61 Introduction

Just as plastics and ceramics can be composited, so can metals. One of the newest class of commercially available materials are metal matrix composites (MMCs). These composites are analogous to organic (plastic) and ceramic composites because they are also composed of a reinforcement, usually a fiber, and a matrix. In the case of MMCs, as indicated by the name, the matrix is one or more

Handbook of Advanced Materials Edited by James K. Wessel ISBN 0-471-45475-3 Copyright © 2004 John Wiley & Sons, Inc.

TABLE 6.1 Composites

Range of Common Metal Matrix

Density, kg/m3 2000-5500

Tensile strength, 400-1000

room temperature, MPa

Bend strength, MPa 600-1300

Compression strength, MPa 500-1000

Elastic modulus, GPa 120-300

TABLE 6.2 Properties of Carbon Fiber-Reinforced Aluminum Matrix MMC

Tensile strength, MPa 825

Bend strength, MPa 1300

Elastic modulus, GPa 200

metals. Metal matrices include aluminum, magnesium, nickel, titanium, copper, and other metals. The fiber composition also varies, but the most common are ceramic, usually carbon or silicon carbide. Although they can be reinforced with particulates, MMCs are typically reinforced with fibers in continuous strands or chopped or whiskerlike. Because the matrix and fiber selections are many and varied, a wide range of properties result from the many possible formulas. Table 6.1 gives the range of properties due to the range of compositions.

A popular MMC is carbon-fiber-reinforced aluminum. Table 6.2 gives the properties of one of these compositions.

Composite composition can be further tailored to provide other properties required by specific applications. For instance, weldability can be altered. If the MMCs need to be welded to titanium, titanium is added to the MMC composition to facilitate weldability.

Metal matrix composites can operate at temperatures up to 800°C (1470°F), between that of plastic matrix composites and continuous fiber ceramic composites. At this temperature range and lower, MMCs are used where low weight, stiffness, toughness, fatigue resistance, erosion resistance, high thermal conductivity, and dimensional stability are desired. This has led to applications in aerospace, electronic, automotive, and other industrial applications.

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