Properties Of Dislocation Research Articles

Structural properties of partial dislocation in 3C-SiC

A transferable tight-binding (TB) model is presented within an orthogonal sps ∗ basis set that incorporates the two-center intra-atomic parameters. It is crucial to include such terms in order to get more reliable results for linear defects in 3C-SiC. We tested our TB model for bulk properties, including the equilibrium lattice constant, structural energy difference between the zinc-blende (zb) lattice and the other plytypes of SiC. In our study, the 90° partial dislocation formation energies are obtained. The structural properties of 30° partial dislocation in 3C-SiC are also investigated. The results of reconstruction energies for both 30° and 90° partial dislocations are compared with the available of other theoretical calculations, and the structural stability is shown in 90° partial dislocation case.

The crucial role of chemistry on mobile properties of dislocation

Dislocation–solute interactions are ubiquitous in solids, yet their dual nature in strengthening or softening the material is not well understood. Results of a novel concurrent multiscale approach reveal that the local environment of W solutes in Ta has a dramatic effect both on the dislocation mobility and slip paths. W solutes can enhance or reduce the mobility, and may result in spontaneous dislocation glide. The atomistic mechanism responsible for the dual nature of solutes is elucidated.

TEM observations in Si: An attempt to link deformation microstructures and electrical activity

The deformation microstructures of Si single crystals have been studied by transmission electron microscopy (TEM) in the temperature range of deformation where “dislocation trails” are evidenced. The main features of the deformation microstructures are characterized by dislocations dipoles and their debris. These microscopic observations are discussed in relation with the mesoscopic properties of dislocation trails as well as the possible transformation between two different core structures of dislocations in silicon.

A study of electrical properties of dislocation engineered Si processed by ultrasound

This work presents experimental study of electrical properties of dislocation engineered Si p–n junction before and after the influence of ultrasound waves. We have studied current–voltage characteristics in the dark and upon illumination for forward and reverse biases before and after ultrasound processing. By fitting the theoretically established current–voltage dependence to the experimentally measured ones, the diode ideality factor and saturation current have been estimated. It is found that current transport through the dislocation-engineered Si p–n junction can be controlled by generation-recombination or tunneling recombination mechanisms. Ultrasound is found to modulate electrical properties of the dislocation engineered Si.

The interaction between topicalization and structural constraints: Evidence from Yucatec Maya

This article deals with the syntactic and pragmatic properties of left dislocated constituents in Yucatec Maya. It has been argued that these constituents are topics, which implies that a particular structural configuration, namely left dislocation displays a 1:1 correspondence to a particular discourse function. We present evidence that the discourse properties of left dislocation are not uniform: only a subset of the left dislocated constituents qualify as topics in the strict sense, while other instances of left dislocation are better explained if we assume a structural constraint that bans the postverbal occurrence of subject constituents in a particular syntactic configuration. Our empirical findings show that though the occurrence of word order possibilities in discourse is not random, it is not necessarily determined by a unique licensing condition.

The dissociated properties of dislocation in two-dimensional triangular lattice

Abstract The dissociated core structure of dislocation in two-dimensional triangular lattice is determined by the variational method within lattice theory. The dissociation effect leads to a narrower core width of partial dislocations than the compact one. The equilibrium separation between two partial dislocations is not very sensitive to the intrinsic stacking fault energy and there exists deviation from the intrinsic stacking fault energy criterion in the continuous elastic theory of dislocation. The relationship between the equilibrium separation and intrinsic stacking fault energy is analogous in lattice theory and the Peierls-Nabarro model. But the equilibrium separation obtained in lattice theory is wider than that obtained in the Peierls-Nabarro model for the same intrinsic stacking fault energy.

Dislocation internal friction at random external loadings

Dislocation internal friction under random external forces acting upon a dislocation was investigated. Different types of random forces (telegraph, impulse, others) were considered. Inertial properties of dislocation and effects of potential (parabolic) crystal relief were taken into account. Analytical expressions for decrement were derived and its dependencies on a degree of correlation of random force, dislocation and medium parameters were analyzed.

Dislocations and elastic anisotropy in heteroepitaxial metallic thin films

The influence of elastic anisotropy on the critical thickness for the plastic relaxation of epitaxial layers is examined with the help of a coupled discrete-continuum simulation. The latter incorporates a rigorous treatment of the boundary conditions and of mismatch stresses, as well as the elastic properties of a single threading dislocation. Numerical experiments conducted on model Cu/Cu, Cu/Au and Cu/Ni systems with a (001) interface show that, through several distinct effects, elastic anisotropy induces a significant increase in the critical thickness with respect to the values predicted by Matthews et al. The isotropic model of a comparison of the anisotropic critical thicknesses for (001) and (111) interfaces shows that Cu-(111) films on Ni substrates are about 50% 'harder' than (001) films. This feature is discussed in relation to the strength of thin metallic films.

Dynamic properties of screw dislocations in Cu: A molecular dynamics study

The dynamic properties of a single dislocation in Cu under an applied stress are studied using constant stress and temperature molecular dynamics. The dislocation is found to accelerate to a terminal velocity. The terminal velocity initially increases linearly with stress and finally approaches the shear wave velocity asymptotically. In the linear regime the drag coefficient is determined. The results are comparable with the experimental data at high temperatures and an order of magnitude higher at low temperatures. The dislocation width is found to oscillate periodically, with a period determined by the stacking fault energy and the elastic coefficients.

Flexible boundary condition for a moving dislocation

It is well known that a boundary condition usually affects the result of the computer simulation of defects, especially extended defects like a straight dislocation, where the model size dependence of the result is sometimes observed. In order to solve this problem, a flexible boundary condition is developed for the simulation of a moving dislocation by applying the Lagrange principle in the present study. Under the flexible boundary condition described here, various properties of a screw dislocation, i.e., stable core structure, Peierls stress and glide property, are calculated in a square lattice and the model size dependence of the result is hardly obtained over a wide range. Contrary to the present flexible boundary condition, explicit size dependence is observed in the case of a rigid boundary condition due to a strong image force from the boundary. It is observed, however, that the result tends to approach that obtained in the above flexible boundary model as the size of the model lattice increases. Unfortunately, in the case of a screw dislocation with higher Peierls stress than 10−2G, the flexible boundary condition is not available, because lattice vibrations with a high frequency are emitted from the dislocation line during glide motion and the boundary cannot respond to these waves.

A twinned wedge in a Si-Ge epitaxial film: Twofold Σ = 9 twinning

Abstract A wedge-like defect in a heteroepitaxial Si-22% Ge film on a Si substrate has been investigated. The defect is found to be a twofold Σ = 9 twin with elastic properties of a wedge disclination triangle. From the defect arrangement it follows that two distinct defect morphologies exist: in the first stage, a nascent wedge forms which has the properties of a single disclination; in the second stage, the triangle morphology is established (called a mature wedge) with the long-range elastic properties of an edge dislocation. The formation involves thermally activated nucleation of a nascent wedge, growth of the stable nucleus, transition from the nascent wedge to the mature twin, growth of the mature twin and eventual trapping of the defect. The processes (i) and (ii) can be understood by considering a single defect in an infinite half-space with a homogeneous stress field only. The growth of the nascent wedge is a self-similar process, and thus the transition (iii) requires the presence of inhomogene...

分子動力学法による離散転位動力学のためのせん断応力と転位運動速度の関係式の導出

Recently the discrete dislocation dynamics (DDD) methods have been applied to the problems of mesoscopic phenomena. In the DDD simulations, it is very important to know how a dislocation moves in the stress field. The relationship between the velocity of dislocation and external shear stress is often given artificially by referring to the experimental information or experience of researchers. Most of the relationships obtained are, however, qualitative and involve a lot of complex factors which depend on the experimental condition; temperature, grain boundary effect and so on. In this paper, the dynamic properties of edge dislocation whose Burgers' vector b is [111]/ 2 on 112 plane in bcc iron are studied by molecular dynamics (MD) using N-body potential proposed by Finnis and Sinclair. Then, the relationship between the velocity v of dislocation and external shear stress τ is investigated systematically. It is shown in our simulation that the relationship between v and τ is linear in the low stress region and v becomes close to sound velocity asymptotically in the high stress region. These results agree with the experimental results qualitatively. An experimental expression of v-τ relation for the DDD simulation is also proposed.

Edge and Screw Dislocations in an Amorphous Solid

We have studied, using computer simulation techniques, the properties of edge and screw dislocations in an amorphous Lennard-Jones solid. We find the edge dislocation to be unstable and the screw to be stable. The elastic properties of the screw dislocation in the amorphous solid are like those in a crystal.

The attractive and repulsive forces on a lattice screw dislocation

The properties of a lattice screw dislocation in a crystal in the form of a strip or a circular cylinder or an infinite crystal with a circualr hole or in a composite crystal composed of a soft matrix surrounded by a rigid second phase are determined. It is shown that the misfit stress field in the lattice is altered due to the image stress field. Some important conclusions have been arrived at on the image stress field on the dislocation in all the above situations.

Preparation and properties of rubber dislocations

THE purpose of this note is to describe the construction and properties of a Volterra1 edge dislocation made from two sheets of smooth rubber. A simple theoretical analysis illustrates the key features of the model and illuminates its interesting and unexpected behaviour.

Lattice screw dislocation in a finite crystal

The properties of a lattice screw dislocation in a finite crystal in the form of a strip are determined, taking into account the image forces. It is shown that the properties of a screw dislocation in a finite crystal differ markedly from those of a dislocation in an infinite crystal. When the crystal size becomes infinite the results of the present analysis agree with the results of the P-N model.

The influence of couple-stresses on the elastic properties of an edge dislocation

The exact expressions for stress and displacements around an edge dislocation and the elastic energy are calculated for the couple stress theory. The influence of couple stresses on the elastic properties of a dislocation is studied as a function of the material constant l.

The influence of the shape of load stress pulses on the course of plastic deformation of crystalline materials

The present paper deals with the derivation of the relationship between the course of macroscopic deformation and the dynamic properties of dislocation in loading material with stress pulses of general shape, and duration in tens of microseconds. On the basis of the obtained relationships, the correctness of the definition of the yield point under these conditions of loading, suggested previously (Czech. J. Phys.B 20 (1970), 776) on the basis of the analysis of the phenomenon of delayed deformation at elevated loading rates, is demonstrated.

Screw Dislocations in Thin Rods

In connection with Galt and Herring's observation on thin whiskers of tin, the properties of a screw dislocation in a cylinder are worked out. When all boundary conditions are taken into account, the image force tends to keep the dislocation along the axis. Only when it is displaced about half-way to the surface does the image force tend to pull it out of the rod. Generators of the cylindrical rod become helices when the dislocation is introduced. The dislocation can be ejected from the rod by twisting or bending it suitably.