bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamical Estimations on the Amount of Liquid Phase During Reaction Synthesis of Nickel-Aluminides
Authors: Miura Seiji , Mishima Yoshinao 
Published: April 2011

AbstractThe amounts of intermetallic compounds and liquid phase are estimated as a function of temperature during reaction syntheses for Ni–Al binary alloys having arbitrary compositions under adiabatic conditions. It is assumed that the phases that would present during the process are only those appearing in the equilibrium binary phase diagram. Calculations are done by using available data on heat of formation of intermetallic compounds and those on enthalpy of liquid phase. The results obtained arc discussed in view of the estimation and control of the amount of liquid phase, which is significant for the densification and shape change of materials.
Phase Stabilities in Some B2 Type Ordered Ni-Al-X Alloys
Authors: Shinoda Tetsumori , Mishima Y. , Suzuki T. 
Published: April 2011

AbstractThe difference in developing of solubility lobe (s.l.) of B2 phase from the B2 NiAl point on each isothermal phase diagram of Ni-Al-Co, Ni-Al-Fe and Ni-Al-Mn is expected to be explained in terms of the pattern of free energy minimum (f.e.m.) line in the B2 phase region of these phase diagrams. To calculate such the f.e.m. line, a simple way has been proposed based on the tetrahedron approximation of the cluster variation method (CVM) making use of a relationship to correlate the conventional chemical potential of a species with some kinds of the CVM variables. The calculated results show that the f.e.m. line well reflects the solubility lobe developing of the B2 phase for both Ni-Al-Fe and Ni-Al-Co while some disagreement arises with Ni-Al-Mn. The results also show a theoretical possibility of transition from the high ordered state B2 to a low ordered one under a relatively low temperature regime so far as the present free energy model are concerned.
The Influence of Boron Additions in Cast Ti-47AL-2Cr-2Nb-0.8B
Authors: Schwartz Daniel S. , Shih Donald S. 
Published: April 2011

AbstractMorphology, fine structure, and chemistry of phases formed in cast Ti-47Al-2Cr-2Nb-0.8B due to boron addition were examined in detail. Boron acts an inoculant, refining and stabilizing the cast grain size. A curving ribbon-shaped phase was present throughout the material, related to the ordered phase Ti2AlCr. The ribbon phase had the B2 structure, with a0∼0.318nm. Many ribbons had a low degree of order, i. e. the material was a BCC mixture of Ti, Al, Nb, and Cr. Ribbon phase composition was variable, measured to be: Ti-(20–30)Al-(2–4)Nb-(5–16)Cr. TiB2 was present in small amounts, always in intimate contact with the ribbon phase. A (100)ribbon ‖ {1100}TiB2, (011)ribbon ‖ {1122}TiB2 orientation relationship was observed. It is proposed that the ribbon phase is a remnant of the high-temperature titanium aluminide β-phase, stabilized by dissolved boron.
Nickel Aluminide (Ni3Al) Fabricated By Reactive Infiltration
Authors: Chen Yuyong , Chung D.D.L. 
Published: April 2011

AbstractNickel aluminide Ni3Al in single phase form, with grain size ∼ 10 μm, porosity ∼ 5%, tensile strength 425 MPa, modulus 92 GPa and ductility 9.5% at room temperature, was fabricated by reactive infiltration at 800˚C of liquid aluminum into a porous preform containing 78 vol.% nickel and made by sintering 3–7 μm size nickel particles.
Properties of Hot-Pressed Cr-Cr3Si
Authors: Newkirk Joseph W. , Price Joseph E. 
Published: April 2011

AbstractPreviously, Cr-Cr3Si in-situ composites produced by arc-melting were shown to have good strengths at high temperatures1. For example, samples of a 25% Cr and 75% Cr3Si composite achieved bend strengths of 135 MPa at 1200°C. However, there is potential for even higher strengths at high temperatures and a need for improvement in the low temperature strength and toughness. In order to improve the properties, two approaches were taken. The first used powder metallurgy to develop a better microstructure than in the cast alloys, to try to improve both strength and toughness. The second approach was to incorporate erbia into the composites, to improve the strength and stability of the microstructure at elevated temperatures.High density samples of hot pressed Cr-15.5Si and Cr-18.6Si have been produced by mixing Cr and Gr3Si powders and hot pressing in a graphite die. Erbia powders have been incorporated into some compacts for comparison.Micros true tures have been characterized and mechanical properties determined. Both the hot pressing and the erbia affected the properties. In addition the erbia had a significant effect on consolidation of the samples.
Susceptibility of Iron-Rich Fe-Al Alloys to Embrittlement by Hydrogen and Water
Authors: Lynch R. J. , Heldt L. A. 
Published: April 2011

AbstractIron-rich Fe-Al alloys have been tensile tested in moist air and dry oxygen at a strain rate of 3.3×10−4 s−1. Moist air did not cause embrittlement until the composition reached 18-20% Al. Alloys with lower aluminum contents were embrittled when tested in hydrogen gas. The environmental sensitivity of these alloys was further investigated by examining the effects of strain rate on the ductility. For the most part, no significant strain rate effects were observed in the low aluminum alloys; strain rates of up to 3.3×10−1 s−1 were not fast enough to prevent embrittlement. In contrast, the ductility of Fe-35 at.% Al did increase with increasing strain rate in air and hydrogen; at a strain rate of 3.3×10−1 s−1 the elongations approached that of vacuum.
Fabrication of Sic Matrix Composites by Liquid Phase Infiltration with a Polymeric Precursor
Authors: Interrante Leonard V. , Whitmarsh C.W. , Sherwood W. 
Published: April 2011

ABSTRACTA process for the fabrication of SiC matrix composites has been developed which employs aliquid, highly branched, polycarbosilane (AHPCS). This polymer thermosets on heating at 200-400 °C (or at 100 °C with catalyst) and yields an amorphous SiC with low excess C and O content in 60-80% yield on pyrolysis to 1000 °C. Preforms consisting of C-coated Nicalon SiC fiber cloth, unidirectional Textron SiC SCS-6 fiber layups, or Mo boats packed with SiC whiskers, were infiltrated with the polymer, cured in an autoclave, and pyrolyzed to 1000 °C. Five to eight infiltration cycles gave net shape composites with final densities at 85-94 % of theoretical. The results of 4-point flexure tests on the as-prepared Nicalon composites indicate flexure strengths (aver. 378 MPa) that are comparable to or better than similarly reinforced CVI-SiC matrix composites. The whisker and SCS-6 composites showed a small weight loss (10-20%) on heating to 1500 °C in Ar and little or no weight change or obvious embrittlement in air at 1000 °C.
Microstructure and Mechanical Properties of 2D SiC-Reinforced Carbon Matrix Composites
Authors: Bourrat Xavier , Evans Anthony. G. 
Published: April 2011

ABSTRACTFiber-reinforced composites consisting of combination of SiC and C have been explored as materials having thermostructural characteristics suitable for elevated temperature applications [1–4]. There are two opposing strategies. One uses C fibers and a matrix of SiC, usually produced by CVI [5, 6]. The other uses SiC fibers and a matrix consisting of C ; those are designated CERACARBTM and were studied in this paper.
Solid Solubility and Diffusivity in an Alumina/Zirconia System
Authors: Stough Matithew A. , Hellmann John R. 
Published: April 2011

ABSTRACTPolycrystalline zirconia-coated single crystal sapphire fiber displays reconstruction of the sapphire surface in regions of contact with zirconia grains. This is a concern where ZrO2 -coated sapphire fiber is desired for reinforcement of ceramic matrices. Previous work has demonstrated pitting is partially attributed to impurity-induced transient liquid phase formation with local dissolution of alumina; however, the extent of reconstruction witnessed via microscopy suggests that other mechanisms are active. The present study has addressed the issue of solid solubility and interdiffusivity to more thoroughly understand the solid state mechanisms contributing to pitting. Single crystal sapphire and zirconia were ion implanted with zirconium and yttrium, and aluminum, respectively, and then subjected to diffusion anneals at 1200° - 1600°C to study redistribution of implanted cations. Secondary Ion Mass Spectroscopy (SIMS) was used to profile the redistribution of implanted ions for measurement of diffusion coefficients and solubility limits after heat treatments. The results will offer a significant set of data on interface stability in the alumina/zirconia system.
Radiation-Induced Grain Boundary Segregation in Austenitic Stainless Steels
Authors: Bruemmer S. M. , Charlot L. A. , Vetrano J. S. , Simonen E. P. 
Published: April 2011

AbstractRadiation-induced segregation (RIS) to grain boundaries in Fe-Ni-Cr-Si stainless alloys has been measured as a function of irradiation temperature and dose. Heavyion irradiation was used to produce damage levels from 1 to 20 displacements per atom (dpa) at temperatures from 175 to 550°C. Measured Fe, Ni, and Cr segregation increased sharply with irradiation dose (from 0 to 5 dpa) and temperature (from 175 to about 350°C). However, grain boundary concentrations did not change significantly as dose or temperatures were further increased. Although interfacial compositions were similar, the width of radiation-induced enrichment or depletion profiles increased consistently with increasing dose or temperature. Impurity segregation (Si and P) was also measured, but only Si enrichment appeared to be radiation-induced. Grain boundary Si peaked at levels approaching 8 at% after irradiation doses to 10 dpa at an intermediate temperature of 325°C. No evidence of grain boundary silicide precipitation was detected after irradiation at any temperature. Equilibrium segregation of P was measured in the high-P alloys, but interfacial concentration did not increase with irradiation exposure. Comparisons to reported RIS in neutronirradiated stainless steels revealed similar grain boundary compositional changes for both major alloying and impurity elements.
Radiation Enhanced Diffusion in Fcc Alloys
Authors: SchÜle Wolfgang 
Published: April 2011

AbstractDiffusion mechanisms in fcc materials during irradiation with high energy particles due to vacancies, interstitials, di-interstitials, and dynamic crowdions are discussed. It is shown that in most alloys an increase in the degree of order is obtained by migrating vacancies and interstitials, and only in ∝-copper-zinc alloys mainly interstitials and in nickel-chromium alloys mainly vacancies are able to increase the degree of order during irradiation. The migration activation energies of interstitials and of vacancies for these two alloys are derived.Mass transport also by channeling and by dynamic crowdions is shown for Ni63 in nickel irradiated with 1.85 MeV electrons.
Amorphization of Complex Ceramics by Heavy-Particle Irradiations
Authors: Ewing R.C. , Wang L.M. , Weber W.J. 
Published: April 2011

Abstract“Complex” ceramics, for the purpose of this paper, include materials that are generally strongly bonded (mixed ionic and covalent), refractory and frequently good insulators. They are distinguished from simple, compact ceramics (e.g., MgO and UO2) by structural features which include: 1.) open network structures, best characterized by a consideration of the shape, size and connectivity of coordination polyhedra; 2.) generally, complex compositions which characteristically lead to multiple cation sites and lower symmetry; 3.) directional bonding; 4.) bond-type variations, from bond-to-bond, within the structure. The heavy particle irradiations not only include ion-beam irradiations, but also recoil-nucleus damage resulting from a-decay events from constituent actinides. The latter effects are responsible for the radiation-induced transformation to the metamict state in minerals. The responses of these materials to irradiation are complex, as energy may be dissipated ballistically by transfer of kinetic energy from an incident projectile or radiolytically by conversion of radiation-induced electronic excitations into atomic motion. This results in isolated Frenkel defect pairs, defect aggregates, isolated collision cascades or bulk amorphization; all may occur concurrently. Thus, the amorphization process is heterogeneous. Only recently have there been systematic studies of heavy particle irradiations of “complex” ceramics on a wide variety of structure-types and compositions as a function of dose and temperature. In this paper, we review the conditions for amorphization for the tetragonal orthosilicate, zircon [ZrSiO4]; the hexagonal orthosilicate/phosphate apatite structure-type [X10(ZO4)6(F,Cl,O)2]; the isometric pyrochlores [A1-2B2O6(O,OH,F)o-1pH2O] and its monoclinic derivative zirconolite [CaZrTi2O7]; the olivine (derivative - hcp) structure types, α-VIA2IVBO4, and spinet (ccp,) γ-VIA2IVBO4.
Effects of Ion Dose and Irradiation Temperature on the Microstructure of Three Spinel Compositions
Authors: Wang L.M. , Gong W.L. , Bordes N. , Ewing R.C. , Feit Y. 
Published: April 2011

AbstractThree compositions with the spinel structure (γ-AIVB2VIO4), MgAl2O4, FeCr2O4 and γ-SiFe2O4, have been irradiated with 1.5 MeV Kr+ ions over a temperature range (20 to 873 K). In situ TEM and HRTEM afterwork were conducted to characterize the effects of the ion irradiation on the microstructure. MgAl2O4 was the most “radiation-resistant” among the three materials. After irradiation to lx1016 ions/cm2 at 20 K, the cations were completely disordered among all possible tetrahedral and octahedral sites, but the oxygen sublattice remained intact. At room temperature, a high density of dislocation loops developed after this same dose, but there was no evidence of cation disordering. However, γ-SiFe2O4, a spinel structure type, formed under high pressure (7.0 GPa), was easily amorphized at low ion doses (σ1014 ions/cm 2) below 723 K, even lower than required for radiation-induced amorphization of its olivine polymorph, fayalite (α-SiFe2O4; HCP). At 873 K, the amorphous phase recrystallized to magnetite (Fe2+Fe 3+2O4, an inverse spinel structure) and quartz (SiO2) during continued Kr+ irradiation. Chromite (ideally FeCr2O4) with an actual composition of (Fe0.6Mg0.4)(Cr0.7A10.3)2O4 amorphized at 6x1015 ions/cm2 at 20 K, a dose about 20 times as high as that required to amorphize most other AB2O4 phases under the same irradiation conditions. A structural parameter, which quantifies the deviation from ideal packing in the spinel structure was developed and correlates with themeasured doses required for amorphization among these three spinel compositions.
Fabrication of Optical Channel Waveguides in the GaAs/AlGaAs System by Mev Ion Beam Bombardment
Authors: Taylor T. , Ila D. , Zimmerman R. L. , Ashley P. R. , Poker D. B. 
Published: April 2011

AbstractWe have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3x1013 and 3x1014 ions/cm2. Although disordering of GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors' knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 μm.
Stability of Cascades Under ion and Electron Irradiation in Germanium
Authors: Abe Hiroaki , Kinoshita Chiken , Denda Yasutaka 
Published: April 2011

AbstractConcurrent irradiation with ions and electrons has been done in a high voltage electron microscope interfaced with an ion accelerator. The objective is to clarify the stability of cascades in Ge in terms of the elementary processes associated with the concurrent irradiation. Amorphous-like cascade contrast is observed under ion irradiation and increases in number eventually leading to saturation. The cascade contrast is produced within cascade regions through sequential overlaps of cascades and heavier ions form more stable cascade regions. The concurrent or subsequent electron irradiation recrystallizes cascade regions through shrinkage of the cascade contrast. Point defects and their diffusion induced by electrons contribute to the recrystallization of cascade regions.
Helium and Hydrogen Induced Growth of Microcavities in Silicon; Application to Gas And Impurity Collection
Authors: Veen A. Van , Schut H. , Hakvoort R.A. , Fedorov A. , Westerduin K.T. 
Published: April 2011

AbstractThermal helium desorption spectrometry and positron beam analysis have been used to monitor the growth of helium vacancy clusters during room temperature helium irradiation of silicon and during subsequent annealing to 1300 K. Experimental results obtained with hydrogen irradiation show that also hydrogen can be used to create cavities. There is a rather sharp threshold dose for creating cavities that will survive 1300 K annealing. It appears that positrons form a sensitive probe for the trapping and release of impurities inside the cavities. Results of atomistic calculations are used to discuss thermal stability of helium vacancy complexes. The results are related to recent impurity gettering studies based on impurity trapping at helium induced gettering centers.
Wavelength Dependence of the Non-Linear Transmission of Hitci Using the Z-Scan Technique
Authors: Swatton Stewart , Welford Kevin , Ray Cameron , Till Steven 
Published: April 2011

AbstractThe excited state properties of dyes become important under intense illumination of a short laser pulse. The pulse induces a significant population in an excited state which will have different absorptive properties, this causes a change in absorption of the incident pulse within its duration. An increase in absorption arises from molecules in an excited state having an absorption greater than the corresponding ground state.The z-scan technique has been used to measure the induced absorption of a carbocyanine dye 1,1′,3,3,3′,3′- Hexamethylindtricarbocyanine Iodide (HITCI) for laser pulses of different wavelengths. An optical parametric oscillator pumped by the third harmonic of a Q-switched Nd:YAG laser was used. Z-scans were taken at a number of different wavelengths between 460 and 630 nm. Data is presented which shows the spectral region where induced absorption occurs. An eight level rate equation model is used to predict the non-linear behaviour and to fit to the experimental data, good correlation is found between the model and data.
Development of Solid State Non-Linear Absorbers - Dyes in Polymer Hosts
Authors: Kolinsky Peter V. , Hall Simon R. , Venner Mark R. W. , Croxall Derek F , Welford Kevin , Swatton Stewart 
Published: April 2011

AbstractThis paper describes the development of high quality solid state optical components which have been made by the incorporation of the reverse saturable dye chloro aluminium phthalocyanine (CAP) into polymeric host material.In particular, the effect of using different host materials with CAP is investigated in terms of key parameters such as solubility, integrity of the dye molecules in the polymer host, hardness of the resulting polymer, ease of polishing to the production of a good optical finish, induced stress, and non-linear absorption performance.Results are presented highlighting the above considerations, and problems encountered in material preparation will be described together with details on how, by careful choice of guest/host combination, good optical quality samples can be produced.
Optical Limiter Based on Nonlinear Interface Fibers
Authors: Zhu Zi Zhong , Jiao Hua , Hu Yi 
Published: April 2011

AbstractThis paper presents a design for an optical limiter composed of an optical fiber with a nonlinear interface. Our analysis of this device shows that high linear transmittance is obtained for weak incident light, while at the same time, intense light is attenuated below allowable values through continuous reflection. Moreover, the bandwidth of the device may be quite large when the fibers have small amounts of dispersion. Theoretical calculations are presented along with a characteristic analysis.
Simultaneous Relaxation of Network and Defects in Silicon-Implanted a-Si:H
Authors: Nakata J. , Sherman S. , Wagner S. , Stolk P. A. , Poate J. M. 
Published: April 2011

ABSTRACTWe report extensive optical and electronic transport data on silicon-implanted a-Si:H, annealed in steps in the dark or with additional illumination. All measured properties relax gradually with increasing annealing temperature. The dark conductivity of the as-implanted film is dominated by hopping conduction via midgap defects. This channel is pinched off during the initial stages of annealing. The midgap defect density and the Urbach energy follow an annealing path that agrees qualitatively with the trajectory postulated by the equilibrium theory of the dangling-bond density. Therefore, the silicon network and the defect density equilibrate continuously during network relaxation.
Vacancy-Interstitial Pair-Formation Mechanism of X-Ray-Irradiation-Induced Crystallization in Amorphous Silicon Studied by ab initio Molecular Dynamics Simulation
Authors: Matsumura T. , Katayama-Yoshida H. , Orita N. 
Published: April 2011

ABSTRACTWe have studied the microscopic mechanism of the X-ray-irradiation-enhanced crystallization in amorphous silicon (a-Si) based upon an ab initio molecular-dynamics simulation. We find that the bistable dangling-bonds (sp3- and sp2-like structures) exhibit a large lattice relaxation and are strongly related to the X-ray-irradiation-induced vacancy-interstitial-pair formation. The vacancy-interstitial-pair formation reduces the formation energy of the vacancy to zero and enhances the crystallization with small migration energy of the vacancy. The crystallization rate in X-ray-irradiated a-Si is dominated by the migration energy of the vacancy in this mechanism because the formation energy is zero in X-ray-irradiated a-Si and one order of magnitude larger than the migration energy without X-ray irradiation.
Hydrogen Bond Configuration Changes in PECVD Silicon Nitride Films During RTA
Authors: He S. S. , Shannon V. L. 
Published: April 2011

ABSTRACTPECVD silicon rich (x<4/3) and nitrogen rich (x>4/3) silicon nitride films have been deposited using a silane, ammonia, and nitrogen mixture at 400°C in a dual frequency parallel plate reactor. From FTIR measurements, most of the bonded hydrogen was observed to be present as N-H in the nitrogen rich films and as Si-H in the silicon rich films. In this study, the movement of hydrogen in the various nitride films as a result of Rapid Thermal Annealing (RTA) in N2 for 30 seconds has been investigated. While the intensity of the N-H stretching band was always found to decrease from that measured for the as-deposited film, the intensity of the Si-H stretching band was observed to increase for anneal temperatures up to 650°C. During the anneal process some hydrogen effusion takes place and some of hydrogen changes its bonding to silicon atoms from previous nitrogen atoms in the film. Consistent with the FTIR results, Hydrogen Forward Scattering (HFS), shows that only a small amount of hydrogen effuses from the silicon nitride film as a result of the RTA process below 650°C.