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Synthesis and processing of Al{sub 2}O{sub 3}/Al composites by in situ reaction of aluminum and mullite

Description: Al{sub 2}O{sub 3}/Al composites, were formed by reacting molten aluminum metal with dense mullite ceramic preforms. The composites produced by this reactive metal penetration process (RMP) have a two phase, interpenetrating microstructure in which both the ceramic and the metal are continuous in three dimensions. Scanning electron microscopy (SEM) micrographs of composites produced by RMP show a fine microstructure comprised of interlocked metal and ceramic phases, with a feature size of approx… more
Date: February 1995
Creator: Fahrenholtz, W. G.; Ewsuk, K. G.; Loehman, R. E. & Tomsia, A. P.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Local texture and grain boundary misorientations in high T{sub C} oxide superconductors

Description: The orientations of hundreds of contiguous grains in high J{sub C} TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} deposits and (Bi, Pb){sub 2} Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} powder-in-tube tapes have been determined from electron back scatter diffraction patterns (EBSP). The misorientation angles and axes of rotation (angle/axis pairs) for grain boundaries connecting these grains were calculated. For both materials the population of low angle boundaries was found to be much larger than expected fro… more
Date: February 1, 1995
Creator: Kroeger, D. M.; Goyal, A.; Specht, E. D.; Tkaczyk, J. E.; Sutliff, J.; DeLuca, J. A. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Preparation of high quality YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thick films on flexible Ni-based alloy substrates with textured buffer layers

Description: High current YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) thick films on flexible nickel substrates with textured buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was {approximately} 10{degrees}. A critical current density of 8x10{sup 5} A/cm{sup 2} was obtained at 75 K and zero field for thin YBCO … more
Date: December 31, 1995
Creator: Wu, X. D.; Foltyn, S. R.; Arendt, P.; Townsend, J.; Campbell, I. H.; Tiwari, P. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Diffusion in polycrystalline microstructures

Description: Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and the topological aspects of grain boundaries. In this study, a finite difference scheme is developed to study transient and st… more
Date: July 1, 1995
Creator: Swiler, Thomas P. & Holm, Elizabeth A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Analytical and numerical modeling of surface morphologies in thin films

Description: Experimental studies have show that strains due to thermal expansion mismatch between a film and its substrate can produce very large stresses in the film that can lead to the formation of holes and hillocks. Based on a phenomenological description of the evolution of a solid surface under both capillary and stress driving forces and for surface and grain boundary self-diffusion, this article provides analytical and numerical solutions for surface profiles of model geometries in polycrystalline… more
Date: May 1995
Creator: Genin, F. Y.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Determination of interface structure and bonding by Z-contrast stem

Description: The scanning transmission electron microscope (STEM) provides a route for the determination of interface structure and bonding directly from experimental data. Through an annular detector, Z-contrast images reveal atomic column locations without prior knowledge. The incoherent nature of such images allows a direct structure inversion through a maximum entropy analysis. The Z-contrast image also facilitates atomic-resolution spectroscopy by allowing the probe to be positioned with atomic precisi… more
Date: June 1, 1995
Creator: Pennycook, S. J.; Browning, N. D.; McGibbon, M. M.; McGibbon, A. J.; Chisholm, M. F. & Jesson, D. E.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Thermal depinning of a single superconducting vortex

Description: Thermal depinning has been studied for a single vortex trapped in a superconducting thin film in order to determine the value of the superconducting order parameter and the superfluid density when the vortex depins and starts to move around the film. For the Pb film in Pb/Al/Al{sub 2}O{sub 3}/PbBi junction having a gold line, the vortex depins from the artificial pinning site (Au line) and reproducibly moves through the same sequence of other pinning sites before it leaves the junction area of … more
Date: October 1, 1995
Creator: Sok, J.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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High resolution interface nanochemistry and structure. Progress report, December 1, 1994--November 30, 1995

Description: Progress is described in the following research areas concerned with high resolution interface nanochemistry and structure: ceramic interfaces and grain boundaries; metal/alpha (6H)-SiC(0001) interfaces; oxygen distributions in monolithic silicon carbide; SiC/nitride and metal on nitride interfaces; and interface synthesis.
Date: August 15, 1995
Creator: Carpenter, R.W.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Trace elements and the mechanical properties of intermetallic compounds

Description: In this paper the brittleness of grain boundaries in Ni{sub 3}Al is discussed with special emphasis on the effects of B. The effects of alloy stoichiometry, environment (hydrogen), grain boundary character and B levels are described and interpreted in terms of current theories. It is shown that the grain boundaries in Ni{sub 3}Al are intrinsically weaker than the bulk (the weakness is not an impurity effect), the weakness is exacerbated by atmospheric moisture, and that B in the boundaries both… more
Date: February 1, 1995
Creator: Lin, Hui; Pope, D. P. & George, E. P.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Atomistic studies in grain boundaries in NiAl

Description: This paper presents the results of atomistic studies of grain boundaries in NiAl B2 alloy. The interatomic forces are described by Finnis-Sinclair type N-body potentials, and are fitted to properties of NiAl. The results show that the structure, energy and cohesive strength of a grain boundary depend strongly on its chemical configurations, and a grain boundary with surplus of Al is the weakest. Energies of antisite defects at the grain boundary {Sigma}5 (210) are also calculated, and the resul… more
Date: January 1, 1995
Creator: Yan, M.; Chen, S. P. & Vitek, V.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Grain boundary dissociation by the emission of stacking faults

Description: A range of <110> symmetric tilt grain boundaries (GBs) are investigated in several fcc metals with simulations and high resolution electron microscopy. Boundaries with tilt angles between 50.5{degree} and 109.5{degree} dissociate into two boundaries 0.6 to 1.1 nm apart. The dissociation takes place by the emission of stacking faults from one boundary that are terminated by Shockley partials at a second boundary. This is a general mode of GB relaxation for low stacking fault energy metals. The r… more
Date: May 1995
Creator: Rittner, J. D.; Seidman, D. N. & Merkle, K. L.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Processing and properties of extruded tungsten-hafnium and tungsten-steel composites

Description: The purpose of this study was to evaluate the processing behavior and properties of tungsten-hafnium (W-Hf) and W-steel composites produced by hot extrusion of canned powders. The W-Hf composite was consolidated by extrusion of blended powders with preheat temperatures over the temperature range of 1100 to 1400{degrees}C. All extrusions produced fully dense material which exhibits elongation of the tungsten phase within the hafnium matrix. The flow stress, as characterized by the extrusion cons… more
Date: February 1, 1995
Creator: Ohriner, E. K.; Sikka, V. K. & Kapoor, D.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Influence of dislocation-solute interactions on the mechanical properties of zirconium-doped NiAl

Description: Atom probe field ion microscopy (APFIM) has been used to characterize NiAl microalloyed with molybdenum and zirconium. Field ion images and atom probe analyses revealed segregation of zirconium to dislocation strain fields and ribbon-like morphological features that are probably related to dislocations. These results provide direct experimental evidence in support of the suggestion that the tremendous increase in the ductile-to-brittle transition temperature (DBTI) in zirconium-doped NiAl is du… more
Date: March 1, 1995
Creator: Jayaram, R. & Miller, M. K.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Progress report for UDRI/LANL joint research project

Description: Our work has concentrated mainly on exploring the effect of various additives on the bulk superconductive properties of BSCCO 2223 phase. The first phase of our work started by selecting BSCCO precursor powders from several different sources. Lately, our goal is to improve the current carrying capability.of superconducting tapes in the Ag/BSCCO system. The transport current properties of Ag-clad tapes are mainly controlled by the Ag/superconductor interface or the region very close to it. In a … more
Date: December 31, 1995
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Mechanical properties of, and phase transformation in, V-Cr-Ti-O solid solutions

Description: Incorporation of O in the surface of V-Ti-Cr alloys has been investigated in controlled environments at 550-750{degrees}C. and tests were performed to determine the physical properties of V-Cr-Ti-O solid solutions. The amount of O in the alloys has been determined by weight-change measurements. Microhardness was used to determine O depth profiles in the alloys. X-ray, diffraction indicated a phase transformation from body-centered-cubic (bcc) to tetragonal in the highly stressed lattice because… more
Date: November 1, 1995
Creator: Park, J. H.; Kuppermann, D. & Park, E. T.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Atomistic simulation of the hydrogen-induced fracture process in an iron-based superalloy

Description: Austenitic superalloys exhibit dramatic reductions in ductility and crack growth resistance when high fugacity hydrogen and hydrogen-producing environments trigger a change in fracture mode from microvoid coalescence to slip band and intergranular fracture. Of particular importance is the change to intergranular fracture. We have therefore combined the Embedded Atom Method (EAM) with Monte Carlo simulations and molecular dynamics calculations to help define the effects of hydrogen on segregatio… more
Date: December 31, 1995
Creator: Moody, N. R.; Foiles, S. M.; Baskes, M. I. & Angelo, J. E.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Direct experimental determination of the atomic structure at internal interfaces

Description: A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. As interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscop… more
Date: July 1, 1995
Creator: Browning, N. D. & Pennycook, S. J.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Interfacial segregation and deformation of superplastically deformed Al-Mg-Mn alloys

Description: Microstructural and microchemical studies have been carried out on superplastically deformed Al-Mg-Mn (AA5083-type) alloys. Grain boundary composition was measured using a Scanning Auger Microprobe (SAM) and an Analytical Transmission Electron Microscope (ATEM), while conventional TEM was used for microstructural evaluation. Non-equilibrium segregation of Si to grain boundaries following deformation was measured by both techniques. Significant interfacial Si enrichment was only detected in gage… more
Date: March 1, 1995
Creator: Vetrano, J.S.; Lavender, C.A. & Bruemmer, S.M.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Investigation of high purity beryllium for the International Thermonuclear Experimental Reactor (ITER), Task 002. Final report

Description: The report includes a description of experimental abilities of Solid Structure Research Laboratory of IAE NNC RK, a results of microstructural characterization of A-4 grade polycrystal Beryllium produced at the Ulba metal plant and a technical project-for irradiation experiments. Technical project contains a detailed description of five proposed experiments, clearing behavior of Beryllium materials under the influence of irradiation, temperature, helium and hydrogen accumulation. Complex irradi… more
Date: May 1, 1995
Creator: Vagin, S.P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Characterization of phosphorus segregation in neutron-irradiated pressure vessel steels by atom probe field ion microscopy

Description: An atom probe field ion microscopy characterization of A533B and Russian VVER 440 and 1000 pressure vessel steels has been performed to determine the phosphorus coverage of grain and lath boundaries. Field ion micrographs of grain and lath boundaries have revealed that they are decorated with a semi-continuous film of discrete brightly-imaging precipitates that were identified as molybdenum carbonitride precipitates. In addition, extremely high phosphorus levels were measured at the boundaries.… more
Date: April 1995
Creator: Miller, M. K.; Jayaram, R. & Russell, K. F.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Characterization of pore evolution in ceramics during creep failure and densification. Final report, April 15, 1984--April 14, 1995

Description: This research program was divided into two phases, one involving creep cavitation, the other cavity evolution during sintering. In the former, work was aimed at determining the effect of microstructure and stress state upon creep cavitation, while in the latter, the principal objective was the characterization of pore evolution during sintering. In order to meet these objectives, the creep cavitation portion of the program was centered around small-angle neutron scattering, supplemented by elec… more
Date: April 1, 1995
Creator: Page, R.A. & Chan, K.S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Modeling of stresses at grain boundaries with respect to occurrence of stress corrosion cracking

Description: The distributions of elastic stresses/strains in the grain boundary regions were studied by the analytical and the finite element models. The grain boundaries represent the sites where stress concentration occurs as a result of discontinuity of elastic properties across the grain boundary and the presence of second phase particles elastically different from the surrounding matrix grains. A quantitative analysis of those stresses for steels and nickel based alloys showed that the stress concentr… more
Date: December 31, 1995
Creator: Kozaczek, K. J.; Sinharoy, A.; Ruud, C. O. & McIlree, A. R.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Practical superconductor development for electrical power applications. Annual report for FY 1995

Description: Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds: production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components in the (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bi,V)-(Ba,Sr)-Ca-Cu, and Y-… more
Date: October 1, 1995
Creator: Balachandran, U.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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