Metal matrix composites (MMC) consist of a metal and one or more other materials, typically a ceramic or organic compound. They provide superior specific strengths and good strength-to-weight ratios, resist fire and moisture, and can be used over a wide range of temperatures. They also provide resistance to radiation and excellent electrical and thermal conductivity. MMCs that consist of three different materials (including more than one metal) are called hybrid compounds.
Modulus Phase and Reinforcement Phase
Like other composite materials, MMCs typically have a stronger or high modulus phase to enhance the properties of the matrix metal or alloy. In a composite made of two materials with two different moduli, the load is transferred to the material with the stiffer (higher) modulus. When selecting products, choose MMCs with an appropriate modulus phase for your application.
The interface between the reinforcement phase and the matrix is critical in optimizing properties such as load transfer, wetting characteristics, reactions, and electrical conductivity. In some material systems, the reinforcement phase is coated to prevent the formation of brittle phases at the interface.
MMC Reinforcement Materials
Metal matrix composites use three types of reinforcements: particulate, fibrous, and continuous.
- Particulate reinforcements consist of powders, such as silicon carbide, that are used in metal matrices.
- Fibrous reinforcements include silicon carbide fibers dispersed in an aluminum alloy matrix.
- Continuous reinforcements include filament-wound, carbon fiber, magnesium composites, or woven carbon fiber cloth reinforced aluminum alloys.
The specific reinforcement materials and alloy matrixes can vary depending on the details of the end-use application. Typically, suppliers can provide more information.
Applications for Metal Matrix Composites
Metal matrix composites may have engineered properties for special applications. For instance, welding electrode materials and electrical contact materials consist of a conductive matrix alloy of copper or silver with a tungsten, tungsten carbide, or cadmium oxide second phase, or reinforcement. The second phase improves wear and arc resistance while only slightly reducing conductivity. If reinforcement with high-temperature strength is used, then the reinforcement phase may provide greater strengthening at elevated temperatures.
Metal matrix composites (MMC) are also used in carbide drills, tank armor, automotive disk brakes, drive shafts, aerospace applications, specialized bicycles. They are used in particle accelerators, too.