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Representation of orientation distributions

Description: This paper illustrates the principles presented with a particular experimental texture: from the surface layer of a copper polycrystal cold-rolled to 60% reduction in thickness. Four incomplete pole figures (200, 220, 222, and 113) were determined by x-ray diffraction in reflection geometry. The measured pole figures nearly exhibited orthorhombic symmetry (as expected), which was then strictly enforced by averaging the four quadrants of the pole figure. The orientation distribution function was obtained using the expansion in spherical harmonics (with only even-order coefficients up to l = 18).
Date: January 1, 1985
Creator: Wenk, H.R. & Kocks, U.F.
Partner: UNT Libraries Government Documents Department

Grain boundary dislocations in plane matching grain boundaries

Description: Plane matching (PM) boundaries are defined as boundaries in which a single stack of planes of indices (hkl) in each crystal adjoining the boundary is either parallel, or nearly parallel, and where no other significant lattice matching exists. A search was made (by transmission electron microscopy) for possible intrinsic secondary grain boundary dislocation (GBD) arrays which might be present in such boundaries possessing a variety of deviations from the exact PM condition. (002), (220) and (420) PM boundaries of controlled geometry were prepared in gold thin film bicrystal specimens. Wide ranges of twist and tilt deviations from the exact PM orientation were introduced, and the orientation of the boundary plane was also varied for cases of fixed crystal misorientation. Arrays consisting of parallel GBDs were found in the (002) and (220) boundaries but not in the (420) boundaries. The Burgers vector of the GBDs was parallel to (hkl) with a magnitude given by the (hkl) interplanar spacing. Arrays were found in boundaries with twist deviations as large as 4/sup 0/ and tilt deviations as large as 14/sup 0/ and with a wide range of grain boundary plane orientations. The results suggest that discrete GBDs should be present in a variety of (002), (111) and (220) PM boundaries over a considerable range of misorientation which in certain cases may be as large as 20/sup 0/. Such boundaries should therefore appear rather frequently in general polycrystalline materials in agreement with the estimates of Warrington and Boon. It is pointed out that the physical basis for the stability of such GBD structures is not understood at present.
Date: August 1, 1979
Creator: Schindler, R.; Clemans, J.E. & Balluffi, R.W.
Partner: UNT Libraries Government Documents Department

Recovery of deformed and hydrogen-charge palladium

Description: Positron lifetime and Doppler-broadening studies made at 300 K have been used to investigate the interaction between interstitial hydrogen and lattice defects in deformed Pd. Specimens were charged with hydrogen at 300 K to levels up to 0.1%. The presence of hydrogen was found to have no effect on the recovery curves of Pd upon annealing to 400/sup 0/C. By 400/sup 0/C the values for both lifetime and Doppler-broadening for both cold worked and cold worked plus hydrogen were below the values obtained for annealed pure Pd. This can be interpreted as gaseous-impurity-trapped vacancies being present after the 1200/sup 0/C anneal, but being swept away by the dislocation microstructure recovery between 200 to 400/sup 0/C.
Date: January 1, 1982
Creator: Snead, C.L. Jr.; Lynn, K.G. & Lynch, J.F.
Partner: UNT Libraries Government Documents Department

Internal magnetic fields in hcp-iron

Description: The magnetic behavior of hcp-Fe (epsilon iron) has been investigated by the Moessbauer Effect over a wide range of temperature T, pressure P, and applied magnetic field H/sub 0/. The internal field H/sub i/ of the induced moment is given by H/sub i/ = 0.20 +- .01 H/sub 0/ and is independent of T and P. Enhanced paramagnetism is suggested as the most likely origin for a contribution of this magnitude to H/sub i/.
Date: January 1, 1982
Creator: Taylor, R.D.; Cort, G. & Willis, J.O.
Partner: UNT Libraries Government Documents Department

Positron prevacancy effects in pure annealed metals

Description: The low-temperature prevacancy effects sometimes observed with positrons in well-annealed high-purity metals are discussed. It is shown that these effects are not experimental artifacts, but are due to trapping of the positrons. It is suggested that dislocations are responsible for these trapping effects. 46 references, 5 figures.
Date: June 1, 1981
Creator: Smedskjaer, L.C.
Partner: UNT Libraries Government Documents Department

Quantitative measurement of the development of recrystallization texture in OFE copper

Description: High purity OFE copper samples, cold rolled 58, 73 and 90%, were studied at different fractions recrystallized to follow the change of texture, the associated kinetics, release of stored energy, growth rates and microstructures. Higher strains led to a stronger copper deformation component and a stronger cube recrystallization component. The strength of the cube texture correlated strongly with the frequency of cube nuclei at the early stage of recrystallization for the 73 and 90% reductions. The kinetics had low Avrami exponents of 1.1, 1.2 and 1.8 respectively for the 3 rolling reductions. Average growth rates, G, decreased linearly with fraction recrystallized. However, unlike the study by Hutchinson et al., here the rate of stored energy release was constant with fraction recrystallized. 14 refs., 5 figs.
Date: January 1, 1990
Creator: Necker, C.T.; Doherty, R.D. (Drexel Univ., Philadelphia, PA (USA). Dept. of Materials Engineering) & Rollett, A.D. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Melting of metals above 100 GPa

Description: The optical analyzer technique has been used to determine the pressure at which shock compressed iron, tantalum and aluminum can no longer support a longitudinal elastic wave. At this pressure the release wave velocity drops to a value consistent with a calculated bulk sound velocity, indicating partial melting. At higher shock pressures, the bulk sound velocities follows a constant rho ..gamma.. model, where ..gamma.. is the Grueneisen parameter. With these measurements we have identified melting on the Hugoniot, and we have calibrated three metals as drivers for similar experiments on other materials.
Date: January 1, 1983
Creator: Shaner, J.W.; Brown, J.M. & McQueen, R.G.
Partner: UNT Libraries Government Documents Department

Thermal desorption spectroscopy (TDS) of hydrogen from niobium

Description: Thermal desorption spectroscopy is often used to determine the activation energy of desorption of an adsorbate on a substrate as well as the order of the kinetics. In the case of flash desorption of an adsorbate from a surface obeying second order kinetics, a plot of Log(theta/sub o/T/sub p//sup 2/) vs 1/T/sub p/ (where theta/sub o/ is the initial surface coverage and T/sub P/ is the temperature of the maximum desorption rate, i.e., the desorption temperature) will yield a straight line, the slope of which is determined by the chemisorption energy. However, it is argued that in the case of a system with hydrogen absorbed into the bulk in quasiequilibrium with adsorption sites on the surface, a similar plot, where the coverage theta/sub o/ must now be replaced by the initial concentration x/sub o/, will yield a slope determined by the heat of solution. In the following experiments the functional dependence of the desorption temperature on hydrogen loading as outlined above is verified. Deviations from these theoretical predictions were observed, and numerical kinetic simulations were made to aid in understanding them.
Date: January 1, 1982
Creator: Ghosh, V.J.; Pick, M.A.; Welch, D.O. & Dienes, G.J.
Partner: UNT Libraries Government Documents Department

The determination of interfacial structure and phase transitions in Al/Cu and Al/Ni interfaces by means of surface extended x-ray absorption fine structure

Description: Surface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It become overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting the be CuAl{sub 2} and NiAl{sub 3} respectively. The results of this study that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10{Angstrom} reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30{Angstrom}) and Al on Ni (60{Angstrom}) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.
Date: January 1, 1991
Creator: Barrera, E.V. (Rice Univ., Houston, TX (United States). Dept. of Mechanical Engineering and Materials Science) & Heald, S.M. (Brookhaven National Lab., Upton, NY (United States))
Partner: UNT Libraries Government Documents Department

An embedded atom potential for bcc iron

Description: We have used the embedded atom method (EAM) to construct inter atomic potentials for use with bcc iron. Our original motivation for this work was to model the grain boundaries in iron. The version of the EAM we have used is where the total energy is given as the sum of two body terms summed over pairs of atoms i,j, together with an embedding term given by the sum of embedding functions whose arguments are the total electronic charge density at the sites i. A Morse potential with the three parameters v/sub 1/, v/sub 2/ and v/sub 3/, is used to represent the two-body terms. The total electronic charge densities at each individual site which are the arguments of the embedding functions, are obtained from the linear superposition of atomic 4s Slater function charge densities of form. The fifth parameter v/sub 5/ is taken as the cutoff distance for the atomic charge densities and for phi(r/sub ij/), which are adjusted for smoothness at cutoff. The embedding function itself is determined by the fit of the cohesive energy of bcc iron as a function of interatomic distance to the ''universal'' cohesive energy function described by Rose et al. 15 refs., 1 tab.
Date: January 1, 1988
Creator: Harrison, R.J.; Voter, A.F. & Chen, Shao-Ping
Partner: UNT Libraries Government Documents Department

Reconstruction of twist grain boundaries in gold

Description: The reconstruction of high-angle twist grain boundaries on the four densest atomic planes in gold are investigated using the recently developed method of grand-canonical simulated quenching. It is found that the grain boundaries on the two densest planes, (111) and (100), do not reconstruct, while those on the (110) and (113) planes do.
Date: November 1, 1992
Creator: Phillpot, S.R.
Partner: UNT Libraries Government Documents Department

Peculiarities of structures and meltinglike transition in gold clusters

Description: Structural and dynamical properties of gold clusters are derived from a Gupta-type potential using numerical simulations and are compared to features of nickel clusters derived from the same potential. The major implication of the comparison is that the properties of clusters mimicked by this many-body potential depend, in general, on the values of its parameters.
Date: January 1, 1992
Creator: Garzon, I.L. & Jellinek, J.
Partner: UNT Libraries Government Documents Department

Dynamics of a metal overlayer on metallic substrates: High temperature effects

Description: We have explored the structure and the dynamics of a bimetallic system consisting of a hexagonal (almost) overlayer of Ag on a square lattice (Ni(100) and Cu(100)), as a function of the surface temperature. In each case the structure is nearly'' incommensurate giving rise to a low frequency Goldstone mode. Also, the overlayer atoms slosh back and forth over the substrate in a corrugated fashion. The calculated dispersion of the Ag/metal vertical mode, at room temperature, is in excellent agreement with experimental data. At higher temperatures floater atoms appear on top of the overlayer displaying a variety of cluster formations and also exchanges with the substrate atoms leading to surface disordering, interdiffusion and melting.
Date: January 1, 1992
Creator: Rahman, T.S. (Brookhaven National Lab., Upton, NY (United States)); Black, J.E. & Tian, Zeng Ju (Brock Univ., St. Catherines, ON (Canada). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

Atomistic studies of grain boundaries with segregated impurities. Progress report, July 1, 1980-June 30, 1981

Description: The aim of this research project is to carry out atomistic studies of grain boundaries with impurities. The emphasis of the investigation is on the effect of segregation upon the structure of grain boundaries and their properties. Since the necessary precursor of any atomistic study is a description of interatomic interactions an empirical scheme for the construction of interatomic potentials was first developed. In this scheme which was summarized in a previous report, the interatomic interactions are described by pair potentials together with a volume dependent term which represents a major contribution to the overall energy of the studied system. A new relaxation method had to be developed that includes the volume dependent term into the calculations which are then carried out at constant pressure rather than at constant volume. Furthermore, this method also inlcudes the possibility of dealing with spatially varying concentration of impurities. It is described in more detail in the report.
Date: February 1, 1981
Creator: Vitek, V.
Partner: UNT Libraries Government Documents Department

Contour forming of various metals--deformation and recrystallization characteristics

Description: The effects of different forming and annealing sequences on resultant grain size were investigated for several materials. Deep drawing as well as forging techniques were employed during the course of this study. One evaluation was additionally performed to determine the contribution of size effects.
Date: January 1, 1978
Creator: Muller, J.F.
Partner: UNT Libraries Government Documents Department

High-resolution microdiffraction study of notch-tip deformation in Mo single crystals using x-ray synchrotron radiation

Description: A new technique is presented for the determination of strain fields in single crystals, based on the simultaneous recording of the energy and position of a diffracted beam, with a resolution of 25 micrometers under current experimental conditions. The technique can be profitably used for perfect to highly deformed crystals, in materials as highly absorbing as Molybdenum, and allows a spatial resolution of one part in 10{sup 4}. Indications are given as to possible refinements and improvements of the method.
Date: January 1, 1989
Creator: Ice, G.; Habenschuss, A. (Oak Ridge National Lab., TN (United States)); Bilello, J.C. (California State Univ., Fullerton, CA (United States)) & Rebonato, R. (Oxford Univ. (United Kingdom). Physical Chemistry Lab.)
Partner: UNT Libraries Government Documents Department

Growth of grain boundary cavities under applied stress and internal pressure

Description: Experiments were performed to investigate the growth of grain boundary cavities in nickel under internal pressure and applied stress. Under the experimental conditions the growth kinetics was found to be controlled by stress induced mass transfer. The growth rate was found not to be a linear function of the applied stress. The growth rate was found to depend on grain boundary orientation and grain boundary sliding.
Date: unknown
Creator: Mancuso, J.F. & Li, C.Y.
Partner: UNT Libraries Government Documents Department

Secondary defects in quenched platinum

Description: The structure of secondary defects in two different platinum purities quenched under ultra high vacuum, has been studied by transmission electron microscopy. Faulted loops on (100) planes have been observed in both materials. In the less pure platinum, Pt B (but purer in terms of carbon content), the defects were observed after quenching, whereas in the purest one, Pt A (but less pure in terms of carbon content), the defects were formed after a long annealing. The Burgers vector of the loops formed after the quenching was a/3 <100> and for loops formed during long annealings, was a/2 <100>, apparently. It was found that in Pt B the loop density increased and the loop size decreased as the quenching temperature was lowered.The same effect was produced by increasing the carbon content by a small amount. The loop formation was totally inhibited by adding a larger amount of carbon and also when the quenching was performed in poor vacuum (approx. 0.01 torr) or in air. The defects can be interpreted as pure vacancy loops heterogeneously nucleated at carbon atom clusters or, as plate like precipitates of carbon atoms and vacancies formed by a co-precipitation mechanism. The discussion of the experimental results obtained is based upon these two models.
Date: November 1, 1979
Creator: Perez, M.I.
Partner: UNT Libraries Government Documents Department

Atomic relaxation modes in grain boundaries

Description: High-resolution electron microscopy (HREM) in combination with computer simulations of the fully relaxed atomic structures and energies of symmetric and asymmetric grain boundaries (GBs) in Au <110> tilt bicrystals has been applied to a study of atomic relaxation modes. These investigations indicate that: (1) Atomic relaxations are typically dominated by short-range interactions and the tendency of the solid to assume a local atomic environment similar to the bulk. (2) Misfit localizations are likely within a structural unit whenever the GB unit cell is large. (3) When there is a length mismatch along the GB the atomic relaxations can assume quasiperiodic character, generating densely spaced regions of structural disorder, akin to misfit dislocations. (4) Atomic relaxations can take the form of stacking disorder.
Date: January 1, 1992
Creator: Merkle, K.L. & Wolf, D.
Partner: UNT Libraries Government Documents Department

Evidence of surface migration and formation of catalytically inactive Pt in corrosion studies of Pt/sup +/ implanted Ti

Description: This investigation is part of an ongoing research project directed at applying the techniques of ion implantation doping and ion scattering analysis to identify the mechanisms associated with the anodic dissolution of Ti-Pt alloys. The Ti-Pt alloys produced by ion implantation were electrochemically examined in hydrogen saturated 1 N H/sub 2/SO/sub 4/ by both potentiostatic polarization and open-circuit potential methods. In this study, Ti samples implanted to relatively high doses (5.4 x 10/sup 15/ to 2.9 x 10/sup 16/ atoms/cm/sup 2/) were examined by ion scattering analysis at various stages in the electrochemical measurements. Quantitative measurements showed that the majority of the implanted Pt accumulated on the surface during anodic dissolution and underwent large scale surface migration. Evidence is also presented for the transition of the Pt on the surface from a catalytically active to inactive state. Possible mechanisms for the observed catalytically inactive Pt are discussed.
Date: August 1, 1980
Creator: Appleton, B.R.; Kelly, E.J.; White, C.W.; Thompson, N.G. & Lichter, B.D.
Partner: UNT Libraries Government Documents Department

XAFS studies of interactions at transition-metal/Al interfaces

Description: XAFS measurements on transition metal/Al interfaces have been made using a combination of glancing angle and in-situ UHV techniques. Glancing angle methods provide depth dependent interface structural information for Al on metal bilayers, while SEXAFS methods were used for thin metal layers on Al substrates. In all cases studied (Ni, Cu, and Cr) interfacial O played a crucial role in determining the interface structure. 4 refs., 2 figs.
Date: January 1, 1990
Creator: Heald, S.M. & Barrera, E.V.
Partner: UNT Libraries Government Documents Department

Defect and impurity effects on the initial growth of Ag on Si(111)

Description: Step and impurity effects on the initial growth of a thin film have been demonstrated in the ({radical}3 {times} {radical}3)R30{degree} domain growth of Ag on Si(111) using high angular resolution LEED. Anisotropy in the {radical}3 domain shape and growth during deposition are found on the stepped Si(111) with the preferential growth along the step edge direction. The {radical}3 superlattice grows with coverage principally by domain coalescence at the temperature T {approximately} 450{degree}C and is self-similar at different coverages (scaling) as observed on a flat Si(111). The size distribution is shown to follow a Gamma distribution by a simple model calculation. A dramatic change in the growth mechanism is observed when oxygen impurities ({le}0.02 ML) appear. The {radical}3 domains in the presence of impurities grow with coverage more randomly and isotropically in contrast with the step edge effects and coalescence is inhibited. As a result, the {radical}3 superlattice stays in a microdomain morphology without long range order. 17 refs., 6 figs.
Date: October 1, 1990
Creator: Zuo, J.K. & Wendelken, J.F.
Partner: UNT Libraries Government Documents Department

Studies of defects and surfaces by channeling

Description: Uses of channeling to study defects and surfaces are reviewed briefly with emphasis on ways in which they are currently evolving. Consideration is first given to normalization of yields for channeling directions to the yield for a random direction, this normalization being important to the accuracy of both defect and surface studies. The discussion of atom location concentrates on the use that can be made of quantitative calculations of flux peaking. The treatment of surfaces includes accurate determination of the area of the surface peak as well as basic ways of extracting from experiments information on the positions of surface atoms.
Date: August 1, 1977
Creator: Barrett, J.H.
Partner: UNT Libraries Government Documents Department