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.

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

1984 ◽  
Vol 392 (1802) ◽  
pp. 145-173 ◽  
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.

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.

A dislocation core in titanium dioxide and its electronic structure

RSC Advances ◽  
2015 ◽  
Vol 5 (24) ◽  
pp. 18506-18510 ◽  
Author(s):  
Rong Sun ◽  
Zhongchang Wang ◽  
Naoya Shibata ◽  
Yuichi Ikuhara
Keyword(s):  
Titanium Dioxide ◽  
Electronic Structure ◽  
Electric Conductivity ◽  
Dislocation Core ◽  
Core Structure ◽  
Atomic Resolution ◽  
The Core ◽  
Resolution Imaging

We provide a direct atomic-resolution imaging of the core structure of a dislocation in technologically important TiO2 and predict that every individual impurity-free dislocation exhibits electric conductivity in an otherwise insulating TiO2.

Computer Simulation Study of the Effects of Copper Precipitates on Dislocation Core Structure in Ferritic Steels

1996 ◽  
Vol 439 ◽  
Author(s):  
T. Harry ◽  
D. J. Bacon
Keyword(s):  
Dislocation Core ◽  
Alloy System ◽  
Lattice Parameter ◽  
Transformation Process ◽  
Core Structure ◽  
Metastable Equilibrium ◽  
Precipitate Size ◽  
Ferritic Steels ◽  
Interatomic Potentials ◽  
The Core

AbstractThe small, coherent BCC precipitates of copper that form during fast neutron irradiation of ferritic steels are an important component of in-service irradiation hardening. Many-body interatomic potentials for the Fe-Cu alloy system have been developed and used to simulate the atomic structure of the ½<111> screw dislocation in both pure a-iron and the metastable BCC phase of copper. In iron, the core has the well-known 3-fold form of atomic disregistry. In BCC copper, however, the core structure depends on the lattice parameter. At the metastable equilibrium value, the core is similar to that in iron, but as the lattice parameter is reduced, as in a precipitate, the core becomes delocalised by transformation of the copper. Simulation of dislocated crystals containing precipitates shows that the extent of this effect depends on precipitate size. The energy changes indicate a significant dislocation pinning effect due to this dislocation-induced precipitate transformation process.

Computer simulation of the screw dislocation motion in b. c. c. metals under the effect of the external shear and uniaxial stresses

1976 ◽  
Vol 352 (1668) ◽  
pp. 109-124 ◽  
Keyword(s):  
Computer Simulation ◽  
Shear Stress ◽  
Stress Tensor ◽  
Screw Dislocation ◽  
Dislocation Motion ◽  
Central Force ◽  
The Core ◽  
Empirical Potentials ◽  
Atomistic Study

An atomistic study of the motion of the 1/2 [111] screw dislocation was carried out for a shear stress applied on {112} planes and for uniaxial stresses along [012], [001] and [111]. Central force interactions described by the three different empirical potentials used in the previous work (Duesbery, Vitek & Bowen 1973) were assumed. The distortions of the core and the subsequent dislocation motion always reflected the twinning-antitwinning asymmetry of shear on {112} planes. The non-shear components of the stress tensor introduced further asymmetries which vary with interatomic forces. The application of the results of this study to the theory of slip and twinning in b. c. c. metals, is discussed.

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