Metal Matrix Composites: Properties, Production, and Applications

​Metal matrix composites (MMCs) are a class of materials comprised of a metal fused with another substance. These two components appear in differing phases that are physically and chemically distinct [1]. The base material is a metal matrix, while the other substance appears as fibres or particulates to work as reinforcing material. 

As with most metal matrix composites, the goal of manufacturing such a material is to enhance the existing properties of the metal matrix, by adding supplementary features that the reinforcement provides.​ 

Properties of Metal Matrix Composites 

High Strength 

One of the most common features of metal matrix composite materials is increased strength and stiffness [2]. Its high strength-to-weight ratio makes the material useful in a wide variety of applications. 

This is evident when exposed to tension or compression, as most metal matrix composites have high mechanical strength. 

High Heat Resistance 

Some composites are built to have higher creep resistance than the pure metal counterparts. This reduces the risk of warping or deformation in the material, especially when exposed to welding or tensile stress with high temperature. Metal matrix composites work best in industries with a high risk of creep fatigue or sudden temperature changes. 

In addition, these materials have a lower thermal expansion coefficient, which bodes well for applications that require material integrity in extremely high temperatures. 

Other Unique Properties 

Each composite has its own unique signature set of properties depending on the composition and orientation of the metal and reinforcing material. Some of these properties include the following: 

• Fire resistance 
• Inability to absorb moisture 

• Radiation resistance 
• Increased resistance to wear and tear

​Examples of Metal Matrix Composites 

As more manufacturers produce more materials of this kind, the list of metal matrix composites may change every so often. However, most of the composites available in the market are usually classified under the following: 

Aluminium MMC 

These composites make use of aluminium as the base metal matrix. Examples include SupremEX® 620XF T5 Precision Extrusion (6061B), aluminium-graphite composite, and aluminium-beryllium composites such as AlBeMet® AM162 HIP. 

Magnesium MMC 

Magnesium is another excellent matrix material for composites. Some products in this category include magnesium-silicon carbide (Mg-SiC), magnesium-aluminium oxide (Mg-Al2O3) and magnesium-titanium carbide (Mg-TiC). 

Titanium MMC 

Pure titanium is already a strong material in itself, but its composite form may enhance its superior strength. 

Other MMCs 

Other less common but highly useful matrix base materials used for composites include copper, cobalt, nickel, or a combination of metals. Meanwhile, some of the most common reinforcing materials used are carbon fibre, silicon carbide, alumina, and boron. 

Production and Processing 

Metal matrix composites may be processed in many ways under one of the following procedures [3]:​ 

Solid State Processing 

As the term implies, solid state processing involves mixing the matrix and reinforcing material in their respective solid forms. This may be done through physical vapour deposition, diffusion bonding, or powder blending. 

Powder blending uses a powdered matrix material combined with a binder substance within a stoddard solvent. After drying and rolling, the resulting powder sheet is stacked alternatively with reinforcing fibres. The cloth layers are vacuum-heated and hot-pressed [4]. 

Liquid State Processing 

This type of production involves combining reinforcement material with liquified metal and allowing the mixture to cool down and solidify. This may be conducted through stir casting, squeeze casting, infiltration, or spray decomposition. 

For the latter, liquid metal is sprayed onto a particulate or short-fibre reinforcing material. 

In-Situ Processing 

This kind of processing produces the reinforcement material through chemical reactions within the matrix. This results in a pure metal composite mixture with strong matrix dispersion bonding forces. 

When a composite material is formed, it may fall under any of these orientations: particle reinforcement, whisker reinforcement, and sheet reinforcement. The differences are seen in the way the reinforcing material is embedded or integrated into the metal matrix. 

Applications of Metal Matrix Composites 

Aerospace and Aircraft Industry 

Metal matrix composites work well as components in transmission systems, gearboxes, engine parts and accessories, and other internal elements. 

Sports 

The superior strength-to-weight ratio of most metal matrix composites makes the material suitable for tennis rackets, bicycle frames, and other sports that involve speed and strength. 

Automotive Applications 

Car and motor racing make use of metal matrix composites for engine and vehicle body parts due to the lightweight nature of the material. 

​[1] Chawla, N. and Chawla, K. K. (2006) Matrix Materials. In Metal Matrix Composites. Springer Science & Business Media. 

[2] (n.d.) Metal Matrix Composites. UNSW School of Materials Science and Engineering. Retrieved from: http://www.materials.unsw.edu.au/tutorials/online-tutorials/7-metal-matrix-composites 

[3] Trinh, S. N. and Sastry, S. (2016) Processing and Properties of Metal Matrix Composites. Mechanical Engineering and Materials Science Independent Study. Paper 10. 

[4] Stephens, J. R. (1987) High Temperature Metal Matrix Composites for Future Aerospace Systems. NASA Technical Memorandum 100212.​