Materials Behavior for Industry-Basics (1)

7/30/2019 Materials Behavior for Industry-Basics (1)

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BASIC of MATERIALS SCIENCE

The Structure of Materials


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Course Contents

By type of Materials Metals

Polymers (Plastics, Rubber,foams)

Ceramics (glass) Composites

Semiconductors

Protective Coatings

Functional Materials(Sensors)

By Automotive SystemBody (chasis)EngineExhaust System (catalysis)

TrimSuspensionBrakesTiresHybrid SystemsSensorsCoatings (paint)


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Course Contents

By Property-PerformanceCategory

Tribological resistance

Mechanical Strength

Light weight Environmental friendliness

Wear

High Temperature Resistance

Design by ExperimentationFatigue (suspension)Wear (tires)Friction (piston rings)Material resistance

Scratch testsXRD, SEM

Special TopicsSOFC

ThermoelectricsCoatingsHybrid systemsHydrogen usageLithium-ion baterries


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Introduction

What is materials science vs materialsengineering?

Why should we know about it?

Materials drive our society Stone Age Bronze Age Iron Age Now?

Silicon Age? Polymer Age?

Structure, Processing, & Properties, Performancematerials science materials engineering


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ex: hardness vs structure of steel Properties depend on structure

Data obtained from Figs. 10.30(a)and 10.32 with 4 wt% C composition,and from Fig. 11.14 and associateddiscussion, Callister & Rethwisch 8e.Micrographs adapted from (a) Fig.10.19; (b) Fig. 9.30;(c) Fig. 10.33;and (d) Fig. 10.21, Callister & Rethwisch 8e.

ex: structure vs cooling rate of steel Processing can change structure

Structure, Processing, & Properties

Hardness(BHN)

Cooling Rate (C/s)

100

2 00

3 00

4 00

5 00

6 00

0.01 0.1 1 10 100 1000

(d)

30mm(c)

4mm

(b)

30mm

(a)

30mm


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Types of Materials Metals:

Strong, ductile High thermal & electrical conductivity

Opaque, reflective.

Polymers/plastics: Covalent bonding sharing of es

Soft, ductile, low strength, low density Thermal & electrical insulators

Optically translucent or transparent.

Ceramics: ionic bonding (refractory) compounds of metallic & non-

metallic elements (oxides, carbides, nitrides, sulfides) Brittle, glassy, elastic

Non-conducting (insulators)


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1. Pick Application Determine required Properties

Processing: changes structure and overall shapeex: casting, sintering, vapor deposition, doping

forming, joining, annealing.

Properties: mechanical, electrical, thermal,magnetic, optical, deteriorative.

Material: structure, composition.2. Properties

Identify candidate Material(s)

3. Material Identify required Processing

The Materials Selection Process


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ELECTRICAL Electrical Resistivity of Copper:

Adding impurity atoms to Cu increases resistivity. Deforming Cu increases resistivity.

Adapted from Fig. 18.8, Callister &Rethwisch 8e. (Fig. 18.8 adapted from:J.O. Linde,Ann Physik5, 219 (1932); andC.A. Wert and R.M. Thomson, Physics ofSolids, 2nd edition, McGraw-HillCompany, New York, 1970.)

T(C)-200 -100 0

1

2

3

4

5

6

Resistivity,

r

(10-8O

hm

-m)

0


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DETERIORATIVE Stress & Saltwater...

-- causes cracks!

Adapted from chapter-opening photograph, Chapter16, Callister & Rethwisch 3e.(from Marine Corrosion, Causes, and Prevention,

John Wiley and Sons, Inc., 1975.)4mm

-- material:7150-T651 Al "alloy"(Zn,Cu,Mg,Zr)

Adapted from Fig. 11.26,Callister & Rethwisch 8e. (Provided courtesy of G.H. Narayanan

and A.G. Miller, Boeing Commercial Airplane Company.)

Heat treatment: slows

crack speed in salt water!

Adapted from Fig. 11.20(b), R.W. Hertzberg, "Deformation and FractureMechanics of Engineering Materials" (4th ed.), p. 505, John Wiley andSons, 1996. (Original source: Markus O. Speidel, Brown Boveri Co.)

held at

160C for 1 hrbefore testing

increasing loadcrack

speed(m/s) as-is

10 -10

10 -8

Alloy 7178 tested insaturated aqueous NaCl

solution at 23C


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Use the right material for the job.

Understand the relation between properties,

structure, and processing.

Recognize new design opportunities offeredby materials selection

Develop entrepreneurial projects.

Course Goals:SUMMARY


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Application of the tetrahedron of materials science and engineering to sheet steels for

automotive chassis. Note that the microstructure-synthesis and processing-composition

are all interconnected and affect the performance-to-cost ratio

2003Brooks/ColePubli

shing/ThomsonLearning


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What is Materials Science and

Engineering? Materials Science and Engineering

Composition means the chemical make-up of a material.

Structure means a description of the arrangements of atoms orions in a material.

Synthesis is the process by which materials are made fromnaturally occurring or other chemicals.

Processing means different ways for shaping materials into

useful components or changing their properties.


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2003 Brooks/Cole Publishing / Thomson

Learning

Figure 2.23 Atoms or ions areseparated by an equilibrium

spacing that corresponds to

the minimum inter-atomic

energy for a pair of atoms or

ions (or when zero force is

acting to repel or attract the

atoms or ions)


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Cermicos

Polimeros

Metales


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(c) 2003 Brooks/Cole Publishing / Thomson Learning

Figure 3.1 Levels of atomicarrangements in materials: (a)Inert monoatomic gases haveno regular ordering of atoms:(b,c) Some materials, includingwater vapor, nitrogen gas,amorphous silicon and silicate

glass have short-range order.(d) Metals, alloys, manyceramics and some polymershave regular ordering ofatoms/ions that extendsthrough the material.


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Unit Cell and Crystals DuringSolidification

UNIT CELLS, and CRYSTALS


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SolidificationSchematic illustration of the

stages during solidificationof molten metal; each smallsquare represents a unit cell.(a) Nucleation of crystals atrandom sites in the moltenmetal; note that thecrystallographic orientationof each site is different. (b)

and (c) Growth of crystalsas solidification continues.(d) Solidified metal,showing individual grainsand grain boundaries; notethe different angles at whichneighboring grains meeteach other. Source: W.

Rosenhain.


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(a) Photograph of a silicon single crystal. (b)Micrograph of a polycrystalline stainless steelshowing grains and grain boundaries (CourtesyDr. M. Hua, Dr. I. Garcia, and Dr. A.J. Deardo.)


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(c) 2003 Brooks/Cole Publishing / Thomson Learning

Figure 3.11 The fourteentypes of Bravais latticesgrouped in seven crystalsystems. The actual unitcell for a hexagonalsystem is shown inFigures 3.12 and 3.16.


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Determine the relationship between the atomic radius and the latticeparameter in SC, BCC, and FCC structures when one atom is located ateach lattice point.

ExampleDetermining the Relationship between Atomic

Radius and Lattice Parameters

(c) 2003 Brooks/Cole Publishing / Thomson

Learning

Figure 3.14 The relationships between the atomic radius and the Lattice parameter incubic systems (for Example 3.2).


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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) single

crystal 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) single

crystal 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 hexagonalclose-packed (hcp) crystalstructure: (a) unit cell; and (b)single crystal with many unitcells. Source: W. G. Moffatt, etal., The Structure and

Properties of Materials, Vol. 1,

John Wiley & Sons, 1976.


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Allotropy - The characteristic of an element being able to exist in morethan one crystal structure, depending on temperature and pressure.

Polymorphism - Compounds exhibiting more than one type of crystal

structure.

Both are similar terms, allotropy is regularly used for pure metals, whereaspolymorphism is a general term.

Allotropic or Polymorphic Transformations


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Figure 3.17 Oxygen gas sensors used in cars and otherapplications are based on stabilized zirconia compositions.(Image courtesy of Bosch Robert Bosch GmbH.)

Case Study: Oxygen gas sensors of Stabilized Zirconia

The principle: The addition of for example, yttria, to pure zirconia replaces some of theZr4+ ions in the zirconia lattice with Y3+ ions. This produces oxygen vacancies, as three O2-ions replace four O2- ions. It also permits yttrium stabilized zirconia to conduct O2- ions(and thus conduct an electrical current), provided there is sufficient vacancy sitemobility, a property that increases with temperature. This ability to conduct O2- ionsmakes yttria-stabilized zirconia well suited to use in solid oxide fuel cells, although it

requires that they operate at high enough temperatures


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Yttria-stabilized zirconia (YSZ) is a zirconium-oxide based ceramic, in which the

particular crystal structure of zirconium oxide is made stable at room temperature byan addition ofyttrium oxide. These oxides are commonly called "zirconia" (ZrO2) and"yttria" (Y2O3), hence the name.

Yttria-stabilized zirconia (YSZ)
http://en.wikipedia.org/wiki/Zirconium_dioxidehttp://en.wikipedia.org/wiki/Yttrium_oxidehttp://en.wikipedia.org/wiki/Zirconiumhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Yttriumhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Yttriumhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Zirconiumhttp://en.wikipedia.org/wiki/Yttrium_oxidehttp://en.wikipedia.org/wiki/Zirconium_dioxidehttp://en.wikipedia.org/wiki/Zirconium_dioxidehttp://en.wikipedia.org/wiki/Zirconium_dioxide


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Calculate the percent volume change as zirconia transforms from atetragonal to monoclinic structure.[9] The lattice constants for themonoclinic unit cells are: a = 5.156, b = 5.191, and c = 5.304 ,respectively. The angle for the monoclinic unit cell is 98.9. The lattice

constants for the tetragonal unit cell are a = 5.094 and c = 5.304 ,respectively.[10] Does the zirconia expand or contract during thistransformation? What is the implication of this transformation on themechanical properties of zirconia ceramics?

Example 3.5Calculating Volume Changes in Polymorphs of

Zirconia
http://www.google.com.ec/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=E98dOfCzoO1fuM&tbnid=v37IebyKiTpDtM:&ved=0CAUQjRw&url=http://commons.wikimedia.org/wiki/File:Monoclinic-base-centered.png&ei=n6X2UYH_Ncfd4AOn9IGIBA&bvm=bv.49784469,d.dmg&psig=AFQjCNH1f0R7NA0PaQOqPdJq5vB4BWbj_w&ust=1375205112606160


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Example 3.5 SOLUTION

The volume of a tetragonal unit cell is given byV= a2c = (5.094)2 (5.304) = 134.33 3.

The volume of a monoclinic unit cell is given byV= abc sin = (5.156) (5.191) (5.304) sin(98.9) = 140.25 3.

Thus, there is an expansion of the unit cell as ZrO2 transforms from a tetragonal tomonoclinic form.

The percent change in volume= (final volume initial volume)/(initial volume) 100

= (140.25 - 134.33 3)/140.25 3 * 100 = 4.21%.

Most ceramics are very brittle and cannot withstand more than a 0.1%

change in volume. The conclusion here is that ZrO2 ceramics cannot be used intheir monoclinic form since, when zirconia does transform to the tetragonal form,it will most likely fracture. Therefore, ZrO2 is often stabilized in a cubic form usingdifferent additives such as CaO, MgO, and Y2O3.
http://www.google.com.ec/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=E98dOfCzoO1fuM&tbnid=v37IebyKiTpDtM:&ved=0CAUQjRw&url=http://commons.wikimedia.org/wiki/File:Monoclinic-base-centered.png&ei=n6X2UYH_Ncfd4AOn9IGIBA&bvm=bv.49784469,d.dmg&psig=AFQjCNH1f0R7NA0PaQOqPdJq5vB4BWbj_w&ust=1375205112606160


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Point defects - Imperfections, such as vacancies, that are locatedtypically at one (in some cases a few) sites in the crystal.

Extended defects - Defects that involve several atoms/ions and thusoccur over a finite volume of the crystalline material (e.g., dislocations,stacking faults, etc.).

Vacancy - An atom or an ion missing from its regular crystallographic site.

Interstitial defect - A point defect produced when an atom is placed intothe crystal at a site that is normally not a lattice point.

Substitutional defect - A point defect produced when an atom isremoved from a regular lattice point and replaced with a different atom,usually of a different size.

Point Defects


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(c)2003Brooks/ColePublish

ing/ThomsonLearning

Figure : Point defects: (a) vacancy, (b) interstitial atom, (c) small substitutional atom, (d) large

substitutional atom, (e) Frenkel defect, (f) Schottky defect. All of these defects disrupt the

perfect arrangement of the surrounding atoms.


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Defects in a Single-Crystal Lattice

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


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Edge and ScrewDislocations

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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Movement of an EdgeDislocation

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 bytheory.

ACTUAL PLASTIC

DEFORMATION (MIGHT BE A

CRITERIUM OF FAILURE)


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Slip and TwinningFigure. Permanent deformation (alsocalled plastic deformation) of a single

crystal 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 .(a) Permanent deformation of a single crystal under a tensileload. Note that the slip planes tend to align themselves in thedirection of the pulling force. This behavior can be simulated using adeck of cards with a rubber band around them. (b) Twinning in asingle crystal in tension.


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Slip Lines and Slip BandsFigure Schematic illustration of slip lines and

slip bands in a single crystal (grain) subjectedto a shear stress. A slip band consists of anumber of slip planes. The crystal at the centerof the upper illustration is an individual grainsurrounded by other grains.


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Alloying Effects on DislocationMovement

Effect of a smallsubstitutional atom

Effect of a LARGEsubstitutional atom

Effect of anintersticial atom


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SolidificationFigure 1.11 Schematic

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

of each site is different. (b)and (c) Growth of crystalsas solidification continues.(d) Solidified metal,showing individual grainsand grain boundaries; notethe different angles at whichneighboring grains meeteach other. Source: W.Rosenhain.


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Grain Sizes

TABLE 1.1ASTM No. Grains/mm

2Grains/mm

3

3

2

1

0

1

2

3

4

5

6

7

8

9

10

11

12

1

2

4

8

16

32

64

128

256

512

1,024

2,048

4,096

8,200

16,400

32,800

0.7

2

5.6

16

45

128

360

1,020

2,900

8,200

23,000

65,000

185,000

520,000

1,500,000

4,200,000


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Grain Sizes

G i Si


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Grain Sizes

IMAGE ANALYSIS


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IMAGE ANALYSIS


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(c)2003Brooks/ColePub

lishing/ThomsonLearning

Figure . The effect of grain size on the yield strength of steel atroom temperature.


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The yield strength of mild steel with an average grain size of 0.05 mm is 20,000psi. The yield stress of the same steel with a grain size of 0.007 mm is 40,000psi. What will be the average grain size of the same steel with a yield stress of30,000 psi? Assume the Hall-Petch equation is valid and that changes in theobserved yield stress are due to changes in dislocation density.

Example SOLUTION

Design of a Mild Steel

Thus, for a grain size of 0.05 mm the yield stress is

20 6.895 MPa = 137.9 MPa.

(Note:1,000 psi = 6.895 MPa). Using the Hall-Petch equation


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Example 4.13 SOLUTION (Continued)

For the grain size of 0.007 mm, the yield stress is 40 6.895 MPa = 275.8MPa. Therefore, again using the Hall-Petch equation:

Solving these two equations K = 18.43 MPa-mm1/2, and 0 = 55.5 MPa.Now we have the Hall-Petch equation as

y= 55.5 + 18.43 d-1/2

If we want a yield stress of 30,000 psi or 30 6.895 = 206.9 MPa, thegrain size will be 0.0148 mm.


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Figure 4.18 Microstructure of palladium (x

100). (From ASM Handbook, Vol. 9,Metallography and Microstructure (1985),

ASM International, Materials Park, OH

44073.)

Plastic deformation of polycrystalline


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2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under

license.

Plastic deformation of polycrystalline

metals

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Figure During hot working, the elongated anisotropic grains immediately

recrystallize. If the hot-working temperature is properly controlled, the final hot-

worked grain size can be very fine

Cold Working:


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Cold Working:Increase in Strength due to:

* Entanglement of dislocations with grain boundaries*The more the grain boundaries, the higher the strength,

therefore SMALLER GRAIN SIZE increases strength

Preferred Orientation

Figure 1.12 Plastic deformation ofidealized (equiaxed) grains in aspecimen subjected to compression(such as occurs in the rolling orforging of metals): (a) beforedeformation; and (b) afterdeformation. Note the alignment ofgrain boundaries along a horizontaldirection; this effect is known as

preferred orientation. ProducingANISOTROPY.


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AnisotropyIn Ductility

Figure (a) Schematic illustration of a crack in sheet metal that has been subjected to bulging (causedby, for example, pushing a steel ball against the sheet). Note the orientation of the crack with respectto 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 wasvertical. Source: J.S. Kallend, Illinois Institute of Technology.

(b)

Annealing: Recovery


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Annealing: Recovery,Recrystallization and Grain Growth

Figure. Schematic illustration of theeffects of recovery, recrystallization, andgrain growth on mechanical propertiesand on the shape and size of grains.

Note the formation of small new grainsduring recrystallization. Source: G.Sachs.

*Recrystallization is a DIFFUSION

process

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Materials Behavior for Industry-Basics (1)