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Internal combustion engines are made from a wide variety of materials. These materials must contain the fuel and combustion pressures, transmit forces to the drivetrain, deliver electrical power, and give form and structure to the engine. In the context of this chapter, some of those materials must withstand bearing pressures and rub smoothly and reliably, without seizing or excessive wear, for thousands of hours. Although bronzes and other nonferrous alloys are used, by far, iron-based metals and alloys, particularly gray cast iron, have comprised the major bearing materials. Cast iron remains available in bulk quantities, is relative inexpensive, and is familiar to engine makers. However, with a density of 7.1–7.7 g/cm3, cast iron parts are more than 1.6 times heavier than titanium, 2.5 times heavier than aluminum, and 4.2 times heavier than magnesium parts of equal size. With a drive toward reducing the weight of engines to improve fuel economy, vehicle designers are motivated to find cost-competitive, lighter weight materials for engines and drivetrains that function well in advanced engines and drivetrains. Engine designers have historically been interested in finding workable alternatives to cast iron for more than three quarters of a century. As early as 1923, Audi announced an aluminum alloy engine and became an early leader in applying lightweight alloys to engines . By 2006, the average aluminum content in U.S. automobiles was 319 lb (149 kg), a nearly 24 % increase over the preceding 5 years . Most of this substitution was in the area of structural materials, but lightweight alloys are not ideally suited for tribocomponents such as engine castings, valvetrains, fuel injector plungers, roller followers, and disc brakes. This is mainly because of high contact pressures for the valvetrain components.
Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN
Tung, Simon C.
RT Vanderbilt Company, Norwalk, CT