Search results
Results from the WOW.Com Content Network
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 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 ...
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.
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 ...
Non-planar movement of edge dislocations is achieved through climb. Since the Burgers vector of a perfect screw dislocation is parallel to the dislocation line, it has an infinite number of possible slip planes (planes containing the dislocation line and the Burgers vector), unlike an edge or mixed dislocation, which has a unique slip plane ...
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 ...
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.
They can be formed during crystal growth, during plastic deformation as partial dislocations move as a result of dissociation of a perfect dislocation, or by condensation of point defects during high-rate plastic deformation. [3] The start and finish of a stacking fault are marked by partial line dislocations such as a partial edge dislocation.