A
grain boundary is the interface between two grains, or
crystallites, in a polycrystalline material. Grain boundaries are
defects in the
crystal structure, and tend to decrease the
electrical and
thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the
precipitation of new phases from the solid. They are also important to many of the mechanisms of
creep. On the other hand, grain boundaries disrupt the motion of
dislocations through a material, so reducing crystallite size is a common way to improve strength, as described by the
Hall–Petch relationship.