Low-angle grain boundary

Definition

A low-angle grain boundary is a type of planar defect that occurs between two grains with a small misorientation, typically less than 15 degrees. These boundaries form when adjacent crystalline regions are slightly misaligned, resulting in a region where the atomic arrangement is not perfectly continuous. This slight misorientation can influence the mechanical and electrical properties of materials, affecting their overall performance.

5 Must Know Facts For Your Next Test

1. Low-angle grain boundaries typically consist of an array of dislocations that help accommodate the slight misalignment between grains.
2. They are often found in polycrystalline materials and can influence the material's mechanical strength and ductility.
3. The presence of low-angle grain boundaries can lead to phenomena such as strain hardening, which increases material strength through dislocation interactions.
4. Low-angle grain boundaries are generally less energetic than high-angle grain boundaries, resulting in different thermodynamic behaviors in materials.
5. These boundaries can serve as barriers to dislocation motion, impacting how materials deform under stress.

Review Questions

• How do low-angle grain boundaries affect the mechanical properties of materials?
  • Low-angle grain boundaries can enhance the mechanical properties of materials by introducing an array of dislocations that act as barriers to further dislocation movement. This phenomenon leads to strain hardening, making the material stronger as it deforms. The slight misorientation at these boundaries helps accommodate stresses without causing catastrophic failure, thus improving ductility while simultaneously increasing strength.
• In what ways do low-angle grain boundaries differ from high-angle grain boundaries in terms of their structure and energy characteristics?
  • Low-angle grain boundaries feature small misorientations (less than 15 degrees) and are characterized by an ordered arrangement of dislocations, which makes them lower in energy compared to high-angle grain boundaries. High-angle grain boundaries involve larger misorientations and create more significant disruptions in the atomic structure, leading to higher energy states. Consequently, low-angle grain boundaries contribute to better mechanical properties while high-angle boundaries often result in increased brittleness.
• Evaluate the role of low-angle grain boundaries in influencing material behavior during processes like cold working and recrystallization.
  • Low-angle grain boundaries play a crucial role during cold working by acting as obstacles to dislocation motion, enhancing work hardening and improving material strength. As materials undergo deformation, these boundaries help manage stress distribution and prevent localized failure. In recrystallization processes, low-angle grain boundaries can transform into high-angle boundaries as they promote nucleation sites for new grains. This transition significantly impacts the material's microstructure and overall mechanical properties after processing.

Related terms

high-angle grain boundary:

A high-angle grain boundary is characterized by a larger misorientation between adjacent grains, usually greater than 15 degrees, leading to more significant disruptions in the crystal lattice.

tilt boundary: A tilt boundary is a specific type of low-angle grain boundary that forms when the misorientation occurs about a specific crystallographic axis, resulting in a series of edge dislocations along the boundary.

dislocation: A dislocation is a line defect within a crystal structure that represents an irregularity in the arrangement of atoms, playing a key role in the plastic deformation of materials.