The simplest of the point defects is a vacancy, or vacant lattice site, one normally occupied from which an atom is missing.
Impurity point defects are found in solid solutions, of which there are two types: substitutional and interstitial.
A dislocation is a linear or one-dimensional defect around which some of the atoms are misaligned.
An edge dislocation moves in response to a shear stress applied in a direction perpendicular to its line;
One type of dislocation is an extra portion of a plane of atoms, or half-plane, the edge of which terminates within the crystal. This is termed an edge dislocation; it is a linear defect that centers around the line that is defined along the end of the extra half-plane of atoms. This is sometimes termed the dislocation line, which, for the edge dislocation, is perpendicular to the plane of the page.Within the region around the dislocation
line there is some localized lattice distortion. The atoms above the dislocation line are squeezed together, and those below are pulled apart; this is reflected in the slight curvature for the vertical planes of atoms as they bend around this extra half-plane.The magnitude of this distortion decreases with distance away from the dislocation line; at positions far removed, the crystal lattice is virtually perfect.
Another type of dislocation, called a screw dislocation, exists, which may be thought of as being formed by a shear stress that is applied to produce the distortion: the upper front region of the crystal is shifted one atomic distance to the right relative to the bottom portion.
The magnitude and direction of the lattice distortion associated with a dislocation is expressed in terms of a Burgers vector, denoted by a b. Also, even though a dislocation changes direction and nature within a crystal (e.g., from edge to mixed to screw), the Burgers vector will be the same at all points along its line.
Interfacial defects are boundaries that have two dimensions and normally separate regions of the materials that have different crystal structures and/or crystallographic orientations. These imperfections include external surfaces, grain boundaries, twin boundaries, stacking faults, and phase boundaries.
Other possible interfacial defects include stacking faults, phase boundaries, and ferromagnetic domain walls. Stacking faults are found in FCC metals when there is an interruption in the ABCABCABC . . . stacking sequence of close-packed planes.
Other defects exist in all solid materials that are much larger than those heretofore discussed. These include pores, cracks, foreign inclusions, and other phases. They are normally introduced during processing and fabrication steps. Some of these defects and their effects on the properties of materials.
Every atom in a solid material is vibrating very rapidly about its lattice position within the crystal. In a sense, these atomic vibrations may be thought of as imperfections or defects. At any instant of time not all atoms vibrate at the same frequency and amplitude, nor with the same energy. At a given temperature there will exist a distribution of energies for the constituent atoms about an average energy.
The process by which plastic deformation is produced by dislocation motion is termed slip; the crystallographic plane along which the dislocation line traverses is the slip plane
