Glossary

Dislocation motion is the movement of dislocations—defects or irregularities in the atomic structure—within a crystal lattice when a material is subjected to stress. This motion is the primary mechanism by which plastic deformation occurs in metals and crystalline materials.

In a perfect crystal, atoms are arranged in a repeating, orderly pattern. However, real materials contain small imperfections known as dislocations. These are typically line defects, meaning that along a line within the crystal, the arrangement of atoms is slightly displaced. When an external force (such as tension or shear) is applied, the dislocation moves through the crystal, allowing layers of atoms to slip past each other one atomic spacing at a time instead of all at once. This makes deformation much easier and requires far less energy than breaking all atomic bonds simultaneously.

The most common types of dislocations are edge dislocations and screw dislocations. In an edge dislocation, an extra half-plane of atoms is inserted into the lattice, while in a screw dislocation, the crystal layers spiral around the dislocation line like a thread on a screw. As these dislocations move, they cause atoms to shift incrementally, producing permanent (plastic) deformation.

Dislocation motion is influenced by obstacles such as grain boundaries, precipitates, impurities, and other dislocations. Strengthening mechanisms like work hardening, alloying, and heat treatment are designed to impede this movement, making the material stronger but less ductile.