Atomistic Modeling of Extended Defects in Metalic Alloys: Dislocations and Grain Boundaries in Ll2 Compounds

1990 ◽  
Vol 186 ◽  
Author(s):  
V. Vitek ◽  
G. J. Ackland ◽  
J. Cserti
Keyword(s):  
Grain Boundaries ◽  
Dislocation Core ◽  
Extended Defects ◽  
Atomistic Modeling ◽  
Many Body ◽  
Deformation And Fracture ◽  
Governing Factor ◽  
Atomic Interactions ◽  
Total Energies ◽  
Physical Features

AbstractExtended defects, such as dislocations and grain boundaries, control a wide variety of material properties and their atomic structure is often a governing factor. A necessary precursor for modeling of these structures is a suitable description of atomic interactions. We present here empirical many-body potentials for alloys which represent a very simple scheme for the evaluation of total energies and yet reflect correctly the basic physical features of the alloy systems modeled. As examples of atomistic studies we show results of calculations of the core structures of screw dislocations in Ll2 compounds. The same potentials have also been used to calculate structures of grain boundaries in these compounds. The deformation and fracture behavior of Ll2 alloys is then discussed in the light of grain boundary and dislocation core studies.

A Comparative Atomistic Study of the Structure of Grain Boundaries in Tungsten

1992 ◽  
Vol 291 ◽  
Author(s):  
A. Marinopoulos ◽  
M. Sob ◽  
V. Vitek ◽  
A. E. Carlsson
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Characteristics ◽  
Many Body ◽  
Electronic Density ◽  
Atomic Interactions ◽  
Symmetrical Tilt ◽  
Tilt Grain Boundary ◽  
Atomistic Study ◽  
Central Forces

ABSTRACTMost atomistic studies of grain boundaries have been carried out using central forces to describe atomic interactions. However, in transition metals with unfilled d-bands the angular dependence of interatomic forces may be important. The purpose of this paper is to investigate the significance of angular forces in the case of Tungsten. The calculations have been performed for the Σ5(210) symmetrical tilt grain boundary using two alternate approaches. First are the central-force many-body potentials of the Finnis-Sinclair type. The second are the angular dependent potentials obtained via a moment analysis of the electronic density of states. The results of these two approaches are compared by analyzing the boundary structures, the relative displacements of the adjoining grains and the expansion. Differences in structural characteristics are discussed in terms of the effect of angular forces.

DYNAMIC STUDIES OF DEFORMATION AND FRACTURE AT GRAIN BOUNDARIES

1988 ◽  
Vol 49 (C5) ◽  
pp. C5-677-C5-680
Author(s):  
I. M. ROBERTSON ◽  
G. M. BOND ◽  
T. C. LEE ◽  
D. S. SHIH ◽  
H. K. BIRNBAUM
Keyword(s):  
Grain Boundaries ◽  
Dynamic Studies ◽  
Deformation And Fracture

Atomistic Modeling of Interfacial Diffusion in the Lamellar Li0 TiAl

1999 ◽  
Vol 578 ◽  
Author(s):  
M. Nomura ◽  
D. E. Luzzi ◽  
V. Vitek
Keyword(s):  
Atomistic Simulation ◽  
Effective Activation Energy ◽  
Surprising Result ◽  
Atomistic Modeling ◽  
Many Body ◽  
Interfacial Diffusion ◽  
Self Diffusion ◽  
Diffusion Mechanisms ◽  
And Migration ◽  
Lamellar Interfaces

AbstractAtomistic simulation employing many-body central-force potentials was performed to elucidate the diffusion mechanisms in the bulk and at lamellar interfaces assuming a vacancy mechanism. First the self- diffusion of Ti and Al in stoichiometric structures was studied. It was found that the diffusion was faster along lamellar interfaces than in the bulk; the effective activation energy for the diffusion coefficient is about ∼15% lower. The simulations were then extended to investigate diffusion along lamellar boundaries with segregated Ti which is likely in Ti rich alloys. The surprising result is that diffusion remains practically unchanged when compared with the stoichiometric case. The reason is that while the path controlling the diffusion is different, the corresponding effective formation and migration energies are practically the same as in the stoichiometric case.

Interaction Between Lattice Dislocations and Grain Boundaries In Ordered Compounds

1990 ◽  
Vol 213 ◽  
Author(s):  
B.J. Pestman ◽  
J. Th. M. De Hosson ◽  
V. Vitek ◽  
F.W. Schapink
Keyword(s):  
Shear Stress ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Partial Dislocation ◽  
Atomistic Simulations ◽  
Many Body ◽  
Shockley Partial Dislocation ◽  
Screw Dislocations ◽  
Applied Shear Stress ◽  
Tilt Boundaries

ABSTRACTThe interaction of 1/2<1 1 0> screw dislocations with symmetric [1 1 0] tilt boundaries was investigated by atomistic simulations using many-body potentials representing ordered compounds. The calculations were performed with and without an applied shear stress. The observations were: absorption into the grain boundary, attraction of a lattice Shockley partial dislocation towards the grain boundary and transmission through the grain boundary under the influence of a shear stress. It was found that the interaction in ordered compounds shows similarities to the interaction in fcc.

The Sites of Premelting in Organic Compounds

1991 ◽  
Vol 46 (10) ◽  
pp. 917-919 ◽  
Author(s):  
Gilberte Dosseh ◽  
Alain H. Fuchs
Keyword(s):  
Nmr Spectroscopy ◽  
Grain Boundaries ◽  
Organic Compounds ◽  
Molecular Crystals ◽  
Proton Nmr ◽  
Crystalline Solids ◽  
Extended Defects ◽  
Proton Nmr Spectroscopy

AbstractBartis recently proposed a theory which should allow to determine whether impurities or defects are responsible for the premelting phenomena in crystalline solids. We have tested this model on several orientationally disordered molecular crystals studied by proton NMR spectroscopy. This showed that extended defects, and more likely grain boundaries are at the origin of the premelting phenomena in these crystals.

Experimental Evidence For Sulfur Induced Loss Of Ductility In Copper Shaped-Charge Jets

1995 ◽  
Vol 409 ◽  
Author(s):  
D. K. Chan ◽  
D. H. Lassila ◽  
W. E. King ◽  
E. L. Baker
Keyword(s):  
Grain Boundaries ◽  
Sulfur Content ◽  
Fracture Behavior ◽  
High Strain ◽  
Shaped Charge ◽  
X Ray ◽  
Jet Breakup ◽  
Deformation And Fracture ◽  
Breakup Time ◽  
Content Of Oxygen

AbstractWe have observed that a change in the bulk sulfur content of oxygen-free electronic copper markedly affects its high temperature (400–1000°C), high strain-rate (> 103 s−1) deformation and fracture behavior. These conditions are typical of those found in "jets" formed from the explosive deformation of copper shaped-charge liners. Specifically, an increase in the bulk sulfur concentration from 4 ppm to 8 ppm shortens the breakup time, tb, of the copper jets by nearly 20% as measured using flash x-ray radiographs recorded during breakup of the jets. At bulk concentrations of 4 ppm, the jet was observed to be uniform and axisymmetric with a breakup time of 186 µs. Jet particles exhibited length-to-diameter ratios of roughly 8:1. The addition of sulfur transformed the jet breakup behavior to non-uniform, non-axisymmetric rupture and reduced the breakup time to 147 µs. The length-to-diameter ratios decreased to roughly 5:1 in the sulfurdoped samples. Previously measured sulfur solubilities and diffusivities in copper at the temperatures where this material was processed indicates nearly all of the sulfur was localized to grain boundaries. Therefore, we infer that the increase in sulfur content at grain boundaries is directly responsible for the change in breakup performance of the shaped-charge jets.

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