Calculate the ipf for uo2, which has the caf2 structure shown in the figure below.

Introduction to MaterIals scIence for engIneers

James F. Shackelford University of California, Davis

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Cover photo: The scanning electron microscope (SEM) is a powerful tool for inspecting materials in order to better understand their performance in engineering designs. In this SEM image of a carbon fiber-reinforced ceramic brake disc, the silicon carbide matrix is shown in yellow and carbon fibers in blue. This composite material provides features of both materials––the hardness and abrasion resistance of silicon carbide with the stress absorbing character of the embedded carbon fibers. The ceramic composite can last four times longer than a conventional steel brake disc.

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Library of Congress Cataloging-in-Publication Data Shackelford, James F. Introduction to materials science for engineers / James F. Shackelford, University of California, Davis. — Eighth Edition. pages cm ISBN 978-0-13-382665-4 — ISBN 0-13-382665-1 1. Materials. I. Title. TA403.S515 2014 620.1'1—dc23 2013048426

10 9 8 7 6 5 4 3 2 1

ISBN-13: 978-0-13-382665-4 ISBN-10: 0-13-382665-1

Dedicated to Penelope, Scott, Megumi, and Mia

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contents

Preface ix

About the Author xvi

1 Materials for Engineering 1

1.1 the Material World 1 1.2 Materials science and engineering 2 1.3 six Materials that changed Your World 3

steel BrIDges— IntroDUcIng Metals 3

lUcalox laMPs— IntroDUcIng ceraMIcs 4

oPtIcal fIBers— IntroDUcIng glasses 9

nYlon ParacHUtes— IntroDUcIng PolYMers 10

Kevlar®-reInforceD tIres— IntroDUcIng coMPosItes 13

sIlIcon cHIPs— IntroDUcIng seMIconDUctors 14

1.4 Processing and selecting Materials 15 1.5 looking at Materials by Powers of ten 17

PArt I the Fundamentals

2 Atomic Bonding 23

2.1 atomic structure 23 2.2 the Ionic Bond 29

coorDInatIon nUMBer 33

2.3 the covalent Bond 41 2.4 the Metallic Bond 47 2.5 the secondary, or van der Waals, Bond 49 2.6 Materials— the Bonding classification 52

3 Crystalline Structure— Perfection 59

3.1 seven systems and fourteen lattices 59 3.2 Metal structures 63 3.3 ceramic structures 67

3.4 Polymeric structures 76 3.5 semiconductor structures 77 3.6 lattice Positions, Directions, and Planes 81 3.7 x- ray Diffraction 93

4 Crystal Defects and Noncrystalline Structure— Imperfection 104

4.1 the solid solution— chemical Imperfection 104 4.2 Point Defects— Zero- Dimensional

Imperfections 110 4.3 linear Defects, or Dislocations— one- Dimensional

Imperfections 112 4.4 Planar Defects— two- Dimensional

Imperfections 114 4.5 noncrystalline solids— three- Dimensional

Imperfections 118

5 Diffusion 126

5.1 thermally activated Processes 126 5.2 thermal Production of Point Defects 130 5.3 Point Defects and solid- state Diffusion 132 5.4 steady- state Diffusion 142 5.5 alternate Diffusion Paths 146

6 Mechanical Behavior 152

6.1 stress versus strain 152 Metals 153

ceraMIcs anD glasses 164

PolYMers 168

6.2 elastic Deformation 173 6.3 Plastic Deformation 174 6.4 Hardness 181 6.5 creep and stress relaxation 185

vi Contents

6.6 viscoelastic Deformation 192 InorganIc glasses 194

organIc PolYMers 196

elastoMers 199

7 thermal Behavior 210

7.1 Heat capacity 210 7.2 thermal expansion 213 7.3 thermal conductivity 216 7.4 thermal shock 221

8 Failure Analysis and Prevention 227

8.1 Impact energy 228 8.2 fracture toughness 233 8.3 fatigue 237 8.4 nondestructive testing 246 8.5 failure analysis and Prevention 249

9 Phase Diagrams— Equilibrium Microstructural Development 257

9.1 the Phase rule 258 9.2 the Phase Diagram 261

coMPlete solID solUtIon 262

eUtectIc DIagraM WItH no solID solUtIon 265

eUtectIc DIagraM WItH lIMIteD solID solUtIon 267

eUtectoID DIagraM 270

PerItectIc DIagraM 271

general BInarY DIagraMs 275

9.3 the lever rule 281 9.4 Microstructural Development During slow

cooling 285

10 Kinetics— Heat treatment 304

10.1 time— the third Dimension 304 10.2 the ttt Diagram 309

DIffUsIonal transforMatIons 310

DIffUsIonless (MartensItIc) transforMatIons 311

Heat treatMent of steel 316

10.3 Hardenability 324 10.4 Precipitation Hardening 327 10.5 annealing 331

colD WorK 331

recoverY 332

recrYstallIZatIon 332

graIn groWtH 334

10.6 the Kinetics of Phase transformations for nonmetals 335

PArt II Materials and their Applications

11 Structural Materials— Metals, Ceramics, and Glasses 349

11.1 Metals 349 ferroUs alloYs 350

nonferroUs alloYs 356

11.2 ceramics and glasses 360 ceraMIcs— crYstallIne MaterIals 361

glasses— noncrYstallIne MaterIals 362

glass- ceraMIcs 364

11.3 Processing the structural Materials 366 ProcessIng of Metals 367

ProcessIng of ceraMIcs anD glasses 374

12 Structural Materials— Polymers and Composites 383

12.1 Polymers 383 PolYMerIZatIon 384

strUctUral featUres of PolYMers 389

tHerMoPlastIc PolYMers 393

tHerMosettIng PolYMers 394

aDDItIves 396

12.2 composites 398 fIBer- reInforceD coMPosItes 398

aggregate coMPosItes 404

ProPertY averagIng 406

MecHanIcal ProPertIes of coMPosItes 412

12.3 Processing the structural Materials 417 ProcessIng of PolYMers 417

ProcessIng of coMPosItes 420

13 Electronic Materials 429

13.1 charge carriers and conduction 430 13.2 energy levels and energy Bands 434

Contents vii

13.3 conductors 440 tHerMocoUPles 443

sUPerconDUctors 444

13.4 Insulators 452 ferroelectrIcs 453

PIeZoelectrIcs 456

13.5 semiconductors 460 IntrInsIc, eleMental seMIconDUctors 461

extrInsIc, eleMental seMIconDUctors 466

coMPoUnD seMIconDUctors 478

ProcessIng of seMIconDUctors 482

seMIconDUctor DevIces 485

13.6 composites 495 13.7 electrical classification of Materials 496

14 Optical and Magnetic Materials 504

14.1 optical Materials 505 oPtIcal ProPertIes 508

oPtIcal sYsteMs anD DevIces 518

14.2 Magnetic Materials 526 ferroMagnetIsM 530

ferrIMagnetIsM 536

MetallIc Magnets 540

ceraMIc Magnets 546

15 Materials in Engineering Design 557

15.1 Material Properties— engineering Design Parameters 557

15.2 selection of structural Materials— case studies 562 MaterIals for HIP- anD Knee- JoInt rePlaceMent 563

Metal sUBstItUtIon WItH coMPosItes 566

15.3 selection of electronic, optical, and Magnetic Materials— case studies 567 lIgHt- eMIttIng DIoDe 568

glass for sMart PHone anD taBlet toUcH screens 571

aMorPHoUs Metal for electrIc- PoWer DIstrIBUtIon 572

15.4 Materials and our environment 573 envIronMental DegraDatIon of MaterIals 573

envIronMental asPects of DesIgn 589

recYclIng 592

APPENDIx 1

Physical and Chemical Data for the Elements A- 1

APPENDIx 2

Atomic and Ionic radii of the Elements A- 4

APPENDIx 3

Constants and Conversion Factors A- 7

APPENDIx 4

Properties of the Structural Materials A- 8

APPENDIx 5

Properties of the Electronic, Optical, and Magnetic Materials A- 17

APPENDIx 6

Glossary A- 22

Answers to Practice Problems (PP) and Odd-Numbered Problems AN-1

Index I-1

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ix

This book is designed for a first course in engineering materials. The field that covers this area of the engineering profession has come to be known as “materi- als science and engineering.” To me, this label serves two important functions. First, it is an accurate description of the balance between scientific principles and practical engineering that is required in selecting the proper materials for modern technology. Second, it gives us a guide to organizing this book. After a short introductory chapter, “science” serves as a label for Part I on “The Fun- damentals.” Chapters 2 through 10 cover various topics in applied physics and chemistry. These are the foundation for understanding the principles of “mate- rials science.” I assume that some students take this course at the freshman or sophomore level and may not yet have taken their required coursework in chem- istry and physics. As a result, Part I is intended to be self- contained. A previous course in chemistry or physics is certainly helpful, but should not be necessary. If an entire class has finished freshman chemistry, Chapter 2 (atomic bonding) could be left as optional reading, but it is important not to overlook the role of bonding in defining the fundamental types of engineering materials. The remain- ing chapters in Part I are less optional, as they describe the key topics of materials science. Chapter 3 outlines the ideal, crystalline structures of important materi- als. Chapter 4 introduces the structural imperfections found in real, engineering materials. These structural defects are the bases of solid- state diffusion (Chap- ter 5) and plastic deformation in metals (Chapter 6). Chapter 6 also includes a broad range of mechanical behavior for various engineering materials. Similarly, Chapter 7 covers the thermal behavior of these materials. Subjecting materials to various mechanical and thermal processes can lead to their failure, the subject of Chapter 8. In addition, the systematic analysis of material failures can lead to the prevention of future catastrophes. Chapters 9 and 10 are especially important in providing a bridge between “materials science” and “materials engineering.” Phase diagrams (Chapter 9) are an effective tool for describing the equilibrium microstructures of practical engineering materials. Instructors will note that this topic is introduced in a descriptive and empirical way. Since some students in this course may not have taken a course in thermodynamics, I avoid the use of the free- energy property. Kinetics (Chapter 10) is the foundation of the heat treat- ment of engineering materials.

The words “materials engineering” give us a label for Part II of the book that deals with “Materials and Their Applications.” First, we discuss the five categories of structural materials: metals, ceramics, and glasses (Chapter 11) and polymers and composites (Chapter 12). In both chapters, we give examples of each type of structural material and describe their processing, the techniques used to produce the materials. In Chapter 13, we discuss electronic materials and discover a sixth

Preface

x Preface

category of materials, semiconductors, based on an electrical rather than bond- ing classification system. Metals are generally good electrical conductors, while ceramics, glasses, and polymers are generally good insulators, and semiconduc- tors are intermediate. The exceptional discovery of superconductivity in certain ceramic materials at relatively high temperatures augments the long- standing use of superconductivity in certain metals at very low temperatures. Chapter 14 covers optical behavior that determines the application of many materials, from traditional glass windows to some of the latest advances in telecommunications. A wide variety of materials is also discussed in Chapter 14. Traditional metallic and ceramic magnets are being supplemented by superconducting metals and ceramics, which can provide some intriguing design applications based on their magnetic behavior. Finally, in Chapter 15 (Materials in Engineering Design), we see that our previous discussions of properties have left us with “design param- eters.” Herein lies a final bridge between the principles of materials science and the use of those materials in modern engineering designs. We also must note that chemical degradation, radiation damage, wear, and recycling must be considered in making a final judgment on a materials application.

I hope that students and instructors alike will find what I have attempted to produce: a clear and readable textbook organized around the title of this impor- tant branch of engineering. It is also worth noting that materials play a central role across the broad spectrum of contemporary science and technology. In the report Science: The End of the Frontier? from the American Association for the Advancement of Science, 10 of the 26 technologies identified at the forefront of economic growth are various types of advanced materials.

In the presentation of this book, I have attempted to be generous with examples and practice problems within each chapter, and I have tried to be even more generous with the end- of- chapter homework problems (with the level of difficulty for the homework problems clearly noted). Problems dealing with the role of materials in the engineering design process are noted with the use of a design icon . One of the most enjoyable parts of writing the book was the preparation of biographical footnotes for those cases in which a person’s name has become intimately associated with a basic concept in materials science and engineering. I suspect that most readers will share my fascination with these great contributors to science and engineering from the distant and not- so- distant past. In addition to a substantial set of useful data, the Appendices provide convenient location of materials properties and key term definitions.

The various editions of this book have been produced during a period of fundamental change in the field of materials science and engineering. This change was exemplified by the change of name in the Fall of 1986 for the “American Society for Metals” to “ASM International”—a society for materials, as opposed to metals only. An adequate introduction to materials science can no longer be a traditional treatment of physical metallurgy with supplementary introductions to nonmetallic materials. The first edition was based on a balanced treatment of the full spectrum of engineering materials.

Subsequent editions have reinforced that balanced approach with the timely addition of new materials that are playing key roles in the economy of the twenty- first century: lightweight metal alloys, “high tech” ceramics for advanced structural applications, engineering polymers for metal substitution, advanced composites for aerospace applications, increasingly miniaturized semiconductor devices, high- temperature ceramic superconductors, fullerene carbons, graphene,

Preface xi

engineered biomaterials, and biological materials. Since the debut of the first edi- tion, we have also seen breakthroughs in materials characterization, such as the evolution of the high-resolution transmission electron microscope (HRTEM), and in materials processing, such as additive manufacturing (AM). “Feature boxes” have been introduced in recent editions. These one- or two-page case stud- ies labeled “The Material World” are located in each chapter to provide a focus on some fascinating topics in the world of both engineered and natural materials. A feature continued from the Seventh Edition is to emphasize the concept of “Powers of Ten.” In Chapter 1, we point out that an underlying principle of mate- rials science is that understanding the behavior of materials in engineering designs (on the human scale) is obtained by looking at mechanisms that occur at various fine scales, such as the atomic-scale diffusion of carbon atoms involved in the heat treatment of steel. There is a full ten orders of magnitude difference between the size of typical engineered products and the size of typical atoms. Much of modern engineering practice has depended on engineering designs based on microme- ter-scale structures, such as the transistors in an integrated circuit. Increasingly, engineers are designing systems involving the nanometer-scale. At various times throughout the text, a Powers of Ten icon will be used to highlight discussions that demonstrate this structure-property relationship.

New to this Edition

As with previous editions, an effort has been made to add the most important advances in engineering materials, as well as respond to recommendations of previous users for additional content coverage. The results are:

• Updated discussions of the expanding importance of materials in nanotech- nology throughout the text;

• Examples of the role of materials in flat screen and flat panel technology throughout the text;

• Addition of graphene to the discussion of advances in carbon materials in Chapter 3;

• Coverage of the rapidly emerging field of additive manufacturing (by 3D printing) in Chapter 11;

• A candid discussion of the increasing role of biological materials in materi- als science and how that expands the definition of this field (Feature Box in Chapter 12);

• Expanded coverage of ferroelectrics and piezoelectrics in Chapter 13; • Coverage of optical and magnetic materials in a new Chapter 14; • Expanded coverage of corrosion in Chapter 15.

Supplementary Material

A Solutions Manual is available to adopters of this textbook. The Solutions Manual contains fully worked- out solutions to the practice and homework prob- lems only. The Solutions Manual is available from the publisher. The Instructors

xii Preface

Resource Center (IRC) for this book contains the entire Solutions Manual in PDF format. An important addition to the IRC is a complete set of all figures and tables from the textbook in PowerPoint® format. This set of slides was prepared by the University of California, Davis Extension in conjunction with an online course based on this book and can be very useful to faculty in preparing their own lectures. Information about the online course can be obtained from the author.

MasteringEngineeringTM. www.masteringengineering.com. The MasteringTM plat- form is the most effective and widely used online tutorial, homework, and assess- ment system for the sciences and engineering. Now including Materials Science and Engineering, this online tutorial homework program provides instructors cus- tomizable, easy-to-assign, and automatically graded assessments, plus a powerful gradebook for tracking student and class performance.

Pearson eText. The integration of Pearson eText within MasteringEngineering gives students with eTexts easy access to the electronic text when they are logged into MasteringEngineering. Pearson eText pages look exactly like the printed text, offering additional functionality for students and instructors including highlighting, bookmarking, and multiple view formats.

Acknowledgments

Finally, I want to acknowledge a number of people who have been immensely helpful in making this book possible. My family has been more than the usual “patient and understanding.” They are a constant reminder of the rich life beyond the material plane. Peter Gordon (first edition), David Johnstone (second and third editions), Bill Stenquist (fourth and fifth editions), Dorothy Marrero (sixth edition), and Holly Stark (seventh edition) are much appreciated in their roles as editors. Program Manager Clare Romeo has been indispensible in shep- herding this edition to completion. Lilian Davila at the University of California, Merced skillfully produced the computer- generated crystal structure images. A special appreciation is due to my colleagues at the University of California, Davis and to the many reviewers of all editions, especially D. J. Montgomery, John M. Roberts, D. R. Rossington, R. D. Daniels, R. A. Johnson, D. H. Morris, J. P. Mathers, Richard Fleming, Ralph Graff, Ian W. Hall, John J. Kramer, Enayat Mahajerin, Carolyn W. Meyers, Ernest F. Nippes, Richard L. Porter, Eric C. Skaar, E. G. Schwartz, William N. Weins, M. Robert Baren, John Botsis, D. L. Douglass, Robert W. Hendricks, J. J. Hren, Sam Hruska, I. W. Hull, David B. Knoor, Harold Koelling, John McLaughlin, Alvin H. Meyer, M. Natarajan, Jay Samuel, John R. Schlup, Theodore D. Taylor, Ronald Kander, Alan Lawley, Joanna Mc Kittrick, Kathleen R. Rohr, James F. Fitz- Gerald. Valery Bliznyuk, David Bahr, K. Srinagesh, Stacy Gleixner, and Raj Vaidyanathan. I would espe- cially like to thank the reviewers for the eighth edition: Jeffrey Fergus, Auburn University; Christoph Steinbruchel, Rensselaer Polytechnic Institute; Wayne Elban, Loyola University Maryland; Giovanni Zangari, University of Virginia; Guanshui Xu, University of California at Riverside; Atin Sinha, Albany State

www.masteringengineering.com
Preface xiii

University; Yu-Lin Shen, University of New Mexico; Qiuming Wei, University of North Carolina at Charlotte; Blair London, California Polytechnic State Univer- sity; James Chelikowsky, University of Texas at Austin.

James F. Shackelford Davis, California

xiv Preface

your work...

Preface xv

your answer specific feedback

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xvi Preface

About the Author

James F. Shackelford has BS and MS degrees in Ceramic Engineering from the University of Washington and a Ph.D. in Materials Science and Engineering from the University of California, Berkeley. He is currently Distinguished Professor Emeritus in the Department of Chemical Engineering and Materials Science at the University of California, Davis. For many years, he served as the Associate Dean for Undergraduate Studies in the College of Engineering and later as the Director of the University Honors Program that serves students from a wide spectrum of majors. He teaches and conducts research in the structural char- acterization and processing of materials, focusing on glasses and biomaterials. A member of the American Ceramic Society and ASM International, he was named a Fellow of the American Ceramic Society in 1992, was named a Fellow of ASM International in 2011, and received the Outstanding Educator Award of the American Ceramic Society in 1996. In 2003, he received a Distinguished Teach- ing Award from the Academic Senate of the University of California, Davis. In 2012, he received the Outstanding Teaching Award of the College of Engineer- ing at UC Davis. He has published well over 100 archived papers and books including Introduction to Materials Science for Engineers now in its eighth edition and which has been translated into Chinese, German, Italian, Japanese, Korean, Portuguese, and Spanish.

1

Chapter 1 Materials for engineering

1.1 The Material World

We live in a world of material possessions that largely define our social rela- tionships and economic quality of life. The material possessions of our earliest ancestors were probably their tools and weapons. In fact, the most popular way of naming the era of early human civilization is in terms of the materials from which these tools and weapons were made. The Stone Age has been traced as far back as 2.5 million years ago when human ancestors, or hominids, chipped stones to form weapons for hunting. The Bronze Age roughly spanned the period from 2000 b.c. to 1000 b.c. and represents the foundation of metallurgy, in which alloys of copper and tin were discovered to produce superior tools and weapons. (An alloy is a metal composed of more than one element.)

Contemporary archaeologists note that an earlier but less well known “Copper Age” existed between roughly 4000 b.c. and 3000 b.c. in Europe, in which relatively pure copper was used before tin became available. The limited utility of those copper products provided an early lesson in the importance of proper alloy additions. The Iron Age defines the period from 1000 b.c. to 1 b.c. By 500 b.c., iron alloys had largely replaced bronze for tool and weapon making in Europe (Figure 1.1).

Although archaeologists do not refer to a “pottery age,” the presence of domestic vessels made from baked clay has provided some of the best

1.1 The Material World 1.2 Materials Science and Engineering 1.3 Six Materials That Changed Your World 1.4 Processing and Selecting Materials 1.5 Looking at Materials by Powers of Ten

The future of transportation will include new advances in materials such as this glass road sign allowing instantaneous route changes and updates. (Courtesy of Corning Glass Works.)

2 chapter 1 Materials for Engineering

descriptions of human cultures for thousands of years. Similarly, glass artifacts have been traced back to 4000 b.c. in Mesopotamia.

Modern culture in the second half of the 20th century is sometimes referred to as “plastic,” a not entirely complimentary reference to the lightweight and economical polymeric materials from which so many products are made. Some observers have suggested instead that this same time frame should be labeled the “silicon age,” given the pervasive impact of modern electronics largely based on silicon technology.

1.2 Materials Science and Engineering

Since the 1960s, the term that has come to label the general branch of engineering concerned with materials is materials science and engineering. This label is accu- rate in that this field is a true blend of fundamental scientific studies and practical engineering. It has grown to include contributions from many traditional fields, including metallurgy, ceramic engineering, polymer chemistry, condensed matter physics, and physical chemistry.

Figure 1.1 Celtic Iron Age tools from 1st century b.c. Germany. (© Ancient Art & Architecture Collection Ltd / Alamy.)

Section 1.3 Six Materials That Changed Your World 3

The term “materials science and engineering” will serve a special function in this introductory textbook; it will provide the basis for the text’s organiza- tion. First, the word science describes the topics covered in Chapters 2 through 10, which deal with the fundamentals of structure, classification, and properties. Second, the word materials describes Chapters 11 through 13, which deal with the five types of structural materials (Chapters 11 and 12) and various electronic materials, especially semiconductors (Chapter 13), along with optical and mag- netic materials (Chapter 14). Finally, the word engineering describes Chapter 15, which puts the materials to work with discussions of key aspects of the selection of the right materials for the right job, along with some caution about the issue of environmental degradation in those real-world applications.

1.3 Six Materials That Changed Your World

The most obvious question to be addressed by the engineering student entering an introductory course on materials is, “What materials are available to me?” Various classification systems are possible for the wide-ranging answer to this question. In this book, we distinguish six categories that encompass the materi- als available to practicing engineers: metals, ceramics, glasses, polymers, compos- ites, and semiconductors. We will introduce each of these categories with a single example.

Steel BridgeS—introducing MetalS If there is a “typical” material associated in the public’s mind with modern engi- neering practice, it is structural steel. This versatile construction material has several properties that we consider metallic: First, it is strong and can be readily formed into practical shapes. Second, its extensive, permanent deformability, or ductility, is an important asset in permitting small amounts of yielding to sud- den and severe loads. For example, many Californians have been able to observe moderate earthquake activity that leaves windows of glass, which is relatively brittle (i.e., lacking in ductility), cracked, while steel-support framing still func- tions normally. Third, a freshly cut steel surface has a characteristic metallic lus- ter; and fourth, a steel bar shares a fundamental characteristic with other metals: It is a good conductor of electrical current.

Among the most familiar uses of structural steel are bridges, and one of the most famous and beautiful examples is the Golden Gate Bridge connect- ing San Francisco, California with Marin County to the north (Figure 1.2). The opening on May 27, 1937, allowed 200,000 local residents to stroll across the impressive new structure. The following day, a ribbon cutting ceremony inau- gurated automobile traffic that has continued to be an important part of the fabric of life in the San Francisco Bay area for more than 75 years. For many years, the Golden Gate held the title of “longest suspension bridge” in the world (2,737 meters). Although new bridge technologies have provided newer holders of that title, the Golden Gate is still, in the words of a local historian, a “symphony in steel.”

4 chapter 1 Materials for Engineering

Steel bridges continue to provide a combination of function and beauty with the Sundial Bridge in Redding, California being a stunning example (Figure 1.3). The Redding Bridge is a 66-meter pedestrian walkway designed by the famous Spanish architect Santiago Calatrava. It connects a walking trail system with the Turtle Bay Exploration Park. New bridges like this one are not merely serving as sculptural art projects. The aging infrastructure, including many bridges built as long as a century ago, also provides a challenge to engineers and the requirement for both maintenance and replacement of these important structures.

In Chapter 2, the nature of metals will be defined and placed in perspec- tive relative to the other categories. It is useful to consider the extent of metallic behavior in the currently known range of chemical elements. Figure 1.4 highlights the chemical elements in the periodic table that are inherently metallic. This is a large family indeed. The shaded elements are the bases of the various engineer- ing alloys, including the irons and steels (from Fe), aluminum alloys (Al), mag- nesium alloys (Mg), titanium alloys (Ti), nickel alloys (Ni), zinc alloys (Zn), and copper alloys (Cu) [including the brasses (Cu, Zn)].

lucalox laMpS—introducing ceraMicS Aluminum (Al) is a common metal, but aluminum oxide, a compound of alu- minum and oxygen such as Al2O3, is typical of a fundamentally different fam- ily of engineering materials, ceramics. Aluminum oxide has two principal advantages over metallic aluminum. First, Al2O3 is chemically stable in a wide

Figure 1.2 The Golden Gate Bridge north of San Francisco, California, is one of the most famous and most beautiful examples of a steel bridge. (© LOOK Die Bildagentur der Fotografen GmbH / Alamy.)

Section 1.3 Six Materials That Changed Your World 5

1 H

3 Li

4 Be

I A

II A III A IV A V A VI A VII A

VIII III B IV B V B VI B VII B I B II B

11 Na

12 Mg

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

5 B

6 C

7 N

8 O

9 F

10 Ne

2 He

0

19 K

20 Ca

21 Sc

22 Ti

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

29 Cu

30 Zn

31 Ga

32 Ge

33 As

34 Se

35 Br

36 Kr

37 Rb

38 Sr

39 Y

40 Zr

41 Nb

42 Mo

43 Tc

44 Ru

45 Rh

46 Pd

47 Ag

48 Cd

49 In

50 Sn

51 Sb

52 Te

53 I

54 Xe

55 Cs

56 Ba

57 La

87 Fr

88 Ra

89 Ac

104 Rf

105 Db

106 Sg

72 Hf

73 Ta

74 W

75 Re

76 Os

77 Ir

78 Pt

79 Au

80 Hg

81 Tl

82 Pb

83 Bi

84 Po

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

71 Lu

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

103 Lw

85 At

86 Rn

Figure 1.4 Periodic table of the elements. Those elements that are inherently metallic in nature are shown in color.

variety of severe environments, whereas metallic aluminum would be oxidized (a term discussed further in Chapter 15). In fact, a common reaction product in the chemical degradation of aluminum is the more chemically stable oxide. Second, the ceramic Al2O3 has a significantly higher melting point (2020°C) than does the metallic Al (660°C), which makes Al2O3 a popular refractory (i.e., a

Figure 1.3 The Sundial Bridge in Redding, California is a modern masterpiece of bridge design.

6 chapter 1 Materials for Engineering

high-temperature-resistant material of wide use in industrial furnace construction). The production of such oxide ceramics for modern industry is shown in Figure 1.5.

With its superior chemical and temperature-resistant properties, why isn’t Al2O3 used for applications such as automotive engines in place of metallic alumi- num? The answer to this question lies in the most limiting property of ceramics— brittleness. Aluminum and other metals have high ductility, a desirable property that permits them to undergo relatively severe impact loading without fracture, whereas aluminum oxide and other ceramics lack this property. Thus, ceramics are eliminated from many structural applications because they are brittle.

A significant achievement in materials technology is the development of transparent ceramics, which has made possible new products and substantial improvements in others (e.g., commercial lighting). To make traditionally opaque ceramics, such as aluminum oxide (Al2O3), into optically transparent materials required a fundamental change in manufacturing technology. Commercial ceram- ics are frequently produced by heating crystalline powders to high temperatures until a relatively strong and dense product results. Traditional ceramics made in this way contained a substantial amount of residual porosity (see also the Feature Box, “Structure Leads to Properties”), corresponding to the open space between the original powder particles prior to high-temperature processing. A significant reduction in porosity resulted from a relatively simple invention* that involved adding a small amount of impurity (0.1 wt % MgO), which caused the high- temperature densification process for the Al2O3 powder to go to completion.

*R. L. Coble, U.S. Patent 3,026,210, March 20, 1962.

Figure 1.5 A technician observes the production of chemically stable and high- temperature resistant oxide ceramics. Such materials have a wide range of applications in modern industry. (Maximilian Stock Ltd / Photo Researchers, Inc.)

Section 1.3 Six Materials That Changed Your World 7

Figure 1.6 These high-temperature sodium vapor street lamps are made possible by use of a translucent Al2O3 cylinder for containing the sodium vapor. (David Nunuk / Photo Researchers, Inc.)

Cylinders of translucent Al2O3 became the heart of the design of high-temper- ature (1000°C) sodium vapor lamps, which provide substantially higher illumina- tion than do conventional lightbulbs (100 lumens/W compared to 15 lumens/W). Commercial sodium vapor lamps are shown in Figure 1.6.

Aluminum oxide is typical of the traditional ceramics, with magnesium oxide (MgO) and silica (SiO2) being other good examples. In addition, SiO2 is the basis of a large and complex family of silicates, which includes clays and clay- like minerals. Silicon nitride (Si3N4) is an important nonoxide ceramic used in a variety of structural applications. The vast majority of commercially important ceramics are chemical compounds made up of at least one metallic element (see Figure 1.4) and one of five nonmetallic elements (C, N, O, P, or S). Figure 1.7 illustrates the various metals (in light color) and the five key nonmetals (in dark color) that can be combined to form an enormous range of ceramic materials. Bear in mind that many commercial ceramics include compounds and solutions of many more than two elements, just as commercial metal alloys are composed of many elements.

1 H

3 Li

4 Be

I A

II A III A IV A V A VI A VII A

VIII III B IV B V B VI B VII B I B II B

11 Na

12 Mg

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

5 B

6 C

7 N

8 O

9 F

10 Ne

2 He

0

19 K

20 Ca

21 Sc

22 Ti

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

29 Cu

30 Zn

31 Ga

32 Ge

33 As

34 Se

35 Br

36 Kr

37 Rb

38 Sr

39 Y

40 Zr

41 Nb

42 Mo

43 Tc

44 Ru

45 Rh

46 Pd

47 Ag

48 Cd

49 In

50 Sn

51 Sb

52 Te

53 I

54 Xe

55 Cs

56 Ba

57 La

87 Fr

88 Ra

89 Ac

72 Hf

73 Ta

74 W

75 Re

76 Os

77 Ir

78 Pt

79 Au

80 Hg

81 Tl

82 Pb

83 Bi

84 Po

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

71 Lu

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

103 Lw

85 At

86 Rn

104 Rf

105 Db

106 Sg

Figure 1.7 Periodic table with ceramic compounds indicated by a combination of one or more metallic elements (in light color) with one or more nonmetallic elements (in dark color). Note that elements silicon (Si) and germanium (Ge) are included with the metals in this figure but were not included in the periodic table shown in Figure 1.4. They are included here because, in elemental form, Si and Ge behave as semiconductors (Figure 1.16). Elemental tin (Sn) can be either a metal or a semiconductor, depending on its crystalline structure.

8 chapter 1 Materials for Engineering

the Material World

Structure Leads to Properties

To understand the properties or observable char- acteristics of engineering materials, it is necessary to understand their structure. Virtually every major property of the six materials’ categories outlined in this chapter will be shown to result directly from mechanisms occurring on a small scale (usually either the atomic or the microscopic level).

The dramatic effect that fine-scale structure has on large-scale properties is well illustrated by the development of transparent ceramics, just dis- cussed in the introduction to ceramic materials. The microscopic-scale residual porosity in a traditional aluminum oxide leads to loss of visible light trans- mission (i.e., a loss in transparency) by providing a light-scattering mechanism. Each Al2O3—air inter- face at a pore surface is a source of light refraction (change of direction). Only about 0.3% porosity can cause Al2O3 to be translucent (capable of trans- mitting a diffuse image), and 3% porosity can cause the material to be completely opaque. The elimi- nation of porosity provided by the Lucalox pat- ent (adding 0.1 wt % MgO) produced a pore-free microstructure and a nearly transparent material

with an important additional property—excellent resistance to chemical attack by high-temperature sodium vapor.

The example of translucent ceramics shows a typical and important demonstration of how properties of engineering materials follow directly from structure. Throughout this book, we shall be alert to the continuous demonstration of this inter- relationship for all the materials of importance to engineers. A contemporary example is given in the images below, a microstructure and the resulting translucent disc of hydroxyapatite ceramic devel- oped for biomedical applications. By using the Field-Assisted Sintering Technique (FAST) as high- lighted in the Feature Box in Chapter 10, research- ers were able to produce a material with minimal porosity (note the densely packed nano-scale grain structure in part a) and the resulting ability to trans- mit a visual image (part b). The effect of porosity on light transmission is discussed further in Chapter 14 (e.g., Figures 14.8 and 14.9), and the importance of hydroxyapatite in orthopedic prostheses is dis- cussed further in Chapter 15.

(Courtesy of T. B. Tien and J. R. Groza, University of California, Davis.)

(a) (b)

Section 1.3 Six Materials That Changed Your World 9

optical FiBerS—introducing glaSSeS The metals and ceramics just introduced have a similar structural feature on the atomic scale: They are crystalline, which means that their constituent atoms are stacked together in a regular, repeating pattern. A distinction between metallic- and ceramic-type materials is that, by fairly simple processing techniques, many ceramics can be made in a noncrystalline form (i.e., their atoms are stacked in irregular, random patterns), which is illustrated in Figure 1.8. The general term for noncrystalline solids with compositions comparable to those of crystalline ceram- ics is glass (Figure 1.9). Most common glasses are silicates; ordinary window glass is approximately 72% silica (SiO2) by weight, with the balance of the material

Figure 1.9 Some common silicate glasses for engineering applications. These materials combine the important qualities of transmitting clear visual images and resisting chemically aggressive environments. (Courtesy of Corning Glass Works.)

(a) (b)

Figure 1.8 Schematic comparison of the atomic-scale structure of (a) a ceramic (crystalline) and (b) a glass (noncrystalline). The open circles represent a nonmetallic atom, and the solid black circles represent a metal atom.

10 chapter 1 Materials for Engineering

being primarily sodium oxide (Na2O) and calcium oxide (CaO). Glasses share the property of brittleness with crystalline ceramics. Glasses are important engineer- ing materials because of other properties, such as their ability to transmit visible light (as well as ultraviolet and infrared radiation) and chemical inertness.

A major revolution in the field of telecommunications occurred with the transition from traditional metal cable to optical glass fibers (Figure 1.10). Although Alexander Graham Bell had transmitted speech several hundred meters over a beam of light shortly after his invention of the telephone, technol- ogy did not permit the practical, large-scale application of this concept for nearly a century. The key to the rebirth of this approach was the invention of the laser in 1960. By 1970, researchers at Corning Glass Works had developed an optical fiber with a loss as low as 20 dB/km at a wavelength of 630 nm (within the visible range). By the mid-1980s, silica fibers had been developed with losses as low as 0.2 dB/km at 1.6 mm (in the infrared range). As a result, telephone conversations and any other form of digital data can be transmitted as laser light pulses rather than as the electrical signals used in copper cables. Glass fibers are excellent examples of photonic materials, in which signal transmission occurs by photons rather than by the electrons of electronic materials.

Glass-fiber bundles of the type illustrated in Figure 1.10 were put into com- mercial use by Bell Systems in the mid-1970s. The reduced expense and size, com- bined with an enormous capacity for data transmission, led to a rapid growth in the construction of optical communication systems. Now, virtually all telecom- munications are transmitted in this way. Ten billion digital bits can be transmit- ted per second along an optical fiber in a contemporary system carrying tens of thousands of telephone calls.

nylon parachuteS—introducing polyMerS A major impact of modern engineering technology on everyday life has been made by the class of materials known as polymers. An alternative name for this category is plastics, which describes the extensive formability of many polymers

Figure 1.10 The small cable on the right contains 144 glass fibers and can carry more than three times as many telephone conversations as the traditional (and much larger) copper-wire cable on the left. (© Bettmann/CORBIS.)

Section 1.3 Six Materials That Changed Your World 11

during fabrication. These synthetic, or human-made, materials represent a special branch of organic chemistry. Examples of inexpensive, functional polymer prod- ucts are readily available to each of us (Figure 1.11). The “mer” in a polymer is a single hydrocarbon molecule such as ethylene (C2H4). Polymers are long-chain molecules composed of many mers bonded together. The most common com- mercial polymer is polyethylene -(C2H4)-n where n can range from approximately 100 to 1,000. Figure 1.12 shows the relatively limited portion of the periodic table that is associated with commercial polymers. Many important polymers, includ- ing polyethylene, are simply compounds of hydrogen and carbon. Others con- tain oxygen (e.g., acrylics), nitrogen (nylons), fluorine (fluoroplastics), and silicon (silicones).

Nylon is an especially familiar example. Polyhexamethylene adipamide, or nylon, is a member of the family of synthetic polymers known as polyamides invented in 1935 at the DuPont Company. Nylon was the first commercially suc- cessful polymer and was initially used as bristles in toothbrushes (1938) followed by the highly popular use as an alternative to silk stockings (1940). Developed as a synthetic alternative to silk, nylon became the focus of an intensive effort dur- ing the early stages of World War II to replace the diminishing supply of Asian silk for parachutes and other military supplies. At the beginning of World War II, the fiber industry was dominated by the natural materials cotton and wool. By the end, synthetic fibers accounted for 25% of the market share. A contemporary example of a nylon parachute is shown in Figure 1.13. Today, nylon remains a popular fiber material, but it is also widely used in solid form for applications such as gears and bearings.

As the descriptive title implies, plastics commonly share with metals the desirable mechanical property of ductility. Unlike brittle ceramics, polymers are frequently lightweight, low-cost alternatives to metals in structural design appli- cations. The nature of chemical bonding in polymeric materials will be explored in Chapter 2. Important bonding-related properties include lower strength

Figure 1.11 Miscellaneous internal parts of a parking meter are made of an acetal polymer. Engineered polymers are typically inexpensive and are characterized by ease of formation and adequate structural properties. (Courtesy of the DuPont Company, Engineering Polymers Division.)

12 chapter 1 Materials for Engineering

Figure 1.13 Since its development during World War II, nylon fabric remains the most popular material of choice for parachute designs. (Courtesy of Stringer/Agence France Presse/Getty Images.)

1 H

3 Li

4 Be

I A

II A III A IV A V A VI A VII A

VIII III B IV B V B VI B VII B I B II B

11 Na

12 Mg

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

5 B

6 C

7 N

8 O

9 F

10 Ne

2 He

0

19 K

20 Ca

21 Sc

22 Ti

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

29 Cu

30 Zn

31 Ga

32 Ge

33 As

34 Se

35 Br

36 Kr

37 Rb

38 Sr

39 Y

40 Zr

41 Nb

42 Mo

43 Tc

44 Ru

45 Rh

46 Pd

47 Ag

48 Cd

49 In

50 Sn

51 Sb

52 Te

53 I

54 Xe

55 Cs

56 Ba

57 La

87 Fr

88 Ra

89 Ac

72 Hf

73 Ta

74 W

75 Re

76 Os

77 Ir

78 Pt

79 Au

80 Hg

81 Tl

82 Pb

83 Bi

84 Po

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

71 Lu

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

103 Lw

85 At

86 Rn

104 Rf

105 Db

106 Sg

Figure 1.12 Periodic table with the elements associated with commercial polymers in color.

Section 1.3 Six Materials That Changed Your World 13

compared with metals and lower melting point and higher chemical reactiv- ity compared with ceramics and glasses. In spite of their limitations, polymers are highly versatile and useful materials. Substantial progress has been made in recent decades in the development of engineering polymers with sufficiently high strength and stiffness to permit substitution for traditional structural metals.

Kevlar®-reinForced tireS—introducing coMpoSiteS The structural engineering materials we have discussed so far—metals, ceramics/ glasses, and polymers—contain various elements and compounds that can be classified by their chemical bonding. Metals are associated with metallic bond- ing, ceramics/glasses with ionic bonding, and polymers with covalent bonding. Such classifications are described further in Chapter 2. Another important set of materials is made up of some combinations of individual materials from the previous categories. This fourth group is composites, and an excellent example is fiberglass. This composite of glass fibers embedded in a polymer matrix is com- monplace (Figure 1.14). Characteristic of good composites, fiberglass has the best properties of each component, producing a product that is superior to either of the components separately. The high strength of the small-diameter glass fibers is combined with the ductility of the polymer matrix to produce a strong material capable of withstanding the normal loading required of a structural material. There is no need to illustrate a region of the periodic table as characteristic of composites, since they involve virtually the entire table except for the noble gases (column 0), equivalent to an overlay of the periodic table coverage for met- als, ceramics, and polymers combined.

Kevlar fiber reinforcements provide significant advances over traditional glass fibers for polymer–matrix composites. Kevlar is a DuPont trade name for

Figure 1.14 Example of a fiberglass composite composed of microscopic-scale reinforcing glass fibers in a polymer matrix. (Courtesy of Owens-Corning Fiberglas Corporation.)

14 chapter 1 Materials for Engineering

poly p-phenyleneterephthalamide (PPD-T), a para-aramid. Substantial progress has been made in developing new polymer matrices, such as polyetherether- ketone (PEEK) and polyphenylene sulfide (PPS). These materials have the advantages of increased toughness and recyclability. Kevlar-reinforced polymers are used in pressure vessels, and Kevlar reinforcement is widely used in tires (Figure 1.15). Kevlar was developed in 1965 and has been used commercially since the early 1970s. It is especially popular for demanding applications given that its strength-to-weight ratio is five times that of structural steel. The modern automobile tire is an especially good example.

Silicon chipS—introducing SeMiconductorS Although polymers are highly visible engineering materials that have had a major impact on contemporary society, semiconductors are relatively invisible but have had a comparable social impact. Technology has clearly revolutionized society, but solid-state electronics has revolutionized technology itself. A rela- tively small group of elements and compounds has an important electrical prop- erty, semiconduction, in which they are neither good electrical conductors nor good electrical insulators. Instead, their ability to conduct electricity is intermedi- ate. These materials are called semiconductors, and in general they do not fit into any of the structural materials categories based on atomic bonding. As discussed earlier, metals are inherently good electrical conductors. Ceramics and polymers (nonmetals) are generally poor conductors, but good insulators. An important section of the periodic table is shown in dark color in Figure 1.16 These three

Figure 1.15 Kevlar reinforcement is a popular application in modern high-performance tires. In this case, an automobile is subjected to aquaplaning at a test track. (© Culture-images GmbH / Alamy.)

semiconducting elements (Si, Ge, and Sn) from column IV A serve as a kind of boundary between metallic and nonmetallic elements. Silicon (Si) and germa- nium (Ge), widely used elemental semiconductors, are excellent examples of this class of materials. Precise control of chemical purity allows precise control of electronic properties. As techniques have been developed to produce variations in chemical purity over small regions, sophisticated electronic circuitry has been produced in exceptionally small areas (Figure 1.17). Such microcircuitry is the basis of the current revolution in technology.

The elements shaded in light color in Figure 1.16 form compounds that are semiconducting. Examples include gallium arsenide (GaAs), which is used as a high-temperature rectifier and a laser material, and cadmium sulfide (CdS), which is used as a relatively low-cost solar cell for conversion of solar energy to useful electrical energy. The various compounds formed by these elements show similarities to many of the ceramic compounds.