Edge Dislocations: Understanding the Most Common Type of Crystal Imperfection

An edge dislocation is a linear crystal defect where an extra half-plane of atoms terminates within the lattice. It is the most common dislocation type in plastically deformed metals, ceramics, and some polymers.

Characteristics

• Burgers vector (b) is perpendicular to the dislocation line.
• Creates localized lattice strain: compression above the extra half-plane, tension below.
• Moves by slip (glide) on its slip plane under shear stress; enables plastic deformation at stresses far below theoretical strength.
• Can climb (move out of slip plane) via vacancy diffusion at high temperatures.

Formation

• Mechanical deformation (cold working, bending).
• Thermal stress (uneven cooling).
• Crystal growth (e.g., snowflakes, epitaxial films).
• Irradiation damage.

Significance

Edge dislocations govern yield strength, work hardening, ductility, creep, and fatigue. Their density (dislocation density, ρ) increases with deformation; annealing reduces ρ via recovery/recrystallization.