ABSTRACT
This chapter describes some of these aspects that are of particular importance and relevance to metals, notably, ductility, plasticity and grain structure, and then show how these lead to methods of strengthening and forming metals, subjects often collectively known as physical metallurgy. Pure metals in the ‘as-cast’ condition after slow cooling are generally soft, have low yield stresses and are very ductile; this is a consequence of the ease of dislocation movement or slip. In a single crystal of a pure metal the shear stress required to move a dislocation is small, in some cases maybe only ∼1MPa. Control of grain size in castings is generally achieved by ‘inoculating’ the liquid metal with substances that can react with ingredients in the metal to form small solid particles that act as nucleation sites for crystal growth. Metals, especially those with the face-centred and body-centred cubic systems, have many different planes on which dislocations can move to produce slip.
