Grain Boundaries

Grain boundaries are an interface between two different grains in a polycrystalline material. They are defects in the crystal structure that can significantly change the material's properties.

Structure

Generally, there are two different categories of grain boundaries: low-angle and high-angle. Low-angle boundaries occur when there is a misorientation of grains of generally less than 15 degrees. High-angle boundaries generally occur when the misorientation is greater than 15 degrees. These misorientations are different from the low-angle boundaries since the dislocations of the boundary are too small. These boundaries generally are more unstable than low-angle boundaries.

Tilt Boundary

Tilt boundaries are formed when the misorientation is caused by the defect plane rotating about an axis parallel to the boundary plane. These boundaries are generally low energy, since the bending of the lattice can be supported by a wedge of supporting atoms.

Twist Boundary

Twist boundaries occur when the rotation is perpendicular to the boundary plane.