Grain growth

Grain growth is the enlargement of crystals in a polycrystalline material as smaller grains shrink and larger grains expand. It reduces total grain-boundary area and is driven by the energy of those boundaries.

Grain boundary: An interface separating crystals with different crystallographic orientations in a polycrystalline material. Grain growth occurs when these interfaces migrate, reducing their total area.
Polycrystalline material: A solid composed of many crystalline regions with different orientations, separated by grain boundaries. Grain growth changes the sizes and number of its constituent crystals.
Annealing: A heat treatment that changes a material's microstructure and properties through controlled heating and cooling. Annealing often permits grain boundaries to migrate and grains to grow.
Normal grain growth: Statistical coarsening in which the grain-size distribution retains a broadly self-similar shape as its mean increases. It is the standard regime described by simple grain-growth laws.
Grain-boundary energy: The excess free energy per unit area associated with a grain boundary. Reducing boundary area lowers this energy and provides the driving force for growth.
Crystallite: A small crystal region with a regular atomic arrangement and a distinct crystallographic orientation. Each growing grain is a crystallite whose boundaries move relative to its neighbors.
Recrystallization: The formation of new, relatively strain-free grains in a deformed material during heating. Grain growth commonly follows recrystallization when the new grains continue to coarsen.
Abnormal grain growth: A coarsening regime in which a small number of grains grow much faster than the rest. It departs from the broadly uniform coarsening assumed in normal grain growth.
Grain-boundary migration: The movement of a grain boundary through a material as atoms rearrange across the interface. Migration lets growing grains consume neighboring grains.
Curvature-driven grain growth: Grain growth driven by differences in boundary curvature, with highly curved regions tending to shrink. It describes why small grains often disappear while larger ones expand.

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