ENGI1002 - Topic 1

What are the four material classes?

• Metals

• Ceramics

• Polymers

• Composites

What is the relationship between microstructure, properties, and processing history?

They are all linked, changing one changes the others.

What is atomic number Z?

Number of protons and number of electrons.

Ionic bonds?

Electron transfer, non-directional, hard, brittle, insulating, high melting point.

When does ionic bonding occur?

Between a metal and a non-metal.

Covalent bonds?

Electron sharing, polymers, diamonds.

When does covalent bonding occur?

Between two non-metals.

Metallic bonds?

Electron, sea, conductive, ductile.

When does metallic bonding occur?

Between two metals.

What are the secondary bonds?

• Van der Waals

• Hydrogen

What is hydrogen bonding?

Hydrogen is the strongest secondary bond and occurs between H and F, O, or N.

What are point defects?

• Vacancy

• Self-interstitial

• Substitutional

• Interstitial solute

What is a vacancy defect?

A missing atom at a normal lattice site.

What is a self-interstitial defect?

An extra atom of the same type in the interstitial site.

What is a substitutional defect?

A foreign atom replaces a host atom at a lattice site.

What is an interstitial solute defect?

A foreign atom occupies the space between two host atoms.

What are the types of line defects?

• Edge dislocation

• Screw dislocation

What is an edge dislocation?

An extra half-plane of atoms inserted in the crystal lattice.

What is a screw dislocation?

A spinal planar ramp resulting from shear deformation.

What do line defects control?

Mechanical strength and plastic deformation in crystal solids.

How do electrons move in the Bohr atomic model?

Electrons revolve around the nucleus in discrete orbitals.

Properties of crystalline materials?

• Periodic stacking

• Metals and ceramics

Properties of amorphous materials?

• No predictable atom location

• No repeating units

• Glass

Coordination number of simple cubic?

6

Coordination number of BCC cubic?

8

Coordination number of FCC cubic?

12

Coordination number of HCP?

12

Isotropic material properties?

Isotropic materials have the same properties in all directions.

Anisotropic material properties?

Anisotropic materials have direction dependent properties.

What is a grain boundary?

A grain boundary is a planar defect where crystals of different orientation intersect.

What happens to atoms at grain boundaries?

In grain boundaries, atoms have:

1. High mobility

2. High diffusivity

3. High chemical reactivity