Metal Matrix Composite

1. A metal matrix composite (MMC) is a type of composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. An MMC is complementary to cermet.

2. Each part of the material is either the matrix or a reinforcement. The reinforcement surface can be coated to prevent a chemical reaction with the matrix.

3. The matrix is the " frame" into which the reinforcement is embedded, and is completely continuous. This means that there is a path through the matrix to any point in the material, unlike two materials sandwiched together. The matrix is usually a lighter metal such as aluminum, magnesium or titanium and provides a compliant support for the reinforcement.

4. The reinforcement material is embedded into the matrix. The reinforcement does not always serve a purely structural task (reinforcing the compound), but is also used to change physical properties such as wear resistance, friction coefficient or thermal conductivity. The reinforcement can be either continuous or discontinuous.

Discontinuous MMCs are isotropic and can be worked with standard metalworking techniques.

Continuous reinforcement uses monofilament wires or fibers such as carbon fiber or silicon carbide. Because the fibers are embedded into the matrix in a certain direction, the result is an anisotropic structure in which the alignment of the material affects its strength. One of the first MMCs used boron filament as reinforcement. Discontinuous reinforcement uses " whiskers", short fibers, or particles.

5. MMC manufacturing can be broken into three types: solid, liquid and vapor.

Solid type implies powder blending and consolidation when powdered metal and discontinuous reinforcement are mixed and then bonded through a process of compaction, air extraction and heating (possibly via hot isostatic pressing (HIP) or extruding). Foil diffusion bonding is the type manufacture in the processing of which layers of metal foil are sandwiched with long fibers, and then melted through to form a matrix.

Liquid type in turn is divided into stir casting. Stir casting employs discontinuous reinforcement stirred into molten metal which is allowed to solidify. Another liquid types include squeeze casting (molten metal is injected into a form with fibers preplaced inside it) and spray deposition (molten metal is sprayed onto a continuous fiber substrate). Recently due to advanced technologies one more promising method has appeared. It’s reactive processing when a chemical reaction occurs with one of the reactants forming the matrix and the other the reinforcement.

Physical vapor deposition is one of the latest methods. The fiber is passed through a thick cloud of vaporized metal, coating it.

6. MMCs are always more expensive than the more conventional materials they are replacing. As a result, they are found where improved properties and performance can justify the added cost (aircraft components, space systems, " boutique" sports equipment). Today these applications are found most often in. Thus the F-16 Fighting Falcon uses monofilament silicon carbide fibres in a titanium matrix for a structural component of the jet's landing gear. Modern high-performance sport cars, such as those built by Porsche, use rotors made of carbon fiber within a silicon carbide matrix because of its high specific heat and thermal conductivity. A preformed aluminum matrix insert for strengthening cast aluminum disc brake calipers, allows them to weigh as much as 50% less while increasing stiffness.

It goes without saying that military industry engineers employ all the properties to improve military technique. Some tank armors may be made from metal matrix composites, probably steel reinforced with boron nitride. Boron nitride is a good reinforcement for steel because it is very stiff and it does not dissolve in molten steel. Carbide drills are often made from a soft cobalt matrix with tough tungsten carbide particles inside. The scope of applications will certainly increase as manufacturing costs are reduced.

Notes to the text:

1. to embed – укладывать, укреплять

2. compliant – податливый

3. filament – нитевидное волокно

5. squeeze casting – литье под давлением

14. Answer the question to the text Metal Matrix Composite:

1.How many constituents doesa metal matrix composite combine? 2.What is a hybrid composite? 3.Can each part of the material be either a matrix or reinforcement? 4. Why the reinforcement surface can be coated? 5.What does the matrix provide? 6. What discontinuous MMCs can be worked with? 7. What types of fibers are used for continuous reinforcement? 8.What types the MMC manufacturing can be broken into? 9. Which of them is one of the latest methods? What technology does it employ? 10. Why are MMCs not in common use yet? What cases can be the added cost justified in?

15. Look through the text Metal Matrix Composite again. Choose the keywords and write a short abstract (no more than 100 words).