In certain materials and under certain conditions, the boundaries between the grains are the weakest regions in the material. An intergranular fracture is a fracture that grows along the grain boundaries of the material. In a wall of bricks it would correspond to a fracture that takes place in the mortar that keeps the bricks together. In metals with multiple lattice organizations, when one lattice ends and another begins, the fracture changes direction to follow the new grain. This results in a fairly jagged looking fracture with straight edges of the grain and shiny surface may be seen.
In ceramics, interganular fractures propagate through grain boundaries, producing smooth bumpy surfaces where grains can be easily identified.
Intergranular cracking is likely to occur if there is a hostile environmental influence. In addition, there are several other processes that can lead to intergranular fracture:
This is also known as intercrystalline fracture or grain-boundary separation.
This is to be distinguished from the more commonly seen Transgranular fracture, where the crack grows through the material grains.