bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Modified Transmission Line Approach to The Analysis of Superconducting Microwave Resonators
Authors: Goff Edward D. , Weber Robert J. 
Published: April 2011

AbstractA technique for modeling a superconductor contacted piezoelectric microwave resonator is presented. A transmission line method of modeling the superconductor as a two fluid model is shown to agree with the London penetration depth, and is modeled to take into account the superconductor to normal transition. By including both the normal conductor effects along with the superconductor effects, crystal quality can be factored into this model using an analytical approximation. A two dimensional model for the superconductor, applying experimental results from Y1Ba2Cu3O7−x for circuit elements, is analyzed. The superconducting layer is modeled as an electrical circuit in combination with an acoustical circuit to model its effect on a piezoelectric resonator. The acoustical equivalent of the superconductor including mass loading effects and terminations are taken into account in the Mason model acoustical equivalent circuit.
Pressure-Sensitive Microvalves Made from Polymer Brushes
Authors: Sevick E.M. , Williams D.R.M. 
Published: April 2011

AbstractWe describe a novel microvalve, constructed from polymer chains end-grafted onto opposing surfaces of a narrow slit. The assembly of polymer chains acts as both sensor and valve for microflow control and bypasses the need to construct an external feedback mechanism. This microflow control results from densely grafted chains which repel one another and stretch away from the surface, forming a brush which acts as an elastic and impenetrable layer. The height of a sheared brush increases or decreases depending upon solvent quality, i.e the layer can show a negative Poission's ratio. The discharge through the brushlined conduit is a non-linear function of pressure enabling different modes of valve operation. For brushes which extend moderately into the inter-slit region the valve assembly maintains constant discharge over a wide range of pressure. For brushes which extend far into the inter-slit region the valve assembly cuts off flow above a critical pressure, limiting the maximum discharge.
High Temperature X-Ray Diffraction Study of the Effect of Nb and Si on Oxidation behavior of Ti3Al Alloy
Authors: Qiu Guohua , Wu Jiansheng , Zhang Lanting , Lin Dongliang 
Published: April 2011

AbstractA disadvantage to the application of Ti3Al is its poor high temperature oxidation resistance. It is found that the element Nb or(and) Si can greatly reduce the oxidation rate of Ti3A1. A hot stage in situ X-ray diffractometer was used to determine the formation sequence of the oxide layers. At 800°C, TiO2 as well as Al2O3 was detected on the surface of binary Ti3Al at the beginning of the oxidation process. The addition of 5 at % Si to Ti3Al alloy did not favor the formation of an A12O3 layer. On the contrary, it inhibited the onset of Al2O3 to nearly 20 hours from the start of the oxidation process at the temperature of 800°C. The Nb addition also did not promote the formation of Al2O3. TiO2 formed first on the surface of Ti3Al-11 at % Nb alloy while TiN and TiAl formed consequently. Al2O3 was further delayed to 20 hours from the beginning of the oxidation process. When the Nb addition increased to 15 at %, however, TiN and TiAl were not found. It is suggested that the favorable effect of Nb and Si to the oxidation resistance of Ti3Al alloy is not due to their promotion of A12O3 layer, but probably due to some other mechanisms, such as the formation of TiN which serves as a diffusion barrier and decreases porosity in the TiO2 layer.
Alloying of Cubic Alloys Based on Al3Ti: Phase Instabilities and the Control of Fault Energies
Authors: Morris David G. , Lerf Reto , Leboeuf Mireille 
Published: April 2011

AbstractAlloys based on Al3Ti with the ordered L12 structure show slight ductility when the Ti content is near 25% and about 8% of Mn or Cr is present as ternary addition. Such materials are relatively soft due to the easy movement of APB-dissociated superdislocations but remain almost completely brittle. While the precise reasons for such brittleness are not clear, it seems reasonable to consider that alloying to lower fault energies may soften the material and enhance ductility. In the present study, new alloys are selected on the basis of electronic structure calculations using the discrete variational cluster method, and the ordered state, mechanical behaviour, and dislocation and fault characteristics examined.The alloys examined were based on the Al-26%Ti-8%Mn composition, with lower Ti and Mn contents, in an attempt to maintain a single-phase matrix and weaker, less-directional bonding and lower fault energies. In addition, for some alloys, Al was partially substituted by Mg.The single-phase region of the L12 Al-Ti-Mn phase is very small and second phases such as DO22 and complex AlxMn can appear which lead to hardening and strain ageing, much as Al2Ti does in more Ti-rich alloys. Mg substitution is limited to a few percent before a Mg-rich phase appears and the alloys examined are complex mixtures of this, the L12 phase, and γTiAl. The dislocation structures observed after deformation are examined to determine fault energies, and it is shown that these values can be rationalised in terms of the structural instabilities of the matrix phases and the secondary phases produced.
Effects of Processing on the Mechanical Properties and Oxidation behavior of Al2Ti
Authors: Ma John C. , Benci John E. , Feist Thomas P. 
Published: April 2011

AbstractAl2Ti is a promising material for use in elevated temperature structural applications. It has a lower density than Ti3Al and TiAl. We have previously shown that the compressive yield strength of Al2Ti is higher than that of similarly processed TiAl and Al3Ti between room temperature and 900°C. In this study, two additional processing methods were utilized to produce the material: uniaxial hot pressing of rapidly solidified powder and hot forging of cast ingots. Effects of hot forging or annealing of as-cast Al2Ti on the microhardness and load for crack initiation were studied. The microhardness and crack initiation load were also used to compare powder processed material consolidated either by hot pressing or hot isostatic pressing. The oxidation behavior of as-cast, cast & hot isostatically pressed (cast & hip’ed), and powder processed & hip’ed (PP) Al2Ti was also investigated. The oxidation tests were performed in air at 815°C and 982°C for 100 hr. PP Al2Ti exhibited the lowest weight gain and as-cast exhibited the highest. Al2Ti shows superior oxidation resistance compared to Ti3Al- and TiAl- based alloys tested under similar conditions and shows comparable oxidation resistance to Al3Ti at 800°C. SEM/EDS was used to study the morphological development of the oxide scale and to identify the chemical constituents present in the various layers of the scale.
Study of The Microstructure and Oxidation of NbSi2 Base Alloys
Authors: Pitman S.H. , Tsakiropoulos P. 
Published: April 2011

AbstractThe microstructures of arc melted ingots and melt spun ribbons of NbSi2 and NbSi2-(8,20 at%)Cr alloys are discussed. Rapid quenching from the melt refined the grain size of the alloys by two orders of magnitude and suppressed the formation of Nb5Si3 in Zone A of the binary alloy ribbons. In the ternary alloy ingots and ribbons formation of the Nb5Si3 was suppressed, and the C40 NbSi2 and CrSi2 and orthorhombic Nb2Si6Cr3 phases were formed. Zone A was not formed in the ribbons of the ternary alloys. The microhardness of these phases and the oxidation behaviour of the alloys up to 1350°C in air and an Ar atmosphere are discussed. NbSi2 did not form a protective silica layer on oxidation. Instead a mixed oxide scale of silica and α-Nb2O5 formed which cracked during growth of the oxide and hindered protection of the alloy. It is shown that the addition of Cr modifies the oxide to a duplex oxide of SiO2 and Cr2O3 and that the underlying matrix becomes depleted in Cr. Pest oxidation at 750°C was suppressed in Nb-60Si-20Cr.
Experimental And Theoretical Studies On The C15 Intermetallic Compounds MV2 (M=Zr, Hf AND Ta): Elasticity And Phase Stability
Authors: Chu F. , Mitchell T. E. , Chen S. P. , Šob M. , Siegl R. , Pope D. P. 
Published: April 2011

AbstractThe phase stability of C15 HfV2 was studied by specific heat measurements. The elastic constants of C15 HfV2 were measured by the resonant ultrasound spectroscopy. Total energy and electronic structure of CI5 intermetallic compounds MV2 (M=Zr, Hf and Ta) were calculated using the linear muffin tin orbital (LMTO) method. The band structures at the X-point near the Fermi level were used to understand the anomalous shear moduli of HfV2 and ZrV2. It was found that the double degeneracy with a linear dispersion relation of electronic levels at the X-point near the Fermi surface is mainly responsible for the C15 anomalous elasticity at high temperatures. The density of states at the Fermi level and the geometry of the Fermi surface were used to explain the low temperature phase instability of C15 HfV2 and ZrV2 and the stability of C15 TaV2. The relationship between the anomalous elasticity and structural instability of C15 HfV2 and ZrV2 were also studied.
Effect of Heat Treatment at 1150°C on Creep-Rupture Properties of a Fe3Al-Based Alloy
Authors: McKamey C. G. , Marrero-Santos Y. , Maziasz P. J. 
Published: April 2011

AbstractThe effects of heat treatment at 1150°C on the creep-rupture properties of a Fe3Al-based alloy were studied. Tests were conducted in air using various test temperatures and stresses. By plotting the data to a power-law equation, the activation energy for creep was determined to be approximately 150 kcal/mole and the creep exponent to be about 8. Optical metallography and scanning electron microscopy of ruptured specimens indicated that failure occurred in a ductile manner by microvoid coalescence at grain boundaries and triple points. Analytical electron microscopy was used to study characteristics of the microstructure and to identify Zr-rich precipitates that formed during heat treatment or creep testing. These precipitates were found to provide strengthening by pinning dislocations and grain boundaries.
The Influence of Iron on the Physical and Mechanical Properties of β-Nial
Authors: Lim Y. J. , Hong K. T. , Levit V. , Kaufmann M. J. 
Published: April 2011

AbstractThe influence of iron on the the microstructure and properties of B2 NiAl has been investigated using electrical resistivity, magnetic susceptibility, microhardness and transmission electron microscopy. The resistivity data suggest that quenched-in vacancies (1) enhance iron rearrangement at low temperatures (600–800 K) and (2) annihilate above 800 K. These effects depend strongly on Ni/Al ratio and are greatest for Ni/Al=1. It is also shown that these data correlate directly with the results obtained using the other experimental techniques.
Assessment of Microalloying Effects on the High Temperature Fatigue Behavior of NiAl
Authors: Noebe R. D. , Lerch B. A. , Bhanu K. , Rao Sankara 
Published: April 2011

AbstractBinary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involves microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.
Microstructure and Mechanical Properties of Ni3Al-Based Alloy/Tic Composites
Authors: Yin W. M. , Guo J. T. , Wang S. H. , Li H. , Tan M. H. , Lai W. H. 
Published: April 2011

AbstractThe microstructure and mechanical properties of Ni3Al-based composites reinforced with TiC particles have been investigated. The composites, which contained 2, 6, 10 vol.%TiC particulate reinforcement, were fabricated by solidification processing method. The matrix alloy selected for this study was the advanced nickel-aluminide (Ni-16Al-8Cr-1Zr-0.8Mo-0.04B at.%).The optical micrographs revealed that the carbides in the composites distributed uniformly in the martix and appeared as fairly equiaxed particles. SEM observation showed that the interface between TiC and matrix is quite smooth, sharp and free of any phase. The test results indicated that the hardness was increased with increasing volume fraction of TiC particles at ambient temperature, and the composites exhibited higher hardness after 1100°C × 8h heat treatment. The yield strength has been improved due to reinforcement by the TiC particles at ambient and elevated temperature, but their ductility was reduced obviously. From SEM fractography, it could be seen that tensile failure occurred at the matrix / particulate interface.
A Dislocation Model for Flow at Intermediate Temperatures in Hard-Oriented NiAl
Authors: Mills M. J. , Daw M. S. , Angelo J.E. , Miracle D. B. 
Published: April 2011

AbstractRecent studies of single crystals and bicrystals indicate that dislocations of the type a<011> are important, and may actually control, deformation at intermediate temperatures (above the brittle-to-ductile transition temperature) in hard-oriented NiAl. In the present work, the fine structure of a<011> dislocations has been examined using both high resolution and diffraction-contrast transmission electron microscopy. Evidence has been found for the decomposition of a<011> dislocations into two a<001> dislocations. The initial driving force for the decomposition is due to core effects, as revealed by molecular statics and dynamics Embedded Atom Method calculations. Additional decomposition occurs by a combination of climb and glide. A continuum-based dislocation model is introduced which incorporates these relevant microstructural features.
The Effects of Interstitial Content and Annealing on the Flow and Fracture behavior of Polycrystalline ÿ-NiAl
Authors: Weaver M. L. , Levit V. , Kaufman M. J. , Noebe R. D. 
Published: April 2011

AbstractThe strain aging behavior of three polycrystalline NiAl alloys has been investigated at temperatures between 300 and 1200 K. Yield stress plateaus, yield stress transients upon a tenfold increase in strain rate, work hardening peaks, and dips in the strain rate sensitivity (SRS) have been observed between 700 and 800 K. These observations are indicative of dynamic strain aging (DSA) and are discussed in terms of conventional strain aging theories.
A Preliminary Research on the Mechanical Properties of TiAl+Ti5Si3 Dual Phase Alloys
Authors: Zhang Lanting , Qiu Guohua , Wu Jiansheng 
Published: April 2011

AbstractA sufficient Si addition to TiAl matrix has led to TiAl + Ti5Si3 dual phase alloys, showing coupled-growth microstructure. Compression tests at R.T. as well as high temperatures indicated that the yield stress increased with increasing Ti5Si3 volume fraction, and decreased at higher temperature. The reinforcement from Ti5Si3 phase was obvious, while high Si and Al contents resulted in low ductility. The fracture surfaces were quasi-cleavage. Further research should concern with the adjustment of the shape and amount of the second phase.
Fracture Toughness and Microstructure of Nial-Based Composite with TiC Reinforcement
Authors: Xing Z. P. , Guo J. T. , Dai J. Y. , Yu L. G. , Hu Z. Q. , An G. Y. , Chen Q. Y. 
Published: April 2011

AbstractFracture toughness of NiAl–based composite reinforced by TiC particulate was measured using single–edge notched three–point bend specimens. The composite was fabricated by HPES (hot pressing aided exothermic synthesis) technique. It is shown that the ambient toughness of stoichiometric NiAl was increased from 5.9 MPa m1/2 to 8.9 MPa m1/2 by incorporating 20 vol.% TiC particulates. From fracture surface analysis along with the high–resolution electron microscopy (HREM) observation, toughening mechanisms of the NiAl–TiC composite were also discussed.
A New Approach to Study Vacancy Defects in High-Temperature Intermetallic Compounds
Authors: Collins Gary S. , Sinha Praveen 
Published: April 2011

AbstractPerturbed angular correlations of gamma rays (PAC) is being applied to study defects in ordered intermetallic alloys. Vacancies on both Pd and In sublattices in the B2 system Pdln were detected after quenching through quadrupole interactions induced at nearby 111In probe atoms. Fractions of probe atoms having each type of neighboring defect were observed to increase monotonically with quenching temperature over the range 8251500 K. For compositions close to 50.15 at.% Pd, nearly equal site fractions were observed for Pd and In vacancies, indicating that the Schottky vacancy-pair defect is the thermal defect at high temperature. The formation enthalpy of the Schottky defect was determined to be 1.3(2) eV through analysis of quenching data from in the range 825–1200 K. Above 1200 K, however, the vacancy concentration was observed to saturate at a value of 1.4(2) atomic percent, perhaps due to breakdown of the law of mass action for high defect concentrations.
Effect of Rotation Relationship Between γ Grains on Compatibility of Deformation of Ti-A1 Alloys
Authors: Morris M. A. , Luster J 
Published: April 2011

AbstractThe specific rotation relationships between adjacent γ grains have been measured in an alloy of composition Ti-47.5Al-2.5Cr consisting of lamellar and equiaxed distributions of γ grains in which the α2 phase was distributed as long lamellae or smaller globules respectively. Detailed analyses of active slip systems have been carried out by TEM observations of deformed samples and from these, the effect that specific rotations between γ grains have on the compatibility of deformation across adjacent grains has been discussed. Theoretical calculations of the geometric compatibility factor characterising the best slip transfer across adjacent grains have been used and compared to the experimental results. It has been possible to deduce the role played by the type of orientation relationship between grains in producing active deformation systems that allow the maximum compatibility of deformation.
Strength, Ductility, and Fracture Mode of Ternary FeAl Alloys
Authors: Schneibel J. H. , George E. P. , Specht E. D. , Horton J. A. 
Published: April 2011

AbstractIron aluminides with the composition Fe-45Al-5X-0.2B-0.1Zr (at. %), where X stands for the first row transition metals Ti, V, Cr, Mn, Fe, Co, Ni, Cu, were examined at room temperature with respect to their strength, ductility, environmental sensitivity, and fracture mode. The extruded materials were annealed at 1273 K to produce similar grain sizes and subsequently at 673 K to reduce the amount of quenched in vacancies. All alloys were essentially single phase. Their solid solution strengthening was found to correlate with the atomic size misfit derived from the lattice parameters. The “binary” alloy Fe-45Al-0.2B-0.1Zr exhibited predominantly transgranular fracture. Ternary alloying additons with atomic numbers less than that of Fe tended to enhance intergranular fracture, whereas those with atomic numbers higher than that of Fe favored substantial amounts of transgranular fracture. Tensile testing in a partial pressure of dry oxygen increased the ductilities of the ternary alloys only slightly, whereas the ductility of the binary alloy increased from about 8 to about 19%. The ductilities in air correlated inversely with the yield strength. However, those alloys exhibiting substantial amounts of transgranular fracture always showed higher ductilities than those fracturing intergranularly. We interpret our fracture results in terms of yield strengths and ternary element site occupations.
Development of Tial-Based Automotive Engine Valves
Authors: Dowling William E. , Donlon William T. , Allison John E. 
Published: April 2011

AbstractThe application of TiAl-based alloys as an exhaust valve material would allow automotive engines to operate at higher temperatures with increased efficiencies. Development of these materials at Ford initially concentrated on the Ti-48A1-1V (at%) system. This included; 1) room and elevated temperature fatigue, 2) creep and 3) tensile ductility optimization. Results from this test program in conjunction with other available data, previous ceramic experience and limited engine testing led to the conclusion that the major roadblock to implementation was not optimizing mechanical properties, but rather low cost and reliable valve manufacturing technology. When a cost effective manufacturing technology is developed, then the emphasis will shift to ensuring the product durability. Hence, the focus of the current program is the development of valve manufacturing technologies, in particular valve blank fabrication. Currently, casting appears to be the lowest cost alternative for valve blank fabrication. This paper reviews the technology development process as it pertains to TiAl-based valves.
Properties of Reactively Synthesized Titanium Aluminides
Authors: Alman D. E. , Hawk J. A. , Wilson R. D. 
Published: April 2011

AbstractReactive synthesis directly forms compounds from their elemental constituents. In this U.S. Bureau of Mines study the microstructure, hot-hardness and tensile properties of alloys and composites based on TiAl and Ti2AlNb were studied. Ti2AlNb sheets were processed from elemental Ti, Al and Nb foils. The elemental foils were consumed during processing, leaving a microstructure consisting of three phases: O (orthorhombic Ti2AlNb), B2 (ordered cubic Ti), and α2 (Ti3Al). The composite sheet structures were heat-treated to produce a microstructure consisting of O lathes in a B2 matrix. A significant advantage of reactive synthesis is the ease of formation of complex shapes prior to synthesis of the aluminide. TiAl-based alloys and in situ TiAl/boride and TiAl/Ti5Si3 composites were produced from elemental mixtures of Ti and Al with either additions of B or Si powders. The hot-hardness and tensile properties of these alloys and composites are reported. The Kirkendall porosity associated with reactive sintering of TiAl can be eliminated by simultaneously reactive sintering TiAl and Ti5Si3.
Strength and Ductility of Ni3Al Alloyed with Boron and Substitutional Elements
Authors: Ishikawa K. , Aoki K. , Masumoto T. 
Published: April 2011

AbstractThe effect of simultaneous alloying of boron (B) and the substitutional elements M on mechanical properties of Ni3Al was investigated by the tensile test at room temperature. The yield strength of Ni3Al+B increases by alloying with M except for Fe and Ga. In particular, it increases by alloying with Hf, Nb, W, Ta, Pd and Si. The fracture strength of Ni3Al+B increases by alloying with Pd, Ga, Si and Hf, but decreases with the other elements. Elongation of Ni3Al+B increases by alloying with Ga, Fe and Pd, but decreases with other elements. Hf and Pd is the effective element for the increase of the yield strength and the fracture strength of Ni3Al+B, respectively. Alloying with Hf leads to the increases of the yield strength and the fracture strength of Ni3Al+B, but to the lowering of elongation. On the other hand, alloying with Pd improves all mechanical properties, i.e. the yield strength, the fracture strength and elongation. On the contrary, alloying with Ti, V and Co leads to the lowering of mechanical properties of Ni3Al+B. The reason why ductility of Ni3Al+B is reduced by alloying with some elements M is discussed.