"[C]ompanies produce a class of structural materials called metal matrix composites (MMCs) that blend the technologies of metal alloys with engineered resin-matrix substances such as carbon fiber. Unlike alloys, which combine their elements at a molecular level, MMCs consist of a base metal (aluminum is common) reinforced with bits of higher-strength materials, such as silicon carbide, held in suspension in the metal matrix. The result is a material that can be stronger, stiffer, and lighter than its base metal.
"Univega Unveils Boralyn.
Prior to January `92 Boraylin (pronounced bore-Al´-in) was a classified defense material used in missile fuselages and the ballistic armor sheeting of Apache helicopters and M-1 tanks. The weldable MMC comprises particulates of titanium and boron carbide (the hardest man-made substance, equal to diamond), suspended in an aluminum base. The resulting material is 40% lighter than titanium, 83% stiffer than steel, and ductile enough to avoid the catastrophic failures possible with aluminum. The material's crystalline structure is also said to diffuse road/trail shock better than straight metal."
John Kukoda, Bicycling, Nov. 1993, p. 88.
| Layer Two|
"The Allison Gas Turbine division of General Motors achieved a milestone a year ago by making the first rotating part, a compressor ring, from a titanium alloy embedded with silicon carbide fibers. The thin ring, which holds compressor blades on the engine shaft, weighs 10 pounds and replaces a nearly 60-pound solid disk. Because metal-matrix composites are stronger than the alloy parts, fewer rotors are needed. `You can get a rotor that runs faster and one that is able to achieve higher pressures,' says Ronald E. York, Allison's director for advanced engine projects.
"Allison made the ring by interleaving helical coils of titanium with others that contain the woven fibers. The coils are then squeezed together at high temperatures and pressures, a process York compares with fusing Slinkies that are sandwiched together. Designing the coils severely challenged Allison materials and structural engineers: each fiber has to be carefully oriented within the metal matrix to provide the maximum resistance to centrifugal forces generated as the rotor turns."
--- Scientific American, December, 1992
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