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- Intergranular fracture, intergranular cracking or intergranular embrittlement occurs when a crack propagates along the grain boundaries of a material, usually when these grain boundaries are weakened. The more commonly seen transgranular fracture, occurs when the crack grows through the material grains. As an analogy, in a wall of bricks, intergranular fracture would correspond to a fracture that takes place in the mortar that keeps the bricks together. Intergranular cracking is likely to occur if there is a hostile environmental influence and is favored by larger grain sizes and higher stresses. Intergranular cracking is possible over a wide range of temperatures. While transgranular cracking is favored by strain localization (which in turn is encouraged by smaller grain sizes), intergranular fracture is promoted by strain homogenization resulting from coarse grains. Embrittlement, or loss of ductility, is often accompanied by a change in fracture mode from transgranular to intergranular fracture. This transition is particularly significant in the mechanism of impurity-atom embrittlement. Additionally, hydrogen embrittlement is a common category of embrittlement in which intergranular fracture can be observed. Intergranular fracture can occur in a wide variety of materials, including steel alloys, copper alloys, aluminum alloys, and ceramics. In metals with multiple lattice orientations, 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 a shiny surface may be seen. In ceramics, intergranular fractures propagate through grain boundaries, producing smooth bumpy surfaces where grains can be easily identified. (en)
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