Ruuvedislokaatio

Ruuvedislokaatio, meaning “screw dislocation” in crystallography, is a type of line defect in crystalline materials. It is characterized by a helical distortion of the lattice around the dislocation line, so that the lattice planes rotate as one moves around the defect. The Burgers vector of a screw dislocation is parallel to the dislocation line, and tracing a loop around the defect yields a lattice mismatch equal to the Burgers vector.

Formation and motion: Screw dislocations form during plastic deformation or crystal growth and can move under applied shear stress through glide along slip planes. At higher temperatures or in the presence of impurities, cross-slip and climb can alter the path and character of the dislocation. The overall motion of screw dislocations under stress is a central mechanism of plastic flow in many crystalline metals.

Implications: The density and interactions of screw dislocations influence mechanical properties such as yield strength, work hardening, and ductility. They also interact with other defects and can pin or entangle, affecting creep resistance and fatigue behavior.

Observation and theory: The concept is described within dislocation theory and linear elastic models that relate the screw dislocation to the Burgers vector and the slip system. It can be observed directly with transmission electron microscopy and inferred from diffraction patterns and mechanical testing.

See also: Dislocation theory, edge dislocation, mixed dislocation, Burgers vector, slip system.