The Structure of Metals and Alloys

The properties of metals and alloys are dependent on their atomic structure. Metals are an aggregation of atoms that, apart from mercury, are solid at room temperature. These atoms are held together by “metallic bonds” that result from sharing available electrons. A negative electron bond pervades the structure, and heat and electricity can be conducted through the metal by the free movement of electrons. The atoms are regularly arranged, forming a symmetrical three-dimensional group, which repeats itself periodically and which is called a unit cell. Unit cells of identical characteristics form a crystal with regular spatial distribution of atoms, which can be defined by a space lattice. Atoms can be stacked in different ways to create a variety of simple lattice types. There are three common types of lattice structure that most metals belong to (Fig. 4.1): face-centred cubic (fcc), body-centred cubic (bcc) and close-packed hexagonal (cph).