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

Most engineering materials are polycrystalline, with individual grains separated by grain boundaries. The mutual rotation of these grains disrupts the periodicity of the atoms at the grain boundary, resulting in higher energy compared to a perfect single crystal. However, for low-angle rotations, the boundaries can reduce this disruption by forming periodic arrays of dislocations. At higher angles of rotation, the destabilization of the grain boundary can be mitigated through the formation of Coincidence Site Lattices, characterized by specific “Sigma” values. This video, designed for materials science undergraduates, provides a brief overview of the formation and characteristics of these special types of grain boundaries.