Grain boundary

A grain boundary is the interface between crystalline regions with different crystallographic orientations. Its atomic structure and energy influence a material’s strength, transport, and stability.

Grain boundary energy: The excess free energy per unit area associated with a grain boundary. It reflects the energetic cost of the misfit between neighboring crystal lattices.
Hall–Petch relationship: An empirical relationship connecting decreasing grain size with increasing yield strength in many materials. More boundaries can impede dislocation motion and strengthen a polycrystal.
Crystal structure: The periodic arrangement of atoms, ions, or molecules in a crystalline solid. A grain boundary separates regions that each possess an ordered crystal structure.
Twin boundary: A planar defect across which the crystal lattice is related by a specific mirror or rotation symmetry. It is a special, often highly ordered boundary rather than a generic grain interface.
Grain boundary migration: The movement of a grain boundary through a material, changing the sizes of adjoining grains. Boundary motion drives grain growth and can respond to temperature or applied stress.
Recrystallization: The formation and growth of new, relatively strain-free grains in a deformed material during heating. New boundaries replace deformed structures and reset grain size and texture.
Crystallographic orientation: The alignment of a crystal’s lattice axes relative to a chosen reference frame. The orientations on either side define a boundary’s misorientation.
Phase boundary: An interface separating regions of different thermodynamic phases or compositions. A grain boundary separates orientations within a crystalline phase, not necessarily distinct phases.
Coincidence site lattice: A description of a boundary between crystals whose lattices share periodic sites after relative rotation. Some special misorientations create more ordered boundaries with distinctive properties.
Sintering: The consolidation of powder particles by heating, typically below the material’s melting point. Boundary diffusion and motion help densify particles and reshape the grain network.

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