7: Metal Matrix Composites

Metal matrix composites, as the name suggests, consist of fibres or particles surrounded by a matrix of metal.

The use of a metal matrix offers the potential of producing a composite with very high stiffness and strength as well as very high temperature resistance. The temperature resistance is not only superior to polymer matrix composites but also to the pure metal itself.

While metal matrix composites enjoy other advantages over polymer matrix composites such as better abrasion resistance, creep resistance, resistance to degradation by fluids, dimensional stability, and non-flammability, they are limited in application due to their much higher weight and cost of production.

The main matrix materials employed in MMCs are aluminium, titanium, magnesium, and copper. The main reinforcements employed are silicon carbide and alumina.

Metal matrix composites can be classed as having either continuous or discontinuous fibre reinforcement. Discontinuous reinforced MMCs appear to offer more potential due to their ease of manufacture. Discontinuous fibres can exist in the form of short fibres, whiskers, platelets, or particles.

The common manufacturing processes used to achieve these composites are powder metallurgy techniques, vapour deposition, diffusion bonding, and infiltration of liquid metal into the fibre bundles under pressure.