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Dislocations of edge (left) and screw (right) type. In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms.
The dislocation line is presented in blue, the Burgers vector b in black. Edge dislocations are caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the adjacent planes are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side.
The edge dislocation can be imagined as the introduction of a half plane (gray boxes) that does not fit the crystal symmetry. The screw dislocation can be imagined as cut and shear operation along a half plane. The vector's magnitude and direction is best understood when the dislocation-bearing crystal structure is first visualized without the ...
Pure-edge and screw dislocations are conceptually straight in order to minimize its length, and through it, the strain energy of the system. Low-angle mixed dislocations, on the other hand, can be thought of as primarily edge dislocation with screw kinks in a stair-case structure (or vice versa), switching between straight pure-edge and pure-screw dislocation segments.
There are two types of dislocations in crystals that can induce slip - edge dislocations and screw dislocations. Edge dislocations have the direction of the Burgers vector perpendicular to the dislocation line, while screw dislocations have the direction of the Burgers vector parallel to the dislocation line. The type of dislocations generated ...
An edge dislocation produces a stress field which is compressive above the slip plane and tensile below. [6] In Al-Mg alloys, the Mg atom is larger than an Al atom and has lower energy on the tension side of the dislocation slip plane; therefore, Mg atoms in the vicinity of an edge dislocation are driven to diffuse across the slip plane (see ...
Splitting into two partial dislocations is favorable because the energy of a line defect is proportional to the square of the burger’s vector magnitude. For example, an edge dislocation may split into two Shockley partial dislocations with burger’s vector of 1/6<112>. [4] This direction is no longer in the closest packed direction, and ...
Apart from the Darwin width of the reflection, the width of single dislocation images may additionally depend on the Burgers vector of the dislocation, i.e. both its length and its orientation (relative to the scattering vector), and, in plane wave topography, on the angular departure from the exact Bragg angle. The latter dependence follows a ...