Many others have been tried over the last few decades, and still others undoubtedly will be developed in the future. The most important have been aluminum, titanium, magnesium, and copper alloys and superalloys. An important characteristic of MMCs, however, and one they share with other composites, is that by appropriate selection of matrix materials, reinforcements, and layer orientations, it is possible to tailor the properties of a component to meet the needs of a specific design. For example, within broad limits, it is possible to specify strength and stiffness in one direction, coefficient of expansion in another, and so forth. This is rarely possible with monolithic materials.
Monolithic metals tend to be isotropic, that is, to have the same properties in all directions.
Some processes such as rolling, however, can impart anisotropy, so that properties vary with direction. Most structural metals have considerable ductility and fracture toughness. The wide variety of MMCs have properties that differ dramatically. Residual stresses arising from the thermal and mechanical history of the composite Possible degradation of the reinforcement resulting from chemical reactions at high temperatures, and mechanical damage from processing, impact, etc. Particulate-reinforced MMCs, like monolithic metals, tend to be isotropic.