Dislocation

Definition - What does Dislocation mean?

In materials science, dislocations are line defects that exist in metals. A dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many properties of materials. Dislocations are generated and move when a stress is applied. The motion of dislocations allows slip-plastic deformation to occur.

There are two types of dislocations: edge and screw. High dislocation density results in a large number of dislocation interactions, which results in high strength and hardness. Metals are strengthened by making it more difficult for dislocations to move.

Dislocation can cause grain boundary corrosion in metals.

Corrosionpedia explains Dislocation

A dislocation is simply a defect in the lattice structure in which a few ions in a layer are missing. This causes the neighboring layers to be displaced slightly to minimize the strain from the defect. Grain boundary initiation and interface interaction are more common sources of dislocations.

Irregularities at the grain boundaries in materials can produce dislocations which propagate into the grain. The steps and ledges at the grain boundary are an important source of dislocations in the early stages of plastic deformation.

Dislocations normally move under a shear stress. Two dislocations of opposite orientation, when brought together, can cancel each other out, but a single dislocation typically cannot "disappear" on its own.

When a dislocation line intersects the surface of a metallic material, the associated strain field locally increases the relative susceptibility of the material to acidic etching and an etch pit of regular geometrical format results.

The movement of dislocations is hindered by grain boundaries. The more grain boundaries there are, the more difficult it is for the dislocations to move and for the metal to change shape. The result is that the metal is stiffer, stronger and harder. A fine-grained metal is stronger than a coarse-grained metal.

Dislocations give rise to the characteristic malleability of metals. The effects of strain hardening by accumulation of dislocations and the grain structure formed at high strain can be removed by appropriate heat treatment (annealing), which promotes the recovery and subsequent recrystallization of the material.

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