SlipPlanes

Slip planes are crystallographic planes along which dislocations glide during plastic deformation of crystalline solids. In metals and other crystals, permanent shape change occurs when dislocations move by glide along preferred planes, which have relatively low lattice resistance. The plane together with a specific slip direction forms a slip system; the activity of these systems governs how a crystal deforms under applied stress.

The external stress must produce a resolved shear stress on a slip system that exceeds a material-specific critical resolved shear stress (CRSS). The resolved shear stress depends on the magnitude and orientation of the applied stress relative to the slip plane and slip direction. Temperature, alloying, and microstructure can alter the CRSS and thus influence which slip systems are active.

Common crystal structures exhibit characteristic slip planes. In face-centered cubic (FCC) metals, the primary slip plane is the {111} plane with the <110> directions, providing many slip systems and typically high ductility. In body-centered cubic (BCC) metals, slip occurs on several planes, primarily {110}, {112}, and {123} with <111> directions, with activity strongly temperature dependent. In hexagonal close-packed (HCP) materials, slip is easiest on the basal {0001} plane with <11-20> directions; when basal slip is insufficient, other planes such as prismatic or pyramidal can contribute to deformation, affecting ductility.

Slip planes are distinct from fracture surfaces; they describe orderly dislocation glide that enables plastic deformation, whereas fracture involves bond breaking and crack propagation.