Grain Boundaries in Materials (Low Angle Boundaries, Coincidence Site Lattices)

Most engineering materials are polycrystalline where the individual grains are separated by grain boundaries. Because of the mutual rotation of individual grains, the periodicity of the atoms at the grain boundary is disrupted and they have higher energies compared to a perfect single crystal. However, for low angle rotations the boundaries can minimize the disruption by forming periodic arrays of dislocations; at higher angles of rotation the destabilization of the grain boundary can also be reduced through the formation of Coincidence Site Lattices with so-called “Sigma” values. This video, presented at a level accessible to a materials science undergraduate, provides a brief overview of the formation and description of these special types of grain boundaries.