grain boundary

This term is a specialized technical expression used primarily in materials science, metallurgy, and crystallography. It describes the structural discontinuity where two crystals of the same material meet but are oriented in different directions. Because these boundaries are regions of high atomic disorder, they often act as sites for impurity segregation or the initiation of corrosion.

In a practical engineering context, the density and orientation of these boundaries directly influence the mechanical properties of a metal, such as its hardness and ductility. For instance, smaller grains result in more boundaries, which typically increases the strength of the material through a process known as grain-boundary strengthening.