Wednesday, PM Room: Orange County 2
February 7, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: TBA
TOMOGRAPHY OF POLYCRYSTALLINE MATERIALS: S. R. Stock, D. P. Piotrowski, A. Guvenili, C. P. Patterson, J. D. Haase, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245; Z. U. Rek, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, CA 94309-0210
In understanding the macroscopic response of polycrystalline structural materials to loading, it is frequently essential to know both the three-dimensional distribution of strain and of micro-texture. The methods must be nondestructive, however, if the evolution of quantities such as strain at a fatigue crack tip are to be studied. This paper describes approaches for high resolution synchrotron x-ray diffraction tomography of polycrystalline materials. Preliminary experiments are reported on partially cracked compact tension samples of Al-Li 2090 and on model samples of randomly-packed, millimeter-sized pieces of single crystals. Polychromatic beams collimated to diameters as small as 30 um have been used, and collecting the spatial distribution of diffracted intensity on image storage plates as a function of sample to detector separation allowed inference of the depth of the volume elements contributing to diffraction. This research was supported by the US Office of Naval Research and was partially done at SSRL which is operated by the Department of Energy, Office of Basic Energy Sciences.
NANO-STRUCTURAL INVESTIGATION OF NICKEL-BASE SINGLE CRYSTAL SUPERALLOYS USING MONTE-CARLO SIMULATIONS AND ATOM PROBE MICROANALYSES: H. Murakami, Y. Saito, H. Harada, National Research Institute for Metals, 1-2-1 Sengen, Tsukuba-City, 305, Japan
The atomic structure of some multicomponent Ni-base multicomponent single crystal superalloys has been numerically estimated using the Monte-Carlo Simulation (MCS), and experimentally analysed using Atom-Probe field ion microscopy (APFIM), respectively. The MCS was programmed so as to produce ladder diagrams, composition profiles etc. which are also experimentally obtained using APFIM analysis. The verification of MCS was thus carried out by comparing and contrasting the two simultaneously-formatted graphs, obtained by the two methodologies. In this study, the chemistry of and' interface, partitioning behaviour of alloying elements and substituting behaviour of alloying elements in the y phase will mainly be discussed. This work was carried out under the auspices of the U.K.-Japan cooperative Science program, organized by the Royal Society and the Japan Society fo the Promotion of Science.
SURFACE SHORT-RANGE ORDERING OF CU3AU ABOVE TC IN THE NEAR SURFACE REGION (001); M. Kimura, Advanced Materials & Technology Research Laboratories, Nippon Steel Co., 1618 Ida, Nakahara-ku, Kawasaki 211 Japan; J. B. Cohen, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208; S. Chandavarkar, Department of Physics, University of Tennessee, Knoxville, TN, 37966; K. Liang, Exxon Corporate Research Laboratory, Annadale, NJ 08801
The short-range order in the near surface region of the Cu3Au (001) face was investigated above the critical temperature by glancing-incidence x-ray diffraction, measuring the diffuse intensity throughout a two-dimensional region of reciprocal space. This intensity was analyzed quantitatively to obtain the two-dimensional Cowley-Warren short-range-order parameters and atomic displacements. Monte-Carlo simulation based on these values have revealed that the atomic configurations in the surface consist of ordered domains and clusters in a disordered matrix. There is a large number of  anti-phase domain boundaries (APDB).
THE LOCAL ATOMIC STRUCTURE OF FE-31% PD ABOVE THE TRANSFORMATION TEMPERATURE: J. J. Felten, Containerless Research, Inc., 910 University Place, Evanston, IL 60201; J. B. Cohen, Department of Materials Science & Engineering, Northwestern University Evanston, IL, 60208
The diffuse x-ray scattering from an Fe-Pd single crystal quenched from 900°C containing 31 atomic percent palladium was analyzed to obtain information about the local atomic environment around each atom in the form of the short-range order parameters and the average atomic displacements from the normal latticepositions. A computer program was used to simulate the lattice based on experimentally observed short-range order parameters and displacements. We found an interconnected distribution of ordered and clustered Fe regions no more than a few atoms wide which appeared similar to spinodal decomposition and small distorted regions that may be related to the formation of the face-centered tetragonal (FCT) embryos surmised by Oshima et al. and others.
3:20 pm BREAK
QUANTITATIVE EVALUATION OF 1 PRECIPITATE SHAPES IN BINARY Ni-BASE ALLOYS: T.-H. Cho, A. J. Ardell, Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095-1595
We introduce a new parameter, = 4A/P2, to characterize the morphology of precipitates in Ni-base binary alloys; A is the projected area and P the perimeter of the image of a dark-field TEM image of a ' precipitate in a oriented thin foil. The main advantage of using , which decreases from 1 to 0.785 as the shape changes from spheres to cubes, is that is conveniently measured using available image-analysis software. In addition to re-examining some previous data on Ni-Al, Ni-Ge, and Ni-Gaalloys, we examined the morphology of Ni3Si precipitates in alloys containing 6.50 and 7.42 wt. % Si. As expected, decreases as the "radius", r, increases in all the alloys. The rate at which changes with r, the "Inorphological evolution rate" M = [[arrowvertex]]d/dr[[arrowvertex]], is smallest in Ni-Si alloys (for which is the smallest), but there is no systematic relationship between and M in any of the other alloys. M is independent of f' in Ni-Si alloys, but there is some evidence that M is larger the larger the value of f' in the other alloys; more data are needed to make a definitive statement, however. We find a very good correlation between and a modified elastic energy parameter, W'f = 2r/f1/3, for all the alloys. This work is supported by the National Science Foundation.
THROUGH THICKNESS MICROSTRUCTURAL GRADIENTS IN THE THICK PLATE ALUMINUM 7050-T7451 ALLOYS: M. A. Przystupa, J.Zhang, A. J. Luvano, Department of Materials Science and Engineering, University of California, Los Angeles, CA 90024
The purpose this work was to characterize through-thickness microstructural gradients in the six-inch- thick new and old variants of the aluminum 7050-T7451 plate alloys. The features characterized included micropores, constituent particles and grain structures. They were all measured at the plates surface, quarter depth and center locations on the TL, ST and LS planes. In all cases the size distributions, shapes and directional alignment were analyzed using the linear intercept method. For micropores and constituent particles the characterizations also involved measurements of the volume fractions and spatial distributions. The latter were quantified using the nearest neighbor spacing obtained via Voronoi (Dirichlet) tessellation techniques. Results of all above measurements will be discussed in details during the talk. Work supported by Office of Naval Research under Grant No. N00014-91-J-1299.
DISSOLUTION OF THETA PHASE PRECIPITATES IN AL-CU: C. M. Malam, B. R. Patterson, R. G. Thompson University of Alabama at Birmingham 1150 10th Ave. So. BEC 360 Birmingham, AL 35294-4461
There have been several studies done on the solution kinetics of the the ta phase precipitate in a binary Al-Cu system. Each of these studies employs a rapid up-quench from an equilibrium two phase condition, followed by an isothermal treatment of varying time. The presentation of these data has been in various formats which do not allow for ready comparison of experimental results. Some studies have used a quantitative microscopy approach while others have used measurements of single particles to obtain kinetic data. The present study seeks to combine each of the previous experiment's results into the readily useable format of radius vs time. Such a single format will allow for comparison of results between studies.
KINETIC PARAMETERS FOR PRECIPITATION IN Al-Li ALLOY: AN IMPROVED ANALYTICAL METHOD: W. V. Youdelis, Dept. of Mechanical & Materials Engineering, University of Windsor, Windsor, Ontario, Canada N9B 3P4; A. Luo, Institute of Magnesium Technology, Inc., 357, rue Franquet, Sainte-Foy, Quebec, Canada GlP 4N7
Using a modified Avrami-Johnson-Mehl equation, a new analytical method is developed for the study of precipitation reactions using differential scanning calorimetric (DSC) methods. The kinetic parameters for GPB zone formation and S' (Al2CuMg) precipitation in Al-Li 8090 alloy, determined using the new method, are in good agreement with previously published data. The new method has the advantage of economy over the conventional method (which necessitates using several heating rates) in that all the required kinetic parameters for the transformation are obtained from a single heating rate.
KINETIC STUDIES OF NANOCRYSTALLINE GROWTH AND THE ONSET OF EQUILIBRIUM PHASES IN AL90FE5GD5 METALLIC GLASSES: A. A. Csontos, W. A. Jesser, G. J. Shiflet, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
Observations of nanocrystalline growth from an amorphous Al90Fe5Gd5 matrix and the subsequent transformation to the equilibrium phases were conducted. Al90Fe5Gd5 metallic glasses were melt spun and heat treated from one minute to two weeks through a temperature series from 483 to 773K. Kinetic growth data were established for the nanocrystalline growth and the onset of the equilibrium phases determined by conventional transmission electron microscope (TEM). Clarification regarding the stability and cessation of the nanocrystalline growth before and after the formation of the equilibrium phases were further analyzed and correlated by use of high resolution in-situ electron microscopy with a high resolution transmission electron microscope equipped with a hot-stage. We thank the University of Virginia Academic Enhancement Program which made this research possible.
DISLOCATION MECHANISM OF PHASE TRANSITION IN POTASSIUM CHLORIDE, E. Zaretsky, Pearlston Center for Aeronautical Engineering Studies, Department of Mechanical Engineering, Ben-Guiron University of the Negev, P. O. Box 653, Beer-Sheva, 84105, Israel
A dislocation mechanism of shock induced phase transition in potassium chloride is suggested. The mechanism employs a high-speed dislocation source described in (1). Triggering of this source (a pinned segment of partial dislocation) by a strong shock induced shear stress results in the generation, motion and multiplication of transformation dislocations in the initial B1 lattice (rocksalt-type; two face-centered cubic sub-lattices of ions of opposite sign). The first stage of the transformation results in the development of an intermediate structure B* containing two ionic sub lattices of the same-sign, the unchanged face-centered cubic sub-lattice and a transformed simple cubic (or orthorhombic) sub-lattice. At the second stage the transformation of B* into the final B2 (cesium chloride) structure with two simple cubic sub-lattices of ions of opposite sign, takes place. In the first B1 to B* stage, the unrelaxed shear stress favors easy dislocation climb and the high-speed dislocation multiplication. In this stage the transformation rate is very high, about 1-10 nsec-1. In the second B* to B2 stage, easy crossing of the dislocations and their forward motion are inhibited because of the decrease of shear stress and overlapping of the regions of new phase. In this stage the transformation rate is comparatively low, about 5-25 sec-1. The suggested mechanism is in agreement with results of experimental measurements of the kinetics of phase transformation in potassium chloride (2), and flash x-ray diffraction study of structural changes accompanying the transformation (3).
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