Metals account for about two thirds of all the elements and about
24% of the mass of the planet. Metals have useful properties including
strength, ductility, high melting points, thermal and electrical
conductivity, and toughness. From the periodic table, it can be
seen that a large number of the elements are classified as being
a metal. A few of the common metals and their typical uses are
Common Metallic Materials
- Iron/Steel - Steel alloys are used for strength critical applications
- Aluminum - Aluminum and its alloys are used because they are
easy to form, readily available, inexpensive, and recyclable.
- Copper - Copper and copper alloys have a number of properties
that make them useful, including high electrical and thermal
conductivity, high ductility, and good corrosion resistance.
- Titanium - Titanium alloys are used for strength in higher
temperature (~1000° F) application, when component weight
is a concern, or when good corrosion resistance is required
- Nickel - Nickel alloys are used for still higher temperatures
(~1500-2000° F) applications or when good corrosion resistance
- Refractory materials are used for the highest temperature
(> 2000° F) applications.
The key feature that distinguishes metals from non-metals is
their bonding. Metallic materials have free electrons that are
free to move easily from one atom to the next. The existence of
these free electrons has a number of profound consequences for
the properties of metallic materials. For example, metallic materials
tend to be good electrical conductors because the free electrons
can move around within the metal so freely. More on the structure
of metals will be discussed later.