Dynamics of Dissociated Dislocations in SI: A Micro-Meso Simulation Methodology

AbstractThe theory of dislocation motion in materials with high Peierls stress relates dislocation mobility to the underlying kink mechanisms. While one has been able to describe certain qualitative features of dislocation behavior, important details of the atomic core mechanisms are lacking. We present a hybrid micro-meso approach to modeling the mobility of a single dislocation in Si in which the energetics of defect cores and kink mechanisms are treated by atomistic simulation, while dislocation motion under applied stress and at finite temperature is described through kinetic Monte Carlo. Three important aspects pertaining to treating the details of local structure and dynamics of kinks are incorporated in our approach: (1) Realistic complexity of (multiple) kink mechanisms in the dislocation core. (2) Full Peach-Koehler formalism for treatment of curved dislocation. (3) Detailed investigation of interaction between partials. This simulation methodology is used to calculate micron-scale dislocation mobility, with no adjustable parameters; specifically we obtain temperature and stress dependent velocity results that can be compared with experimental measurements.

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Simple Flexible Boundary Conditions for the Atomistic Simulation of Dislocation Core Structure and Motion

MRS Proceedings ◽

10.1557/proc-291-85 ◽

1992 ◽

Vol 291 ◽

Cited By ~ 7

Author(s):

Roberto Pasianot ◽

Eduardo J. Savino ◽

Zhao-Yang Xie ◽

Diana Farkas

Keyword(s):

Atomistic Simulation ◽

Dislocation Line ◽

Dislocation Core ◽

Dislocation Motion ◽

Peierls Stress ◽

Rigid Boundary ◽

The Past ◽

Structure And Motion ◽

Linear Effects ◽

Dislocation Core Structure

ABSTRACTFlexible boundary codes for the atomistic simulation of dislocations and other defects have been developed in the past mainly by Sinclair [1], Gehlen et al.[2], and Sinclair et al.[3]. These codes permitted the use of smaller atomic arrays than rigid boundary codes, gave descriptions of core non-linear effects and allowed fair assessments of the Peierls stress for dislocation motion. Green functions (continuum or discrete) or surface traction forces were used to relax the boundary atoms.A much simpler approach is followed here. Core and mobility effects at the boundary are accounted for by a dipole tensor centered at the dislocation line, whose components constitute six more parameters of the minimization process. Results are presented for [100] dislocations in NiAl. It is shown that, within the limitations of the technique, reliable values of the Peierls stress are obtained.

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Kinetic Monte Carlo Method

Computer Simulations of Dislocations ◽

10.1093/oso/9780198526148.003.0014 ◽

2006 ◽

Author(s):

Vasily Bulatov ◽

Wei Cai

Keyword(s):

Monte Carlo ◽

Kinetic Monte Carlo ◽

Dislocation Core ◽

Dislocation Motion ◽

Coarse Grained ◽

Solid Thin Films ◽

Finite Set ◽

And Migration ◽

Dynamics Simulations ◽

Straight Segments

The PN model discussed in the preceding chapter is a continuum approach that requires some atomistic input to account for non-linear interactions in the dislocation core. In this chapter, we introduce yet another continuum model that uses atomistic input for a different purpose. The kinetic Monte Carlo (kMC) model does not consider any details of the core structure but instead focuses on dislocation motion on length and time scales far greater than those of the atomistic simulations. The model is especially effective for diamond-cubic semiconductors and other materials in which dislocation motion is too slow to be observed on the time scale of molecular dynamics simulations. The key idea of the kMC approach is to treat dislocation motion as a stochastic sequence of discrete rare events whose mechanisms and rates are computed within the framework of the transition state theory. Built around its unit mechanisms, the kMC model simulates dislocation motion and predicts dislocation velocity as a function of stress and temperature. This data then can be used to construct accurate mobility functions for dislocation dynamics simulations on still larger scales (Chapter 10). In this sense, kMC serves as a link between atomistic models and coarse-grained continuum models of dislocations. The kMC approach is most useful in situations where the system evolves through a stochastic sequence of events with only a few possible event types. The method has been used in a wide variety of applications other than dislocations. For example, the growth of solid thin films from vapor or in solution is known to proceed through attachment and diffusion of adatoms deposited on the surface. Based on a finite set of unit mechanisms of the motion of adatoms, kMC models accurately describe the kinetics of growth and the resulting morphology evolution of the epitaxial films [95, 96, 97]. Similar kMC models have been applied to dislocation motion in crystals with high lattice resistance, such as silicon. In these materials, dislocations consist of long straight segments interspersed with atomic-sized kinks, depicted schematically in Fig. 9.1(a) as short vertical segments. As was explained in Section 1.3, dislocation motion proceeds through nucleation and migration of kink pairs and can be described well by a kMC model.

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Trends in Dislocation Core Structures and Mechanical Behavior in B2 Aluminide

MRS Proceedings ◽

10.1557/proc-364-395 ◽

1994 ◽

Vol 364 ◽

Cited By ~ 4

Author(s):

C. Vailhe ◽

D. Farkas

Keyword(s):

High Temperature ◽

Mechanical Behavior ◽

Deformation Mechanism ◽

Dislocation Core ◽

Peierls Stress ◽

Atomistic Simulations ◽

Dislocation Behavior ◽

B2 Structure

AbstractIn an effort to understand the deformation mechanism in high temperature B2 intermetallics, atomistic simulations were carried out for dislocation cores in a series of compounds exhibiting the B2 structure (FeAl, NiAl, CoAl). A comparison was made on the basis of core structures, dislocation splittings and Peierls stress values. The (110) and (112) γ surfaces were computed for these three compounds. The importance of the APB values and the maximum shear faults for explaining the dislocation behavior is discussed.

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Atomistic Simulation of Dislocation Motion as Determined by Core Structure

MRS Proceedings ◽

10.1557/proc-350-293 ◽

1994 ◽

Vol 350 ◽

Cited By ~ 5

Author(s):

Kevin Ternes ◽

Diana Farkas ◽

Zhao-Yang Xie

Keyword(s):

Atomistic Simulation ◽

Dislocation Core ◽

Dislocation Motion ◽

Core Structure ◽

Planar Structure ◽

Interatomic Potentials ◽

Atom Type ◽

The Core ◽

Embedded Atom ◽

Structure And Motion

AbstractTwo different interatomic potentials of the embedded atom type were used to study the relationships between dislocation core structure and mobility. Core structures were computed for a variety of dislocations in B2 NiAl. Several non-planar cores were studied as they reacted to applied stress and moved. The results show that in some cases, the dislocation core transforms to a planar structure before the dislocation glides, whereas in some other cases the core retains the non-planar structure at stresses sufficient to sustain glide. The effects of stoichiometry deviations on the core structure and motion were also studied.

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Critical Evaluation of Atomistic Simulations of 3D Dislocation Configurations

MRS Proceedings ◽

10.1557/proc-408-243 ◽

1995 ◽

Vol 408 ◽

Author(s):

Vijay B. Shenoy ◽

Rob Phillips

Keyword(s):

Atomistic Simulation ◽

Critical Evaluation ◽

Line Tension ◽

Peierls Stress ◽

Atomistic Simulations ◽

Lattice Resistance ◽

New Challenges ◽

Fixed Boundaries ◽

Important Objective ◽

Approximate Scheme

AbstractThough atomistic simulation of 3D dislocation configurations is an important objective for the analysis of problems ranging from point defect condensation to the operation of Frank-Read sources such calculations pose new challenges. In particular, use of finite sized simulation cells produce additional stresses due to the presence of fixed boundaries in the far field which can contaminate the interpretation of these simulations. This paper discusses an approximate scheme for accounting for such boundary stresses, and is illustrated via consideration of the lattice resistance encountered by straight dislocations and simulations of 3D bow out of pinned dislocation segments. These results allow for a reevaluation of the concepts of the Peierls stress and the line tension from the atomistic perspective.

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On non-glide stresses and their influence on the screw dislocation core in body-centred cubic metals I. The Peierls stress

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1984.0027 ◽

1984 ◽

Vol 392 (1802) ◽

pp. 145-173 ◽

Cited By ~ 40

Keyword(s):

Screw Dislocation ◽

Applied Stress ◽

Strong Dependence ◽

Dislocation Core ◽

Peierls Stress ◽

Exact Nature ◽

Theoretical Shear Strength ◽

Stress Variation ◽

Cubic Model ◽

Model Lattice

The response of the screw dislocation core in a body-centred cubic model lattice to a general applied stress tensor is examined by means of computer simulation. The Peierls stress is found to have the symmetry required by Neumann’s principle but is found also to have a very strong dependence on shear components of the applied stress which should not interact with the screw dislocation. Rather than having the constant value suggested by the Schmid law of critical resolved shear stress, the Peierls stress can vary from zero to the theoretical shear strength of the lattice, depending upon the exact nature of the critical applied stress components. Calculations with different interatomic binding potentials show that the Peierls stress variation, while different in detail, remains broadly the same, suggesting an origin in the dislocation core geometry rather than the specific characteristics of the force laws. Specialization to the case of uniaxial applied stress shows that the similar Peierls stress variation can nevertheless lead to quite different orientation dependences of the flow stress in different materials. Applications to the problem of brittle fracture and possible sources of the Peierls stress variation are discussed briefly.

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