Influence of Shear Stress on Screw Dislocations in a Model Sodium Lattice

1971 ◽  
Vol 49 (16) ◽  
pp. 2160-2180 ◽  
Author(s):  
Z. S. Basinski ◽  
M. S. Duesbery ◽  
Roger Taylor
Keyword(s):  
Shear Stress ◽  
First Principles ◽  
Dislocation Core ◽  
The Body ◽  
Peierls Stress ◽  
Screw Dislocations ◽  
Hexagonal Close Packed ◽  
Applied Shear Stress ◽  
Dislocation Movement ◽  
Twinning Direction

The behavior of the screw dislocation core in the presence of an external shear stress has been examined for the body-centered cubic and hexagonal close-packed phases of a model sodium lattice, using an effective ion–ion potential calculated from first principles. The Peierls stress for screw dislocations in the b.c.c. lattice at 0 °K is dependent on the orientation of the applied shear stress, and has a minimum value of 0.0105G, where G is the shear modulus, for slip in the twinning direction on {112} planes. The Peierls stress in the h.c.p. lattice is at least 25 times smaller. Dislocation movement in the model b.c.c. lattice takes place by unit translations on {110} planes, with the selection rule that no two consecutive translations can take place on the same slip plane.

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.

First-Principles Study of Structural and Defect Properties in FeCo Intermetallics

2004 ◽  
Vol 842 ◽  
Author(s):  
M. Krcmar ◽  
C. L. Fu ◽  
J. R. Morris
Keyword(s):  
Shear Stress ◽  
Ab Initio ◽  
Structural Stability ◽  
First Principles ◽  
Statistical Thermodynamic ◽  
Internal Stresses ◽  
Applied Shear Stress ◽  
Defect Energies ◽  
Antisite Defects ◽  
B2 Structure

ABSTRACTEmploying ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {110} and {112} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stresses near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.

Dislocation—like Defects in an Amorphous Lennard—jones Solid

1986 ◽  
Vol 82 ◽  
Author(s):  
L. T. Shi ◽  
P. Chaudhari
Keyword(s):  
Computer Simulation ◽  
Shear Stress ◽  
Screw Dislocations ◽  
Lennard Jones ◽  
Simulation Techniques ◽  
Applied Shear Stress ◽  
Computer Simulation Techniques

ABSTRACTIt has been found, using computer simulation techniques, that both edge and screw dislocations can be stably introduced into an amorphous Lennard-Jones solid, and can be moved through the model under an applied shear stress.

Dislocation mobility and the concept of flow stress

1975 ◽  
Vol 344 (1638) ◽  
pp. 375-385 ◽  
Keyword(s):  
Shear Stress ◽  
Flow Stress ◽  
First Principles ◽  
Unstable State ◽  
Burgers Vector ◽  
Applied Shear Stress ◽  
Set Up ◽  
The Stability ◽  
Definition Of ◽  
Hurwitz Theorem

A formal definition of the flow stress of a metal is established rigorously from first principles for a certain model by studying the stability of equilibrium of the leader in a group of n ( n large) coplanar screw dislocations with Burgers vector b, moving on a plane a distance h from a non-coplanar locked dislocation with Burgers vector mb ( m < n ) under the action of an applied shear stress p yz = o.A ‘ characteristic equation’ of the model is set up and the onset of instability of the leader is identified with the bifurcation of its equilibrium state, which is predicted by the Routh-Hurwitz theorem, well-known in the theory of stability. As an aid in simplifying this process recourse is had to another well-known the orem -that due to Liénard & Chipart. The applied shear stress required to achieve this unstable state is specified within certain bounds. Since these bounds are very close to each other, especially for small m , the critical flow stress can be estimated accurately. It is shown that the flow stress is closer to the lower bound obtained previously and that the superdislocation approach overestimates the critical stress. The paper also discusses certain implications of the present work.

Origin of dramatic oxygen solute strengthening effect in titanium

Science ◽  
2015 ◽  
Vol 347 (6222) ◽  
pp. 635-639 ◽  
Author(s):  
Qian Yu ◽  
Liang Qi ◽  
Tomohito Tsuru ◽  
Rachel Traylor ◽  
David Rugg ◽  
...  
Keyword(s):  
First Principles ◽  
Dislocation Core ◽  
Strengthening Effect ◽  
First Principles Calculations ◽  
Screw Dislocations ◽  
Elastic Fields ◽  
Transmission Electron ◽  
Short Range Repulsion ◽  
Solute Atoms ◽  
Solute Strengthening

Structural alloys are often strengthened through the addition of solute atoms. However, given that solute atoms interact weakly with the elastic fields of screw dislocations, it has long been accepted that solution hardening is only marginally effective in materials with mobile screw dislocations. By using transmission electron microscopy and nanomechanical characterization, we report that the intense hardening effect of dilute oxygen solutes in pure α-Ti is due to the interaction between oxygen and the core of screw dislocations that mainly glide on prismatic planes. First-principles calculations reveal that distortion of the interstitial sites at the screw dislocation core creates a very strong but short-range repulsion for oxygen that is consistent with experimental observations. These results establish a highly effective mechanism for strengthening by interstitial solutes.

Stacking Faults and Dislocation Dissociation in MoSi2

2008 ◽  
Vol 1128 ◽  
Author(s):  
Miroslav Cak ◽  
Mojmir Sob ◽  
Vaclav Paidar ◽  
Vaclav Vitek
Keyword(s):  
Shear Stress ◽  
Slip System ◽  
Density Functional ◽  
Deformation Behaviour ◽  
Stacking Faults ◽  
Dislocation Core ◽  
Orientation Dependence ◽  
The Body ◽  
Anisotropic Elastic ◽  
Critical Resolved Shear Stress

AbstractThe intermetallic compound MoSi2 crystallises in the body-centred-tetragonal C11b structure and while it is brittle when loaded in tension, it deforms plastically in compression even at and below the room temperature. The ductility of MoSi2 is controlled by the mobility of 1/2〈331] dislocations on {013) planes but the critical resolved shear stress for this slip system depends strongly on the orientation of loading and it is the highest for compression along the 〈001] axis. Such deformation behaviour suggests that the dislocation core is controlling the slip on the {013)〈331] system. Since the most important core effect is dissociation into partial dislocations connected by metastable stacking faults the first goal of this paper is to ascertain such faults. This is done by employing the concept of the γ-surface. The γ-surfaces have been calculated for the (013) and (110) planes using a method based on the density functional theory. While there is only one possible stacking fault on the (110) plane, three distinct stacking faults have been found on the (013) plane. This leads to a variety of possible dislocation splittings and the energetics of these dissociations has been studied by employing the anisotropic elastic theory of dislocations. The most important finding is the non-planar dissociation of the 1/2〈331] screw dislocation that is favoured over the planar splittings and may be responsible for the orientation dependence of the critical resolved shear stress for the {013)〈331] slip system.

scholarly journals First-Principles Calculation of the Structure of Mercury

1995 ◽  
Vol 408 ◽  
Author(s):  
Michael J. Mehl
Keyword(s):  
Ground State ◽  
First Principles ◽  
Rhombohedral Phase ◽  
The Body ◽  
First Principles Calculation ◽  
First Principles Calculations ◽  
Hexagonal Close Packed ◽  
Close Packed Structure ◽  
Hexagonal Close Packed Structure ◽  
Packed Structure

AbstractMercury has perhaps the strangest behavior of any of the metals. Although the other metals in column IIB have an hcp ground state, mercury's ground state is the body centered tetragonal βHg phase. The most common phase of mercury is the rhombohedral αHg phase, which is stable from 79K to the melting point and meta-stable below 79K. Another rhombohedral phase, γ71Hg, is believed to exist at low temperatures. First-principles calculations are used to study the energetics of the various phases of mercury. Even when partial spin-orbit effects are included, the calculations indicate that the hexagonal close packed structure is the ground state. It is suggested that a better treatment of the spinorbit interaction might alter this result.

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.

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