Page 122 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 4.2 Structure of Alloys l0l

and dies. These properties also enhance the service performance of
the metals when used in machine components (such as gears, cams,
and shafts; Fig. 4.1) or in tools, dies, and molds.
This chapter follows the outline shown in Fig. 4.2, beginning
with the effects of various alloying elements, the solubility of one
element in another, phases, equilibrium phase diagrams, and the
influence of composition, temperature, and time. The chapter also
discusses methods and techniques of heating, quenching, tempering,
and annealing, and describes the characteristics of the equipment
involved.
FIGURE 4.l Cross section of gear teeth
showing induction-hardened surfaces. Source:
TOCCO Div., Park-Ohio Industries, Inc.
lron-Carbon system

iA|i<>yii6§i _ t' s o is
Feffgus, Heat Setgqengrnang, annealing,
< < i t»~ e e 4 treatment norrhalizigig etc

l\/licrostructures
Solid solutions
Substitutional solid solutions
Interstitial solid solutions
Intermetallics
FIGURE 4.2 Outline of topics described in Chapter 4.

4.2 Structure of Alloys

When describing the basic crystal structure of metals in Chapter 1, it was noted that
the atoms are all of the same type, except for the presence of rare impurity atoms.
These metals are known as pure metals, even though they may not be completely
pure. Corninercially pure metals are used for various purposes: aluminum for foil,
copper for electrical conductors, nickel or chromium for plating, and gold for elec-
trical contacts. However, pure metals have somewhat limited properties; these prop-
erties can be enhanced and modified by alloying. An alloy is composed of two or
more chemical elements, at least one of which is a metal. The majority of metals
used in engineering applications are some form of alloy. Alloying consists of two
basic forms: solid solutions and interrnetailic cornpounds.

4.2.l Solid Solutions
Two terms are essential in describing alloys: solute and solvent. The solute is the
minor element (such as salt or sugar) that is added to the solvent, which is the major
element (such as water). In terms of the elements involved in a crystal structure, the