Structural Energetics of Thin Coherently Strained Metallic Overlayers

1986 ◽  
Vol 83 ◽  
Author(s):  
Brian W. Dodson ◽  
Paul A. Taylor
Keyword(s):  
Optimization Procedure ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Growth Stability ◽  
Atomistic Calculations ◽  
Bimetallic System ◽  
The Stability ◽  
Bimetallic Structures ◽  
Metal Overlayers ◽  
The Continuum

ABSTRACTUnderstanding of the growth, stability, and structural properties of coherently strained metal overlayers has achieved considerable importance because of the recent discovery of unique interfacial electronic states and catalytic properties of such systems. The structural stability of coherently strained metal films grown on a substrate composed of a different and lattice-mismatched metal is determined via atomistic calculations. An equilibrium energy balance criterion is used, which is evaluated with a Monte Carlo annealing optimization procedure in which the structural energy of the bimetallic system is obtained using the embedded atom method. The stability of coherently strained (100) bimetallic structures chosen from combinations of the fcc metals Ag, Au, Cu, Ni, Pd, and Pt has been studied. The predicted critical thicknesses agree remarkably well with experimental results, but disagree quantitatively with the continuum models.

Stucture of 1/2 Dislocations In γ-Tial by High Resolution Tem and Embedded Atom Method Modelling

1994 ◽  
Vol 364 ◽  
Author(s):  
J. P. Simmons ◽  
M. J. Mills ◽  
S. I. Rao
Keyword(s):  
High Resolution ◽  
Atomistic Simulation ◽  
Embedded Atom Method ◽  
Simulation Methods ◽  
Embedded Atom ◽  
A Value ◽  
High Resolution Tem ◽  
Atomistic Calculations ◽  
Range Of Values ◽  
Limit Estimate

AbstractHigh Resolution TEM (HRTEM) observations of a dislocation in γ-TiAl are compared directly with atomistic calculations of dislocation structures performed with atomistic potentials in order to obtain an estimate of the Complex Stacking Fault Energy (γcsf). A value of between 470 and 620 mJ/M2 was obtained. HRTEM observations are presented of a Ti-52AI sample, containing a dislocation with Burgers vector 1/2<110> and 60° line orientation. This image is matched against images simulated from the outputs of Embedded Atom Method (EAM) simulations, using potentials that were fit to bulk γ-TiAl properties. Two atomistic simulation methods were employed in order to give the range of values for γcsf. In the first of these methods, three EAM potentials were used to simulate the stress-free core structure. These were fit so as to produce three different values of γcsf, all other properties being roughly the same as the literature values for γ-TiAI. All of these potentials produced cores that were more extended than the experimental observation. Thus a value of 470 mJ/M2, being the highest value of γcsf obtainable for the EAM potentials, is reported as a low limit estimate of γcsf for γ-TiAl. An upper limit estimate of the value of γcsf was obtained by applying an external ‘Escaig’ stress that forced the Shockley partials to further constrict, simulating the effect of an increase in γcsf, The preliminary value calculated from this procedure was 620 mJ/M2.

Embedded atom calculations of the equilibrium shapes of 5–60 atom palladium nanocrystals

1993 ◽  
Vol 8 (3) ◽  
pp. 455-461 ◽  
Author(s):  
A. Sachdev ◽  
R.I. Masel
Keyword(s):  
Minimum Energy ◽  
Wide Distribution ◽  
Embedded Atom Method ◽  
Palladium Clusters ◽  
Embedded Atom ◽  
Equilibrium Shapes ◽  
The Stability ◽  
Highly Strained ◽  
Palladium Particles ◽  
Particle Shapes

The embedded atom method (EAM) has been used to compare the stability of a series of small palladium clusters with 5–60 atoms and a variety of shapes. It is found that the 13- and 55-atom icosahedra and cubo-octahedra are stable at 0 K. However, other sized icosahedra and cubo-octahedra are unstable at 0 K. Upon annealing, the icosahedra and cubo-octahedra reconstruct into nonpolyhedral structures which are highly strained. The strained structures are much more stable than the icosahedron or cubo-octahedron except when there are 13 or 55 atoms in the cluster. Further, there are many disordered shapes which are within 0.01 eV of the minimum energy structures at all cluster sizes including 13 and 55 atoms. We observe transitions between these low energy structures in Monte Carlo calculations. These results suggest that at equilibrium one should rarely observe polyhedral palladium particles. Instead, most of the particles should be disordered. Further, there should be a wide distribution of particle shapes in agreement with experiment.

Ab-Inito Data for Interatomic Interactions in Zr-Rich ZrCu Alloys and Embedded-Atom-Method Potentials

2007 ◽  
Vol 561-565 ◽  
pp. 1259-1262 ◽  
Author(s):  
M. Asato ◽  
R. Tamura ◽  
N. Fujima ◽  
T. Hoshino
Keyword(s):  
Ab Initio ◽  
Dynamics Simulation ◽  
Embedded Atom Method ◽  
Atomic Structures ◽  
Embedded Atom ◽  
Atomic Interactions ◽  
The Stability ◽  
Ab Inito ◽  
Physical Quantities ◽  
Reliable Interaction

The quantitative study for the stability of local atomic structures in bulk metallic glasses (BMGs) with temperature effect on physical quantities of BMGs needs the molecular dynamics simulation with the reliable interaction parameter model such as the Embedded-atom-method potentials (EAMPs) which reproduce the ab-initio data as well as the experimental data. We present the ab-initio data for inter-atomic interactions of Zr-rich ZrCu alloys and a preliminary result for the EAMPs of Zr-rich ZrCu alloys.

Application of the Embedded Atom Method to Pb and Be

1990 ◽  
Vol 193 ◽  
Author(s):  
M. Karimi ◽  
Z. Yang ◽  
P. Tibbits ◽  
D. Ila ◽  
I. Dalins ◽  
...  
Keyword(s):  
Energy Functional ◽  
Embedded Atom Method ◽  
Single Vacancy ◽  
Embedded Atom ◽  
Equilibrium Lattice Constant ◽  
The Stability ◽  
Two Parameters ◽  
Body Potential ◽  
Embedding Energy ◽  
Embedding Function

ABSTRACTWe have derived the embedding energy functional and two body potential of the Embedded Atom Method (EAM) using decreasing exponentials for both the electron density and the two body potential. The embedding function was obtained from the equation of state given by Rose et al. Because of the form of the embedding function, the equilibrium lattice constant, cohesive energy, and bulk modulus are automatically satisfied. The two parameters Φe and γ of the two body potential were determined by fitting to shear modulus and the single vacancy formation energy. Contributions of up to the third nearest neighbors were included in the evaluation of the charge density ρ and the two body potential Φ. The stability and anisotropy of each structure were estimated and compared with the available experimental data.

Interfacial Strengthening in Semi-Coherent Metallic Multilayers

1994 ◽  
Vol 362 ◽  
Author(s):  
S. I. Rao ◽  
P. M. Hazzledine ◽  
D. M. Dimiduk
Keyword(s):  
Yield Stress ◽  
Continuum Theory ◽  
Lattice Parameter ◽  
Embedded Atom Method ◽  
Metallic Multilayers ◽  
Parameter Mismatch ◽  
Multilayer Systems ◽  
Embedded Atom ◽  
Atomistic Calculations ◽  
Stress Drops

AbstractExperimental results show that a nanolayered composite structure made of two kinds of metals strengthens dramatically as the layer thickness is reduced. In epitaxial systems, this strengthening has been attributed classically, to the modulus and lattice parameter mismatches between adjacent layers. The modulus mismatch introduces a force between a dislocation and its image in the interface. The lattice parameter mismatch generates stresses and mismatch dislocations which interact with mobile dislocations. In addition to these two interactions, there is the difficulty of operating a Frank-Read source in any very thin layer. However, the calculations suffer from the drawback that elasticity theory is being used at such short range from the dislocations that it is not strictly valid. In this paper the issues in strengthening of multilayer systems are defined within a simple analytical model. Additionally, a parametric approach using the atomistic embedded atom method (EAM), is developed to study, dislocation-interface interactions in metallic multilayers. Preliminary results of the atomistic calculations verify that Koehler strengthening is significant especially when the lamellae are very thin. For thicker lamellae the lattice parameter mismatch effects, which have been modelled within continuum theory, contribute increasingly to the strength. In Cu-Ni, the peak in the yield stress occurs when single dislocations must overcome both barriers. The yield stress drops in thicker lamellae as pile ups of increasing length form in the lamellae, finally conforming to the Hall-Petch equation.

Hrtem Observations Of A Σ=3 {112} Bicrystal Boundary In Aluminum

1992 ◽  
Vol 295 ◽  
Author(s):  
D. L. Medlin ◽  
M. J. Mills ◽  
W. M. Stobbs ◽  
M. S. Daw ◽  
F. Cosandey
Keyword(s):  
Rigid Body ◽  
High Energy ◽  
Low Energy ◽  
Boundary Structure ◽  
Energy Structure ◽  
Embedded Atom Method ◽  
Fcc Metals ◽  
Embedded Atom ◽  
Grain Boundary Structure ◽  
Atomistic Calculations

AbstractWe present here a study of the Σ=3 {112} incoherent twin boundary in aluminum. Atomistic studies of this boundary indicate that several high energy boundary structures may exist, with the lowest energy structure exhibiting a small rigid body shift parallel to the boundary. The observations presented here indicate that the rigid body shift does in fact occur and that its magnitude, as well as the local grain boundary structure, is well predicted by atomistic calculations using the Embedded Atom Method. The low energy boundary configuration is much narrower than the equivalent boundaries that have been observed in the lower stacking fault energy FCC metals.

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.

Atomistic Finite Deformation Simulations: A Discussion on Length Scale Effects in Relation to Mechanical Stresses

1999 ◽  
Vol 121 (2) ◽  
pp. 114-119 ◽  
Author(s):  
Mark F. Horstemeyer ◽  
M. I. Baskes
Keyword(s):  
Continuum Mechanics ◽  
Simple Shear ◽  
Finite Deformation ◽  
Scale Effects ◽  
Embedded Atom Method ◽  
Length Scale ◽  
Size Scale ◽  
Embedded Atom ◽  
Spatial Size ◽  
The Continuum

In this study, atomistic finite deformation calculations employing the Embedded Atom Method show three items of interest related to continuum field theory. First, a spatial size scale effect on the yield stress is found. In these calculations, mechanical yield point occurred from dislocation initiation at the edge of the numerical specimens. The spatial size scale continued to affect the plastic response up to strains of 30 percent in simple shear for nickel oriented at 〈011〉. The second point is related to the continuum mechanics observation about oscillating global shear stress under simple shear conditions is shown to dampen as the spatial size scale increases. As the spatial length scale increases, the continuum rotational effect coupled with the increase in dislocation population reduces the oscillatory behavior. This confirms the notion proposed by Bammann and Aifantis (1987) in that when more dislocations are initiated with different orientations of the Burger’s vectors then the oscillations decrease. Finally, a length scale bridging idea is proposed by relating a continuum single degree of freedom loss coefficient, which relates the plastic energy to the total strain energy, to varying sizes of blocks of atoms. This study illustrates the usefulness of employing the Embedded Atom Method to study mechanisms related to continuum mechanics quantities.

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