Dislocation Core Structure Evolution During Dislocation Glide in FCC Lattices

2003 ◽  
Vol 779 ◽  
Author(s):  
M.A. Soare ◽  
R.C. Picu
Keyword(s):  
Shear Stress ◽  
Elastic Field ◽  
Dislocation Core ◽  
Peierls Stress ◽  
Atomistic Simulations ◽  
Structure Evolution ◽  
Dislocation Glide ◽  
The Core ◽  
Fcc Lattice ◽  
Dislocation Core Structure

AbstractA dislocation core model is developed in terms of a singular decomposition of the elastic field surrounding the defect in a power series of 1/rn. The decomposition is a Laurent expansion beginning with the term corresponding to the Volterra dislocation and continuing with a series of dipoles and multipoles. The analysis is performed for an edge dislocation in an fcc lattice. The field surrounding the dislocation is derived by means of atomistic simulations. The coefficients of the series expansion are determined from the elastic field using path independent integrals. When loaded by a shear stress smaller than the Peierls stress, the core distorts. The distortion up to the instability (Peierls stress) is monitored based on the variation of these coefficients. The stacking fault separating the two partials is characterized, by using a similar procedure, as a source of elastic field.

The effect of shear stress on the screw dislocation core structure in body-centred cubic lattices

1973 ◽  
Vol 332 (1588) ◽  
pp. 85-111 ◽  
Keyword(s):  
Shear Stress ◽  
Screw Dislocation ◽  
Plastic Flow ◽  
Stacking Faults ◽  
Dislocation Core ◽  
Stacking Fault ◽  
Core Structure ◽  
Cubic Lattices ◽  
The Core ◽  
Dislocation Core Structure

The behaviour of the ½ a <111> screw dislocation core in the presence of an external shear stress on {110} planes has been studied for a variety of effective interionic potentials, each representing a stable b. c. c. lattice. The distortion and motion of the core are described using the concept of fractional dislocations, which are imperfect dislocations bounding a ribbon of generalized (unstable) stacking fault. Three essentially distinct types of movement are found, and the relation of these to plastic flow and twinning in real b. c. c. metals is discussed. It is found that the movement of the dislocation core can be rationalized in terms of the relative stresses needed to create generalized stacking faults on {110} and {112} planes.

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

1992 ◽  
Vol 291 ◽  
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.

Trends in Dislocation Core Structures and Mechanical Behavior in B2 Aluminide

1994 ◽  
Vol 364 ◽  
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.

scholarly journals Computer simulations of hydrostatic pressure influence on screw dislocation slip in Mg

2020 ◽  
Keyword(s):  
Shear Stress ◽  
Hydrostatic Pressure ◽  
Pressure Dependence ◽  
Critical Stress ◽  
Dislocation Core ◽  
Prismatic Slip ◽  
Dislocation Slip ◽  
Atomistic Modeling ◽  
Dislocation Core Structure ◽  
Critical Resolved Shear Stress

Atomistic modeling of hydrostatic pressure influence on critical resolved shear stress was performed for glide of screw <a> dislocation in magnesium. It was found that application of pressure can change the resolved critical stress for basal and prismatic slip. The effect is dependent on dislocation core structure. It can be connected to the pressure dependence transient dilatation of the dislocation core.

The Effect of Growth Stoichiometry on the GaN Dislocation Core Structure

2002 ◽  
Vol 743 ◽  
Author(s):  
Marcus Q. Baines ◽  
David Cherns ◽  
Julia W. P. Hsu ◽  
Michael J. Manfra
Keyword(s):  
Molecular Beam ◽  
Dislocation Core ◽  
Sample Surface ◽  
Plan View ◽  
The Core ◽  
Transmission Electron ◽  
Dislocation Core Structure ◽  
Edge Dislocations ◽  
Open Core ◽  
Lean Conditions

ABSTRACTPlan-view transmission electron microscopy was used to study the core structures of different dislocations in (0001) GaN layers grown under Ga-rich and Ga-lean conditions by molecular beam epitaxy. In Ga-rich samples at least one third of mixed type dislocations were open-core, and edge dislocations were observed to be closed-core. In contrast, under Ga-lean conditions, all dislocations were observed to be closed-core, and many were associated with pits at the sample surface. High resolution studies of the open core dislocations revealed that many were decorated with a disordered deposit, the origin of which is discussed.

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

1984 ◽  
Vol 392 (1802) ◽  
pp. 175-197 ◽  
Keyword(s):  
Stress Tensor ◽  
Screw Dislocation ◽  
Applied Stress ◽  
Elastic Strain ◽  
Elastic Anisotropy ◽  
Dislocation Core ◽  
Core Structure ◽  
Peierls Stress ◽  
The Core ◽  
Anisotropic Elastic

The change in core structure of the screw dislocation in a body-centred cubic lattice subjected to a general applied stress tensor is studied by means of computer simulation. The large variations observed are found not to be correlated with the applied stress, in that the same deformed core structure can be realized by many different combinations of stress components. Instead, the core structure is found to be characterized almost exclusively by the magnitude and orientation of the induced glide strain, with a much smaller dependence on the glide stress. This means that while the force acting on a dislocation is defined by the applied stress, it is the elastic strain within the lattice that determines the resistance to motion. This explains the anomalously large dependence of the Peierls stress upon non-glide components of the applied stress tensor. The Peierls stress varies strongly with the shape of the dislocation core, which depends upon the glide strain. However, the glide strain is in turn dependent on non-glide components of the applied stress by way of anisotropic elastic couplings. Therefore the Peierls stress is itself dependent on the non-glide stresses, to an extent governed by the elastic anisotropy. The possible origin of the strain-dependence of the core structure in elastic strain multiplet forces (equal and opposite generalized forces acting on the dislocation) is discussed briefly, as are implications for the phenomenon of ductile fracture.

scholarly journals Revealing and Controlling the Core of Screw Dislocations in BCC Metals

2021 ◽  
Author(s):  
Zhaoxuan Wu ◽  
Rui Wang ◽  
Lingyu Zhu ◽  
Subrahmanyam Pattamatta ◽  
David Srolov
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Dislocation Core ◽  
Core Structure ◽  
Valence Electron Concentration ◽  
Interatomic Potentials ◽  
Structure Transition ◽  
The Core ◽  
Bcc Metals ◽  
Dislocation Core Structure

Abstract Body-centred-cubic (BCC) transition metals (TMs) tend to be brittle at low temperatures, posing significant challenges in their processing and major concerns for damage tolerance in critical load-carrying applications. The brittleness is largely dictated by the screw dislocation core structure; the nature and control of which has remained a puzzle for nearly a century. Here, we introduce a universal model and a physics-based material index χ that guides the manipulation of dislocation core structure in all pure BCC metals and alloys. We show that the core structure, commonly classified as degenerate (D) or non-degenerate (ND), is governed by the energy difference between BCC and face-centred cubic (FCC) structures and χ robustly captures this key quantity. For BCC TMs alloys, the core structure transition from ND to D occurs when χ drops below a threshold, as seen in atomistic simulations based on nearly all extant interatomic potentials and density functional theory (DFT) calculations of W-Re/Ta alloys. In binary W-TMs alloys, DFT calculations show that χ is related to the valence electron concentration at low to moderate solute concentrations, and can be controlled via alloying. χ can be quantitatively and efficiently predicted via rapid, low-cost DFT calculations for any BCC metal alloys, providing a robust, easily applied tool for the design of ductile and tough BCC alloys.

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