Question

Types of atomic bonding that allows dislocation motion?

Answer 1

Explanation:

Dislocations move easily (glide) at low stress because:

Atom displacements are small

Atom displacements are localised near the dislocation line (i.e. only a small fraction of atoms are displaced at any time.)

Since dislocation glide can happen at low stresses, materials can undergo deformation at stresses much lower than their theoretical strengths.

Photo of a dense pile-up of dislocations along grain boundaries.

Dislocation glide is easy in metals since metallic bonding is non-specific. However it is difficult in ceramics due to the specific nature of covalent or ionic bonding. With covalent bonding the strength and directionality of the bonds inhibit dislocations moving. With ionic bonding, movement of the dislocation disrupts the charge balance around surrounding atoms.