Edge Dislocation

EDGE DISLOCATION

1. What is Edge Dislocation?

✓ Whenever a half plane of atom is inserted between the planes of atoms in a perfect crystals, the defect so produced is known as edge dislocation.

✓ In other words, the edge dislocation may be defined as the plastic movement of atoms, which starts within the crystal and their effects can be seen on the edge of the crystal.

2. Phenomenon of Edge Dislocation

✓ Fig.0.29 shows the edge dislocation caused by an extra half plane of atoms in the crystal.

✓ Fig.0.29 (a) shows the initial arrangement of atoms. In this figure, the atoms 2-6-7 form a line called dislocation line and the plane X-X is called as slip plane.

✓ Fig.0.29 (b) and (c) show the process of dislocation. It can be noted from the Fig.0.29 that the atom '2' moves towards the atom '3' and away from atom '1' due to shear stress. At the same instance, the separation between atoms 1-5 decreases and the distance between atoms 3-4 increases.

✓ When the shear stress is increased further, the atom continues to move towards left, until it merges with atom '4', as shown in Fig.0.29 (c).

✓ Now from Fig.0.29, it can be seen that the dislocation moved to the right side by one atomic distance.

✓ The above procedure is repeated until the dislocation has moved to extreme right, as shown in Fig.0.29 (d).

Fig.0.29 shows the arrangement of atoms after dislocation.

3. Observations

From the above discussions, the following observations can be made.

1. The movement of dislocation takes place in a direction perpendicular to the slip plane.

2. An edge dislocation requires much lower yield stress to produce deformation than that required for slipping.