Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 97

Dislocations are divided into two basic types, called edge dislocations and screw dislocations (Figure 3.19) but they are often more complex in real crystals, composed of some mixture of these two basic types. In a simple sense, an edge dislocation can be visualized as making a cut in a perfect crystal and inserting an additional half‐plane of atoms. The edge of the half‐plane of atoms within the crystal is the dislocation line, that is, defects along a line of atomic sites. Instead of inserting an extra half‐plane of atoms after making a cut in the crystal, we can displace one part of the crystal relative to the other part in a direction parallel to the bottom of the cut. This gives the other basic type of dislocation, called a screw dislocation because, if traced in the direction of the dislocation line, the planes of atoms form a helical surface or a screw.

Figure 3.19 Schematic representation of part of a perfect crystal (a) and the arrangement of atoms near the two basic types of dislocations, edge dislocation (b) and screw dislocation (c).