21 Definition Of Advanced Ceramics

We live in the "age of engineered materials." The properties of materials are either selected or developed to meet the needs of specific applications. Ceramics are a very broad class of materials with a wide range of properties [1]. Some advanced ceramics have special optical, electrical, or magnetic properties. Others have special mechanical or thermal properties. The focus of this chapter and the

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

next chapter will be on ceramics for structural applications where the mechanical and thermal properties are especially important.

Structural applications have varied material requirements. Some require high hardness to provide wear resistance, especially industrial applications that involve sliding, rolling, and fluid or particulate flow. Others require high strength to resist mechanical stresses or thermal stresses. Examples include bearings, cutting tools, and heat engine components. Others require high-temperature stability, corrosion resistance, or thermal shock resistance.

Several categories of advanced ceramics are discussed in this chapter: (1) monolithic (noncomposite) polycrystalline ceramics, (2) self-reinforced ceramics with composite microstructures, and (3) particle-reinforced or whisker-reinforced ceramic matrix composites. The subsequent chapter addresses continuous fiber-reinforced ceramic matrix composites.

Dramatic advances have occurred in ceramics technology in recent years [2, 3]. New and improved ceramics are now available that have much higher strength and toughness than prior ceramics. New design methods have been developed—especially through the use of finite-element codes for thermal and stress analysis—that are leading to substantial improvements in reliability and reduction in risk. This chapter describes some of the advances in key ceramic materials and reviews some of the success stories of applying these ceramics to challenging applications.

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