38 Matching Results

Search Results

Advanced search parameters have been applied.

Empirical technique to measure x-ray production and detection efficiencies in the analytical electron microscope

Description: In the present work, a technique is proposed to experimentally measure the effective x-ray production and detection efficiency in pure element standards. This technique supplements and in some cases is preferable to the multi-element standard technique. Measurements of effective x-ray production and detection efficiencies are expected to be preferable to the standardless technique in cases where pure element samples can be prepared since the most uncertain parameters in the standardless technique are measured in the proposed technique.
Date: January 1, 1985
Creator: King, W.E.
Partner: UNT Libraries Government Documents Department

Molecular-dynamics simulation of displacement cascades in Cu: analysis of replacement sequences

Description: Molecular-dynamics computer simulations of displacement cascades in copper have been performed for recoil energies up to 450 eV. Statistical analyses of the atomic replacements are presented. Linear replacement sequence lengths are extremely short on the average. The effect of the cooling phase of the cascade is discussed.
Date: January 1, 1981
Creator: King, W.E. & Benedek, R.
Partner: UNT Libraries Government Documents Department

MSTD 2007 Publications and Patents

Description: The Materials Science and Technology Division (MSTD) supports the central scientific and technological missions of the Laboratory, and at the same time, executes world-class, fundamental research and novel technological development over a wide range of disciplines. Our organization is driven by the institutional needs in nuclear weapons stockpile science, high-energy-density science, nuclear reactor science, and energy and environment science and technology. We maintain expertise and capabilities in many diverse areas, including actinide science, electron microscopy, laser-materials interactions, materials theory, simulation and modeling, materials synthesis and processing, materials science under extreme conditions, ultrafast materials science, metallurgy, nanoscience and technology, nuclear fuels and energy security, optical materials science, and surface science. MSTD scientists play leadership roles in the scientific community in these key and emerging areas.
Date: April 1, 2008
Creator: King, W. E.
Partner: UNT Libraries Government Documents Department

Reactive-element effect studied using ion implantation

Description: Implantation of reactive elements into metals that form chromia layers upon exposure to high temperature oxidizing environments has a very large effect on the growth rate of the oxide and adhesion of the oxide to the base alloy. We have investigated the effect of Y ion implantation on the high temperature oxidation of Fe-24Cr using Rutherford backscattering spectroscopy, secondary ion mass spectroscopy, and electron microscopy. Analytical tools have been applied to determine the spatial distribution of Y, the microstructure of the oxide, and contribution of oxygen transport to the oxidation process. Results are compared with similar experiments in Fe-Cr alloys with Y additions and with results of cation and anion tracer diffusion experiments. 51 refs., 17 figs., 3 tabs.
Date: November 1, 1988
Creator: King, W.E. & Grabowski, K.S.
Partner: UNT Libraries Government Documents Department

In-situ study of cascade defects in silver by simultaneous transmission electron microscopy and electrical resistivity measurements at low temperatures

Description: A helium-cooled double-tilt specimen stage for transmission electron microscopy (TEM) with the capability of simultaneous electrical resistivity measurements was constructed and used to study defect-production, migration, clustering and recovery processes in ion-irradiated silver. Vacuum-evaporated thin film specimens were irradiated with 1 MeV Kr -ions up to a dose of 4.0 x 10 ions/cmS, at T = 10K in the microscope, using the HVEM-tandem accelerator ion beam interface system in the Argonne National Laboratory Electron Microscopy Center. Cascade defect formation during ion bombardment at the low temperature was directly observed both by TEM and electrical resistivity measurements. Ion bombardment created groups of defect clusters with strong strain fields which gave rise to TEM contrast. The specimen resistivity was increased by 16% during the irradiation. Subsequent microstructural changes and resistivity recovery during isochronal annealing were monitored up to room temperature. 58.3% of the irradiation induced resistivity was recovered, while significant reduction in the size of black spot defect clusters was observed by TEM. A small fraction of clusters disappeared, while no nucleation of new defect clusters was observed.
Date: December 1, 1985
Creator: Haga, K.; King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Atomic structure of the {sigma}5 (210)/[001] symmetric tilt grain boundary in yttrium aluminum garnet

Description: The {Sigma}5(210)/[100] symmetric tilt grain boundary in YAG was produced by UHV diffusion bonding precisely oriented single crystals. The boundary has been characterized by HREM along two different directions, parallel and perpendicular to the tilt axis. Models of the atomic structure of the boundary were formed following the Coincident Site Lattice scheme. The resulting models are equivalent to twins formed at the atomic scale. The high resolution images show no rigid crystal translations away from the perfect mirror reflection relation. Comparison of the simulated images using the atomic model as input with the experimental images identifies the plane of mirror symmetry. The atomic model is shown to be in good agreement with the experimental images when viewed parallel to tilt axis, but disagrees with the images perpendicular to tilt axis. Agreement between simulated and experimental images can be improved by changing the composition of the grain boundary with respect to the bulk. To reach a more certain conclusion on the structure of the grain boundary will require additional theoretical calculations.
Date: June 24, 1996
Creator: Campbell, G.H. & King, W.E.
Partner: UNT Libraries Government Documents Department

LLNL Workshop on TEM of Pu

Description: On Sept. 10, 1996, LLNL hosted a workshop aimed at answering the question: Is it possible to carry out transmission electron microscopy (TEM) on plutonium metal in an electron microscope located outside the LLNL plutonium facility. The workshop focused on evaluation of a proposed plan for Pu microscopy both from a technical and environment, health, and safety point of view. After review and modification of the plan, workshop participants unanimously concluded that: (1) the technical plan is sound, (2) this technical plan, including a proposal for a new TEM, provides significant improvements and unique capabilities compared with the effort at LANL and is therefore complementary, (3) there is no significant environment, health, and safety obstacle to this plan.
Date: September 10, 1996
Creator: King, W.E.
Partner: UNT Libraries Government Documents Department

Use of strain-annealing to evolve the grain boundary character distribution in polycrystalline copper

Description: We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries was {similar_to}70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special GBs while both the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.
Date: November 6, 1996
Creator: King, W.E. & Schwartz, A.J.
Partner: UNT Libraries Government Documents Department

Toward optimization of the grain boundary character distribution in copper by strain annealing

Description: We have used a two step (low and high temperature) strain-annealing process to evolve the two grain boundary character distribution (GBCD) in fully recrystallized oxygen (OFE) copper bar that was forged and rolled. Orientation imaging microscopy (OIM) has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries, special fraction was about 70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high temperature process resulted in a reduction in the fraction of special grain boundaries while both of the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher-temperature anneal and commensurate increase in the special fraction.
Date: November 10, 1996
Creator: King, W.E. & Schwartz, A.J.
Partner: UNT Libraries Government Documents Department

Multilength-scale modeling: Crystal-plasticity models in implicit finite element codes

Description: A multidisciplinary team of researchers from Chemistry & Materials Science and Mechanical Engineering have recently completed the first year of an LDRD Director`s Initiative. This initiative involves the development of physics-based multilength-scale models to optimize casting and deformation processing of polycrystalline materials. The purpose of this initiative is to develop models to simulate the material`s mechanical response on the meso length-scale. The meso length-scale refers to the realm where the material microstructure (e. g., grain size and shape, crystallite orientation, etc.) is resolved but dislocations are homogenized. The recent development of two experimental technologies has provided a unique capability to validate material models on the mesolength-scale. The first of these technologies is the ultrahigh-vacuum diffusion bonding machine. This machine has been demonstrated to build bicrystals with high-precision planar grain boundaries joining two precisely oriented crystallites. The second technology is Orientation Imaging Microscopy. This technology has been demonstrated to precisely determine the local lattice orientation in a microstructure. Hence, this provides a powerful tool to characterize local lattice rotations following specified levels of deformation. The coupling of these two technologies provides a tool for detailed study of a material`s mechanical response due to the presence of an interface or grain boundary. 6 refs., 6 figs.
Date: March 1, 1996
Creator: Sam, D.D. & King, W.E.
Partner: UNT Libraries Government Documents Department

Threshold energy surface and Frenkel-pair resistivity for Cu

Description: In-situ electrical resistivity damage-rate measurements in the high voltage electron microscope have been used to study electron-irradiation-induced defect production in copper single crystals at T < 10/sup 0/K. Analysis of the directional and energy dependence yields a threshold energy surface that is significantly different from those of previous investigations: two pockets of low threshold energy centered at <100> and <110> surrounded by regions of much higher threshold energy. The corresponding damage function exhibits a plateau of 0.6 Frenkel pairs. the present results imply a Frenkel pair resistivity for C of (2.75/sub -0.2//sup +0.6/) x ..cap omega..-cm.
Date: January 1, 1982
Creator: King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Solvent refined coal (SRC) process: prepilot SRC-II development project, hydrogen consumption kinetics. Interim report for the period February 1, 1981-September 30, 1981. [A-1 unit, 16 experiments]

Description: This report summarizes the experimental work performed on the A-1 Unit for investigating the rate of hydrogen consumption in the SRC-II reactor variable space of interest. Sixteen experiments were carried out with an Ireland coal at process conditions where the reaction rate ranged from the highest to the lowest expected values. The major variables of interest were temperature (430 to 470/sup 0/C), hydrogen partial pressure (1500 to 3000 psig), recycle ash content (2 to 10.4 wt %), and nominal slurry residence time (0.57 to 1.5 hr). Very definitive values of the hydrogen consumption rate as a function of the nominal slurry residence times were determined at three distinct levels within the parameter space, namely those process conditions which correspond to maximum, minimum, and baseline values for the intrinsic reaction rate. The reaction rate measurements indicated a significant variation in hydrogen consumption with the reaction severity levels investigated. This report provides the experimental data for future analysis and rate model building.
Date: January 1, 1982
Creator: Carr, N.L.; King, W.E. Jr. & Moon, W.G.
Partner: UNT Libraries Government Documents Department

Study of the anisotropy of the threshold energy in copper using in-situ electrical resistivity measurements in the HVEM

Description: In the past, electrical-resistivity measurements and high voltage electron microscopy-(HVEM) have been used separately to investigate the anisotropy of the threshold energy for Frenkel-pair production. Electrical resistivity, measured in a conventional electron accelerator, has been used to observe small changes in the concentration of isolated Frenekel pairs at low temperatures, while HVEM experiments have focussed on the observation of measurable changes in visible defect clusters, primarily at elevated temperatures. However, quantitative comparison of the threshold energies obtained with the two techniques has proved difficult. As a first step toward resolving this dilemma, the threshold-energy surface for copper was determined by in-situ electrical-resistivity measurements below 10 K in the HVEM. By combining the advantages of both techniques, this approach allowed a precise and detailed study of the anisotropy of the threshold energy for Frenkel-pair production.
Date: January 1, 1980
Creator: King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Re-examination of the threshold energy surface in copper

Description: Radiation-induced defect production in copper has been studied using in-situ electrical resistivity damage-rate measurements in the HVEM and molecular dynamics simulations. Analysis of the results yields a threshold energy surface characterized by two isolated pockets of low threshold energy centered at <100> and <110> surrounded by regions of much higher threshold energy; the corresponding damage function exhibits a plateau at 0.65 Frenkel pairs. A Frenkel pair resistivity of (2.75/sub -0.2//sup +0/ /sup 6/) x 10/sup -4/ ..cap omega..-cm is proposed. A model damage function is constructed and compared to results from ion irradiation damage-rate measurements. 7 figures.
Date: January 1, 1981
Creator: King, W.E.; Benedek, R.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Nanosecond Time Resolved Electron Diffraction Studies of the (Alpha) to (Beta) Transition in Pure Ti Thin Films using the Dynamic Transmission Electron Microscope (DTEM)

Description: The transient events of the {alpha}-{beta} martensitic transformation in nanocrystalline Ti films were explored via single shot electron diffraction patterns with 1.5 ns temporal resolution. The diffraction patterns were acquired with a newly constructed dynamic transmission electron microscope (DTEM), which combines nanosecond pulsed laser systems and pump-probe techniques with a conventional TEM. With the DTEM, the transient events of fundamental material processes, that are far too fast to be studied by conventional bulk techniques, can be captured in the form of electron diffraction patterns or images with nanosecond temporal resolution. The transient phenomena of the martensitic transformations in nanocrystalline Ti is ideally suited for study in the DTEM, with their rapid nucleation, characteristic interface velocities {approx}1 km/s, and significant irreversible microstructural changes. Free-standing 40-nm-thick Ti films were laser-heated at a rate of {approx}10{sup 10} K/s to a temperature above the 1155 K transition point, then probed at various time intervals with a 1.5-ns-long, intense electron pulse. Diffraction patterns show an almost complete transition to the {beta} phase within 500 ns. Postmortem analysis (after the sample is allowed to cool) shows a reversion to the {alpha} phase coupled with substantial grain growth, lath formation, and texture modification. The cooled material also shows a complete lack of apparent dislocations, suggesting the possible importance of a ''massive'' short-range diffusion transformation mechanism.
Date: December 9, 2005
Creator: LaGrange, T; Campbell, G H; Colvin, J D; Reed, B & King, W E
Partner: UNT Libraries Government Documents Department

In-situ observation of the energy dependence of defect production in Cu and Ni

Description: The damage function, the average number of Frenkel pairs created as a function of lattice atom recoil energy, was investigated in Cu and Ni using in-situ electrical-resistivity damage-rate measurements in the high-voltage electron micrscope (HVEM) at T < 10K. Electron and proton irradiations were performed in-situ on the same polycrystalline specimens using the Argonne National Laboratory HVEM-Ion Beam Interface. Both Ni and Cu exhibit a sharp rise in the damage function above the minimum threshold energy (approx. 18 eV for Cu and approx. 20 eV for Ni) as displacements in the low-threshold energy regions of the threshold energy surface become possible. A plateau is observed for both materials (0.54 Frenkel pairs for Cu and 0.46 Frenkel pairs for Ni) indicating that no further directions become productive until much higher recoil energies. These damage functions show strong deviations from simple theoretical models, such as the Modified Kinchin-Pease damage function. The results are discussed in terms of the mechanisms of defect production that govern the single-displacement regime of the damage function and are compared with results from recent molecular-dynamics simulations.
Date: January 1, 1983
Creator: King, W.E.; Merkel, K.L.; Baily, A.C.; Haga, K. & Meshii, M.
Partner: UNT Libraries Government Documents Department

In-situ studies of cascade defect formation at T < 10/sup 0/K

Description: Thin films of Ag and Au were ion-irradiated at temperature (T) < 10/sup 0/K and simultaneously observed using the Argonne National Laboratory high-voltage electron microscope (HVEM) ion-beam interface system. Displacement cascades were produced by Kr/sup +/ ion bombardment in the energy range 20 to 140 keV. For Ag, 20% of the 20-keV cascades and 100% of the 100-keV cascades produced observable contrast. Analysis of the observed dynamical black-white (BW)-contrast indicates that the clusters are of vacancy type. Subcascades were observed in the high-energy irradiations. The present results demonstrate that, during the evolution of displacement cascades in Ag and Au, extensive athermal rearrangement of vacancies occurs which gives rise to clustering and collapse to dislocation loops.
Date: May 1, 1983
Creator: Haga, K.; Baily, A.C.; King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

A high resolution electron microscopy study of the {Sigma}11 (113)/[110] symmetric tilt grain boundary in pure Al and Al-1.5 wt% Cu

Description: Identical bicrystals of pure Al and Al-1.5 wt.% Cu were prepared by diffusion bonding in ultra-high vacuum. The boundary chosen was the {Sigma}11 (113)/[1{bar 1}0] symmetric tilt grain boundary. Characterization of the atomic structure of and segregation to the boundary was performed by high resolution transmission electron microscopy along the common [110]. The stable sites for Cu segregation were probed using electronic structure calculations. Boundary atomic structures were simulated using embedded atom potentials. The Cu was found to segregate to this boundary by occupying sites removed from the mirror plane boundary by one (113) plane. This prediction was compared to experimental micrographs through high resolution image simulation. The experimental results are consistent with the predictions of the theoretical calculations.
Date: March 1996
Creator: Campbell, G. H.; King, W. E.; Wien, W. L. & Foiles, S. M.
Partner: UNT Libraries Government Documents Department

Correlating Observations of Deformation Microstructures by TEM and Automated EBSD Techniques

Description: The evolution of the deformed microstructure as a function of imposed plastic strain is of interest as it provides information on the material hardening characteristics and mechanism(s) by which cold work energy is stored. This has been extensively studied using transmission electron microscopy (TEM), where the high spatial and orientational resolution of the technique is used to advantage to study local phenomenon such as dislocation core structures and interactions of dislocations. With the recent emergence of scanning electron microscope (SEM) based automated electron backscatter diffraction (EBSD) techniques, it has now become possible to make mesoscale observations that are statistical in nature and complement the detailed TEM observations. Correlations of such observations will be demonstrated for the case of Ni-base alloys, which are typically non-cell forming solid solution alloys when deformed at ambient temperatures. For instance, planar slip is dominant at low strain levels but evolves into a microstructure where distinct crystallographic dislocation-rich walls form as a function of strain and grain orientation. Observations recorded using both TEM and EBSD techniques are presented and analyzed for their implication on subsequent annealing characteristics.
Date: June 5, 2000
Creator: Schwartz, A.J. & King, W.E.
Partner: UNT Libraries Government Documents Department

Influence of Processing Method on the Grain Boundary Character Distribution and Network Connectivity

Description: There exists a growing body of literature that correlates the fraction of ''special'' boundaries in a microstructure, as described by the Coincident Site Lattice Model, to properties such as corrosion resistance, intergranular stress corrosion cracking, creep, etc. Several studies suggest that the grain boundary character distribution (GBCD), which is defined in terms of the relative fractions of ''special'' and ''random'' grain boundaries, can be manipulated through thermomechanical processing. This investigation evaluates the influence of specific thermomechanical processing methods on the resulting GBCD in FCC materials such as oxygen-free electronic (ofe) copper and Inconel 600. We also demonstrate that the primary effect of thermomechanical processing is to reduce or break the connectivity of the random grain boundary network. Samples of ofe Cu were subjected to a minimum of three different deformation paths to evaluate the influence of deformation path on the resulting GBCD. These include: rolling to 82% reduction in thickness, compression to 82% strain, repeated compression to 20% strain followed by annealing. In addition, the influence of annealing temperature was probed by applying, for each of the processes, three different annealing temperatures of 400, 560, and 800 C. The observations obtained from automated electron backscatter diffraction (EBSD) characterization of the microstructure are discussed in terms of deformation path, annealing temperature, and processing method. Results are compared to previous reports on strain-annealed ofe Cu and sequential processed Inconel 600. These results demonstrate that among the processes considered, sequential processing is the most effective method to disrupt the random grain boundary network and improve the GBCD.
Date: December 20, 1999
Creator: Kumar, M & King, W.E.
Partner: UNT Libraries Government Documents Department

Experimental determination of the energy dependence of defect production

Description: The damage function nu(T), i.e., the number of Frenkel pairs as a function of recoil energy is determined for Cu from electron and ion damage-rate measurements. nu(T) shows a plateau at nu = 0.54 which extends up to approx. 7xT/sub d//sup min/. Therefore, simple damage models, such as the modified Kinchin-Pease expression, are inappropriate not only at high recoil energies where stimulated recombination in cascades reduces defect production, but also in the single displacement regime. As a consequence, no simple relation between T/sub d//sup min/ and T/sub d//sup av/ is expected to exist. A procedure is suggested which uses anisotropy measurements in combination with polycrystal electron and ion irradiations to construct absolute damage functions in metals.
Date: January 1, 1982
Creator: Merkle, K.L.; King, W.E.; Baily, A.C.; Haga, K. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Quantitative high resolution electron microscopy of grain boundaries

Description: The {Sigma}11 (113)/[1{bar 1}0] symmetric tilt grain boundary has been characterized by high resolution transmission electron microscopy. The method by which the images are prepared for analysis is described. The statistics of the image data have been found to follow a normal distribution. The electron-optical imaging parameters used to acquire the image have been determined by nonlinear least-square image simulation optimization within the perfect crystal region of the micrograph. A similar image simulation optimization procedure is used to determine the atom positions which provide the best match between the experimental image and the image simulation.
Date: December 12, 1996
Creator: Campbell, G.H., King, W.E., Cohen, D., Carter, C.B.
Partner: UNT Libraries Government Documents Department

Role of twinning in the optimization of the grain boundary character distribution

Description: The grain boundary character distribution (GBCD) is a microstructural property that describes the proportions of �special� and �random� boundaries as defined by the coincident site lattice model. Recently, there has been increased attention on determination of the GBCD and manipulation of the relative fractions in the microstructure through thermomechanical processing in order to improve material� s properties like corrosion and creep resistance. Most of the �optimization� treatments reported in the literature have been performed on fee materials with relatively low stacking fault energies and have resulted in microstructures with high fractions of {Sigma}3, {Sigma}9, and {Sigma}27 boundaries. It could be interpreted that annealing twins are solely required to improve the GBCD. However, in order to optimize the properties, it appears imperative that the formation of annealing twins disrupt the connectivity of the random boundary network, thus implying that {Sigma}3{sup n} reactions and resultant triple lines are critical. Experiments to modify the GBCD of oxygen-free electronic Cu and Inconel 600 through thermomechanical processing are presented and discussed in light of observations of the deformed and recrystallized microstructures.
Date: January 8, 1999
Creator: King, W E; Kumar, M & Schwartz, A J
Partner: UNT Libraries Government Documents Department