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Kalpakjian SchmidManufacturing Engineering and Technology 2001 Prentice-Hall Page 1-1

CHAPTER 1

The Structure of Metals


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Chapter 1 Outline

Figure 1.1 An outline of the topics described in Chapter 1


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Body-Centered Cubic Crystal Structure

Figure 1.2 The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) singlecrystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1,John Wiley & Sons, 1976.


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Face-Centered Cubic Crystal Structure

Figure 1.3 The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) singlecrystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1,John Wiley & Sons, 1976.


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Hexagonal Close-Packed Crystal Structure

Figure 1.4 The hexagonal close-packed (hcp) crystal structure:(a) unit cell; and (b) singlecrystal with many unit cells.Source: W. G. Moffatt, et al., TheStructure and Properties of

Materials, Vol. 1, John Wiley &Sons, 1976.


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Slip and Twinning

Figure 1.5 Permanent deformation (alsocalled plastic deformation) of a singlecrystal subjected to a shear stress: (a)structure before deformation; and (b)

permanent deformation by slip. The sizeof the b/a ratio influences the magnitudeof the shear stress required to cause slip.

Figure 1.6 (a) Permanent deformation of a singlecrystal under a tensile load. Note that the slip planestend to align themselves in the direction of the pullingforce. This behavior can be simulated using a deck ofcards with a rubber band around them. (b) Twinningin a single crystal in tension.


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Slip Lines and Slip Bands

Figure 1.7 Schematic illustration of slip linesand slip bands in a single crystal (grain)subjected to a shear stress. A slip band consistsof a number of slip planes. The crystal at thecenter of the upper illustration is an individualgrain surrounded by other grains.


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Edge and Screw Dislocations

Figure 1.8 Types of dislocations in a single crystal: (a) edge dislocation; and (b) screw dislocation.Source: (a) After Guy and Hren,Elements of Physical Metallurgy, 1974. (b) L. Van Vlack,Materials for

Engineering, 4th ed., 1980.


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Defects in a Single-Crystal Lattice

Figure 1.9 Schematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional.


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Movement of an Edge Dislocation

Figure 1.10 Movement of an edge dislocation across the crystal lattice under a shear stress.Dislocations help explain why the actual strength of metals in much lower than that predicted by

theory.


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Solidification

Figure 1.11 Schematicillustration of the stagesduring solidification ofmolten metal; each smallsquare represents a unit cell.(a) Nucleation of crystals atrandom sites in the moltenmetal; note that the

crystallographic orientationof each site is different. (b)and (c) Growth of crystals assolidification continues. (d)Solidified metal, showingindividual grains and grain

boundaries; note the differentangles at which neighboringgrains meet each other.

Source: W. Rosenhain.


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Grain Sizes

TABLE 1.1

ASTM No. Grains/mm2

Grains/mm3

3

2

1

0

1

2

3

4

5

6

78

9

10

11

12

1

2

4

8

16

32

64

128

256

512

1,0242,048

4,096

8,200

16,400

32,800

0.7

2

5.6

16

45

128

360

1,020

2,900

8,200

23,00065,000

185,000

520,000

1,500,000

4,200,000


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Preferred Orientation

Figure 1.12 Plastic deformation ofidealized (equiaxed) grains in aspecimen subjected to compression(such as occurs in the rolling or forgingof metals): (a) before deformation; and(b) after deformation. Note htealignment of grain boundaries along ahorizontal direction; this effect isknown as preferred orientation.


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Anisotropy

Figure 1.13 (a) Schematic illustration of a crack in sheet metal that has been subjected to bulging(caused by, for example, pushing a steel ball against the sheet). Note the orientation of the crack withrespect to the rolling direction of the sheet; this sheet is anisotropic. (b) Aluminum sheet with a crack(vertical dark line at the center) developed in a bulge test; the rolling direction of the sheet was vertical.Source: J.S. Kallend, Illinois Institute of Technology.

(b)


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Annealing

Figure 1.14 Schematic illustration of theeffects of recovery, recrystallization, andgrain growth on mechanical propertiesand on the shape and size of grains. Notethe formation of small new grains duringrecrystallization. Source: G. Sachs.


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Homologous Temperature Ranges for VariousProcesses

TABLE 1.2

Process T/Tm

Cold workingWarm working

Hot working

< 0.30.3 to 0.5

> 0.6

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