Metal Matrix Composites

August 26, 2016

While metal matrix composites (MMCs) can provide a higher strength material with the possibility other more favorable physical properties, their manufacture can be more complicated and labor intensive. Therefore, an engineer must determine whether the advantages of using MMCs justify the excessive manufacturing costs.

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Metal matrix composites (MMCs) are composite materials in which at least one of the two components is a metal. To form a MMC, the reinforcing material (which may or may not be a metal) is dispersed within a metal matrix. The matrix is the monolithic material that has the reinforcement embedded within it and is always continuous. The reinforcement material, on the other hand, is the material that is embedded into the matrix and can be either continuous or discontinuous. Additionally, although it generally serves a structural role to increase the strength of the composite, the reinforcement can also serve to change other physical properties, such as wear resistance, thermal conductivity, or corrosion resistance.

MMC Solid State Manufacturing

MMCs can be manufactured in a variety of ways from both the solid and liquid states. Solid state manufacturing methods include powder metallurgy and foil diffusion bonding. In powder metallurgy, powdered metal and discontinuous reinforcement are mixed and then bonded through a process of compaction, degassing, and thermos-mechanical treatment. In foil diffusion bonding, layers of metal foil are sandwiched with long fibers, and both are then pressed to form a matrix.

MMC Liquid State Manufacturing

In contrast, there are many more methods of manufacturing MMCs from the liquid state. Electroplating involves using a solution that contains both the metal matrix ions and reinforcing particles, which are then deposited to form the composite material. With stir casting, discontinuous reinforcement is stirred into a molten metal matrix, and the mixture is then solidified. In pressure infiltration, the process is reversed. The molten metal is infiltrated into the reinforcement under pressure instead of introducing the reinforcement to the molten metal. Finally, squeeze casting and spray deposition are much more similar to traditional composite manufacturing. In squeeze casting, molten metal is injected into a preform with reinforcement already placed inside of it and in spray deposition, the molten metal is sprayed onto a continuous reinforcement substrate.

While metal matrix composites can provide a higher strength material with the possibility other more favorable physical properties, their manufacture can at times be more complicated and labor intensive than that of conventional composites. Therefore, an engineer must determine whether or not an MMC is needed for certain applications to avoid excessive manufacturing costs. Additionally, the reinforcement and matrix materials must be chosen carefully to maximize the MMC’s potential, especially for specialized applications. However, metal matrix composites offer many well-rounded benefits that can far exceed their drawbacks.

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