primary solidification and a solid state disorder/order reaction is presented.
Characterization of the High Temperature Dislocation Substructure of Mosi2
Authors: Campbell J. P. , Chang H. , Gibala R. 
Published: April 2011

AbstractThe dislocation substructure of polycrystalline MoSi2 deformed in compression at temperatures ranging from 900°C to 1300°C has been investigated. Slip is found to occur primarily by <100> Burgers vectors. A quantitative characterization of the <100> dislocation substructure is developed for several deformation temperatures, including the slip systems present and the relative occurrence of each. Orientation distributions showing the screw/edge character of the <100> dislocations are generated at each deformation temperature. Variations in these distributions with temperature are noted, and the implications of these variations to the deformation behavior of MoSi2 are discussed. Notable observations include the onset of dislocation climb between 900°C and 1100°C, a strong preference for dislocations of mixed character at 900°C, and the complete absence of pure screw dislocations from 900°C to 1300°C.
Toughened Microstructures for Ductile Phase Reinforced Molybdenum Disilicide
Authors: Packard S. M. , Ghosh A.K. 
Published: April 2011

AbstractVarious morphologies of ductile Nb refractory metal reinforcement are incorporated into a MoSi2 matrix using powder metallurgy, including single-ply laminates, continuous metal ribbons and sections of 2-dimensional wire mesh. Hot forging techniques are used to redistribute the reinforcement and change the dimensions and the aspect ratio of the reinforcing metal ligaments. Work-of-rupture measurements are conducted on bend test specimens and precracked tensile specimens of the composite so that the toughness contribution from the various ductile metal morphologies can be assessed according to its effectiveness. Accompanying microstructural examination of crack bridging interaction with the reinforcement is conducted.
The Effect of Grain Refinement on the Room-Temperature Ductility of As-Cast Fe3Al-Based Alloys
Authors: Viswanathan S. , Andleigh V. K. , McKamey C. G. 
Published: April 2011

AbstractFe3Al-based alloys exhibit poor room temperature ductility in the as-cast condition. In this study, the effect of grain refinement of the as-cast alloy on room-temperature ductility was investigated. Small melts of Fe-28 at. % Al-5 at. % Cr were inoculated with various alloying additions and cast into a 50- × 30- × 30-mm graphite mold. The resulting ingots were examined metallographically for evidence of grain refinement, and three-point bend tests were conducted on samples to assess the effect on room-temperature ductility. Ductility was assumed to correlate with the strain corresponding to the maximum stress obtained in the bend test. The results showed that titanium was extremely effective in grain refinement, although it severely embrittled the alloy in contents exceeding 1%. Boron additions strengthened the alloy significantly, while carbon additions reduced both the strength and ductility. The best ductility was found in an alloy containing titanium, boron, and carbon.
Silicon Nitride Ceramic Matrix for CMCs from Silane Derived Si Powders and Preceramic Polymers
Authors: Rhine Wendell E. , Lightfoot Annamarie , Seyferth Dietmar , Haggerty John S. 
Published: April 2011

ABSTRACTSi powders synthesized by the laser pyrolysis of silane can be nitrided at 1200–1250°C, producing an improved reaction bonded silicon nitride. This RBSN is a potential matrix for composites since it can be formed at temperatures which do not degrade the strengths of commercially available amorphous ceramic fibers. However, the density of the RBSN matrix has been limited to about 75% using the silane-derived Si powder. Combining Si powders and preceramic polymers offers an approach for increasing the density and mechanical properties of the reaction-formed Si3N4matrix. The incorporation of polysilazanes inhibited the nitridation at 1250°C, but samples could be effectively nitrided at 1400°C. These higher nitriding temperatures are compatible with SCS-6 and other lowoxygen, crystalline SiC fibers which can be used as reinforcements for ceramic composites.
Interface Characterisation Using an SEM-Based Micro-Indentor
Authors: Lewis M.H. , Daniel A.M. , Cain M.G. 
Published: April 2011

ABSTRACTThe design and performance of an SEM-based microindentor, for interfacial property measurements in CMCs, is described. It enables high resolution imaging and simultaneous load/displacement monitoring with capacity and resolution of 20N ± lmN (load) and 100μm ± 10nm (displacement). Its application to measurement of interface debond and shear stresses for a wide range of fibres and monofilaments is described.
Growth of Diamond Film By CVD on Near Net Shape Fabricated β-SiC/TiC Composites Synthesized Using SHS
Authors: Raghunathan R. , Chowdhury R. , Jagannadham K. , Narayan J. 
Published: April 2011

ABSTRACTβ-SiC/TiC composites were synthesized using the process of self propagating-high temperature combustion synthesis (SHS). The heat released during the exothermic reaction between Si and C powders (with a δH of -14kcal/mole) and that Ti and C powders (with a δH of -44.1 kcal/mole) is sufficient to cause the melting of the powders into which the carbon diffuses and from which β-SiC and TiC precipitate out of the supersaturated solution. The composite was characterized using X-ray diffraction techniques, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. An attempt was made to understand the mechanism of formation of the composite. We have proposed a mechanism to understand the formation of the SHS compounds based on dissolution, diffusion and precipitation from the supersaturated solution. There is no evidence for the presence of TiSi2 and an attempt was made to explain this observation based on free energy considerations. Diamond film was then grown on the pellet by hot filament CVD technique using methane and hydrogen gas as the reactants. The deposition was conducted for a period of four hours. A continuous film of diamond was found to grow on β-SiC/TiC composite using this technique. The diamond film was characterized by using Raman spectroscopy and SEM. The diamond film showed both (001) and (11) facets with average grain size of 5 μm.
Displacement Reactions in the Ni-Al-O System Resulting in Periodic Layer Structures
Authors: Song Daniel W. , Subramanian Ramesh , Dieckmann RÜdiger 
Published: April 2011

ABSTRACTDisplacement reactions may play an important role in in situ processing technologies for the production of metal-ceramic composites. To better understand such reactions displacement reactions between NiO and Al were studied at high temperatures. Different reaction layers with periodic structures were observed involving Al2O3, Al3Ni, Al3Ni2, Ni and Al. The experimental observations are presented and discussed with regard to the reaction mechanism.
Computer Simulation of Displacement Cascade Damage in Metals
Authors: Gao F. , Wooding S.J. , Calder A.F. , Bacon D.J. 
Published: April 2011

AbstractMD simulations of displacement cascades in a variety of metals of different crystal structure and an ordered alloy are discussed. Frenkel-pair production at the end of the cascade process is well below the NRT theoretical value in all cases and a new empirical relationship between Frenkel-pair number and damage energy is assessed. In contrast with this, antisite production efficiency in ordered alloys increases with increasing energy, as does the atomic mixing of the different atomic species. The degree of clustering of interstitials in cascades is materialdependent. These results are discussed in relation to the highly disordered zone formed in the thermal spike.