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Manufacturing Processes for Engineering Materials, 5th ed.

Kalpakjian • Schmid

© 2008, Pearson Education

ISBN No. 0-13-227271-7

• Crystal structures, grains and grain boundaries, plastic

deformation, and thermal effects.

• Characteristics and applications of cold, warm, and hot

working of metals.

• Ductile and brittle behavior of materials, modes of failure, and

the effects of various factors on fracture behavior.

• Physical properties of materials and their relievance to mfg

processes.

• General properties and engineering applications of ferrousand nonferrous metals and alloys.

Chapter 3: Structure and Mfg. Properties of Metals

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Turbine Blades




ISBN No. 0-13-227271-7

FIGURE 3.1 Turbine blades for jet engines, manufactured by three different methods: (a) conventionally

cast; (b) directionally solidified, with columnar grains, as can be seen from the vertical streaks; and (c)

single crystal. Although more expensive, single-crystal blades have properties at high temperatures that

are superior to those of other blades. Source: Courtesy of United Technologies Pratt and Whitney.

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Common Crystal Structures

FIGURE 3.2 The body-centered cubic (bcc) crystal

structure: (a) hard-ball model; (b) unit cell; and (c) single

crystal with many unit cells. Common bcc metals include

chromium, titanium, and tungsten. Source: After W.G.

Moffatt.

FIGURE 3.3 The face-centered cubic (fcc) crystal

structure: (a) hard-ball model; (b) unit cell; and (c) singlecrystal with many unit cells. Common fcc metals include

aluminum, copper, gold and silver.Source: After W.G.

Moffatt.

FIGURE 3.4 The hexagonal close-packed (hcp) crystal

structure: (a) unit cell; and (b) single crystal with many

unit cells. Common hcp metals include zinc, magnesium

and cobalt. Source: After W.G. Moffatt.

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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid


ISBN No. 0-13-227271-7

Plastic Deformation in Crystals

FIGURE 3.5 Permanent deformation of a single crystal under a tensile load. The highlighted grid of atoms emphasizesthe motion that occurs within the lattice.(a) Deformation by slip. The b/a ratio influences the magnitude of the shear

stress required to cause slip. Note that the slip planes tend to align themselves in the direction of pulling. (b)

Deformation by twinning, involving generation of a “twin” around a line of symmetry subjected to shear. Note that the

tensile load results in a shear stress in the plane illustrated.

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Shear Stress at Atomic Scale

FIGURE 3.6 Variation of shear stress in moving a plane of

atoms over another plane.

Shear stress:

Leads to:

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Slib Bands in a Single Crystal

FIGURE 3.7 Schematic illustration of slip lines and slipbands in a single crystal subjected to a shear stress. A slip

band consists of a number of slip planes. The crystal at the

center of the upper drawing is an individual grain surrounded

by other grains.

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Normal Stress in a Single Crystal

FIGURE 3.8 Variation of cohesive

stress as a function of distance

between a row of atoms.

Work:

Leads to:

This is ideal or theoretical tensile strength

of metals based on pure atomic cohesion

strength. Actual UTS is likely

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Crystal Defects

FIGURE 3.9 Various defects in a single-

crystal lattice. Vacancy (point defects)Source: After W.G. Moffatt.

FIGURE 3.10 (a) Edge dislocation (1D), a linear

defect at the edge of an extra plane of atoms. (b)Screw dislocation, a helical defect in a three-

dimensional lattice of atoms. Screw dislocations

are so named because the atomic planes form a

spiral ramp. Grain or phase boundaries (2D), voids

or inclusions ((3D).

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Movement of Edge Dislocation

FIGURE 3.11 Movement of an edge dislocation across the crystal lattice under a shear stress.

Dislocations help explain why the actual strength of metals is much lower than that predicted by

atomic theory.

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Grains During Solidification

FIGURE 3.12 Schematic illustration of the various stages during solidification of molten metal. Each small

square represents a unit cell. (a) Nucleation of crystals at random sites in the molten metal. Note that the

crystallographic orientation of each site is different. (b) and (c) Growth of crystals as solidificationcontinues. (d) Solidified metal, showing individual grains and grain boundaries. Note the different angles at

which neighboring grains meet each other. Source: After W. Rosenhain.

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Tensile Stress in Polycrystalline

Material

FIGURE 3.13 Variation of tensile stress across aplane of polycrystalline metal specimen subjected to

tension. Note that the strength exhibited by each

grain depends on its orientation.

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Grain Sizes

TABLE 3.1 Grain sizes.

ASTM Grain Size Number: n is ASTM grain-size number

N is the number of grains per sq inch at a magnificationof 100X (equal to 0.01 sq inch or 0.0645 sq mm)

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Embrittlement & Plastic Deformation

FIGURE 3.14 Embrittlement of copper by lead

and bismuth at 350°C (660°F). Embrittlement

has important effects on the strength, ductility,

and toughness of materials. Source: After W.

Rostoker. When close atomic contact with

certain low-melting-point metals, weakening the

grain boundaries, may result to crack under

very low stress.

FIGURE 3.15 Plastic deformation (cold work) of

idealized (equiaxed) grains in a specimen subjected

to compression, such as is done in rolling or forging

of metals: (a) before deformation; and (b) after

deformation. Note the alignment of grain boundaries

along a horizontal direction.

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Crack Due to Bulging

FIGURE 3.16 (a) Illustration of a crack in sheet metal subjected to bulging, such as by

pushing a steel ball against the sheet. Note the orientation of the crack with respect to therolling direction of the sheet. This material is anisotropic. (b) Aluminum sheet with a crack

(vertical dark line at the center) developed in a bulge test. Source: Courtesy of J.S. Kallend,

Illinois Institute of Technology.

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Recovery, Recrystallization

and Grain Growth

FIGURE 3.17 Schematic illustration of the effects

of recovery, recrystallization, and grain growth on

mechanical properties and shape and size of

grains. Note the formation of small new grains

during recrystallization. Source: After G. Sachs.

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Recrystallization

FIGURE 3.19 The effect of prior cold work on the recrystallized grain

size of alpha brass. Below a critical elongation (strain), typically 5%, no

recrystallization occurs.

FIGURE 3.18 Variation of strength

and hardness with recrystallization

temperature, time, and prior cold

work. Note that the more a metal is

cold worked, the less time it takes

to recrystallize, because of the

higher stored energy from cold

working due to increased

dislocation density.

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Surface Roughness; Homologous

Temperature

FIGURE 3.20 Surface roughness on the

cylindrical surface of an aluminum specimen

subjected to compression. Source: A. Mulc and S.Kalpakjian. Grain growth, larger grain size, results

to rough surface appearance, orange-peel effect.

TABLE 3.2 Homologous Temperature Ranges for

Various Processes. T is working temperature andTm is the melting point of the metal (abs. scale).

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Failure

FIGURE 3.22 Schematic illustration of the types of

fracture in tension: (a) brittle fracture in

polycrystalline metals; (b) shear fracture in ductile

single crystals (see also Fig. 3.5a); (c) ductile cup-

and-cone fracture in polycrystalline metals (see

also Fig. 2.2); (d) complete ductile fracture in

polycrystalline metals, with 100% reduction of area.

FIGURE 3.21 Schematic illustration of types of

failure in materials: (a) necking and fracture of

ductile materials; (b) buckling of ductile materials

under a compressive load; (c) fracture of brittle

materials in compression; (d) cracking on the

barreled surface of ductile materials incompression. (See also Fig. 6.1b)

General types of failure: (1) fracture: ductile/brittle

(2) buckling.

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Ductile Fracture Surface

FIGURE 3.23 Surface of ductile fracture in low-carbon steel, showing dimples.Fracture is usually initiated at impurities, inclusions, or preexisting voids in the

metal. Source: K.-H. Habig and D. Klaffke. Photo courtesy of BAM, Berlin,

Germany.

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Sequence in Necking and Fracture

FIGURE 3.24 Sequence of events in necking and fracture of a tensile-test specimen: (a) early stage of

necking; (b) small voids begin to form within the necked region; (c) voids coalesce, producing an

internal crack; (d) rest of cross-section begins to fail at the periphery by shearing; (e) final fracture

surfaces, known as cup-(top fracture surface) and-cone (bottom surface) fracture.

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Effect of Inclusions

FIGURE 3.25 Schematic illustration of the deformation of soft and hard inclusions and

their effect on void formation in plastic deformation. Note that hard inclusions, because

they do not comply with the overall deformation of the ductile matrix, can cause voids.

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Transition Temperature & Strain

Aging

FIGURE 3.26 Schematic illustration of

transition temperature. Note the narrow

temperature range across which the

behavior of the metal undergoes a major transition.

FIGURE 3.27 Strain aging and its effect on the shapeof the true-stress-true-strain curve for 0.03% C rimmed

steel at 60°C (140°F). Source: A.S. Keh and W.C.

Leslie. Accelerated strain aging by processing at a

higher temperature, e.g. blue brittleness for steels.

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Brittle and Intergranular Fracture

FIGURE 3.29 Intergranular fracture, at two different

magnifications. Grains and grain boundaries are

clearly visible in this micrograph. The fracture path is

along the grain boundaries. Mag 100X and 500X

Source: Courtesy of Packer Engineering.

FIGURE 3.28 Typical fracture surface of steel

that has failed in a brittle manner. The fracture

path is transgranular (through the grains).

Compare this surface with the ductile fracture

surface shown in Fig. 3.23. Source: Courtesyof Packer Engineering.

Defects: Stress α 1 / sqrt(Crack Length)FIGURE 3.23 Surface

of ductile fracture

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Fracture Mode & Surface

FIGURE 3.30 Three modes of fracture for

cracks. Mode I has been studied extensively,

because it is the most commonly observed in

engineering structures and components. Mode IIis rare. Mode III is the tearing process; examples

include opening a pop-top can, tearing a piece of

paper, and cutting materials with a pair of

scissors.

FIGURE 3.31 Typical fatigue fracture surface on metals,

showing beach marks (each has series of striations/ridges).

Most components in machines and engines fail by fatigue and

not by excessive static loading. Source: Courtesy of Packer Engineering.

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Fatigue

FIGURE 3.32 Reduction in fatigue strength of cast steels subjected to various surface-finishing operations. (a)

Effect of surface roughness. Note that the reduction is greater as the surface roughness and strength of the

steel increase. (b) Effect of residual stress, as developed by shot peening. Conversely, the following factors and

processes can reduce fatigue strength: decarburization, surface pits due to corrosion that act as stress raisers,

hydrogen embrittlement, galvanizing, and electroplating (Section 4.5.1). Stress-corrosion cracking (SCC).

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Physical Properties of Materials

TABLE 3.3 Physical Properties of Various

Materials at Room Temperature.

Resistance to Corrosion: (good or bad)

degradation, pitting, galvanic corrosion,

SCC, passivation

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Effect of Carbon on Steel Properties

FIGURE 3.33 Effect of carbon content on

the mechanical properties of carbon steel.

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Annealed Stainless Steels

TABLE 3.4 Room-Temperature Mechanical Properties and Typical

Applications of Annealed Stainless Steels: corrosion resistance, highstrength and ductility, and high chromium content (+oxygen -> Cr-oxide).

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Tool & Die Materials

TABLE 3.5 Basic Types of Tool and Die

Steels.

TABLE 3.5 Typical Tool and Die Materials for Various

Processes.

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Non-Ferrous Alloys in Aircraft Engine

FIGURE 3.34 Cross-section of a jet engine (PW2037) showing various

components and the alloys used in making them. Source: Courtesy of United

Aircraft Pratt & Whitney.

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Aluminum Alloys

TABLE 3.7 Properties of Various Aluminum Alloys at Room Temperature

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Wrought Aluminum Alloys

TABLE 3.8 Manufacturing Properties and Typical Applications of Wrought Aluminum

Alloys.

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Magnesium Alloys

TABLE 3.9 Properties and Typical Forms of Various Wrought Magnesium Alloys.

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Copper & Brass

TABLE 3.10 Properties and Typical Applications of Various Wrought Copper and Brasses.

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Wrought Bronzes

TABLE 3.11 Properties and Typical Applications of Various Wrought

Bronzes.

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Nickel Alloys

TABLE 3.12 Properties and Typical Applications of Various Nickel Alloys (All Alloy Names are Trade

Names).

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Nickel-Base Superalloys

TABLE 3.13 Properties and Typical Applications of Various Nickel-Base Superalloys at 870°C

(1600°F) (All Alloy Names Are Trade Names)

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Titanium Alloys

TABLE 3.14 Properties and Typical Applications of Wrought Titanium Alloys.

Problems 3.36, 3.39, 3.40

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