Transgranular fracture is a type of fracture that occurs through the crystal grains of a material. In contrast to intergranular fractures, which occur when a fracture follows the grain boundaries, this type of fracture traverses the material's microstructure directly through individual grains. This type of fracture typically results from a combination of high stresses and material defects, such as voids or inclusions, that create a path for crack propagation through the grains. A broad range of ductile or brittle materials, including metals, ceramics, and polymers, can experience transgranular fracture. When examined under scanning electron microscopy, this type of fracture reveals cleavage steps, river patterns, feather markings, dimples, and tongues.[1] The fracture may change directions somewhat when entering a new grain in order to follow the new lattice orientation of that grain but this is a less severe direction change then would be required to follow the grain boundary. This results in a fairly smooth looking fracture with fewer sharp edges than one that follows the grain boundaries.[2] This can be visualized as a jigsaw puzzle cut from a single sheet of wood with the wood grain showing. A transgranular fracture follows the grains in the wood, not the jigsaw edges of the puzzle pieces. This is in contrast to an intergranular fracture which, in this analogy, would follow the jigsaw edges, not the wood grain.
The mechanism of transgranular fracture may vary depending on the material and surrounding conditions under which the fracture occurs.[3] However, some general steps are typically involved in the transgranular fracture process:
In ductile metals, the plastic deformation of the material can be a critical factor in the transgranular fracture process, while in brittle materials such as ceramics, the formation and growth of cracks can be influenced by factors such as grain size, porosity, and the presence of impurities or other defects.
The fracture behavior of materials can be significantly changed by the use of precipitation-based grain boundary design. For example, Meindlhumer et. al.[9] produced a thin film of AlCrN containing a specific distribution of precipitates within the grain boundaries in precipitation-based grain boundary design. The precipitates acted as a barrier to crack propagation, increasing the material's resistance to intergranular cracking. Additionally, the precipitates altered the stress distribution within the material, promoting transgranular crack propagation instead. Furthermore, smaller precipitates with a more uniform distribution have been shown to be more effective at promoting transgranular fracture.