Structure of a Near-Coincidence Σ9 Tilt Grain Boundary in Aluminum

1989 ◽  
Vol 159 ◽  
Author(s):  
M. J. Mills ◽  
G. J. Thomas ◽  
M. S. Daw ◽  
F. Cosandey
Keyword(s):  
Grain Boundary ◽  
Interface Structure ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Grain Boundary Plane ◽  
Transmission Electron ◽  
Symmetric Structures ◽  
Atomically Flat ◽  
Image Simulations

ABSTRACTA systematic study of the structure of tilt grain boundaries in aluminum has been initiated. High resolution transmission electron microscopy is being used to examine the interface structure of several bicrystals with <110> tilt axes. In this paper, we report the structure determination of a grain boundary close to the Σ9 (221) symmetric orientation. The grain boundary plane, which appears wavy at lower magnification, is actually composed of atomically flat microfacets. Two distinct, symmetric structures with (221) boundary planes have been identified within individual microfacets. These observations have been compared with structures calculated using the Embedded Atom Method. The semi-quantitative comparison between the observed and predicted grain boundary structures is accomplished using multislice image simulations based on the calculated structures. The results of these comparisons and the evaluation of the relative energies of the microfacets are discussed.

The Influence of Grain Boundary Inclination on the Structure and Energy of Σ3 Twin Boundaries in Copper

1991 ◽  
Vol 238 ◽  
Author(s):  
Ulrich Wolf ◽  
F. Ernst ◽  
T. Muschik ◽  
M. W. Finnis ◽  
H. F. Fischmeister
Keyword(s):  
Grain Boundary ◽  
Twin Boundary ◽  
Boundary Plane ◽  
Embedded Atom Method ◽  
Twin Boundaries ◽  
Atomic Structures ◽  
Embedded Atom ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Small Angle Boundary

ABSTRACTIn a combined theoretical and experimental study, the energies and structures of Σ3 [011] twin boundaries in Cu were investigated. The atomic structures and the grain boundary energies were calculated using the Embedded Atom Method (EAM). Grain boundary energies of welded Cu bicrystals of the same boundary orientations were also obtained by the thermal grooving technique. The atomic structure of the symmetric {211} incoherent twin boundary (SITB) was investigated by High Resolution Transmission Electron Microscopy (HRTEM). Calculated grain boundary energies γb plotted against the inclination angle Φ of the boundary plane relative to the {111} coherent twin boundary (CTB) plane show a mininmm for the CTB (Φ = 0°) and a second minimum at Φ = 82°. This dependence on the inclination is also confirmed by the measured energies. Common to all calculated boundary structures is a microface 11 ing into CTB and SITB segments with a symmetric orientation of the adjacent crystals. Additionally, strong relaxations occur for the grain boundaries near the second energy minimum. This relaxation can be interpreted as a sequence of stacking faults located almost perpendicular to the mean boundary plane. They are terminated by partial dislocations which form a small angle boundary. The most apparent feature of these structures is a bending of the {111} planes running across the boundary. The structural properties were confirmed by HRTEM.

Atomistic Simulation of Grain Boundaries of the Twin Limited Structure in Ni3Al

1994 ◽  
Vol 364 ◽  
Author(s):  
Maria-Lynn Turi ◽  
R. Zugic ◽  
B. Szpunar ◽  
U. Erb ◽  
G. Palumbo ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Atomistic Simulation ◽  
Boundary Energy ◽  
Boundary Plane ◽  
Embedded Atom Method ◽  
Grain Boundary Energy ◽  
Embedded Atom ◽  
Grain Boundary Plane ◽  
Dynamics Simulations

AbstractEmbedded atom method molecular dynamics simulations of low Σ grain boundaries in Ni3Al are presented. The results show that the grain boundary plane has a larger effect on grain boundary energy than the Σ value, rigid body translations and stoichiometry. Assessment of the energies of Σ3n (n ≥ 1) grain boundaries in Ni3Al for various grain boundary planes indicates that only the Σ3 grain boundary is energetically preferred. The implications of this result for the development of the twin limited structure based on energetic considerations are discussed.

scholarly journals Determination of grain boundary geometry using TEM

1992 ◽  
Vol 7 (7) ◽  
pp. 1707-1717 ◽  
Author(s):  
H. Jang ◽  
D. Farkas ◽  
J.T.M. De Hosson
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Transmission Electron Microscope ◽  
Boundary Plane ◽  
Statistical Distribution ◽  
Special Boundaries ◽  
Grain Boundary Plane ◽  
Transmission Electron ◽  
Boundary Geometry

An experimental method to obtain the grain boundary geometry using the transmission electron microscope is presented. The method allows Σ determination including grain boundary plane orientation. In order to determine the specialness of the grain boundary, three different criteria for maximum allowable deviations from exact CSL misorientations were examined. We tested these three criteria from a statistical distribution of grain boundary types in terms of Σ. We compared grain boundary distributions from other studies in Ni3Al and found discrepancies among them. It seems that the discrepancy came from the different criteria for special boundaries in Σ determination and different experimental procedures they used. The statistical distribution of grain boundary plane orientations showed that low Σ boundaries (Σ < 11) were oriented to the plane of high density of coincident sites.

The Study of Defects in Metals Using High Resolution Transmission Electron Microscopy and Atomistic Calculations

1990 ◽  
Vol 183 ◽  
Author(s):  
M. J. Mills ◽  
M. S. Daw
Keyword(s):  
Grain Boundary ◽  
Good Description ◽  
Dislocation Core ◽  
Thin Foil ◽  
Core Structure ◽  
Embedded Atom ◽  
Pair Potentials ◽  
Transmission Electron ◽  
Atomistic Calculations ◽  
Stringent Test

AbstractThe coupling of HRTEM with atomistic calculations is described for the study of grain boundaries and dislocations in aluminum. HRTEM images of the Σ9 (221) [110] grain boundary are compared with molecular statics calculations using both the Embedded Atom Method (EAM) and two pair potentials. Comparison between observed and simulated images are shown to serve as a stringent test of the theoretical methods. Atomistic calculations can in turn provide threedimensional information about the defect structure. Using the EAM, it is also possible to account for the effects of thin foil geometries on the minimim energy configuration of defects. While these effects are found to be minimal for grain boundary structures, the influence of the thin-foil geometries on the core structure of the 60° dislocation in aluminum is discussed. These comparisons indicate that the EAM function provides a good description of grain boundary structures, but fails to reproduce the observed dislocation core structure due to a low predicted value of the intrinsic stacking fault energy (SFE) on the (111). In contrast, the pair potentials used in this study provide reasonable SFE values, but appear to be less accurate for the prediction of the Σ9 (221) [110] grain boundary structures.

An Experimental and Computational Study of the Elastic-Plastic Transition in Thin Films

2001 ◽  
Vol 673 ◽  
Author(s):  
Erica T. Lilleodden ◽  
Jonathan A. Zimmerman ◽  
Stephen M. Foiles ◽  
William D. Nix
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Computational Study ◽  
Strong Dependence ◽  
Embedded Atom Method ◽  
Shear Stresses ◽  
Gradient Plasticity ◽  
Embedded Atom ◽  
Low Dislocation Density ◽  
Dislocation Sources

ABSTRACTNanoindentation studies of thin metal films have provided insight into the mechanisms of plasticity in small volumes, showing a strong dependence on the film thickness and grain size. It has been previously shown that an increased dislocation density can be manifested as an increase in the hardness or flow resistance of a material, as described by the Taylor relation [1]. However, when the indentation is confined to very small displacements, the observation can be quite the opposite; an elevated dislocation density can provide an easy mechanism for plasticity at relatively small loads, as contrasted with observations of near-theoretical shear stresses required to initiate dislocation activity in low-dislocation density materials. Experimental observations of the evolution of hardness with displacement show initially soft behavior in small-grained films and initially hard behavior in large-grained films. Furthermore, the small-grained films show immediate hardening, while the large grained films show the ‘softening’ indentation size effect (ISE) associated with strain gradient plasticity. Rationale for such behavior has been based on the availability of dislocation sources at the grain boundary for initiating plasticity. Embedded atom method (EAM) simulations of the initial stages of indentation substantiate this theory; the indentation response varies as expected when the proximity of the indenter to a Σ79 grain boundary is varied.

Structure and Dissociation of 15° Tilt Boundaries in Germanium

1983 ◽  
Vol 25 ◽  
Author(s):  
W. Skrotzki ◽  
H. Wendt ◽  
C. B. Carter ◽  
D. L. Kohlstedt
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundary ◽  
Czochralski Method ◽  
Boundary Plane ◽  
First Order ◽  
Grain Boundary Plane ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Tilt Boundaries

ABSTRACTThe structure and dissociation of grain boundaries in Ge bicrystals, grown by the Czochralski method, have been analyzed by visible light and transmission electron microscopy. The seed crystals were oriented to yield either a symmetric or an asymmetric grain boundary plane with a 15° rotation about a common <110> direction. The asymmetric boundary, with a {111} boundary plane, dissociated along most of its length into a first order twin boundary (Σ 3) and a symmetric 55° grain boundary (Σ 41c). The symmetric 15° boundary is composed of an array of Lomer dislocations. Contrary to theoretical predictions, this boundary is stable.

Role of Vacancies and Solute Atoms on Grain Boundary Sliding

1999 ◽  
Vol 601 ◽  
Author(s):  
J.S. Vetrano ◽  
C.H. Henager ◽  
E.P. Simonen
Keyword(s):  
Grain Boundary ◽  
Solute Atom ◽  
Vacancy Concentration ◽  
Grain Boundary Sliding ◽  
Fine Grained ◽  
Grain Boundary Plane ◽  
Transmission Electron ◽  
Boundary Sliding ◽  
Solute Atoms

AbstractIt is necessary for grain boundary dislocations to slide and climb during the grain boundary sliding process that dominates fine-grained superplastic deformation. The process of climb requires either an influx of vacancies to the grain boundary plane or a local generation of vacancies. Transmission electron microscopy (TEM) observations of grain boundaries in superplastically deformed Al-Mg-Mn alloys quenched under load from the deformation temperature have revealed the presence of nano-scale cavities resulting from a localized supersaturation of vacancies at the grain boundary. Compositional measurements along interfaces have also shown an effect of solute atoms on the local structure. This is shown to result from a coupling of vacancy and solute atom flows during deformation and quenching. Calculations of the localized vacancy concentration indicate that the supersaturation along the grain boundary can be as much as a factor often. The effects of the local supersaturation and solute atom movement on deformation rates and cavity nucleation and growth will be discussed.

Effect of Hydrogen on The Electronic Structure of a Grain Boundary In Iron

1990 ◽  
Vol 209 ◽  
Author(s):  
Genrich L. Krasko ◽  
Ralph J. Harrison ◽  
G. B. Olson
Keyword(s):  
Grain Boundary ◽  
Magnetic Moments ◽  
Covalent Bond ◽  
Magnetic Contribution ◽  
Structural Vacancy ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Modified Embedded Atom Method ◽  
Almost All ◽  
Supercell Model

ABSTRACTLMTO-ASA calculations were performed on a 26-atom supercell model of a Σ3(111) grain boundary (GB) in bcc Fe. The supercell emulated two GB's with 11 (111)planes of Fe atoms between the GB planes. One of the GB's was clean, with a structural vacancy at the GB core in the center of a trigonal prism of Fe atoms, while on the other GB this site was occupied by a H atom. The interplanar spacings of the supercell were relaxed using a modified embedded atom method. As in the case of P and S in a similar GB environment in Fe there is only a weak interaction between H and nearest Fe atoms. Almost all the Fe d-states are nonbonding. A very weak covalent bond exists between H and Fe due to s-d hybridization, the hybrid bonding part located far below the Fermi energy. This bond is mostly of σ-type, connecting H with the Fe atoms in the GB plane; the δ-component of this bond across the GB is weaker. A weak electrostatic interaction attracts Fe-atoms across the clean GB, but results in repulsion if a H atom is present. The magnetic contribution to intergranular cohesion is decreased when H is present due the suppression of the magnetic moments of the nearest Fe atoms both in the GB plane and directly across the GB.

Computer Simulation of Grain Boundary in BCC Fe by Embedded Atom Method

1996 ◽  
Vol 204-206 ◽  
pp. 227-232 ◽  
Author(s):  
Ryuzo Watanabe ◽  
Atsushi Nogami ◽  
T. Matsumiya
Keyword(s):  
Computer Simulation ◽  
Grain Boundary ◽  
Embedded Atom Method ◽  
Embedded Atom
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