We can define a composite material as a material consisting of two or more physically and/or chemically distinct phases, suitably arranged or distributed. A composite material usually has characteristics that are not depicted by any of its components in isolation. Generally, the continuous phase is referred to as the matrix, while the distributed phase is called the reinforcement. Three items determine the characteristics of a composite: the reinforcement, the matrix, and the interface between them. In this chapter, we provide a brief survey of different types of composite materials, highlight some of their important features, and indicate their various applications.
Types of Composites
We may classify composites on the basis of the type of matrix employed in them – for example, polymer matrix composites (PMCs), metal matrix composites (MMCs), and ceramic matrix composites (CMCs). We may also classify composites on the basis of the type of reinforcement they employ (see Figure 15.1):
Particle reinforced composites.
Short fiber, or whisker reinforced, composites.
Continuous fiber, or sheet reinforced, MMCs.
Figure 15.2 shows typical microstructures of some composites: boron fiber/Al (Figure 15.2(a)), short alumina fiber/Al (Figure 15.2(b)), and NbC/Ni–Cr, an in situ (eutectic) composite (Figure 15.2(c)). Examples of microstructure of a silicon carbide particle (three different volume fractions) reinforced aluminium matrix are given in Figure 15.3. These were made by hot pressing of powders followed by hot extrusion. Note the preferential alignment of SiC particles in the extrusion direction.