Grain boundary strengthening

Grain boundary strengthening is the increase in a polycrystalline material’s strength when boundaries between crystals impede dislocation motion. Its dependence on grain size is often described by the Hall–Petch relationship.

Dislocation: A line defect in a crystal lattice around which atomic planes are misaligned. Dislocations carry plastic deformation and are impeded as they encounter grain boundaries.
Polycrystalline material: A solid composed of many crystalline regions, or grains, with different orientations. Grain boundary strengthening arises from the interfaces within this structure.
Grain refinement: Processing that reduces the average grain size of a material. It is the direct microstructural strategy used to increase strength through grain boundaries.
Solid-solution strengthening: Strengthening caused by solute atoms distorting a crystal lattice and impeding dislocation motion. It obstructs the same dislocations through atomic-scale obstacles rather than grain boundaries.
Hall–Petch relationship: An empirical relationship linking a polycrystalline material’s yield strength to the inverse square root of its grain size. It quantifies the usual increase in strength as grain size decreases.
Plastic deformation: Permanent change in a material’s shape caused by irreversible rearrangement of its internal structure. Strengthening concerns resistance to the onset and progress of plastic deformation.
Thermomechanical processing: The controlled combination of deformation and heat treatment used to shape and alter a material’s microstructure. Rolling, forging, and annealing can control grain size and resulting strength.
Work hardening: Strengthening caused by plastic deformation that increases the density and interaction of dislocations. It raises strength by adding dislocation obstacles, unlike grain refinement’s boundary obstacles.
Slip system: A crystallographic plane and direction along which dislocations move during plastic deformation. Boundary misorientation disrupts the alignment of slip systems across adjacent grains.
Yield strength: The stress at which a material begins to deform plastically under a specified test condition. Hall–Petch strengthening is commonly measured as an increase in yield strength.

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Tensile strengthRelated: It is one way to raise a metal’s resistance to tensile deformation.