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.

Atomic Mechanisms of Grain Boundary Motion

2005 ◽  
Vol 502 ◽  
pp. 157-162 ◽  
Author(s):  
A. Suzuki ◽  
Yuri M. Mishin
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Geometric Model ◽  
Lattice Rotation ◽  
Shear Stresses ◽  
Translation Rate ◽  
Embedded Atom ◽  
Local Lattice ◽  
Symmetrical Tilt ◽  
Grain Boundary Motion

We present results of atomistic computer simulations of spontaneous and stress-induced grain boundary (GB) migration in copper. Several symmetrical tilt GBs have been studied using the embedded-atom method and molecular dynamics. The GBs are observed to spontaneously migrate in a random manner. This spontaneous GB motion is always accompanied by relative translations of the grains parallel to the GB plane. Furthermore, external shear stresses applied parallel to the GB and normal to the tilt axis induce GB migration. Strong coupling is observed between the normal GB velocity vn and the grain translation rate v||. The mechanism of GB motion is established to be local lattice rotation within the GB core that does not involve any GB diffusion or sliding. The coupling constant between vn and v|| predicted within a simple geometric model accurately matches the molecular dynamics observations.

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.

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

Molecular dynamics simulations of grain boundary diffusion in Al using embedded atom method potentials

1995 ◽  
Vol 10 (7) ◽  
pp. 1589-1592 ◽  
Author(s):  
Chun-Li Liu ◽  
S.J. Plimpton
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Md Simulations ◽  
Embedded Atom Method ◽  
Melting Temperatures ◽  
Embedded Atom ◽  
Pair Potentials ◽  
Dynamics Simulations ◽  
First Time

Molecular dynamics (MD) simulations of diffusion in a Σ5(310) [001] Al tilt grain boundary were performed using for the first time three different potentials based on the embedded atom method (EAM). The EAM potentials that produce more accurate melting temperatures also yield activation energies in better agreement with experimental data. Compared to pair potentials, the EAM potentials also give more accurate results.

Atomistic computer study on Mg segregation in the Ni3Al grain boundary

1998 ◽  
Vol 13 (7) ◽  
pp. 1741-1744 ◽  
Author(s):  
Bingyao Jiang ◽  
Xianghuai Liu ◽  
Shichang Zou ◽  
Jian Sun ◽  
Jian Wang
Keyword(s):  
Free Surface ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Embedded Atom Method ◽  
Computer Study ◽  
Mg Doping ◽  
Embedded Atom

The embedded atom method (EAM) was applied to calculate the energy on Mg doping in polycrystalline Ni3Al. The EAM predicted the energy of Mg in Al site in grain boundary is lower than that of Mg in Ni site and much lower than that of Mg in Al or Ni site in bulk and in free surface. It means that Mg would segregate to grain boundary rather than bulk and free surface and Mg will favor to be the substitute of Al rather than of Ni in grain boundary. These results were consistent with the experiments that Mg segregated to grain boundaries with Al depletion and Ni enrichment.

Ab Initio Electronic Structure Calculations of the Σ 5 (210) [001] Tilt Grain Boundary in Ni3Al

1997 ◽  
Vol 472 ◽  
Author(s):  
Gang Lu ◽  
Nicholas Kioussis
Keyword(s):  
Electronic Structure ◽  
Grain Boundary ◽  
Boundary Energy ◽  
Boundary Region ◽  
Embedded Atom Method ◽  
Full Potential ◽  
Plane Wave Method ◽  
Embedded Atom ◽  
Tilt Grain Boundary ◽  
Linearized Augmented Plane Wave

ABSTRACTThe atomic and the electronic structure of the Σ 5 (210) [001] tilt grain boundary in Ni3Al have been calculated using the full potential linearized-augmented plane-wave method. The strain field normal to the boundary plane and the excess grain boundary volume are calculated and compared with the results obtained using the embedded-atom method (EAM). The interlayer strain normal to the grain boundary oscillates with increasing distance from the grain boundary. The bonding charge distributions suggest that bonding in the boundary region is significantly different from that in the bulk. The grain boundary energy and the Griffith cohesive energy are calculated and compared with the EAM results.

A Molecular Dynamics Study of Cu Segregation to the Σ11 Grain Boundary In Al

1996 ◽  
Vol 428 ◽  
Author(s):  
Hanchen Huang ◽  
T. Diaz de la Rubia ◽  
M. J. Fluss
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Md Simulation ◽  
Atomic Level ◽  
Embedded Atom Method ◽  
Simulation Studies ◽  
Embedded Atom

AbstractWe present results of molecular dynamics (MD) simulation studies of Cu segregation to the Σ11 grain boundary (GB) in Al. The simulations were performed with Embedded Atom Method (EAM) potentials for Al and Al-Cu. The results predict that copper atoms tend to order along either side of the interface even at the pure symmetrical GB, forming alternating chains along the direction. The nucleation of the chains is driven by a change in the local atomic level stress induced by the pre-existing Cu atoms at the GB.

High-Temperature Behavior of Grain Boundaries from Embedded Atom Method Molecular Dynamics Simulation

1988 ◽  
Vol 141 ◽  
Author(s):  
J. F. Lutsko ◽  
D. Wolf ◽  
S. R. Phillpot
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Molecular Dynamics Simulation ◽  
Melting Point ◽  
Grain Boundary ◽  
Dynamics Simulation ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
The Stability ◽  
Atom Potential

AbstractThe behavior of a metallic grain boundary at high temperatures is studied using an embedded atom potential. A recently developed molecular dynamics code is used which allows the simulation of an isolated grain boundary at temperatures as high as the bulk melting point. The stability of the boundary below the melting point is studied and compared with earlier investigations which have suggested the existence of a “premelting“ transition. It is found that the boundary migrates at high temperature but remains well defined up to the bulk melting point. In contrast to simulations of ideal crystals, it was not possible to superheat the grain boundary due to the nucleation of bulk melting at the boundary.

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