Fundamental concepts of metals science Properties of metals Metallic crystal structures What is crystalline lattice? Atomic bonding in solids Lattice parameters Crystal systems Polymorphism of metals Anisotropy Imperfections in solids

Imperfections in solids Idealized solid and real crystalline solids What are imperfections in crystal structures? Classification of crystalline defects Point defects Linear defects Interfacial defects Volume imperfections Imperfections and strength of crystalline solids

Classification of imperfections in solids

Point defects Self-interstitial

Point defects

Linear defects Edge dislocation

Linear defects Screw dislocation

Linear defects Mixed dislocation

Linear defects Dislocations in titanium alloy (transmission electron micrograph, 51,450 x)

Linear defects Strength depends on the density of dislocations: 1 – idealized crystal, 2 – single crystals, 3 – annealed metals (polycrystalline), 4 – strained metals Dislocation density ρ is the total dislocation length per unit volume:

Interfacial defects Grain boundaries

Interfacial defects The grain boundary acts as a barrier to dislocation motion

Grain boundaries in iron are visible due to the etching Interfacial defects Grain boundaries in iron are visible due to the etching

Nonmetallic inclusions Volume, or bulk defects Nonmetallic inclusions

Nonmetallic inclusions Volume, or bulk defects Nonmetallic inclusions

Nonmetallic inclusions are the sites of crack formation Volume, or bulk defects Nonmetallic inclusions are the sites of crack formation

Brittle fracture of ship hull Volume defects Wrought rivet Brittle fracture of ship hull One of the possible reasons is the presence of nonmetallic inclusions in the metal of the hull (or in welded seams, in rivets).

Volume defects At an angle of 22 °, the Titanic's stern broke off from the hull between the third and fourth funnels.