Page 35 - Materials Science and Engineering An Introduction

1.4 Classification of Materials • 7

Figure 1.4 40
Bar chart of room- Metals
temperature density 20 Platinum
values for various
metals, ceramics, 10 Silver Ceramics
Density (g/cm 3 ) (logarithmic scale) 1.0 Aluminum SiC,Si N 4 PTFE PS CFRC
polymers, and 8 Copper
Iron/Steel
composite materials. 6 Titanium ZrO 2 Al O Polymers Composites
2 3
4
3
Glass
GFRC
2
Concrete
Magnesium
PVC
PE
0.8
Rubber
0.6
0.4
0.2 Woods
0.1
Metals
Metals are composed of one or more metallic elements (e.g., iron, aluminum, copper,
titanium, gold, nickel), and often also nonmetallic elements (e.g., carbon, nitrogen,
8
oxygen) in relatively small amounts. Atoms in metals and their alloys are arranged in a
very orderly manner (as discussed in Chapter 3) and are relatively dense in comparison
to the ceramics and polymers (Figure 1.4). With regard to mechanical characteristics,
these materials are relatively stiff (Figure 1.5) and strong (Figure 1.6), yet are ductile
(i.e., capable of large amounts of deformation without fracture), and are resistant to
fracture (Figure 1.7), which accounts for their widespread use in structural applications.
Tutorial Video: Metallic materials have large numbers of nonlocalized electrons—that is, these electrons
Metals
are not bound to particular atoms. Many properties of metals are directly attributable
to these electrons. For example, metals are extremely good conductors of electricity

Figure 1.5
Bar chart of room- Metals Ceramics
temperature stiffness 1000 Composites
Stiffness [elastic (or Young’s) modulus (in units of gigapascals)] (logarithmic scale) 1.0 PVC PS, Nylon
(i.e., elastic modulus) Tungsten SiC 2 3
AI O
Iron/Steel
values for various 100 Titanium Si N 4 CFRC
3
metals, ceramics, Aluminum ZrO 2 GFRC
polymers, and Magnesium Glass
Concrete
composite materials. 10 Polymers Woods

PTFE
PE
0.1

0.01

0.001 Rubbers

8 The term metal alloy refers to a metallic substance that is composed of two or more elements.