Dislocation creep

Dislocation creep is a deformation mechanism in crystalline materials. Dislocation creep involves the movement of dislocations through the crystal lattice of the material. It causes plastic deformation of the individual crystals and in the end the material itself.

Dislocation creep is highly sensitive to the differential stress on the material. At relatively low temperatures it is the dominant deformation mechanism in most crystalline materials.

Dislocation creep takes place due to the movement of dislocations through a crystal lattice. Each time a dislocation moves through a crystal, part of the crystal moves one lattice point along a plane, relative to the rest of the crystal. The plane that separates both parts and along which the movement takes place is called a slip plane. To allow the movement, all ionic bonds along the plane have to be broken. If all bonds were broken at once, this would require so much energy that dislocation creep would only in theory be possible. When it is assumed that the movement takes place step by step, the breaking of bonds is immediately followed by the creation of new ones and the energy required is much lower. Calculations of molecular dynamics and analysis of deformed materials have shown that deformation creep can be an important factor in deformation processes, under certain circumstances.

By moving a dislocation step by step through a crystal lattice a linear lattice defect is created between parts of the crystal lattice, which is called a dislocation. Two types of dislocations exist. Edge dislocations form the edge of an extra layer of atoms inside the crystal lattice. Screw dislocations form a line along which the crystal lattice jumps one lattice point. In both cases the dislocation line forms a linear defect through the crystal lattice, the crystal can be perfect on all sides of the line.

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