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Defects and dislocations

Crystal lattices always have defects. A vacancy (empty lattice site) is a point defect, while a dislocation is a line defect that makes plastic deformation possible — as a dislocation moves through the lattice, atomic layers slip slightly relative to each other without the whole plane having to move at once.

vacancy: point defectdislocation: line defect\text{vacancy: point defect} \quad \text{dislocation: line defect}two basic defect types

Example

Work hardening occurs because more dislocations form during deformation and start blocking each other's further movement.

Without dislocations, metals would be far stronger, but also impossible to shape plastically.
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Part of Materials Technology: Structure.