stackingfault

Stacking fault is a planar crystallographic defect in which the regular sequence of close-packed atomic layers is locally disrupted. In close-packed metals, atoms are arranged into repeating planes with characteristic stacking: ABCABC... in face-centered cubic (fcc) materials and ABAB... in hexagonal close-packed (hcp) materials. A stacking fault creates a misregistered region across a fault plane, altering the local stacking sequence.

There are two common types in fcc crystals: intrinsic and extrinsic stacking faults. An intrinsic fault results from removing a plane of atoms in the stacking sequence, changing the local order from ABCABC... to ABCACABC.... An extrinsic fault results from inserting an extra plane, modifying the sequence to ABABC... The fault is bounded by partial dislocations; in fcc metals, a perfect dislocation can decompose into partials separated by a stacking fault. The energy associated with creating a stacking fault is the stacking fault energy (gamma_sf), which varies by material and temperature. Materials with low gamma_sf tend to form wider stacking faults and are more prone to deformation twinning.

In hcp structures, basal stacking faults disrupt the ABAB... sequence on the basal plane and are similarly described by the insertion or removal of a plane within the basal stacking.

Formation and consequences: Stacking faults arise during crystal growth, plastic deformation, or recovery processes. They influence mechanical behavior by affecting dislocation motion, cross-slip, and work hardening; they can promote twinning in metals with low stacking-fault energy. They are detectable by transmission electron microscopy and can influence diffraction patterns.