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Influence of Cr Substitution and Temperature on Hierarchical Phase Decomposition in the AlCoFeNi High Entropy Alloy

Description: This article investigates the length scale of the decomposition into a two-phase mixture of ordered B22 and disordered BCC solid solution as determined by the combination of composition and annealing temperature.
Date: October 22, 2018
Creator: Chaudhary, V.; Gwalani, Bharat; Soni, V.; Ramanujan, R. V. & Banerjee, Rajarshi
Partner: UNT College of Engineering

Atomistic Potentials for the Molybdenum-Silicon System

Description: Using a modified version of the Embedded Atom Method (EAM) that includes angular forces, potentials are developed for the Mo/Si system. Previously developed potentials for Mo and Si are used. The cross potential is fit to properties of MoSi2, Mo3Si, and Mo5Si3. Predictions are presented for phase stability, lattice constants, elastic constants, and point and planar defect energies. In general the agreement with experiment is good, but the predicted lattice constants are somewhat greater than experiment.
Date: November 1, 1998
Creator: Baskes, M. I.
Partner: UNT Libraries Government Documents Department

Phase stability of a standing-wave free-electron laser

Description: The standing-wave free-electron laser (FEL) differs from a conventional linear-wiggler microwave FEL in using irises along the wiggler to form a series of standing-wave cavities and in reaccelerating the beam between cavities to maintain the average energy. The device has been proposed for use in a two-beam accelerator because microwave power can be extracted more effectively than from a traveling-wave FEL. A simplified numerical simulation indicates that, with appropriate prebunching, the standing-wave FEL can produce an output signal that is effectively the same in all cavities. However, changes in the beam energy of less than 1% are found to introduce unacceptably large fluctuations of signal phase along the device. Analytic calculations and single-particle simulations are used here to show that the phase fluctuations result from beam synchrotron motion in the initial signal field, and an approximate analytic expression for the signal phase is derived. Numerical simulations are used to illustrate the dependence of phase fluctuations on the beam prebunching, the beam-current axial profile, and the initial signal amplitude.
Date: January 1, 1991
Creator: Sharp, W.M.; Rangarajan, G.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

The Role of Misfit Strain and Oxygen Content on Formation and Evolution of Omega Precipitate in Metastable Beta-titanium Alloys

Description: β-Ti alloys are widely used in airframe and biomedical applications due to their high ductility, high hardenability, and low elastic modulus. The phase transformations in β-Ti alloys are rather complex due to formation of metastable phases during various thermo-mechanical treatments. One such critical metastable phase, the hexagonal omega (ω) phase, can form in β-Ti alloys under quenching from the high temperature β phase and/or isothermal aging at intermediate temperature. Despite a substantial amount of reported works on the ω phase, there are several critical issues related to the ω formation need to be resolved, e.g. role of alloying elements and oxygen content. Therefore, this dissertation has attempted to provide insights into ω transformation in low misfit (Ti-Mo) and high misfit (Ti-V) binary systems as well as multicomponent (Ti-Nb-Zr-Ta) alloys. The evolution of ω structure, morphology and composition from the early stage (β-solution+quenched) to later stages after prolonged aging are systematically investigated by coupling transmission electron microscopy (TEM), atom probe tomography (APT) and high-energy synchrotron X-ray diffraction techniques. The influence of aging temperature and duration on characteristic of ω phase in Ti-Mo, and Ti-V alloys is addressed in details. It is found that compositional changes during aging can alter the structure, size and morphology of ω precipitates. In low misfit alloys, the ellipsoidal morphology of ω phase was retained during isothermal aging, while in high misfit alloys it changed from ellipsoidal to cuboidal morphology after prolonged aging. Secondly, ω transformation in biomedical Ti-Nb-Zr-Ta alloy is probed in which the micro-hardness was sensitive to microstructural changes. Furthermore, the evolution of oxygen concentration in ω precipitates during various aging conditions in binary Ti-Mo and Ti-V alloys are reported. It has been accepted that interstitial elements such as oxygen can largely alter mechanical behavior and the microstructure of Ti-alloys. Recently, oxygen is intentionally added ...
Date: December 2016
Creator: Hendrickson, Mandana
Partner: UNT Libraries

Immiscibility in the Nickel Ferrite-Zinc Ferrite Spinel Binary

Description: Immiscibility in the trevorite (NiFe{sub 2}O{sub 4}) - franklinite (ZnFe{sub 2}O{sub 4}) spinel binary is investigated by reacting 1:1:2 molar ratio mixtures of NiO, ZnO and Fe{sub 2}O{sub 3} in a molten salt solvent at temperatures in the range 400-1000 C. Single phase stability is demonstrated down to about 730 C (the estimated consolute solution temperature, T{sub cs}). A miscibility gap/solvus exists below Tcs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n - values = 0.15, 0.8 at 300 C. A thermodynamic analysis, which accounts for changes in configurational and magnetic ordering entropies during cation mixing, predicts solvus phase compositions at room temperature in reasonable agreement with those determined by extrapolation of experimental results. The delay between disappearance of magnetic ordering above T{sub C} = 590 C (for NiFe{sub 2}O{sub 4}) and disappearance of a miscibility gap at T{sub cs} is explained by the persistence of long-range ordering correlations in a quasi-paramagnetic region above T{sub C}.
Date: June 21, 2006
Creator: Ziemniak, SE; Gaddipati, AR; Sander, PC & Rice, SB
Partner: UNT Libraries Government Documents Department

Phase and Frequency Locked Magnetrons for SRF Sources

Description: Magnetrons are low-cost highly-efficient microwave sources, but they have several limitations, primarily centered about the phase and frequency stability of their output. When the stability requirements are low, such as for medical accelerators or kitchen ovens, magnetrons are the very efficient power source of choice. But for high energy accelerators, because of the need for frequency and phase stability - proton accelerators need 1-2 degrees source phase stability, and electron accelerators need .1-.2 degrees of phase stability - they have rarely been used. We describe a novel variable frequency cavity technique which will be utilized to phase and frequency lock magnetrons.
Date: May 1, 2009
Creator: Neubauer, M.; Johnson, R.P.; /Muons Inc., Batavia; Popovic, M.; Moretti, A. & /Fermilab
Partner: UNT Libraries Government Documents Department

Phase Stability under Irradiation of Precipitates and Solid Solutions in Model ALloys and in ODS Alloys Relevant for Gen IV

Description: The overall objective of this program is to investigate the irradiation-altered phase stability of oxide precipitates in ODS steels and of model alloy solid solutions of associated systems. This information can be used to determine whether the favorable mechanical propertiies of these steels are maintained under irradiation, thus addressing one of the main materials research issues for this class of steels as identified by the GenIV working groups. The research program will also create fundamental understanding of the irradiation precipitation/dissolution problem by studying a "model" system in which the variables can be controlled and their effects understood individually.
Date: October 17, 2007
Creator: Motta, Arthur T. & Birtcher, Robert C.
Partner: UNT Libraries Government Documents Department

Laser Timing Jitter Measurements using a Dual-Sweep Streak Camera at the A0 Photoinjector

Description: Excellent phase stability of the drive laser is a critical performance specification of photoinjectors such as Fermilab's A0 photoinjector (A0PI). Previous efforts based on the measurement of the power spectrum of the signal of a fast photodiode illuminated by the mode locked infrared laser pulse component indicated a phase jitter of less than 1.4 ps (technique limited). A recently procured dual sweep plugin unit and existing Hamamatsu C5680 streak camera were used to study the phase stability of the UV laser pulse component. Initial measurements with the synchroscan vertical sweep unit locked to 81.25 MHz showed that the phase slew through the micropulse train and the phase jitter micropulse to micropulse were two key aspects that could be evaluated. The phase slew was much less than 100 fs per micropulse, and the total phase jitter (camera, trigger, and laser) was approximately 300 fs RMS for measurements of 50-micropulse trains. Data on the macropulse phase stability were also obtained. A possible upgrade to achieve better phase stability will be also discussed.
Date: April 30, 2009
Creator: Ruan, J.; Lumpkin, A.H.; Santucci, J.K. & /Fermilab
Partner: UNT Libraries Government Documents Department

Spinodal Decomposition and Ordering Transformation in U-6 wt% Nb

Description: Phase stability and aging mechanisms in a water-quenched (WQ) U-6wt% Nb (WQ-U6Nb) alloy artificially aged at 200 C (16 hours) and naturally aged at room temperature for 15 years have been investigated. Age hardening/softening phenomenon is recorded from the artificially aged samples by microhardness measurement. The age hardening can be readily rationalized by the occurrence of spinodal decomposition (or fine-scaled Nb segregation), which results in the formation of a modulated structure in the aged samples. Prolonged aging leads to age softening of the alloy by coarsening of the modulated structure. Disorder-order or chemical ordering transformation is found within the naturally aged alloy according to TEM observations of antiphase domain boundaries (APBs) and superlattice diffraction patterns. The formation of a partially ordered phase in the naturally aged alloy is proposed and identified.
Date: August 15, 2005
Creator: Hsiung, L M
Partner: UNT Libraries Government Documents Department

Diffraction-limited, high average power phase-locking of four 30J beams from discrete Nd:glass zig-zag amplifiers

Description: A single ND:YLF oscillator beam is amplified in four discrete Nd:glass, flashiamp-pumped, zig-zag amplifiers. The resulting four 30J beams are phase- locked using SBS phase conjugation, resulting in near diffraction-limited 120J pulses from a single aperture at up to a 1 OHz pulse repetition frequency.
Date: April 24, 1997
Creator: Dane, C.B.; Wintemute, J.D.; Bhachu, B. & Hackel, L.A.
Partner: UNT Libraries Government Documents Department

The CEBAF fiber optic phase reference system

Description: The specified phase stability of the CEBAF RF distribution system is 2.9{degree} rms per linac. Stability is achieved through the use of a temperature and pressure regulated coaxial drive line. Purpose of the fiber optic phase reference system is to monitor the relative phase at the beginning and ending of this drive line, between linacs, injector and separator to determine drift due to ambient temperature fluctuations. The system utilizes an Ortel 1310 nm single mode laser driving Sumitumo optical fiber to distribute a reference signal at 1497 MHz. Phase of this reference signal is compared to the 1427 MHz (LO) and the 70 MHz (IF) via a 360{degree} phase detector. The detected information is then routed to the CEBAF control system for display with a specified resolution of {+-}0.2{degree} over a 20{degree} phase delta.
Date: December 31, 1995
Creator: Crawford, K.; Simrock, S.; Hovater, C. & Krycuk, A.
Partner: UNT Libraries Government Documents Department

Crystal structure and phase stability in Fe{sub 1{minus}x}Co{sub x} from AB initio theory

Description: For alloys between Fe and Co, their magnetic properties determine their structure. From the occupation of d states, a phase diagram is expected which depend largely on the spin polarization. A method more elaborate than canonical band models is used to calculate the spin moment and crystal structure energies. This method was the multisublattice generalization of the coherent potential approximation in conjunction with the Linear-Muffin-Tin-Orbital method in the atomic sphere approximation. To treat itinerant magnetism, the Vosko-Wilk-Nusair parameterization was used for the local spin density approximation. The fcc, bcc, and hcp phases were studied as completely random alloys, while the {alpha}{prime} phase for off-stoichiometries were considered as partially ordered. Results are compared with experiment and canonical band model.
Date: June 1, 1996
Creator: Soederlind, P.; Abrikosov, I.A.; James, P.; Johansson, B. & Eriksson, O.
Partner: UNT Libraries Government Documents Department

Effects of temperature variation on the SLC linac RF system

Description: The rf system of the Stanford Linear Collider in California is subjected to daily temperature cycles of up to 15{degrees}C. This can result in phase variations of 15{degrees} at 3 GHz over the 3 km length of the main drive line system. Subsystems show local changes of the order of 3{degrees} over 100 meters. When operating with flat beams and normalized emittances of 0.3*10{sup {minus}5} m-rad in the vertical plane, changes as small as 0.5{degrees} perturb the wakefield tail compensation and make continuous tuning necessary. Different approaches to stabilization of the RF phases and amplitudes are discussed.
Date: June 1, 1995
Creator: Decker, F.J.; Akre, R.; Byrne, M.; Farkas, Z.D.; Jarvis, H.; Jobe, K. et al.
Partner: UNT Libraries Government Documents Department

Effect of alteration phase formation on the glass dissolution rate

Description: The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. It is important to understand the mechanism by which alteration phases affect glass corrosion behavior and the glass dissolution rate to reliably predict whether or not similar effects will occur in a disposal environment and the impact of phase formation on the long-term performance of waste glass. While solid state transformation of a glass to thermodynamically more stable phases in kinetically prohibitive, contact by water provides an energetically favorable pathway for this transformation to occur by a dissolution-reprecipitation mechanism. The kinetics of the transformation depends on the dissolution kinetics of the glass and the precipitation kinetics of the alteration phases. The rates of these two processes are linked primarily through the solution activity of orthosilicic acid (and perhaps also that of an aluminum-bearing species).
Date: October 1, 1997
Creator: Ebert, W.L.
Partner: UNT Libraries Government Documents Department

Phase width reduction project summary

Description: The purpose of the phase width reduction project, 1993--96, was to reduce the phase width of the 88-Inch Cyclotron beam on target from 5--10 ns to 1--2 ns for certain experiments, such as Gammasphere, which use time-of-flight identification. Since reducing the phase width also reduces beam intensity, tuning should be done to also optimize the transmission. The Multi-turn Collimator slits in the cyclotron center region were used to collimate the early turns radially, thus reducing the phase width from about 5 ns to 1--2 ns FWHM for a Gammasphere beam. The effect of the slits on phase width was verified with a Fast Faraday Cup and with particle and gamma-ray detectors in the external beamline.
Date: November 1, 1999
Creator: Clark, D.J.; Xie, Z.Q. & McMahan, M. A.
Partner: UNT Libraries Government Documents Department

Bunched beam echos in the AGS

Description: Beam echos have been measured at FNAL and CERN in coasting beams. A coherent oscillation introduced by a short RF burst decoheres quickly, but a coherent echo of this oscillation can be observed if the decohered oscillation is bounced off a second RF burst. In this report the authors describe first longitudinal echo measurements of bunched beam in the AGS accelerator. They applied a method proposed by Stupakov for transverse beam echos, where the initial oscillation is produced by a dipole kick and is bounced off a quadrupole kick. In the longitudinal case the dipole and quadrupole kicks are produced by cavities operating at a 90 and 0{degree} phase shift, respectively.
Date: August 1, 1998
Creator: Kewisch, J. & Brennan, J.M.
Partner: UNT Libraries Government Documents Department

Some issues on the RF system in the 3 GeV Fermilab pre-booster

Description: Some issues are presented on the rf system in the future Fermilab prebooster, which accelerates 4 bunches each containing 0.25 x 10{sub 14} protons from 1 to 3 GeV kinetic energy. The problem of beam loading is discussed. The proposal of having a non-tunable fixed-frequency rf system is investigated. Robinson's criteria for phase stability are checked and possible Robinson instability growth is computed.
Date: June 1, 1998
Creator: Ng, K. Y.
Partner: UNT Libraries Government Documents Department

Durability of Defense Waste Processing Facility glasses within the Purex range of compositions

Description: Processing in the Defense Waste Processing Facility (DWPF) is controlled by constraints on predicted properties of the product glass. One of these properties is chemical durability, which is measured as the response of various glass constituents to the seven-day Product Consistency Test (PCT) [1]. As currently implemented into the DWPF`s Product Composition Control System (PCCS) the response of boron is taken as representative of all of the constituent responses, and control is in terms of the boron response. This response, in normalized units and in log scale, is taken to be a linear function of the glass`s free energy of hydration, {Delta}G. {Delta}G is a parameter which represents the sum of influences on durability of the various glass oxide components. A generalized relationship between these two variables is documented in [2]. This relationship appears to underpredict releases for glasses in the so-called ``Purex`` range of compositions which comprises a worst-case DWPF operating range. Using a similar methodology as in [2], a linear regression specific to Purex compositions is developed herein.
Date: May 1, 1995
Creator: Edwards, T.B. & Kielpinski, A.L.
Partner: UNT Libraries Government Documents Department

Phase control and intra-pulse phase compensation of the Advanced Photon Source (APS) linear accelerator

Description: Rf power for the APS linear accelerator is provided by five klystrons, each of which feeds one linac ``sector,`` containing accelerating structures and SLED cavities. A VXI-based subsystem measures the phase of each sector of the linac with respect to a thermally stabilized reference line. The resulting information is used to control a linearized varactor phase shifter. Error correction is done by software, using operator-controllable parameters. A second phase shifter provides an intra-pulse correction to the phase of the klystron drive pulse. When the intra-pulse correction is applied, the resulting phase is flat to within 0.5{degrees} after 2.5 {mu}sec. A second correction, made after the PSK trigger to the SLED and during the filling of the accelerating structures, resulted in an energy gain of 5 MeV from a single sector.
Date: July 1, 1995
Creator: Grelick, A.E.; Arnold, N.; Ko, K.; Sereno, N. & White, M.
Partner: UNT Libraries Government Documents Department

Integrated quantum-mechanical approach to stability, chemical order and phase evolution in complex alloys

Description: The authors first briefly review and illustrate the application of a state-of-the-art approach to the study of phase stability properties of substitutional alloys based on periodic lattices with the prediction of the phase diagram of Ta-W. Then, they schematically present a real-space approach based on electronic structure calculations for studying stability, chemical order and phase evolution in the case of multi-component alloys which exhibit both chemical order and topological disorder. Potential applications, and preliminary results are discussed.
Date: August 13, 1999
Creator: Julien, J P; Mayou, D & Turchi, P E
Partner: UNT Libraries Government Documents Department

Phase-stable, microwave FEL amplifier

Description: Free-electron laser (FEL) amplifiers have demonstrated high efficiency and high output power for microwave wavelengths. However, using present technology, microwave FEL amplifiers are not phase stable enough to be suitable for driving linear accelerators, where several much amplifiers need to be phase locked. The growing wave`s phase sensitivity to the beam voltage in the small-signal gain regime is responsible for the largest contribution to this phase instability. We discuss a scheme that reduces the phase sensitivity to the beam voltage by operating off synchronism and matching the phase variation resulting from the desynchronism to the phase variation from the reduced plasma wavenumber as the beam voltage changes.
Date: July 1, 1995
Creator: Carlsten, B.E.; Fazio, M.V.; Haynes, W.B.; May, L. & Potter, M.
Partner: UNT Libraries Government Documents Department

Increase of magnetic transition temperatures by reduction of local disorder for perovskite manganites.

Description: We report the synthesis of Sr{sub 1-x}Ca{sub x}MnO{sub 3} and La{sub 0.5}Ba{sub 0.5}MnO{sub 3} perovskites over extended cation and oxygen composition ranges and describe the dependence of their phase stability on the tolerance factor t = t(x,T,{delta}) that is a function of composition, temperature, and oxygen content. We show that magnetic transition temperatures depend strongly on the tolerance factor and charge disorder while dependence on the structural disorder is less important. By reducing charge and structural disorder we have significantly increased the Curie and Neel temperatures for perovskite manganites.
Date: July 2, 2002
Creator: Dabrowski, B.; Chmaissem, O.; Mais, J.; Kolesnik, S.; Jorgensen, J. D. & Short, S.
Partner: UNT Libraries Government Documents Department

Immiscibility in the NiFe2O4-NiCr2O4 Spinel Binary

Description: The solid solution behavior of the Ni(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary is investigated in the temperature range 400-1200 C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200 C. Air-annealing for one year at 600 C resulted in partial phase separation in a spinel binary having n = 0.5. Spinel crystals grown from NiO, Fe{sub 2}O{sub 3} and Cr{sub 2}O{sub 3} reactants, mixed to give NiCrFeO{sub 4}, by Ostwald ripening in a molten salt solvent, exhibited single phase stability down to about 750 C (the estimated consolute solution temperature, T{sub cs}). A solvus exists below T{sub cs}. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n values of 0.2 and 0.7 at 300 C. The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature.
Date: August 13, 2004
Creator: Ziemniak, S
Partner: UNT Libraries Government Documents Department