Types of Dislocations
There are three types of dislocations:
- Edge dislocations (shown on Section 12.6 and reviewed below)
- Screw dislocations
- Mixed dislocations
Edge Dislocations
Edge dislocations are the result of an extra half plane of atoms being inserted into a crystal (or equivalently a half plane being removed), as shown in Figure 12.6.1. Edge dislocations can exist in either 3D or 2D materials. This is the type of dislocation simulated in NetLogo model 12.4.1.
Figure 12.6.1 Two depictions of edge dislocations.
Martin Fleck, Burgers Vector and dislocations (screw and edge type), Added second example of edge dislocation by Jacob Kelter, CC BY-SA 4.0
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Screw Dislocations
Two depictions of screw dislocations are shown in Figure 12.6.2. You can imagine forming this type of dislocation by trying to tear the crystal apart like a sheet of paper. It is called a screw dislocation because if you imagine starting at the top and sliding along the tops of the atoms, you will spiral downwards like the threads of a screw (see left side of Figure 12.6.2). Screw dislocations can only exist in 3D materials. Video 12.6.1 shows a simulation of a screw dislocation in an ionic material annihilating which sort of looks like a zipper getting zipped up.
Figure 12.6.2 Two depictions of screw dislocations with illustration of why it is called a screw dislocation.
Martin Fleck, Burgers Vector and dislocations (screw and edge type), Added second example of screw dislocation and depiction of screw threads by Jacob Kelter, CC BY-SA 4.0
Mixed Dislocations
Mixed dislocations are the result of a mixture of both an edge and screw dislocations. These are difficult to visualize, but an attempt is made in Figure 12.6.3.
Figure 12.6.3 An example of a mixed dislocation.
By Cdang, Dislocation mixte perspective iso, labels added by Jacob Kelter, CC BY-SA 3.0
