What Does Line Defect Mean?
A line defect is a line along which whole rows of atoms in a solid are arranged anomalously. The resulting irregularity in spacing is most severe along a line called the line of dislocation. Line defects can either weaken or strengthen solids.
A line defect acting as a boundary between the slipped and non-slipped region in the slip plane is called a dislocation. Dislocations are generated and move when a stress is applied. The strength and ductility of metals are controlled by dislocations. Dislocations can move if the atoms from one of the surrounding planes break their bonds and rebond with the atoms at the terminating edge.
Corrosionpedia Explains Line Defect
A dislocation is a line defect within a crystal which arises during crystal growth or as a result of mechanical deformation of a crystal. Dislocations make a crystal mechanically harder. When a metal bar is cold-worked by rolling or hammering, dislocations and grain boundaries are introduced, causing hardening.
There are two basic types of dislocations: edge dislocation and screw dislocation. Mixed dislocations, combining aspects of both types, are also common. When lines of ions are missing in an otherwise perfect array of ions, an edge dislocation appears. Edge dislocation is responsible for ductility and malleability. In fact, the hammering and stretching of materials often involve the movement of edge dislocation. Movements of dislocations give rise to their plastic behavior.
If the misalignment shifts a block of ions gradually downwards or upwards, causing the formation of a screw-like deformation, a screw dislocation is formed. It is the presence of dislocations and their ability to readily move (and interact) under the influence of stresses induced by external loads that leads to the characteristic malleability of metallic materials.
Dislocations can be observed using transmission electron microscopy, field ion microscopy and atom probe techniques. Deep-level transient spectroscopy has been used for studying the electrical activity of dislocations in semiconductors, mainly silicon.
Line defects weaken the structure along, and the defects' type and density affect the mechanical properties of the solids. Thus, formation and study of dislocations are particularly important for structural materials such as metals.