Line Imperfections:

Line imperfections are called dislocations and occur within crystalline materials only. Dislocations could be a screw type, edge type, or mixed type, depending on how they distort the lattice, as display in Figure. It is must to note in which dislocations cannot end within a crystal. They must end at a crystal edge or other dislocation, or they have to close back on themselves.

Edge dislocations consist of an extra row or plane of atoms in the crystal structure. The imperfection might extend in a straight line all the way by the crystal or it might follow an irregular path. It might also be short, extending only a small distance into the crystal causing a slip of one atomic distance along the glide plane (direction the edge imperfection is moving).

Figure: Line Defects (Dislocations)