MATERIALS SCIENCE Materials science investigates the relationships between the structures and properties of materials.

CONTENTS  Introduction: historical perspectives  Materials science: basic concepts  Classification of engineering materials  Structure of solids

Relationships between basic components

Correlation between structure and properties  A single crystal of Al 2 O 3 is transparent.  Compact polycrystal- line specimen of Al 2 O 3 is translucent.  Porous polycrystalline specimen of Al 2 O 3 is absolutely opaque.

Correlation between structure and properties

Classification of constructional materials

Metallic crystalline structures

 Atomic plane (111) of gold. The image was taken with an atomic force microscope.

Metallic crystalline structures  The tip of a pointed tungsten specimen. Field ion microscopy. Individual atoms are represented by white spots. Grain boundary is traced by the arrows. 3,460,000 X

Metallic crystalline structures

 Face-centered cubic crystalline lattice (FCC)

Metallic crystalline structures  Body-centered cubic crystalline lattice (BCC)

Metallic crystalline structures  Hexagonal close-packed crystalline lattice (HCP)

Atomium in Brussels  This building is a giant model of body-centered cubic crystalline lattice of iron – the main metal for human civilization

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

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

Classification of imperfections in solids

Point defects Self-interstitial Self-interstitial

Point defects

Linear defects Edge Edge dislocation dislocation

Linear defects Screw Screw dislocation dislocation

Linear defects Mixed dislocation Mixed dislocation

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

Linear defects Strength depends on the density of dislocations: Strength depends on the density of dislocations: 1 – idealized crystal, 1 – idealized crystal, 2 – single crystals, 2 – single crystals, 3 – annealed metals (polycrystalline), 3 – annealed metals (polycrystalline), 4 – strained metals 4 – strained metals

Interfacial defects Grain boundaries Grain boundaries

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

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

Volume, or bulk defects Nonmetallic inclusions Nonmetallic inclusions

Volume, or bulk defects Nonmetallic inclusions Nonmetallic inclusions

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