TECH 411 Materials
Lecture Notes/Chapter 1	Spring 2008

1. Three fundamental material systems.
1. Polymers
2. Ceramics
3. Metals
4. (Composites "hybrids" of two or more different materials from the same or different systems)
2. Matter consists of atoms
1. Protons and neutrons form nucleus.
2. Electrons in "cloud" make up outer shell.
3. Combination of atoms form compounds, solutions, or mixtures.
1. Compounds
1. Inorganic (metals and ceramics)
2. Organic (polymers)
1. Organic compounds are based on carbon.
2. Normally made from material that once was alive.
2. Solutions

1. Materials are dissolved into each other on an atom by atom basis.
2. Separation of materials by chemical means.
2. Mixtures

1. Materials are intermingled on a macroscopic level.
2. Parts can be separated by mechanical means.
3. Four different types of bonding mechanisms.
1. Ionic

1. One atom "steals" electrons from another atom.
2. Attraction is between charged atoms, or "ions"
1. Covalent

1. Atoms share electrons in attempt to fill outer shells (valences).
2. Attraction is between nuclei and electrons.
2. Metallic

1. Atoms are held together in an electron matrix.
3. Van der Waals

1. Atoms are held together by a weak electrostatic charge.
4. Electrons and their valence properties determine the type of bond.
4. Use of the Periodic Table
5. Engineering materials are used in two ways.
1. As a "pure" material.
2. Combined with other materials.
6. In the solid state -
1. If the atomic bonds are orderly and specific, the material is crystalline.

1. Most metals and ceramics are crystalline.
1. If the bonds are less well ordered, the material is amorphous (w/o order)

1. Glasses and plastics are amorphous.
2. Long range vs. short range order.
3. Many amorphous materials do not have a clearly defined melting point.
2. Crystal formation

1. Unit Cell - smallest arrangement of atoms with full symmetry of crystal
2. Space lattice - group of unit cells
3. Grains and grain boundaries - lattices grow until they intersect other grains
3. Unit cell types - more than twenty known arrangements.

1. FCC - Face centered cubic
2. BCC - Body centered cubic
3. CPH or HCP - Close packed hexagonal
7. Metals
1. An element with a valence of 1, 2, or 3.
2. Atoms held together by a matrix of electrons
3. Properties

1. Conductor of electricity
2. Malleable
3. Opaque
4. Can be strengthened
1. Failure comes from breaking atomic bonds. Line separating failed from unfailed region is known as a dislocation.
2. Dislocations can be produced by:
• solid solution strengthening (alloying)
• mechanical working
• precipitation hardening
• quench hardening
8. Ceramics
1. Nonmetals have a valence of 5, 6, or 7
2. Metalloids have a valence of 4
3. Inert materials (gasses) have a valence of 8 (filled outer shell)
4. Ceramics are a combination of one or metals and one or more nonmetals.
5. Usually have a rigid ionic or covalent bond.
6. Properties

1. Failure by crystal cleavage - slip is difficult - brittle
2. High hardness
3. Chemically inert (atomic bonds are usually difficult to break)
4. Electrical insulator (electrons are "locked up")
5. No melting point - sublimation and decomposition under heat
6. Difficult to strengthen.
9. Polymers
1. Comes from the Greek, means "many mera" or many parts
2. Material is composed of long chain molecules, usually with carbon as the "backbone" (organic based)
3. Bonds within molecules are usually covalent, with Van der Waals bonds between molecules.
4. Can be strengthened by retarding chain movement, adding fillers, cross linking of molecules, chain branching, etc.
10. Composites
1. Made from combinations of two or more different materials, normally from two or more different material systems.
2. Wood is a natural composite consisting of cellulose (a polymer), and lignin.
3. Applications take advantage of the specific properties of the selected materials to meet design requirements.