Metal Matrix Composte ( MMC )
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This document is a training report on metal matrix composites (MMCs) submitted by Shashwat Mishra as part of a bachelor's degree requirement. It covers the composition, manufacturing methods, characteristics, applications, and historical development of MMCs, emphasizing their advantages in strong and lightweight materials for various engineering applications, including aerospace and automotive industries. The report also acknowledges contributions from faculty and peers, highlighting the importance of MMCs in modern engineering solutions.
![eponymous Toyota Matrix. Porsche also uses MMCs to reinforce the engine's cylinder sleeves in
the Boxster and 911.
The F-16 Fighting Falcon uses monofilament silicon carbide fibers in a titanium matrix for a
structural component of the jet's landing gear.
Specialized Bicycles has used aluminum MMC compounds for its top of the range bicycle frames
for several years. Griffen Bicycles also made boron carbide-aluminum MMC bike frames, and
Univega briefly did so as well.
Some equipment in particle accelerators such as Radio Frequency Quadrupoles (RFQs) or
electron targets use copper MMC compounds such as Glidcop to retain the material properties
of copper at high temperatures and radiation levels.[9][10]
Copper-silver alloy matrix containing 55% by volume diamond particles, known as Dymalloy, is
used as a substrate for high-power, high-density multi-chip modules in electronics for its very
high thermal conductivity.
Aluminium-Graphite composites are used in power electronic modules because of their high
thermal conductivity, the adjustable coefficient of thermal expansion and the low density.
MMCs are nearly 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. Today these applications are found most often in aircraft components, space
systems and high-end or "boutique" sports equipment. The scope of applications will certainly
increase as manufacturing costs are reduced.
In comparison with conventional polymer matrix composites, MMCs are resistant to fire, can
operate in wider range of temperatures, do not absorb moisture, have better electrical and
thermal conductivity, are resistant to radiation damage, and do not display outgassing. On the
other hand, MMCs tend to be more expensive, the fiber-reinforced materials may be difficult to
fabricate, and the available experience in use is limited.](https://image.slidesharecdn.com/metalmatrix-171015065316/85/Metal-Matrix-Composte-MMC-8-320.jpg)
Metal Matrix Composte ( MMC )
- 1. Metal Matrix Composite ( MMC ) A Project Training Report Submitted In Partial Fulfilment of the Requirement For the Degree Of Bachelor of Technology Student Name : Shashwat Mishra Roll No: 201410102110068 Co-ordinator : Er Amit Singh FACULTY OF MECHANICAL ENGINEERING INSTITUTE OF TECHNOLOGY SHRI RAMSWAROOP MEMORIAL UNIVERSITY September , 2017
- 2. ACKNOWLEDGEMENT On the occasion of presenting this seminar report I wish to express my deep gratitude to all the people who have contributed to the completion of this seminar. First of all I would like to thank Rohit Kumar Singh (Assistant Professor, Department Of Mechanical Engineering) for being my guide and for the help granted by him and providing me with all facility and guidance. I would also take this opportunity to express my heartfelt Professor Dr. Niraj Gupta. ( HOD Department Of Mechanical Engineering) for his valuable support and cooperation in the presentation of this paper. I am thankful to all faculties for their lively discussions and suggestions. Finally I would like to thank my friends who have given me required suggestions for the successful completion of my seminar.
- 3. Contents 1 Composition Matrix Reinforcement 2 Manufacturing and forming methods Solid state methods Liquid state methods Semi-solid state methods Vapor deposition 2.5 In-situ fabrication technique 3 Residual stress 4 Applications 5 References 6 External links
- 4. INTRODUCTION A metal matrix composite (MMC) is composite material with at least two constituent parts, one being a metal necessarily, 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 a cermet. Composition MMCs are made by dispersing a reinforcing material into a metal matrix. The reinforcement surface can be coated to prevent a chemical reaction with the matrix. For example, carbon fibers are commonly used in aluminium matrix to synthesize composites showing low density and high strength. However, carbon reacts with aluminium to generate a brittle and water- soluble compound Al4C3 on the surface of the fibre. To prevent this reaction, the carbon fibres are coated with nickel or titanium boride. Matrix The matrix is the monolithic material 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. In structural applications, the matrix is usually a lighter metal such as aluminum, magnesium, or titanium, and provides a compliant support for the reinforcement. In high-temperature applications, cobalt and cobalt–nickel alloy matrices are common. Reinforcement The reinforcement material is embedded into a 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 can be isotropic, and can be worked with standard metalworking techniques, such as extrusion, forging, or rolling. In addition, they may be machined using conventional techniques, but commonly would need the use of polycrystaline diamond tooling (PCD).
- 5. 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. The most common reinforcing materials in this category are alumina and silicon carbide. Manufacturing and forming methods MMC manufacturing can be broken into three types—solid, liquid, and vapor. Solid state methods Powder blending and consolidation (powder metallurgy): Powdered metal and discontinuous reinforcement are mixed and then bonded through a process of compaction, degassing, and thermo-mechanical treatment (possibly via hot isostatic pressing (HIP) or extrusion) Foil diffusion bonding: Layers of metal foil are sandwiched with long fibers, and then pressed through to form a matrix
- 6. Liquid state methods Electroplating and electroforming: A solution containing metal ions loaded with reinforcing particles is co-deposited forming a composite material Stir casting: Discontinuous reinforcement is stirred into molten metal, which is allowed to solidify Pressure infiltration: Molten metal is infiltrated into the reinforcement through use a kind of pressure such as gas pressure Squeeze casting: Molten metal is injected into a form with fibers pre-placed inside it Spray deposition: Molten metal is sprayed onto a continuous fiber substrate Reactive processing: A chemical reaction occurs, with one of the reactants forming the matrix and the other the reinforcement Semi-solid state methods Semi-solid powder processing: Powder mixture is heated up to semi-solid state and pressure is applied to form the composites. Vapor deposition Physical vapor deposition: The fiber is passed through a thick cloud of vaporized metal, coating it. In-situ fabrication technique Controlled unidirectional solidification of a eutectic alloy can result in a two-phase microstructure with one of the phases, present in lamellar or fiber form, distributed in the matrix. Residual stress MMCs are fabricated at elevated temperatures, which is an essential condition for diffusion bonding of the fiber/matrix interface. Later on, when they are cooled down to the ambient
- 7. temperature, residual stresses (RS) are generated in the composite due to the mismatch between the coefficients of the metal matrix and fiber. The manufacturing RS significantly influence the mechanical behavior of the MMCs in all loading conditions. In some cases, thermal RS are high enough to initiate plastic deformation within the matrix during the manufacturing process. Applications This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message). High performance tungsten carbide cutting tools are made from a tough cobalt matrix cementing the hard tungsten carbide particles; lower performance tools can use other metals such as bronze as the matrix. Some tank armors may be made from metal matrix composites, probably steel reinforced with boron nitride, which is a good reinforcement for steel because it is very stiff and it does not dissolve in molten steel. Some automotive disc brakes use MMCs. Early Lotus Elise models used aluminum MMC rotors, but they have less than optimal heat properties and Lotus has since switched back to cast-iron. 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. 3M developed a preformed aluminum matrix insert for strengthening cast aluminum disc brake calipers, reducing weight by half compared to cast iron while retaining similar stiffness. 3M has also used alumina preforms for AMC pushrods. Ford offers a Metal Matrix Composite (MMC) driveshaft upgrade. The MMC driveshaft is made of an aluminum matrix reinforced with boron carbide, allowing the critical speed of the driveshaft to be raised by reducing inertia. The MMC driveshaft has become a common modification for racers, allowing the top speed to be increased far beyond the safe operating speeds of a standard aluminum driveshaft. Honda has used aluminum metal matrix composite cylinder liners in some of their engines, including the B21A1, H22A and H23A, F20C and F22C, and the C32B used in the NSX. Toyota has since used metal matrix composites in the Yamaha-designed 2ZZ-GE engine which is used in the later Lotus Lotus Elise S2 versions as well as Toyota car models, including the
- 8. eponymous Toyota Matrix. Porsche also uses MMCs to reinforce the engine's cylinder sleeves in the Boxster and 911. The F-16 Fighting Falcon uses monofilament silicon carbide fibers in a titanium matrix for a structural component of the jet's landing gear. Specialized Bicycles has used aluminum MMC compounds for its top of the range bicycle frames for several years. Griffen Bicycles also made boron carbide-aluminum MMC bike frames, and Univega briefly did so as well. Some equipment in particle accelerators such as Radio Frequency Quadrupoles (RFQs) or electron targets use copper MMC compounds such as Glidcop to retain the material properties of copper at high temperatures and radiation levels.[9][10] Copper-silver alloy matrix containing 55% by volume diamond particles, known as Dymalloy, is used as a substrate for high-power, high-density multi-chip modules in electronics for its very high thermal conductivity. Aluminium-Graphite composites are used in power electronic modules because of their high thermal conductivity, the adjustable coefficient of thermal expansion and the low density. MMCs are nearly 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. Today these applications are found most often in aircraft components, space systems and high-end or "boutique" sports equipment. The scope of applications will certainly increase as manufacturing costs are reduced. In comparison with conventional polymer matrix composites, MMCs are resistant to fire, can operate in wider range of temperatures, do not absorb moisture, have better electrical and thermal conductivity, are resistant to radiation damage, and do not display outgassing. On the other hand, MMCs tend to be more expensive, the fiber-reinforced materials may be difficult to fabricate, and the available experience in use is limited.
- 9. Metal-Matrix Composites for Space Applications From the onset of the space era, both organic-matrix and metal-matrix composites (MMCs), with high specific stiffness and near-zero coefficient of thermal expansion (CTE), have been developed for space applications. Of the organic-matrix composites, graphite/epoxy (Gr/Ep) has been used in space for truss elements, bus panels, antennas, wave guides, and parabolic reflectors in the past 30 years. MMCs possess high-temperature capability, high thermal conductivity, low CTE, and high specific stiffness and strength. Those potential benefits generated optimism for MMCs for critical space system applications in the late 1980s.1,2 The purpose of this article is to detail the history, status, and opportunities of MMCs for space applications. The extreme environment in space presents both a challenge and opportunity for material scientists. In the near-earth orbit, typical spacecraft encounter naturally occurring phenomena such as vacuum, thermal radiation, atomic oxygen, ionizing radiation, and plasma, along with factors such as micrometeoroids and human-made debris. For example, the International Space Station, during its 30-year life, will undergo about 175,000 thermal cycles from +125°C to – 125°C as it moves in and out of the Earth’s shadow. Re-entry vehicles for Earth and Mars missions may encounter temperatures that exceed 1,500°C. Critical spacecraft missions, therefore, demand lightweight space structures with high pointing accuracy and dimensional stability in the presence of dynamic and thermal disturbances. Composite materials, with their high specific stiffness and low coefficient of thermal expansion (CTE), provide the necessary characteristics to produce lightweight and dimensionally stable structures. Therefore, both organic-matrix and metal-matrix composites (MMCs) have been developed for space applications. Despite the successful production of MMCs such as continuous-fiber reinforced boron/aluminum (B/Al), graphite/ aluminum (Gr/Al), and graphite/ magnesium (Gr/Mg),3–7 the technology insertion was limited by the concerns related to ease of manufacturing and inspection, scale-up, and cost. Organic-matrix composites continued to successfully address the system-level concerns related to microcracking during thermal cycling and radiation exposure, and electromagnetic interference (EMI) shielding; MMCs are inherently resistant to those factors. Concurrently, discontinuously reinforced MMCs such as silicon-carbide particulate (p) reinforced aluminum (SiCp/Al) and Gp/Al composites were developed cost effectively both for aerospace applications (e.g., electronic packaging) and commercial applications. This paper describes the benefits, drawbacks, potential for the various MMCs in the U.S. space program.
- 10. HISTORICAL PERSPECTIVE Historically, MMCs, such as steel-wire reinforced copper, were among the first continuous-fiber reinforced composites studied as a model system. Initial work in late 1960s was stimulated by the high-performance needs of the aerospace industry. In these development efforts, performance, not cost, was the primary driver. Boron filament, the first high-strength, high- modulus reinforcement, was developed both for metal- and organic- matrix composites. Because of the fiber-strength degradation and poor wettability in molten-aluminum alloys, the early carbon fibers could only be properly reinforced in organic-matrix composites. Therefore, the development of MMCs was primarily directed toward diffusion-bonding processing. At the same time, optimum (air stable) surface coatings were developed for boron and graphite fibers to facilitate wetting and inhibit reaction with aluminum or magnesium alloys during processing. METAL-MATRIX COMPOSITE PROCESSING Three processing methods have been primarily used to develop MMCs: high-pressure diffusion bonding, casting, and powder-metallurgy techniques. More specifically, the diffusion-bonding and casting methods have been used for continuous- fiber reinforced MMCs. Discontinuously reinforced MMCs have been produced by powder metallurgy and pressure-assist casting processes. MMCs such as B/Al, Gr/Al, Gr/Mg, and Gr/ Cu have been manufactured by diffusion bonding for prototype spacecraft components such as tubes, plates, and panels. Properties Table I lists the typical properties of a few continuous-fiber reinforced MMCs. Generally, measured properties of as-fabricated MMCs are consistent with the analytically predicted properties of each composite. The primary advantage of MMCs over counterpart organic- matrix composites is the maximum operating temperature. For example, B/Al offers useful mechanical properties up to 510°C, whereas an equivalent B/Ep composite is limited to about 190°C. In addition, MMCs such as Gr/Al, Gr/Mg, and Gr/Cu exhibit higher thermal conductivity because of the significant contribution from the metallic matrix. Properties of discontinuously reinforced aluminum (DRA) composites for spacecraft and commercial applications. DRA is an isotropic MMC with specific mechanical properties superior to conventional aerospace materials. For example, DWA Aluminum Composites has produced
- 11. MMCs using 6092 and 2009 matrix alloys for the best combination of strength, ductility, and fracture toughness, and 6063 matrix alloy to obtain high thermal conductivity. Similarly, Metal Matrix Cast Composite (MMCC) Inc. has produced graphite particulate-reinforced aluminum composites for the optimum combination of high specific thermal conductivity and CTE. APPLICATIONS While the desire for high-precision, dimensionally stable spacecraft structures has driven the development of MMCs, applications thus far have been limited by difficult fabrication processes. The first successful application of continuous-fiber reinforced MMC has been the application of B/Al tubular struts used as the frame and rib truss members in the mid-fuselage section, and as the landing gear drag link of the Space Shuttle Orbiter (Figure 1). Several hundred B/Al tube assemblies with titanium collars and end fittings were produced for each shuttle orbiter. In this application, the B/Al tubes provided 45% weight savings over the baseline aluminum design.
- 12. Mid-fuselage structure of Space Shuttle Orbiter showing boron-aluminum tubes. (Photo courtesy of U.S. Air Force/NASA).The P100/6061 Al high-gain antenna wave guides/ boom for the Hubble Space Telescope (HST) shown (a-left) before integration in the HST, and (b-right) on the HST as it is deployed in low-earth orbit from the space shuttle orbiter. The major application of Gr/Al composite is a high-gain antenna boom (Figures 2a and 2b) for the Hubble Space Telescope made with diffusion-bonded sheet of P100 graphite fibers in 6061 Al. This boom (3.6 m long) offers the desired stiffness and low CTE to maintain the position of the antenna during space maneuvers. In addition, it provides the wave-guide function, with the MMC’s excellent electrical conductivity enabling electrical-signal transmission between the spacecraft and the antenna dish. Also contributing to its success in this function is the MMC’s high dimensional stability—the material maintains internal dimensional tolerance of ±0.15 mm along the entire length. While the part currently in service is continuously reinforced with graphite fibers, replacement structures produced with less expensive DRA have been certified. Like the Gr/Al structural boom, a few MMCs have been designed to serve multiple purposes, such as structural, electrical, and thermal-control functions. For example, prototype Gr/Al composites were developed as structural radiators to perform structural, thermal, and EMI shielding functions.5 Also, Gr/Cu MMCs with high thermal conductivity were developed for high-temperature structural radiators.6 A DRA panel is used as a heat sink between two printed circuit boards to provide both thermal management and protection against flexure and vibration, which could lead to premature failure of the components in the circuit board. In technology-development programs sponsored by the U.S. Defense Advanced Research Projects Agency and the U.S. Air Force, graphite/magnesium tubes for truss-structure applications have been successfully produced (jointly by Lockheed Martin Space Systems of Colorado and Fiber Materials of Maine) by the filament-winding vacuum-assisted casting process. Figures 3a and 3b show a few of the cast Gr/Mg tubes (50 mm dia ´ 1.2 m long) that were produced to demonstrate the reproducibility and reliability of the fabrication method. Of the DRA composites, reinforcements of both particulate SiCp/Al and whisker (w) SiCw/Al were extensively characterized and evaluated during the 1980s. Potential applications included joints and attachment fittings for truss structures, longerons, electronic packages, thermal planes, mechanism housings, and bushings. Figures 4a and 4b show a multi-inlet SiCp/Al truss node produced by a near net-shape casting process.
- 13. Discontinuously reinforced aluminum MMCs for electronic packaging applications: (a-top) SiCp/Al electronic package for a remote power controller (photo courtesy of Lockheed Martin Corporation), and (b-bottom) cast Grp/Al components (photo courtesy of MMCC, Inc.). Because of their combination of high thermal conductivity, tailorable CTE (to match the CTE of electronic materials such as gallium arsenide or alumina), and low density, DRA composites are especially advantageous for electronic packaging and thermal-management applications.8,9 Several SiCp/Al and Grp/Al (Figures 5a and 5b) electronic packages have been space-qualified and are now flown on communication satellites and Global Positioning System satellites. These components are not only significantly lighter than those produced from previous metal alloys, but they provide significant cost savings through net-shape manufacturing.9 DRA is also used for thermal management of spacecraft power semiconductor modules in geosynchronous earth-orbit communication satellites, displacing Cu/W alloys with a much higher density and lower thermal conductivity, while generating a weight savings of more than 80%. These modules are also used in a number of land-based systems, which accounts for an annual production near 1 million piece-parts. With these demonstrated benefits, application of DRA MMCs for electronic packages will continue to flourish for space applications. STATUS AND FUTURE When continuous-fiber reinforced MMCs were no longer needed for the critical strategic defense system/missions, the development of those MMCs for space applications came to an abrupt halt. Major improvements were still necessary, and manufacturing and assembly problems remained to be solved. In essence, continuous-fiber reinforced MMCs were not able to attain their full potential as an engineered material for spacecraft applications. During the same period, Gr/Ep, with its superior specific stiffness and strength in the uniaxially-aligned fiber orientation, became an established choice for tube structures in spacecraft trusses. Issues of environmental stability in the space environment have been satisfactorily resolved. However, particle-reinforced metals provide very good specific strength and stiffness, isotropic properties, ease of manufacturing to near net shape, excellent thermal and electrical properties, and affordability, making discontinuous MMCs suitable for a wide range of space applications. The high structural efficiency and isotropic properties of discontinuously
- 14. reinforced metals provide a good match with the required multiaxial loading for truss nodes, where high loads are encountered. DRA is a candidate for lightly-loaded trusses, while discontinuously reinforced Ti (DRTi) is more favorable for highly-loaded trusses. DRTi, now commercially available in both the United States and Japan, offers excellent values of absolute strength and stiffness as well as specific strength and stiffness. A wide range of additional applications exist for discontinuously reinforced metals. Opportunities for thermal management and electronic packaging include radiator panels and battery sleeves, power semiconductor packages, microwave modules, black box enclosures, and printed circuit board heat sinks. For example, the DSCS-III, a military communication satellite, uses more than 23 kg of Kovar for microwave packaging. Replacing this metal with Al/SiCp, which is used for thermal management in land-based systems, would save more than 13 kg of weight and provide a cost savings over Kovar components. Potential satellite subsystem applications include brackets and braces currently made from metals with lower specific strength and stiffness, semimonocoque plates and cylinders, fittings for organic-matrix composite tubes, hinges, gimbals, inertial wheel housings and electro-optical subsystems. MMCs are routinely included as candidate materials for primary and secondary structural applications. However, simply having the best engineered material with extraordinary strength, stiffness, and environmental resistance is no guarantee of insertion. The availability and affordability of continuously reinforced MMC remains a significant barrier to insertion. Designers who often make the decision of material selection must become more familiar with the properties, commercial availability and life-cycle affordability of existing discontinuously reinforced metals. Material performance must be integrated with innovative design and affordable manufacturing methods to produce systems and subsystems that provide tangible benefits. However, in the absence of system-pull and adequate resources, it is difficult to surmount the technical and cost barriers. Recognizing that defense- and aerospace- driven materials need to turn to the commercial market place, Carlson10 cited four recurring principles that will shape the future of advanced materials such as organic-matrix and MMCs. These four principles included system solutions, economical manufacturing processing, diverse markets, and new technologies. In terms of system solutions, the decision regarding designs, processes and materials must be made synergistically to attain maximum benefit. No single mission or system application can sustain the cost of developing new materials and processes. Thus, the use of DRA in diverse markets
- 15. such as automotive, recreational, and aircraft industries has made DRA MMC affordable for spacecraft applications such as electronic packaging. Building upon the success of DRA in electronic packaging and in structural applications in the automotive and aeronautical fields, DRA is also being evaluated for truss end fittings, mechanism housings, and longerons. During the development of MMCs, significant advancements were made on the fundamental science and technology front, including a basic understanding of composite behavior, fiber- matrix interfaces, surface coatings, manufacturing processes, and thermal-mechanical processing of MMCs. Subsequently, the technology experience benefited the latter development of high-temperature intermetallic- matrix composites. (Research activities that will be required to support more widespread use of MMCs for space applications have been discussed in Reference 9.) Lightweight, stiff, and strong Gr/Al and DRA MMCs will continue to be included in material trade studies for spacecraft components, as MMCs offer significant payoffs in terms of performance (e.g., high precision, survivable) for specific systems. For successful use in space applications, continuous MMCs must become more affordable, readily available, reliable/reproducible, and repairable, exhibiting equivalent or better properties than competing graphite/ epoxy or metallic parts. Discontinuous metals, with their broad range of functional properties including high structural efficiency and isotropic properties, offer the greatest potential for a wide range of space-system applications. A good understanding provided by years of research, and a strong industry based on applications in the automotive, recreation, aeronautical, and land-based communications markets, have established the foundation for cost-effective insertion of discontinuously reinforced metals in the space industry.
- 16. References Materials science and Engineering, an introduction. William D. Callister Jr, 7th Ed, Wiley and sons publishing Wu, Yufeng; Gap; Kim, Yong (2011). "Carbon nanotube reinforced aluminum composite fabricated by semi-solid powder processing". Journal of Materials Processing Technology. 211 (8): 1341–1347. doi:10.1016/j.jmatprotec.2011.03.007. Wu, Yufeng; Yong Kim, Gap; et al. (2010). "Fabrication of Al6061 composite with high SiC particle loading by semi-solid powder processing". Acta Materialia. 58 (13): 4398–4405. doi:10.1016/j.jmatprotec.2011.03.007. Wu, Yufeng; Yong Kim, Gap; et al. (2015). "Compaction behavior of Al6061 and SiC binary powder mixture in the mushy state". Journal of Materials Processing Technology. 216: 484–491. doi:10.1016/j.jmatprotec.2014.10.003. University of Virginia's Directed Vapor Deposition (DVD) technology Aghdam, M. M.; Morsali, S. R. (2014-01-01). Residual Stresses in Composite Materials. Woodhead Publishing. pp. 233–255. ISBN 9780857092700. Aluminium matrix composite (AMC) inserts for reinforced brake calipers (Archived) Industry Solutions - Metal Matrix Composites - High performance, high strength, metal matrix composite material (Archived) Ratti, A.; R. Gough; M. Hoff; R. Keller; K. Kennedy; R MacGill; J. Staples (1999). "The SNS RFQ Prototype Module" (PDF). Particle Accelerator Conference, 1999. 2 (1): 884–886. doi:10.1109/PAC.1999.795388. ISBN 0-7803-5573-3.