GTBL042-08 GTBL042-Callister-v3 October 4, 2007 11:51

2nd Revised Pages

Chapter 8 Deformation and Strengthening

Mechanisms

In this photomicrograph of a lithium fluoride (LiF) single crystal, the small pyramidal pits represent those positions at which

dislocations intersect the surface. The surface was polished and then chemically treated; these “etch pits” result from localized

chemical attack around the dislocations and indicate the distribution of the dislocations. 750×. (Photomicrograph courtesy of

W. G. Johnston, General Electric Co.)

WHY STUDYDeformation and Strengthening Mechanisms?

With a knowledge of the nature of dislocations and the

role they play in the plastic deformation process, we are

able to understand the underlying mechanisms of the

techniques that are used to strengthen and harden

metals and their alloys. Thus, it becomes possible to

design and tailor the mechanical properties of

materials—for example, the strength or toughness of a

metal–matrix composite.

Also, understanding the mechanisms by which

polymers elastically and plastically deform allows one to

alter and control their moduli of elasticity and strengths

(Sections 8.17 and 8.18).

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