Material science

1 .1 Historical Perspective

Materials are so important in the development of civilization that we associate Ages with them.

In the origin of human life on Earth, the Stone Age, people used only natural materials, like

stone, clay, skins, and wood. When people found copper and how to make it harder by alloying,

the Bronze Age started about 3000 BC. The use of iron and steel, a stronger material that gave

advantage in wars started at about 1200 BC. The next big step was the discovery of a cheap

process to make steel around 1850, which enabled the railroads and the building of the modern

infrastructure of the industrial world.

1.2 Materials Science and Engineering

Understanding of how materials behave like they do, and why they differ in properties was only

possible with the atomistic understanding allowed by quantum mechanics, that first explained

atoms and then solids starting in the 1930s. The combination of physics, chemistry, and the

focus on the relationship between the properties of a material and its microstructure is the

domain of Materials Science. The development of this science allowed designing materials and

provided a knowledge base for the engineering applications (Materials Engineering).

Properties are the way the material responds to the environment. For instance, the mechanical,

electrical and magnetic properties are the responses to mechanical, electrical and magnetic

forces, respectively. Other important properties are thermal (transmission of heat, heat

capacity), optical (absorption, transmission and scattering of light), and the chemical stability

in contact with the environment (like corrosion resistance).

Processing of materials is the application of heat (heat treatment), mechanical forces, etc. to

affect their microstructure and, therefore, their properties.

1.3 Why Study Materials Science and Engineering?

· To be able to select a material for a given use based on considerations of cost and

performance.

· To understand the limits of materials and the change of their properties with use.

· To be able to create a new material that will have some desirable properties.

All engineering disciplines need to know about materials. Even the most "immaterial", like

software or system engineering depend on the development of new materials, which in turn

alter the economics, like software-hardware trade-offs. Increasing applications of system

engineering are in materials manufacturing (industrial engineering) and complex environmental

systems.

1.4 Classification of Materials

Like many other things, materials are classified in groups, so that our brain can handle the

complexity. One could classify them according to structure, or properties, or use. The one that

we will use is according to the way the atoms are bound together:

Metals: valence electrons are detached from atoms, and spread in an 'electron sea' that "glues"

the ions together. Metals are usually strong, conduct electricity and heat well and are opaque to

light (shiny if polished). Examples: aluminum, steel, brass, gold.

Semiconductors: the bonding is covalent (electrons are shared between atoms). Their electrical

properties depend extremely strongly on minute proportions of contaminants. They are opaque

to visible light but transparent to the infrared. Examples: Si, Ge, GaAs.

Ceramics: atoms behave mostly like either positive or negative ions, and are bound by

Coulomb forces between them. They are usually combinations of metals or semiconductors

with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Examples: glass, porcelain,

many minerals.

1.5 Advanced Materials

Materials used in "High-Tec" applications, usually designed for maximum performance, and

normally expensive. Examples are titanium alloys for supersonic airplanes, magnetic alloys for

computer disks, special ceramics for the heat shield of the space shuttle, etc.

1.6 Modern Material's Needs

· Engine efficiency increases at high temperatures: requires high temperature structural

materials

· Use of nuclear energy requires solving problem with residues, or advances in nuclear

waste processing.

· Hypersonic flight requires materials that are light, strong and resist high temperatures.

· Optical communications require optical fibers that absorb light negligibly.

· Civil construction – materials for unbreakable windows.

· Structures: materials that are strong like metals and resist corrosion like