bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spin-on Silicon Oxide (SOX): Physical Properties of the Sol
Authors: Ryan Vivian , Smolinsky Gerald 
Published: March 2011

ABSTRACTThis paper describes an analysis of the physical properties of the sol using several complementary light scattering techniques. Polymerization and aggregation kinetics were followed through time-dependent changes in the size, shape, and density of the sol particles. The sot growth rate was controlled by choice of solvent and silicon concentration. Changes in viscosity and pH were small during the reaction period. Three different particle-growth regimes exist in which either the particle density increased, decreased, or remained the same. The addition of boron, hydrofluoric acid, or water accelerated the reaction. The sol experimental data correlate with the density and wet-etching rate of the cured films. After curing, high-density films were obtained from sols with three common characteristics: an average particle diameter >450 Å, a relatively high polydispersity, and a low particle density. These criteria were generally satisfied by solutions one to two days old.
Effects of the Selenium Precursor on the Growth of ZnSe by Metalorganic Chemical Vapor Deposition
Authors: Giapis Konstantinos P. , Da-Cheng Lu , Jensen Klavs F. 
Published: March 2011

ABSTRACTThe growth of ZnSe on GaAs substrates by metalorganic chemical vapor deposition was investigated in a specially designed vertical downflow reactor. Dimethylzinc was used as the Zn source while different Se source compounds (hydrogen selenide (H2Se), diethylselenide and methylallylselenide) were employed to determine the effect of different source combinations on morphology, thickness uniformity, growth rate, electrical properties and photoluminescence (PL) characteristics of the grown ZnSe films. The H2Se was produced in situ by reaction of H2 and Se followed by distillation to control the amount of H2Se entering the reaction zone. H2Se produced very high mobility films with good PL spectra but poor surface morphology. Diethylselenide led to layers of good morphology and PL characteristics but the films were highly resistive. Unusual surface features were observed for methylallylselenide.
Microstructure and Magneto-Optical Properties of TbFeCo Films Prepared by Facing Targets Sputtering
Authors: Ito H. , Hirata T. , Naoe M. 
Published: March 2011

ABSTRACTThe microstructure of TbFeCo amorphous films deposited by a facing targets type of sputtering (FTS) method varied with the change of deposition rate Rd. The films deposited at Rd of about 100–200 nm/min did not present any distinguishable columnar structure while the ones at Rd of about 50 nm/min revealed obvious columnar structure. The films with columnless structure exhibited Kerr rotation angle θk of 0.37 deg. of which the value was higher than that of the films with columnar structure over the wide range of Th content. The torque measurement implied that the presence of columnar structure was not mainly necessary for the occurrence of large perpendicular magnetic anisotropy. Under satisfactory confinement of plasma during sputtering, the dense, uniform and columnless TbFeCo films can be obtained on plasma-free substrate even at Rd as high as 200 nm/min, without destroying the excellent magnetic properties and magneto-optical characteristics.
On the Coercivity of Granular Fe-SiO2 Films
Authors: Liou S. H. , Chen C. H. , Chen H. S. , Kortan A. R. , Chien C. L. 
Published: March 2011

ABSTRACTThe coercivity of granular Fe embedded inside an SiO2 matrix was as high as 3 kOe at 6K, and 1.1 kOe at 300K. In this study, we observed a linear temperature (T) dependence of the coercivity for the samples prepared at a high substrate temperature (773K), and a T1/2 dependence of the coercivity for the sample prepared at a low substrate temperature (473K). This indicates that the microstructures of films prepared at different substrate temperatures are not the same. This phenomenon can be explained if we assume that there are interconnections between particles for the sample prepared at a high substrate temperature. We looked for evidence of interconnections between particles with transmission electron microscopy (TEM).
Microstructure of an Al2O3/Metal Composite Containing an Al2O3 Filler Material
Authors: Breval E. , Nagelberg A. S. 
Published: March 2011

ABSTRACTA ceramic matrix composite consisting of 100–200 μm Al2O3 grains (90 grit) embedded an Al2O3/metal matrix was examine. The matrix was produced by the directed oxidation of a molten Al alloy. The microstructure was studied by optical methods, x-ray diffraction and transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS). The matrix A12O3 was interconnected and present as ∼50–500 nm grains in ∼ 10–50 μm regions. Within these regions, the Al2O3 was separated by low angle. Al2O3/Al2O3 grain boundaries. The boundaries between regions consisted either of high angle Al2O3/Al2O3 boundaries with no grain boundary phase or of tortuous metal channels from 50 nm up to 1 μm in width. The metallic constituent within the regions was only partly interconnected, consisting of similar channels or isolated spheres of 1–500 nm. The metal consisted of Al and Si. Large fractions of the filler Al2O3 surface (∼50%) were directly bonded to the matrix Al2O3.
Microsegregation to Antiphase Boundaries in Monolithic γ′ Phase with Ternary Additions
Authors: Wu Y. P. , Sanchez J. M. , Tien J. K. 
Published: March 2011

ABSTRACTThe microsegregation to (111) anti-phase boundaries of the constituents and of the ternary atoms in monolithic γ′ phase is modeled using the tetrahedron approximation of the Cluster Variation Method. Similar to the binary case, alloy stoichiometry and temperature play an important role in determining the type and degree of atomic segregation to anti-phase boundaries. For a given composition, the segregation phenomenon is also found to be dependent on the site preference of the ternary additions. The results of our calculations are also used in order to assess the contribution of anti-phase boundary dislocation dragging to the strength of γ′ intermetallics.
Theoretical Studies of Ni3Al and Nial with Impurities
Authors: Chen S. P. , Voter A. F. , Boring A. M. , Albers R. C. , Hay P. J. 
Published: March 2011

ABSTRACTIntermetallic compounds have been extensively studied because of their superior strength, low creep rate, and high melting point [1,2]. However, room temperature ductility for the L12 and B2 phases are a continuing problem. Both L12 Ni3Al [3,4] and B2 NiAl [5,6] exhibit an intergranular fracture mode. Understanding grain boundaries in these materials is of particular importance since intergranular fracture limits the applicability of these otherwise promising materials. In an effort to understand the fracture mechanism, we have used embedded atom potentials [7] to study the properties of Ni 3Al [8,9,10] and NiAl [11]. We also consider the effect of boron, sulfur, and nickel segregation on the strength of grain boundaries in Ni3Al and NiAl. Many of the results presented here appear in literature elsewhere [8,9,10,11].
Surface Energy Anisotropy of Diffusion-Induced Ni3A1 Crystals
Authors: Chou T. C. , Chou Y. T. 
Published: March 2011

ABSTRACTFaceted crystals with well-defined {100}, {110}, and {1111 surfaces were observed in the interdiffusion zone during chemical interdiffusion of Ni/Ni 3 Al diffusion couple in the temperature range of 800°−1200°C. Composition of the diffusion-induced crystals was determined to be 87.6Ni-12.4A1 (wt%) by electron microprobe.The shape of Ni3Al crystals showed a 26-sided polyhedron (rhombicuboctahedron) with a m3m point group symmetry at low temperature range (800° to 1000°C). At high temperatures, for example at 1212°C, the crystal shape changes to a 14-sided polyhedral form (tetrakaidecahedron) with the same point group symmetry.Based on the crystal geometry, equations describing the surface energy anisotropy, γ{111}/γ{100}, and γ{100}/γ{100}, were obtained. The surface-energy anisotropy was then calculated from the crystal dimension. For the equilibrium crystals with tetrakaidecahedral form, the inequality γ{110} > γ{110} > γ{111} holds. On the other hand, for crystals of rhombicuboctahedral form, the inequality becomes γ{110} > γ{111} > γ{100}. The experimental values were consistent with theoretical calculations based on the broken-bond model.
Compression Deformation Structures of Single Crystal TiAl
Authors: Huang B. Y. , Oliver B. F. , Oliver W. C. 
Published: March 2011

ABSTRACTThe compression deformation behavior of single crystalline TiAl was examined by transmission electron microscopy (T.E.M.). The relatively pure Ti–56 a/o Al crystal was containerless processed in ultrapure hydrogen. The crystal growth direction is 18° off (011) and 60° off [111] in the [011]– [111]-[010] unit triangle. At low stresses, a/2 [110] type dislocations were observed. a/2 [110] dislocations appeared at slightly higher stresses. Additional plastic deformation initiates twinning. Twinning plays an important role at higher stresses. Diffraction results indicate that most of the twins have the (111) mirror plane.A small amount of (111) twins were also observed. Superdislocations of the a<011> type were not observed to contribute to the plastic deformation in this crystal. The results indicate that plastic deformation by twinning follows the low density of ordinary dislocations.
Effect of Preoxidation and Grain Size on Ductility of a Boron-Doped Ni3Al at Elevated Temperatures
Authors: Takeyama M. , Liu C. T. 
Published: March 2011

ABSTRACTThe ductility of preoxidized Ni3Al (Ni-23Al-0.5Hf-0.2B, at.%) specimens with various grain sizes (17∼193 μm) was evaluated by means of tensile tests at 600 and 760°C in vacuum. It was found that the preoxidation does not affect the ductility of the finest-grained material at either temperature, whereas it causes severe embrittlement in the largest-grained material, especially at 760°C. A continuous, thin Al-rich oxide layer, which forms on the fine-grained samples, protects the underlying alloy from oxygen penetration, preventing any loss of ductility, whereas the nickel-rich oxide which forms on the large-grained samples allows oxygen to penetrate along grain boundaries, causing severe embrittlement. The grain boundaries act as short-circuit paths for rapid diffusion of aluminum atoms from the bulk to the surfaces, and this is responsible for the difference in oxidation behavior between fine- and large-grained materials. The embrittlement of large-grained samples can be eliminated through control of oxide formation on Ni3Al surfaces.
Room Temperature Tensile Ductility in Polycrystalline B2 NiAl
Authors: Vedula K. , Hahn K. H. , Boulogne B. 
Published: March 2011

ABSTRACTBinary polycrystalline alloys of B2 NiAl, ranging from 47 to 51.5 at% Al, were prepared by casting and extrusion. These were tested in tension at temperatures ranging from 300 K to 873 K. Significant tensile ductility is observed in the near-stoichiometric alloy at room temperature as well as at 473 K in spite of the presence of only <100> dislocations. This anomaly appears to be related to the recrystallized texture, to the lower yield strength and to the presence of residual dislocations at grain boundaries in this alloy.
The Development of Alloys Based on Ni3Si
Authors: Oliver W. C. 
Published: March 2011

ABSTRACTAlloys with large volume fractions of the intermetallic phase Ni3Si have unique aqueous corrosion resistance that provides the driving force for an alloy design program to improve their generally poor room temperature mechanical properties. The target of the alloy design program at Oak Ridge National Laboratory was to produce wrought alloys with at least 10% room temperature ductility while retaining good aqueous corrosion resistance. In this paper several important findings will be discussed. These include macro and micro alloying (B, C, Be) to produce superplastic wrought alloys with high strength and high room-temperature ductility. Some of the alloys developed are strong enough to be competitive with medium temperature structural alloys such as Inconel® 718.
Structural and Chemical Composition of Ni-Al Powders
Authors: Maurer R. , Galinski G. , Laag R. , Kaysser W. A. 
Published: March 2011

ABSTRACTNi3Al and NiAl pre-alloyed powders produced by argon gas atomization are investigated by light and transmission electron microscopy concerning their structure, chemical and phase composition. For example, Ni3Al powder consists of a L12 matrix (γ′ -phase) with precipitates whose Al content is 6% higher than in the matrix. Selected single powder particles were isothermally deformed in a modified high resolution dilatometer to investigate the creep behavior. From these experiments HIP parameters are predicted and compared with HIP experiments at different pressures and temperatures. HIP diagrams were calculated according to Ashby's model.
On APB Dragging and APB Energy Anisotropy in Binary Ni3Al
Authors: Dimiduk Dennis M. , Williams J. C. , Thompson A. W. 
Published: March 2011

ABSTRACTRecent weak-beam electron microscopic studies of Ni3Al provided evidence indicating that glide of Kear-Wilsdorf locked dislocation segments may occur on {111} planes, accompanied by APB dragging, during deformation at high temperature. A direct implication of those studies is that a mechanism other than the onset of {010} slip may be important in controlling the peak in yield strength in Ni3Al. The present weak-beam investigations of Ni3Al have centered on the possibility that such configurations result from thermally induced dislocation kink and jog activity rather than the APB dragging mechanism. previously proposed.
Dynamic Compaction and Hot-Isostatic-Pressing of Nickelaluminides
Authors: Arkens O. , Delaey L. , de Tavernier J. , Huybrechts B. , Buekenhout L. , Libouton J. C. 
Published: March 2011

ABSTRACTExplosive compaction and HIPping of stoichiometric mixtures of Ni and Al (and B) powder is optimized in order to obtain fine grained NiAl− and Ni3Al(+B) intermetallics.Starting from an appropriate mixture of pure fine Ni− and fine Al− (and B) powders fine nickel-aluminides are produced due to a selfpropagation high temperature synthesis during processing. HIPping experiments are done also on spherical Ni-coated Al-powders. The specimens are characterized by metallography and the homogeneity of the final product is controlled by microanalytical methods.
Notch Effects on Room Temperature Tensile and Bend Properties of Ni3Al and Ni3Al+B
Authors: Khadkikar P. S. , Rigney J. D. , Lewandowski J. J. , Vedula K. 
Published: March 2011

ABSTRACTThe notched mechanical properties of Ni3AI and Ni3Al+B prepared by powder metallurgy techniques have been determined in both tension and bending at room temperature. Ten- sile tests performed using double notched specimens containing relatively blunt notches produced intergranular fracture in both Ni3Al and Ni3AI+B, with evidence of fracture initiating in an intergranular manner ahead of the blunt notch in both cases. Estimates of notched fracture toughness from bend tests and of local grain boundary fracture stress from the notched tensile tests suggest an increase in these values with boron addition.
Processing and Microstructure of Melt Spun Niai Alloys
Authors: Locci I. E. , Noebe R. D. , Moser J. A. , Lee D. S. , Nathal M. 
Published: March 2011

ABSTRACTThe influence of various melt spinning parameters and the effect of consolidation on the microstructure of melt spun NiAl and NiAl + W alloys have been examined by optical and electron microscopy techniques. It was found that the addition of 0.5 at.% W to NiAl results in a fine dispersion of W particles after melt spinning which effectively controls grain growth during annealing treatments or consolidation at temperatures between 1523 and 1723 K. Increased wheel speeds are effective at reducing both ribbon thickness and grain size, such that proper choice of both composition and casting parameters can produce structures with grain sizes as small as 2 μ m. Finally, fabrication of continuous fiber reinforced composites which used pulverized ribbon as the matrix material was demonstrated.
Phase and Microstructure of Fe Modified A13 Ti
Authors: Porter W. D. , Hisatsune K. , Sparks C. J. , Oliver W. C. , Oliver W. C. 
Published: March 2011

ABSTRACTAlloys of Al75-xFexTi25, where x = 0 to 12 at. % Fe, were fabricated by splat cooling and examined primarily with X-ray diffraction to determine the crystallographic phases present, their composition, volume fraction, lattice parameters, and sublattice occupation. The tetragonal DO22 structure of Al3Ti dissolved 0.8 ± 0.4 at. % Fe, with additional iron partitioned to the Ll2 structure containing 6.2 ± 0.4 at. % Fe, and completed the transformation to the Ll2 structure with the addition of about 6 at. % Fe. The lattice parameters of both phases were independent of iron concentration up to about 6 at. %. At 8 at. % Fe, the iron was found to be predominantly distributed on the nominal aluminum sublattice which also contained about 5 at. % Ti. The Al3 Ti composition was similarly found to contain about 5 at. % Ti on the aluminum sublattice. All compositions, including a single crystal of Al67Fe8 Ti25, were found to be brittle.
The mechanisms of plastic deformation of rapidly solidified Al3Ti and Al67Ni8Ti25 intermetallic compounds.
Authors: Vasudevan Vijay K. , Wheeler Robert , Fraser Hamish L. 
Published: March 2011

ABSTRACTThe dislocation structures in rapidly solidified Al3Ti with the DO22 structure and the ternary Al-25Ti-8Ni (at.%) alloy with the L12 structure deformed in compression in the temperature range of 25 to 800°C have been studied by transmission electron microscopy. The room temperature deformation microstructure of the Al3Ti compound is characterized by the presence of stacking faults/order twins on {111} planes bounded by partial dislocations with Burgers vector b=1/6<112], as reported by others. At intermediate temperatures, besides the stacking faults, slip is also observed as bands on the {001] plane delineated by dislocations with b=1/2<110] which bound APB's. At 600°C, the reported increase in ductility is associated here with additional slip on the {001)<110], {001)[100] and {001)[010] systems. Dislocations with b=<110] exist as pairs of partial dislocations with b=1/2<110] connected by APB's. The mean separation between the partials was measured to be 30 nm, corresponding to an APB energy of ≍32 mJ.m-2 on the (001) plane. Observations also indicate that the APB energy is anisotropic, i.e., is considerably higher on the {111} planes compared to the {001) plane. The deformation microstructure of the Al-25Ti-8Ni L12 alloy is characterized by slip of dislocations with b=<110> gliding on {111} planes, a major fraction of which exist as dipoles. Following deformation at 300°C, there is essentially no evidence of dissociation of these dislocations, although some dissociated dislocations on (001) having b=l/2<110> are also observed. With an increase in temperature, there is a considerable increase in dislocation activity and strong evidence for 1/2<110> dissociated dislocations is present.
Microstructure/Processing Relationships in High-Energy High-Rate Consolidated Powder Composites of Nb-Stabilized Ti3Al + TiAl
Authors: Persad C. , Lee B.-H. , Hou C.-J. , Eliezer Z. , Marcus H. L. 
Published: March 2011

ABSTRACTA new approach to powder processing is employed in forming titanium aluminide composites. The processing consists of internal heating of a customized powder blend by a fast electrical discharge of a homopolar generator. The high-energy high-rate “1MJ in 1s” pulse permits rapid heating of an electrically conducting powder mixture in a cold wall die. This short time at temperature approach offers the opportunity to control phase transformations and the degree of microstructural coarsening not readily possible with standard powder processing approaches. This paper describes the consolidation results of titanium aluminide-based powder composite materials. The focus of this study was the definition of microstructure/processing relationships for each of the composite constituents, first as monoliths and then in composite forms. Non-equilibrium phases present in rapidly solidified TiAl powders are transformed to metastable intermediates en route to the equilibrium gamma phase. The initial single phase beta in Nb-stabilized Ti3Al is transformed to alpha two with an intermediate beta two phase. In composite blends of TiAl powders mixed with Nb-stabilized Ti3Al powders a 10 μm thick interfacial layer is formed on the dispersed TiAl. Limited control of post-pulse heat extraction prevents full retention of the rapidly solidified powder microstructures.
Synthesis of Ladder Polymers Via Soluble Precursor Polymers
Authors: Dalton Larry R. , Yu Luping 
Published: March 2011

ABSTRACTAlthough ladder polymers have been known for some time, poor solubility and low molecular weights have prevented processing and have discouraged consideration of these materials for structural and electronic applications. Poor solubility can be associated with strong Van der Waals interactions between delocalized π-electron clouds on adjacent chains. The optimum orbital overlap along the polymer backbone existent for ladder polymers has motivated reexamination of these systems for electronic applications. We have pursued alternatives to the tradiational acid-catalyzed polycondensation of underivatized monomers at elevated temperatures by reacting derivatized (e.g., with alkyl or vinylamine substituents) monomers at reduced temperature in organic solvents (e.g., DMF) to produce open-chain precursors to ladder polymers. These are converted to fully-fused ladder polymers by thermal processing either in solution or as solid state (e.g., thin film) materials. The preparation of precursors of improved solubility greatly enhances processing options and has permitted the utilization of both Langmuir-Blodgett methods and the perparation of optical quality films by casting (including spin casting). By control of thermal processing conditions, both derivatized and underivatized ladder polymers have been prepared. Our approach offers obvious advantages for the investigation of the effect of conformation and of substituents upon electronic properties. The preparation of copolymers with rigid rod and flexible chain segments incorporated in the polymer backbone has also been investigated. For such materials, polymers with fully fused ladder segments can exhibit improved solubility in DMF relative to polymers with open chain segments due to the absence of favorable hydrogen bonding stuctures in the former. Finally, we are investigating the effect of electrochemical polymerization of Langmuir-Blodgett films prepared with derivatized diaminobenzene. Such an approach clearly takes advantage of improved solubility of the derivatized monomer and improved molecular order which can be realized with the Langmuir-Blodgett method. Free radical polymerization may facilitate the realization of improved molecular weight distributions.
Synthesis and Dilute Solution Characterization of Extended Chain Poly(Benzazoles)
Authors: Chow Andrea W. , Bitler Steven P. , Penwell Paul E. , Wolfe James F. 
Published: March 2011

ABSTRACTThis paper reports the synthesis method for polymerizaing poly(2,6-benzothiazole) (ABPBT) and poly(2,5-benzoxazole) (ABPBO), and their dilute solution properties using low angle light scattering and viscometry. Our data indicate that the Mark-Houwink-Sakurada exponents for these extended-chain polymers are near unity, suggesting a semi-rigid conformation in dilute solutions. The solution properties agree well with the Yamakawa-Fujii worm-like chain model when persistence lengths of 130 Å and 90 Å are assumed for ABPBT and ABPBO, respectively. These values of persistence length are also in good agreement with those predicted by Flory's virtual bond model using information on the molecular geometries taken from x-ray crystallographic data on oriented fibers of ABPBT and ABPBO.