Fundamentals of Materials Science and Engineering

Introduction to Materials Science

Materials Science is an extensive discipline that relates the structure, properties, and application of engineering materials.

What are Engineering Materials?

Engineering materials are defined as those materials that, due to their desirable properties, can be used in machinery parts, structural elements, or for other engineering purposes. These materials can be structurally crystalline or amorphous and include:

• Metals
• Polymers
• Ceramics
• Composites (composed of two or more different materials from the families above)

Types of Engineering Materials

Metallic Materials

Metallic materials are substances whose atoms are joined by metallic bonds. These unique chemical bonds permit some atomic mobility and complete mobility for their outer electrons (conduction layer). This generally makes metallic materials ductile, tough, and good conductors of heat and electricity. The excellent ductility of metallic materials (including pure metals and alloys) allows them to be manufactured through processes like plastic deformation. It also means they tend to deform under stress rather than fracture. Metallic materials are generally the toughest of all materials, meaning they can absorb significant impact without fracturing. However, they are often susceptible to corrosion.

Polymeric Materials

Polymeric materials typically have an organic origin. Examples include plastics and wood. They are characterized by their low density and the ease with which objects can be manufactured from them. They are generally poor conductors of heat and electricity, not very tough, and possess lower heat resistance compared to metals or ceramics.

Ceramic Materials

Ceramic materials (such as glass, cement, pottery, and refractories) are typically very hard but brittle (meaning they have low toughness). The vast majority are poor electrical conductors (with exceptions like graphite) and are difficult to shape or manufacture into objects. The high hardness of some ceramics makes them suitable for use as reinforcements in other materials, such as fiber-reinforced composites.

Composite Materials

As mentioned, composites are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic level within the finished structure. They often combine the beneficial properties of their constituent materials.

Atomic Structure of Matter

Matter consists of atoms and their subatomic particles. The most important particles are:

• Protons
• Neutrons
• Electrons

Pure elements are composed of atoms of the same type, meaning each atom has the same number of protons (and, in a neutral atom, the same number of electrons). For instance, all copper atoms have 29 protons and 29 electrons each, and all iron atoms have 26 protons and 26 electrons.

The number of neutrons can vary, creating isotopes; for example, common isotopes of copper have 34 or 36 neutrons, while a common iron isotope has 30 neutrons. The number of protons (the atomic number) is what fundamentally differentiates one element from another. For example, an atom with 29 protons is copper, while an atom with 30 protons is zinc; their properties are distinct.

Protons and neutrons reside in a tiny central region called the atomic nucleus. Electrons occupy a much larger volume surrounding the nucleus (though still minuscule on our scale). Electrons do not orbit randomly but exist in specific regions of probability called electron orbitals.