1. Grain boundaries at temperature

A grain boundary, whose structure differs from that of the surrounding crystals, can be considered as a two-dimensional phase. It is therefore appropriate to consider phase changes (from solid phase to solid phase, or from solid phase to liquid phase) specific to this structure. Generally speaking, phase changes at joints can be of two types ; they either do not affect the geometry of the joint, but modify its core structure, or involve a change in the joint's orientation and/or plane.