Materials science and engineering  an introduction

.” and “Materials of Importance” items as well as case studies that provide relevance to topic discussions • “Concept Check” questions that test whether a student understands the subjec

Characteristics of Selected Elements

Atomic Density of Crystal Atomic Ionic Most Melting Atomic Weight Solid, 20 ⴗC Structure, Radius Radius Common Point Element Symbol Number (amu) (g/cm 3) 20 ⴗC (nm) (nm) Valence (ⴗC)

Quantity Symbol SI Units cgs Units

molecules/mol molecules/molBoltzmann’s constant k 1.38 ⫻ 10⫺23J/atom K 1.38 ⫻ 10⫺16erg/atom K

8.62 ⫻ 10⫺5eV/atom KBohr magneton mB 9.27 ⫻ 10⫺24A m2 9.27 ⫻ 10⫺21erg/gaussa

Electron charge e 1.602 ⫻ 10⫺19C 4.8 ⫻ 10⫺10statcoulb

Permeability of a vacuum m0 1.257 ⫻ 10⫺6henry/m unitya

Permittivity of a vacuum ⑀0 8.85 ⫻ 10⫺12farad/m unityb

Planck’s constant h 6.63 ⫻ 10⫺34J s 6.63 ⫻ 10⫺27erg s

4.13 ⫻ 10⫺15eV sVelocity of light in a vacuum c 3 ⫻ 108m/s 3 ⫻ 1010cm/s

Btu ⫽ British thermal unit K ⫽ degrees Kelvin P ⫽ poise

⬚C ⫽ degrees Celsius lbf⫽ pound force s ⫽ second

cal ⫽ calorie (gram) lbm⫽ pound mass T⫽ temperature

⬚F ⫽ degrees Fahrenheit mm ⫽ millimeter W ⫽ watt

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© Courtney Keating/iStockphoto

9th Edition

Materials Science and Engineering

AN INTRODUCTION

WILLIAM D CALLISTER, JR.

Department of Metallurgical Engineering

The University of Utah

DAVID G RETHWISCH

Department of Chemical and Biochemical Engineering

The University of Iowa

and carbon atoms, respectively.

Back Cover: Three representations of the unit cell for body-centered cubic iron (a-ferrite); each unit cell contains an interstitial carbon

atom.

VICE PRESIDENT AND EXECUTIVE PUBLISHER Donald Fowley

This book was set in 9.5/11.5 Times Ten LT Std by Aptara, Inc., and printed and bound by Quad Graphics/Versailles The cover was printed by Quad Graphics/Versailles.

This book is printed on acid-free paper q

Copyright © 2014, 2010, 2007, 2003, 2000 John Wiley & Sons, Inc All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center,

Inc., 222 Rosewood Drive, Danvers, MA 01923, website www.copyright.com Requests to the Publisher for permission should be

addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, (201) 748-6011,

fax (201) 748-6008, website www.wiley.com/go/permissions.

Evaluation copies are provided to qualified academics and professionals for review purposes only, for use in their courses during the next academic year These copies are licensed and may not be sold or transferred to a third party Upon completion of the review period, please return the evaluation copy to Wiley Return instructions and a free of charge return shipping label are

available at www.wiley.com/go/returnlabel Outside of the United States, please contact your local representative.

ISBN: 978-1-118-32457-8

Wiley Binder Version ISBN: 978-1-118-47770-0

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

Dedicated to

Bill Stenquist, editor and friend

In this ninth edition we have retained the objectives and approaches for teaching

materials science and engineering that were presented in previous editions The first, and primary, objective is to present the basic fundamentals on a level appropriate for

university/college students who have completed their freshmen calculus, chemistry, and physics courses

The second objective is to present the subject matter in a logical order, from the

simple to the more complex Each chapter builds on the content of previous ones

The third objective, or philosophy, that we strive to maintain throughout the text is

that if a topic or concept is worth treating, then it is worth treating in sufficient detail and

to the extent that students have the opportunity to fully understand it without having to consult other sources; in addition, in most cases, some practical relevance is provided

The fourth objective is to include features in the book that will expedite the learning

process These learning aids include the following:

• Numerous illustrations, now presented in full color, and photographs to help visualize what is being presented

• Learning objectives, to focus student attention on what they should be getting from each chapter

• “Why Study ” and “Materials of Importance” items as well as case studies that provide relevance to topic discussions

• “Concept Check” questions that test whether a student understands the subject matter on a conceptual level

• Key terms, and descriptions of key equations, highlighted in the margins for quick reference

• End-of-chapter questions and problems designed to progressively develop

students’ understanding of concepts and facility with skills

• Answers to selected problems, so students can check their work

• A glossary, a global list of symbols, and references to facilitate understanding of the subject matter

• End-of-chapter summary tables of important equations and symbols used in these equations

• Processing/Structure/Properties/Performance correlations and summary concept maps for four materials (steels, glass-ceramics, polymer fibers, and silicon

semiconductors), which integrate important concepts from chapter to chapter

• Materials of Importance sections that lend relevance to topical coverage by

discussing familiar and interesting materials and their applications

The fifth objective is to enhance the teaching and learning process by using the newer

tech-nologies that are available to most instructors and today’s engineering students

Preface

• vii

New/Revised Content

Several important changes have been made with this Ninth Edition One of the most cant is the incorporation of several new sections, as well as revisions/amplifications of other sections These include the following:

• Numerous new and revised example problems In addition, all homework problems requiring computations have been refreshed

• Revised, expanded, and updated tables

• Two new case studies: “Liberty Ship Failures” (Chapter 1) and “Use of Composites

in the Boeing 787 Dreamliner” (Chapter 16)

• Bond hybridization in carbon (Chapter 2)

• Revision of discussions on crystallographic planes and directions to include the use

of equations for the determination of planar and directional indices (Chapter 3)

• Revised discussion on determination of grain size (Chapter 4)

• New section on the structure of carbon fibers (Chapter 13)

• Revised/expanded discussions on structures, properties, and applications of the nanocarbons: fullerenes, carbon nanotubes, and graphene (Chapter 13)

• Revised/expanded discussion on structural composites: laminar composites and sandwich panels (Chapter 16)

• New section on structure, properties, and applications of nanocomposite materials (Chapter 16)

• Tutorial videos In WileyPLUS, Tutorial Videos help students with their “muddiest

points” in conceptual understanding and problem-solving

• Exponents and logarithms In WileyPLUS, the exponential functions and natural

logarithms have been added to the Exponents and Logarithms section of the Math Skills Review

• Fundamentals of Engineering homework problems and questions for most chapters These appear at the end of Questions and Problems sections and provide students the opportunity to practice answering and solving questions and problems similar to those found on Fundamentals of Engineering examinations

Online Learning Resources—Student Companion Site

at www.wiley.com/college/callister.

Also found on the book’s website is a Students’ Companion page on which is posted several important instructional elements for the student that complement the text; these include the following:

• Answers to Concept Check questions, questions which are found in the print book.

• Library of Case Studies One way to demonstrate principles of design in an engineering

curriculum is via case studies: analyses of problem-solving strategies applied to real-world examples of applications/devices/failures encountered by engineers Five case studies are provided as follows: (1) Materials Selection for a Torsionally Stressed Cylindrical Shaft; (2) Automobile Valve Spring; (3) Failure of an Automobile Rear Axle; (4) Artificial Total Hip Replacement; and (5) Chemical Protective Clothing

• Mechanical Engineering (ME) Module This module treats materials science/

engineering topics not covered in the printed text that are relevant to mechanical engineering

• Extended Learning Objectives This is a more extensive list of learning objectives

than is provided at the beginning of each chapter These direct the student to study the subject material to a greater depth

• Index of Learning Styles Upon answering a 44-item questionnaire, a user’s

learning-style preference (i.e., the manner in which information is assimilated and processed) is assessed

Online Resources for Instructors—Instructors Companion Site

at www.wiley.com/college/callister.

The Instructor Companion Site is available for instructors who have adopted this text Please visit the website to register for access Resources that are available include the following:

• All resources found on the Student Companion Site (Except for the Student

Lecture PowerPoint® Slides.)

• Instructor Solutions Manual Detailed solutions for all end-of-chapter questions

and problems (in both Word® and Adobe Acrobat® PDF formats)

• Homework Problem Correlation Guide—8th edition to 9th edition This guide

notes, for each homework problem or question (by number), whether it appeared

in the eighth edition and, if so, its number in this previous edition

• Virtual Materials Science and Engineering (VMSE) This web-based software

package consists of interactive simulations and animations that enhance the learning of key concepts in materials science and engineering Included in VMSE are eight modules and a materials properties/cost database Titles of these modules are as follows: (1) Metallic Crystal Structures and Crystallography; (2) Ceramic Crystal Structures; (3) Repeat Unit and Polymer Structures; (4) Dislocations; (5) Phase Diagrams; (6) Diffusion; (7) Tensile Tests; and (8) Solid-Solution

Strengthening

• Image Gallery Illustrations from the book Instructors can use them in

assignments, tests, or other exercises they create for students

• Art PowerPoint Slides Book art loaded into PowerPoints, so instructors can more easily use them to create their own PowerPoint Slides

• Lecture Note PowerPoints These slides, developed by the authors and Peter M

Anderson (The Ohio State University), follow the flow of topics in the text, and include materials taken from the text as well as other sources Slides are available

in both Adobe Acrobat® PDF and PowerPoint® formats [Note: If an instructor doesn’t have available all fonts used by the developer, special characters may not

be displayed correctly in the PowerPoint version (i.e., it is not possible to embed fonts in PowerPoints); however, in the PDF version, these characters will appear correctly.]

• Solutions to Case Study Problems.

• Solutions to Problems in the Mechanical Engineering Web Module.

• Suggested Course Syllabi for the Various Engineering Disciplines Instructors may consult these syllabi for guidance in course/lecture organization and planning

• Experiments and Classroom Demonstrations Instructions and outlines for

experiments and classroom demonstrations that portray phenomena and/or illustrate principles that are discussed in the book; references are also provided that give more detailed accounts of these demonstrations

WileyPLUS is a research-based online environment for effective teaching and learning WileyPLUS builds students’ confidence by taking the guesswork out of studying by

providing them with a clear roadmap:  what is assigned, what is required for each ment, and whether assignments are done correctly Independent research has shown that students using WileyPLUS will take more initiative so the instructor has a greater impact

assign-on their achievement in the classroom and beyassign-ond WileyPLUS also helps students study and progress at a pace that’s right for them Our integrated resources–available 24/7–function like a personal tutor, directly addressing each student’s demonstrated needs by providing specific problem-solving techniques

What do students receive with WileyPLUS?

• The complete digital textbook that saves students up to 60% of the cost of the in-print text

• Navigation assistance, including links to relevant sections in the online textbook

• Immediate feedback on performance and progress, 24/7

• Integrated, multi-media resources—to include VMSE (Virtual Materials Science &

Engineering), tutorial videos, a Math Skills Review, flashcards, and much more;

these resources provide multiple study paths and encourage more active learning

What do instructors receive with WileyPLUS?

• The ability to effectively and efficiently personalize and manage their course

• The ability to track student performance and progress, and easily identify those who are falling behind

• Media-rich course materials and assessment resources including—a complete Solutions Manual, PowerPoint® Lecture Slides, Extended Learning Objectives, and much more www.WileyPLUS.com

WileyPLUS

We have a sincere interest in meeting the needs of educators and students in the als science and engineering community, and therefore we solicit feedback on this edition Comments, suggestions, and criticisms may be submitted to the authors via email at the following address: billcallister@comcast.net

materi-Feedback

Since we undertook the task of writing this and previous editions, instructors and dents, too numerous to mention, have shared their input and contributions on how to make this work more effective as a teaching and learning tool To all those who have helped, we express our sincere thanks

stu-We express our appreciation to those who have made contributions to this edition

We are especially indebted to the following:

Audrey Butler of The University of Iowa, and Bethany Smith and Stephen Krause

of Arizona State University, for helping to develop material in the WileyPLUS course

Grant Head for his expert programming skills, which he used in developing the

Vir-tual Materials Science and Engineering software.

Eric Hellstrom and Theo Siegrist of Florida State University for their feedback and suggestions for this edition

Acknowledgments

Preface • xi

In addition, we thank the many instructors who participated in the fall 2011 ing survey; their valuable contributions were driving forces for many of the changes and additions to this ninth edition

market-We are also indebted to Dan Sayre, Executive Editor, Jennifer market-Welter, Senior uct Designer, and Jessica Knecht, Editorial Program Assistant, for their guidance and assistance on this revision

Prod-Last, but certainly not least, we deeply and sinc erely appreciate the continual couragement and support of our families and friends

en-William D Callister, Jr.

David G RethwischOctober 2013

1.2 Materials Science and Engineering 2

1.3 Why Study Materials Science and

2.4 The Periodic Table 28

A TOMIC B ONDING IN S OLIDS 30

2.5 Bonding Forces and Energies 30

2.6 Primary Interatomic Bonds 32

2.7 Secondary Bonding or van der Waals

Bonding 39

Materials of Importance—Water (Its

Volume Expansion Upon Freezing) 42

Important Terms and Concepts 47 References 47

Questions and Problems 48 Fundamentals of Engineering Questions and Problems 50

3 The Structure of Crystalline Solids 51

Learning Objectives 523.1 Introduction 52

C RYSTAL S TRUCTURES 52

3.2 Fundamental Concepts 523.3 Unit Cells 53

3.4 Metallic Crystal Structures 543.5 Density Computations 603.6 Polymorphism and Allotropy 60Materials of Importance—Tin (Its Allotropic Transformation) 613.7 Crystal Systems 62

C RYSTALLOGRAPHIC P OINTS , D IRECTIONS , AND

3.8 Point Coordinates 643.9 Crystallographic Directions 673.10 Crystallographic Planes 753.11 Linear and Planar Densities 813.12 Close-Packed Crystal Structures 82

C RYSTALLINE AND N ONCRYSTALLINE

3.13 Single Crystals 843.14 Polycrystalline Materials 843.15 Anisotropy 86

3.16 X-Ray Diffraction: Determination of Crystal Structures 87

3.17 Noncrystalline Solids 92

Summary 93 Equation Summary 95 List of Symbols 96

• xiii

Processing/Structure/Properties/Performance

Summary 96

Important Terms and Concepts 97

References 97

Questions and Problems 97

Fundamentals of Engineering Questions and

5.3 Fick’s First Law 143

5.4 Fick’s Second Law—Nonsteady-State

Diffusion 145

5.5 Factors That Influence Diffusion 149

5.6 Diffusion in Semiconducting

Materials 154

Material of Importance—Aluminum for

Integrated Circuit Interconnects 157

5.7 Other Diffusion Paths 158

Summary 158 Equation Summary 159 List of Symbols 160 Processing/Structure/Properties/Performance Summary 160

Important Terms and Concepts 162 References 162

Questions and Problems 162 Design Problems 166 Fundamentals of Engineering Questions and Problems 167

6 Mechanical Properties of Metals 168

Learning Objectives 1696.1 Introduction 1696.2 Concepts of Stress and Strain 170

E LASTIC D EFORMATION 174

6.3 Stress–Strain Behavior 1746.4 Anelasticity 177

6.5 Elastic Properties of Materials 177

P LASTIC D EFORMATION 180

6.6 Tensile Properties 1806.7 True Stress and Strain 1876.8 Elastic Recovery After Plastic Deformation 190

6.9 Compressive, Shear, and Torsional Deformation 191

Important Terms and Concepts 206 References 207

Questions and Problems 207 Design Problems 213 Fundamentals of Engineering Questions and Problems 214

7 Dislocations and Strengthening Mechanisms 216

Learning Objectives 2177.1 Introduction 217

Contents • xv

7.2 Basic Concepts 218

7.3 Characteristics of Dislocations 220

7.4 Slip Systems 221

7.5 Slip in Single Crystals 223

7.6 Plastic Deformation of Polycrystalline

Materials 226

7.7 Deformation by Twinning 228

M ECHANISMS OF S TRENGTHENING IN M ETALS 229

7.8 Strengthening by Grain Size Reduction 229

8.5 Principles of Fracture Mechanics 257

8.6 Fracture Toughness Testing 265

F ATIGUE 270

8.7 Cyclic Stresses 270

8.8 The S–N Curve 272

8.9 Crack Initiation and Propagation 276

8.10 Factors That Affect Fatigue Life 278

8.11 Environmental Effects 280

8.12 Generalized Creep Behavior 281

8.13 Stress and Temperature Effects 282

8.14 Data Extrapolation Methods 285

8.15 Alloys for High-Temperature Use 286

Summary 287

Equation Summary 290 List of Symbols 290 Important Terms and Concepts 291 References 291

Questions and Problems 291 Design Problems 295 Fundamentals of Engineering Questions and Problems 296

9 Phase Diagrams 297

Learning Objectives 2989.1 Introduction 298

D EFINITIONS AND B ASIC C ONCEPTS 298

9.2 Solubility Limit 2999.3 Phases 300

9.4 Microstructure 3009.5 Phase Equilibria 3009.6 One-Component (or Unary) Phase Diagrams 301

B INARY P HASE D IAGRAMS 302

9.7 Binary Isomorphous Systems 3039.8 Interpretation of Phase Diagrams 3059.9 Development of Microstructure in Isomorphous Alloys 309

9.10 Mechanical Properties of Isomorphous Alloys 312

9.11 Binary Eutectic Systems 3129.12 Development of Microstructure in Eutectic Alloys 318

Materials of Importance—Lead-Free Solders 319

9.13 Equilibrium Diagrams Having Intermediate Phases or Compounds 325

9.14 Eutectoid and Peritectic Reactions 3289.15 Congruent Phase Transformations 3299.16 Ceramic and Ternary Phase

Diagrams 3309.17 The Gibbs Phase Rule 330

T HE I RON –C ARBON S YSTEM 333

9.18 The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram 333

9.19 Development of Microstructure in Iron–Carbon Alloys 336

9.20 The Influence of Other Alloying Elements 344

Summary 344 Equation Summary 346 List of Symbols 347 Processing/Structure/Properties/Performance Summary 347

Important Terms and Concepts 349

References 349

Questions and Problems 349

Fundamentals of Engineering Questions and

Problems 355

10 Phase Transformations: Development

of Microstructure and Alteration of

10.3 The Kinetics of Phase Transformations 358

10.4 Metastable Versus Equilibrium States 369

M ICROSTRUCTURAL AND P ROPERTY C HANGES IN

10.5 Isothermal Transformation Diagrams 370

10.9 Review of Phase Transformations and

Mechanical Properties for Iron–Carbon

Materials of Importance—Metal Alloys

Used for Euro Coins 433

F ABRICATION OF M ETALS 434

11.4 Forming Operations 434

11.5 Casting 43611.6 Miscellaneous Techniques 437

T HERMAL P ROCESSING OF M ETALS 439

11.7 Annealing Processes 43911.8 Heat Treatment of Steels 44111.9 Precipitation Hardening 451

Summary 458 Processing/Structure/Properties/Performance Summary 460

Important Terms and Concepts 460 References 463

Questions and Problems 463 Design Problems 464 Fundamentals of Engineering Questions and Problems 466

12 Structures and Properties of Ceramics 467

Learning Objectives 46812.1 Introduction 468

C ERAMIC S TRUCTURES 468

12.2 Crystal Structures 46912.3 Silicate Ceramics 47712.4 Carbon 481

12.5 Imperfections in Ceramics 48212.6 Diffusion in Ionic Materials 48612.7 Ceramic Phase Diagrams 487

M ECHANICAL P ROPERTIES 490

12.8 Brittle Fracture of Ceramics 49112.9 Stress–Strain Behavior 49512.10 Mechanisms of Plastic Deformation 49712.11 Miscellaneous Mechanical

Considerations 499

Summary 501 Equation Summary 503 List of Symbols 503 Processing/Structure/Properties/Performance Summary 503

Important Terms and Concepts 504 References 505

Questions and Problems 505 Design Problems 509 Fundamentals of Engineering Questions and Problems 509

13 Applications and Processing of Ceramics 510

Learning Objectives 51113.1 Introduction 511

T YPES AND A PPLICATIONS OF C ERAMICS 512

Questions and Problems 577

Fundamentals of Engineering Questions and

Problems 579

15 Characteristics, Applications, and Processing of Polymers 580

Learning Objectives 58115.1 Introduction 581

M ECHANICAL B EHAVIOR OF P OLYMERS 581

15.2 Stress–Strain Behavior 58115.3 Macroscopic Deformation 58415.4 Viscoelastic Deformation 58415.5 Fracture of Polymers 58815.6 Miscellaneous Mechanical Characteristics 590

M ECHANISMS OF D EFORMATION AND FOR

15.7 Deformation of Semicrystalline Polymers 591

15.8 Factors That Influence the Mechanical Properties of Semicrystalline

Polymers 593Materials of Importance—Shrink-Wrap Polymer Films 597

15.9 Deformation of Elastomers 597

C RYSTALLIZATION , M ELTING , AND G LASS

15.10 Crystallization 60015.11 Melting 60115.12 The Glass Transition 60115.13 Melting and Glass Transition Temperatures 60115.14 Factors That Influence Melting and Glass Transition Temperatures 603

P OLYMER T YPES 605

15.15 Plastics 605Materials of Importance—Phenolic Billiard Balls 607

15.16 Elastomers 60815.17 Fibers 61015.18 Miscellaneous Applications 61015.19 Advanced Polymeric Materials 612

P OLYMER S YNTHESIS AND P ROCESSING 616

15.20 Polymerization 61615.21 Polymer Additives 61815.22 Forming Techniques for Plastics 62015.23 Fabrication of Elastomers 62215.24 Fabrication of Fibers and Films 622

Summary 624 Equation Summary 626 List of Symbols 626 Processing/Structure/Properties/Performance Summary 626

Contents • xvii

Important Terms and Concepts 629

F IBER -R EINFORCED C OMPOSITES 642

16.4 Influence of Fiber Length 642

16.5 Influence of Fiber Orientation and

Concentration 643

16.6 The Fiber Phase 651

16.7 The Matrix Phase 653

C ORROSION OF C ERAMIC M ATERIALS 712

Questions and Problems 721 Design Problems 723 Fundamentals of Engineering Questions and Problems 724

18 Electrical Properties 725

Learning Objectives 72618.1 Introduction 726

E LECTRICAL C ONDUCTION 726

18.2 Ohm’s Law 72618.3 Electrical Conductivity 72718.4 Electronic and Ionic Conduction 72818.5 Energy Band Structures in

Solids 72818.6 Conduction in Terms of Band and Atomic Bonding Models 73018.7 Electron Mobility 732

18.8 Electrical Resistivity of Metals 73318.9 Electrical Characteristics of Commercial Alloys 736

Materials of Importance—Aluminum Electrical Wires 736

S EMICONDUCTIVITY 738

18.10 Intrinsic Semiconduction 73818.11 Extrinsic Semiconduction 74118.12 The Temperature Dependence of Carrier Concentration 744

18.13 Factors That Affect Carrier Mobility 745

18.14 The Hall Effect 74918.15 Semiconductor Devices 751

E LECTRICAL C ONDUCTION IN I ONIC C ERAMICS AND IN P OLYMERS 757

18.16 Conduction in Ionic Materials 758

18.17 Electrical Properties of Polymers 758

20.7 Domains and Hysteresis 81620.8 Magnetic Anisotropy 81920.9 Soft Magnetic Materials 820Materials of Importance—An Iron–Silicon Alloy Used in Transformer Cores 82120.10 Hard Magnetic Materials 82220.11 Magnetic Storage 82520.12 Superconductivity 828

Summary 831 Equation Summary 833 List of Symbols 833 Important Terms and Concepts 834 References 834

Questions and Problems 834 Design Problems 837 Fundamentals of Engineering Questions and Problems 837

21 Optical Properties 838

Learning Objectives 83921.1 Introduction 839

B ASIC C ONCEPTS 839

21.2 Electromagnetic Radiation 83921.3 Light Interactions with Solids 84121.4 Atomic and Electronic

Interactions 842

O PTICAL P ROPERTIES OF M ETALS 843

O PTICAL P ROPERTIES OF N ONMETALS 844

21.5 Refraction 84421.6 Reflection 84621.7 Absorption 84621.8 Transmission 85021.9 Color 85021.10 Opacity and Translucency in Insulators 852

A PPLICATIONS OF O PTICAL

21.11 Luminescence 85321.12 Photoconductivity 853Materials of Importance—Light-Emitting Diodes 854

21.13 Lasers 85621.14 Optical Fibers in Communications 860

Contents • xix

22 Economic, Environmental, and

Societal Issues in Materials

Science and Engineering 868

Expansion 897B.7 Thermal Conductivity 900B.8 Specific Heat 903

B.9 Electrical Resistivity 906B.10 Metal Alloy Compositions

Appendix C Costs and Relative Costs for Selected Engineering Materials 911 Appendix D Repeat Unit Structures for Common Polymers 916

Appendix E Glass Transition and Melting Temperatures for Common Polymeric Materials 920

Glossary 921 Answers to Selected Problems 934 Index 939

APF = atomic packing factor (3.4)

a = lattice parameter: unit cell

x-axial length (3.4)

a = crack length of a surface crack

(8.5) at% = atom percent (4.4)

B = magnetic flux density

component i in at% (4.4)

Cy, Cp = heat capacity at constant

volume, pressure (19.2) CPR = corrosion penetration rate

(17.3) CVN = Charpy V-notch (8.6)

%CW = percent cold work (7.10)

c = lattice parameter: unit cell

d = average grain diameter (7.8)

d hkl = interplanar spacing for planes

of Miller indices h, k, and l

-logarithms

F = force, interatomic or

mechanical (2.5, 6.2)

f = Faraday constant (17.2) FCC = face-centered cubic crystal

structure (3.4)

HK = Knoop hardness (6.10) HRB, HRF = Rockwell hardness: B and F

scales (6.10) HR15N, HR45W = superficial Rockwell hardness:

15N and 45W scales (6.10)

HV = Vickers hardness (6.10)

h = Planck’s constant (21.2) (hkl) = Miller indices for a crystallo-

graphic plane (3.10)

• xxi

(hkil) = Miller indices for a

crystal-lographic plane, hexagonal crystals (3.10)

K Ic = plane strain fracture

tough-ness for mode I crack surface displacement (8.5)

N = number of fatigue cycles (8.8)

NA = Avogadro’s number (3.5)

N f = fatigue life (8.8)

n = principal quantum number (2.3)

n = number of atoms per unit cell

(3.5)

n = strain-hardening exponent (6.7)

n = number of electrons in an

electrochemical reaction (17.2)

n = number of conducting

elec-trons per cubic meter (18.7)

n = index of refraction (21.5)

n¿ = for ceramics, the number of

formula units per unit cell (12.2)

n i = intrinsic carrier (electron and

hole) concentration (18.10)

P = dielectric polarization (18.19)

P–B ratio = Pilling–Bedworth ratio (17.10)

p = number of holes per cubic

T g = glass transition temperature (13.10, 15.12)

T m = melting temperature TEM = transmission electron

[uvtw], [UVW] = indices for a crystallographic

direction, hexagonal crystals (3.9)

V = electrical potential difference

W i = mass fraction of phase i (9.8)

List of Symbols • xxiii

tcrss = critical resolved shear stress (7.5)

xm = magnetic susceptibility (20.2)

• 1

C h a p t e r 1 Introduction

A familiar item fabricated from three different material types is the

beverage container Beverages are marketed in aluminum (metal) cans (top), glass (ceramic) bottles (center), and plastic (polymer) bottles (bottom).

After studying this chapter, you should be able to do the following:

1 List six different property classifications of

mate-rials that determine their applicability

2 Cite the four components that are involved in

the design, production, and utilization of

materi-als, and briefly describe the interrelationships

between these components

3 Cite three criteria that are important in the

ma-terials selection process

4 (a) List the three primary classifications

of solid materials, and then cite the distinctive chemical feature of each

(b) Note the four types of advanced materials

and, for each, its distinctive feature(s)

5 (a) Briefly define smart material/system.

(b) Briefly explain the concept of

nanotechnol-ogy as it applies to materials.

Materials are probably more deep seated in our culture than most of us realize Transportation, housing, clothing, communication, recreation, and food production—virtually every segment of our everyday lives is influenced to one degree or another

by materials Historically, the development and advancement of societies have been intimately tied to the members’ ability to produce and manipulate materials to fill their needs In fact, early civilizations have been designated by the level of their materials development (Stone Age, Bronze Age, Iron Age).1

The earliest humans had access to only a very limited number of materials, those that occur naturally: stone, wood, clay, skins, and so on With time, they discovered techniques for producing materials that had properties superior to those of the natural ones; these new materials included pottery and various metals Furthermore, it was discovered that the properties of a material could be altered by heat treatments and by the addition of other substances At this point, materials utilization was totally a selection process that involved deciding from a given, rather limited set of materials, the one best suited for an application

by virtue of its characteristics It was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their proper-ties This knowledge, acquired over approximately the past 100 years, has empowered them

to fashion, to a large degree, the characteristics of materials Thus, tens of thousands of ferent materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society, including metals, plastics, glasses, and fibers

dif-The development of many technologies that make our existence so comfortable has been intimately associated with the accessibility of suitable materials An advance-ment in the understanding of a material type is often the forerunner to the stepwise progression of a technology For example, automobiles would not have been possible without the availability of inexpensive steel or some other comparable substitute In the contemporary era, sophisticated electronic devices rely on components that are made

from what are called semiconducting materials.

1The approximate dates for the beginnings of the Stone, Bronze, and Iron ages are 2.5 million bc, 3500 bc, and

1000 bc, respectively

Sometimes it is useful to subdivide the discipline of materials science and engineering

into materials science and materials engineering subdisciplines Strictly speaking,

materi-als science involves investigating the relationships that exist between the structures and

1.2 MATERIALS SCIENCE AND ENGINEERING

2 •

1.2 Materials Science and Engineering • 3

properties of materials In contrast, materials engineering involves, on the basis of these structure–property correlations, designing or engineering the structure of a material to produce a predetermined set of properties.2 From a functional perspective, the role of a materials scientist is to develop or synthesize new materials, whereas a materials engi-neer is called upon to create new products or systems using existing materials and/or to develop techniques for processing materials Most graduates in materials programs are trained to be both materials scientists and materials engineers

Structure is, at this point, a nebulous term that deserves some explanation In brief,

the structure of a material usually relates to the arrangement of its internal components

Subatomic structure involves electrons within the individual atoms and interactions with

their nuclei On an atomic level, structure encompasses the organization of atoms or molecules relative to one another The next larger structural realm, which contains large

groups of atoms that are normally agglomerated together, is termed microscopic,

mean-ing that which is subject to direct observation usmean-ing some type of microscope Finally,

structural elements that can be viewed with the naked eye are termed macroscopic The notion of property deserves elaboration While in service use, all materials are

exposed to external stimuli that evoke some type of response For example, a specimen subjected to forces experiences deformation, or a polished metal surface reflects light A property is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus Generally, definitions of properties are made independent of mate-rial shape and size

Virtually all important properties of solid materials may be grouped into six ent categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative For each, there is a characteristic type of stimulus capable of provoking different responses Mechanical properties relate deformation to an applied load or force; examples include elastic modulus (stiffness), strength, and toughness For electrical properties, such as electrical conductivity and dielectric constant, the stimulus is an electric field The thermal behavior of solids can be represented in terms of heat capacity and thermal conductivity Magnetic properties demonstrate the response of a material to the ap-plication of a magnetic field For optical properties, the stimulus is electromagnetic or light radiation; index of refraction and reflectivity are representative optical properties Finally, deteriorative characteristics relate to the chemical reactivity of materials The chapters that follow discuss properties that fall within each of these six classifications

differ-In addition to structure and properties, two other important components are

in-volved in the science and engineering of materials—namely, processing and

perform-ance With regard to the relationships of these four components, the structure of a

material depends on how it is processed Furthermore, a material’s performance is a function of its properties Thus, the interrelationship among processing, structure, prop-erties, and performance is as depicted in the schematic illustration shown in Figure 1.1 Throughout this text, we draw attention to the relationships among these four compo-nents in terms of the design, production, and utilization of materials

We present an example of these processing-structure-properties-performance ciples in Figure 1.2, a photograph showing three thin disk specimens placed over some printed matter It is obvious that the optical properties (i.e., the light transmittance) of each

prin-of the three materials are different; the one on the left is transparent (i.e., virtually all prin-of the

2Throughout this text, we draw attention to the relationships between material properties and structural elements

Figure 1.1 The four components of the discipline of materials science and

engineering and their interrelationship

reflected light passes through it), whereas the disks in the center and on the right are, tively, translucent and opaque All of these specimens are of the same material, aluminum

respec-oxide, but the leftmost one is what we call a single crystal—that is, has a high degree of

perfection—which gives rise to its transparency The center one is composed of numerous and very small single crystals that are all connected; the boundaries between these small crystals scatter a portion of the light reflected from the printed page, which makes this ma-terial optically translucent Finally, the specimen on the right is composed not only of many small, interconnected crystals, but also of a large number of very small pores or void spaces These pores also effectively scatter the reflected light and render this material opaque.Thus, the structures of these three specimens are different in terms of crystal boundaries and pores, which affect the optical transmittance properties Furthermore, each material was produced using a different processing technique If optical transmit-tance is an important parameter relative to the ultimate in-service application, the per-formance of each material will be different

Why do we study materials? Many an applied scientist or engineer, whether cal, civil, chemical, or electrical, is at one time or another exposed to a design problem involving materials, such as a transmission gear, the superstructure for a building, an oil refinery component, or an integrated circuit chip Of course, materials scientists and engineers are specialists who are totally involved in the investigation and design

mechani-of materials

Many times, a materials problem is one of selecting the right material from the thousands available The final decision is normally based on several criteria First, the in-service conditions must be characterized, for these dictate the properties required of the material On only rare occasions does a material possess the maximum or ideal com-bination of properties Thus, it may be necessary to trade one characteristic for another The classic example involves strength and ductility; normally, a material having a high strength has only a limited ductility In such cases, a reasonable compromise between two or more properties may be necessary

A second selection consideration is any deterioration of material properties that may occur during service operation For example, significant reductions in mechanical strength may result from exposure to elevated temperatures or corrosive environments

AND ENGINEERING?

Figure 1.2 Three thin disk specimens of

aluminum oxide that have been placed over a

printed page in order to demonstrate their

differences in light-transmittance characteristics

The disk on the left is transparent (i.e., virtually

all light that is reflected from the page passes

through it), whereas the one in the center is

translucent (meaning that some of this reflected

light is transmitted through the disk) The disk

on the right is opaque—that is, none of the light

passes through it These differences in optical

properties are a consequence of differences in

structure of these materials, which have resulted

from the way the materials were processed

1.3 Why Study Materials Science and Engineering? • 5

Finally, probably the overriding consideration is that of economics: What will the finished product cost? A material may be found that has the ideal set of properties but is prohibitively expensive Here again, some compromise is inevitable The cost of a finished piece also includes any expense incurred during fabrication to produce the desired shape.The more familiar an engineer or scientist is with the various characteristics and structure–property relationships, as well as the processing techniques of materials, the more proficient and confident he or she will be in making judicious materials choices based on these criteria

Liberty Ship Failures

C A S E S T U D Y

The following case study illustrates one role that

materials scientists and engineers are called

upon to assume in the area of materials performance:

analyze mechanical failures, determine their causes,

and then propose appropriate measures to guard

against future incidents

The failure of many of the World War II Liberty

ships3 is a well-known and dramatic example of the

brittle fracture of steel that was thought to be

duc-tile.4 Some of the early ships experienced structural

damage when cracks developed in their decks and

hulls Three of them catastrophically split in half when

cracks formed, grew to critical lengths, and then

rap-idly propagated completely around the ships’ girths

Figure 1.3 shows one of the ships that fractured the

day after it was launched

Subsequent investigations concluded one or more

of the following factors contributed to each failure5:

• When some normally ductile metal alloys are

cooled to relatively low temperatures, they

be-come susceptible to brittle fracture—that is, they

experience a ductile-to-brittle transition upon

cooling through a critical range of temperatures

These Liberty ships were constructed of steel that

experienced a ductile-to-brittle transition Some

of them were deployed to the frigid North tic, where the once ductile metal experienced brit-tle fracture when temperatures dropped to below the transition temperature.6

Atlan-• The corner of each hatch (i.e., door) was square; these corners acted as points of stress concentra-tion where cracks can form

• German U-boats were sinking cargo ships faster than they could be replaced using existing con-struction techniques Consequently, it became necessary to revolutionize construction methods

to build cargo ships faster and in greater numbers This was accomplished using prefabricated steel sheets that were assembled by welding rather than by the traditional time-consuming riveting Unfortunately, cracks in welded structures may propagate unimpeded for large distances, which can lead to catastrophic failure However, when structures are riveted, a crack ceases to propagate once it reaches the edge of a steel sheet

• Weld defects and discontinuities (i.e., sites where

cracks can form) were introduced by enced operators

inexperi-3During World War II, 2,710 Liberty cargo ships were mass-produced by the United States to supply food and

materials to the combatants in Europe

4Ductile metals fail after relatively large degrees of permanent deformation; however, very little if any permanent deformation accompanies the fracture of brittle materials Brittle fractures can occur very suddenly as cracks spread rapidly; crack propagation is normally much slower in ductile materials, and the eventual fracture takes longer For these reasons, the ductile mode of fracture is usually preferred Ductile and brittle fractures are discussed in Sections 8.3 and 8.4

5Sections 8.2 through 8.6 discuss various aspects of failure

6This ductile-to-brittle transition phenomenon, as well as techniques that are used to measure and raise the critical temperature range, are discussed in Section 8.6

(continued)

Remedial measures taken to correct these

prob-lems included the following:

• Lowering the ductile-to-brittle temperature of

the steel to an acceptable level by improving steel

quality (e.g., reducing sulfur and phosphorus

im-purity contents)

• Rounding off hatch corners by welding a curved

reinforcement strip on each corner.7

• Installing crack-arresting devices such as riveted

straps and strong weld seams to stop propagating

Figure 1.3 The Liberty ship S.S Schenectady, which, in 1943, failed

before leaving the shipyard

(Reprinted with permission of Earl R Parker, Brittle Behavior of Engineering

Structures, National Academy of Sciences, National Research Council, John

Wiley & Sons, New York, 1957.)

7The reader may note that corners of windows and doors for all of today’s marine and aircraft structures are

rounded

Solid materials have been conveniently grouped into three basic categories: metals, ramics, and polymers, a scheme based primarily on chemical makeup and atomic struc-ture Most materials fall into one distinct grouping or another In addition, there are the composites that are engineered combinations of two or more different materials A brief explanation of these material classifications and representative characteristics is offered next Another category is advanced materials—those used in high-technology applica-tions, such as semiconductors, biomaterials, smart materials, and nanoengineered mate-rials; these are discussed in Section 1.5

1.4 Classification of Materials • 7

Metals

Metals are composed of one or more metallic elements (e.g., iron, aluminum, copper,

titanium, gold, nickel), and often also nonmetallic elements (e.g., carbon, nitrogen, oxygen) in relatively small amounts.8 Atoms in metals and their alloys are arranged in a very orderly manner (as discussed in Chapter 3) and are relatively dense in comparison

to the ceramics and polymers (Figure 1.4) With regard to mechanical characteristics, these materials are relatively stiff (Figure 1.5) and strong (Figure 1.6), yet are ductile (i.e., capable of large amounts of deformation without fracture), and are resistant to fracture (Figure 1.7), which accounts for their widespread use in structural applications Metallic materials have large numbers of nonlocalized electrons—that is, these electrons are not bound to particular atoms Many properties of metals are directly attributable

to these electrons For example, metals are extremely good conductors of electricity

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

2

1.0 0.8 0.6

0.2 0.4

0.1

Metals Platinum Silver Copper Iron/Steel Titanium Aluminum Magnesium

Composites GFRC CFRC

Woods

Polymers PTFE PVC PS PE Rubber

Glass Concrete Ceramics

(i.e., elastic modulus)

values for various

0.01

0.001

Composites

GFRC CFRC

Woods Polymers

PVC

PTFE PE

Rubbers

PS, Nylon

Metals Tungsten Iron/Steel Aluminum Magnesium Titanium

Ceramics SiC

Glass Concrete

Tutorial Video:

Metals

Strength (tensile strength, in units of

1000

100

10

Nylon PS

PE

PVC PTFE Polymers

Steel alloys

Gold

Aluminum alloys

Cu,Ti alloys

Metals

CFRC GFRC Composites

Woods Glass

SiC Ceramics

Figure 1.6

Bar chart of

room-temperature strength

(i.e., tensile strength)

values for various

metals, ceramics,

polymers, and

composite materials

Wood

Nylon Polymers

Polystyrene Polyethylene

Metals Steel alloys Titanium alloys Aluminum alloys

Figure 1.7

Bar chart of

room-temperature

resistance to fracture

(i.e., fracture

tough-ness) for various

and Design, third

edition, M F Ashby and

Figure 1.9 shows several common and familiar objects that are made of metallic materials Furthermore, the types and applications of metals and their alloys are discussed in Chapter 11

Ceramics

Ceramics are compounds between metallic and nonmetallic elements; they are most

fre-quently oxides, nitrides, and carbides For example, common ceramic materials include

aluminum oxide (or alumina, Al2O3), silicon dioxide (or silica, SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and, in addition, what some refer to as the traditional ceramics—those

composed of clay minerals (e.g., porcelain), as well as cement and glass With regard to chanical behavior, ceramic materials are relatively stiff and strong—stiffnesses and strengths are comparable to those of the metals (Figures 1.5 and 1.6) In addition, they are typically very hard Historically, ceramics have exhibited extreme brittleness (lack of ductility) and are highly susceptible to fracture (Figure 1.7) However, newer ceramics are being engineered

me-to have improved resistance me-to fracture; these materials are used for cookware, cutlery, and

Tutorial Video:

Ceramics

Figure 1.9 Familiar objects made of

metals and metal alloys (from left to right): silverware (fork and knife), scissors, coins, a gear, a wedding ring, and a nut and bolt

even automobile engine parts Furthermore, ceramic materials are typically insulative to the passage of heat and electricity (i.e., have low electrical conductivities, Figure 1.8) and are more resistant to high temperatures and harsh environments than are metals and polymers With regard to optical characteristics, ceramics may be transparent, translucent, or opaque (Figure 1.2), and some of the oxide ceramics (e.g., Fe3O4) exhibit magnetic behavior.Several common ceramic objects are shown in Figure 1.10 The characteristics, types, and applications of this class of materials are also discussed in Chapters 12 and 13

Polymers

Polymers include the familiar plastic and rubber materials Many of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic ele-ments (i.e., O, N, and Si) Furthermore, they have very large molecular structures, often chainlike in nature, that often have a backbone of carbon atoms Some common and familiar polymers are polyethylene (PE), nylon, poly(vinyl chloride) (PVC), polycar-bonate (PC), polystyrene (PS), and silicone rubber These materials typically have low densities (Figure 1.4), whereas their mechanical characteristics are generally dissimilar

to those of the metallic and ceramic materials—they are not as stiff or strong as these

other material types (Figures 1.5 and 1.6) However, on the basis of their low densities, many times their stiffnesses and strengths on a per-mass basis are comparable to those

of the metals and ceramics In addition, many of the polymers are extremely ductile and pliable (i.e., plastic), which means they are easily formed into complex shapes In general, they are relatively inert chemically and unreactive in a large number of environ-ments One major drawback to the polymers is their tendency to soften and/or decom-pose at modest temperatures, which, in some instances, limits their use Furthermore, they have low electrical conductivities (Figure 1.8) and are nonmagnetic

Figure 1.11 shows several articles made of polymers that are familiar to the reader Chapters 14 and 15 are devoted to discussions of the structures, properties, applications, and processing of polymeric materials

Figure 1.10 Common objects made of

ceramic materials: scissors, a china teacup, a

building brick, a floor tile, and a glass vase

Figure 1.11 Several common objects

made of polymeric materials: plastic

tableware (spoon, fork, and knife), billiard

balls, a bicycle helmet, two dice, a lawn

mower wheel (plastic hub and rubber tire),

and a plastic milk carton

Tutorial Video:

Polymers

1.4 Classification of Materials • 11

Composites

A composite is composed of two (or more) individual materials that come from the

categories previously discussed—metals, ceramics, and polymers The design goal of a composite is to achieve a combination of properties that is not displayed by any single material and also to incorporate the best characteristics of each of the component ma-terials A large number of composite types are represented by different combinations

of metals, ceramics, and polymers Furthermore, some naturally occurring materials are composites—for example, wood and bone However, most of those we consider in our discussions are synthetic (or human-made) composites

One of the most common and familiar composites is fiberglass, in which small glass fibers are embedded within a polymeric material (normally an epoxy or polyester).9 The glass fibers are relatively strong and stiff (but also brittle), whereas the polymer is more flexible Thus, fiberglass is relatively stiff, strong (Figures 1.5 and 1.6), and flexible In addition, it has a low density (Figure 1.4)

Another technologically important material is the carbon fiber–reinforced polymer (CFRP) composite—carbon fibers that are embedded within a polymer These materials are stiffer and stronger than glass fiber–reinforced materials (Figures 1.5 and 1.6) but more expensive CFRP composites are used in some aircraft and aerospace applications,

as well as in high-tech sporting equipment (e.g., bicycles, golf clubs, tennis rackets, skis/snowboards) and recently in automobile bumpers The new Boeing 787 fuselage is pri-marily made from such CFRP composites

Chapter 16 is devoted to a discussion of these interesting composite materials

Carbonated Beverage Containers

C A S E S T U D Y

One common item that presents some interesting

material property requirements is the container

for carbonated beverages The material used for this

application must satisfy the following constraints: (1)

provide a barrier to the passage of carbon dioxide,

which is under pressure in the container; (2) be

non-toxic, unreactive with the beverage, and, preferably,

recyclable; (3) be relatively strong and capable of

surviving a drop from a height of several feet when

containing the beverage; (4) be inexpensive,

includ-ing the cost to fabricate the final shape; (5) if

opti-cally transparent, retain its optical clarity; and (6) be

capable of being produced in different colors and/or

adorned with decorative labels

All three of the basic material types—metal

(aluminum), ceramic (glass), and polymer

(polyes-ter plastic)—are used for carbonated beverage

con-tainers (per the chapter-opening photographs) All

of these materials are nontoxic and unreactive with

beverages In addition, each material has its pros and cons For example, the aluminum alloy is relatively strong (but easily dented), is a very good barrier to the diffusion of carbon dioxide, is easily recycled, cools beverages rapidly, and allows labels to be painted onto its surface However, the cans are op-tically opaque and relatively expensive to produce Glass is impervious to the passage of carbon dioxide,

is a relatively inexpensive material, and may be cled, but it cracks and fractures easily, and glass bot-tles are relatively heavy Whereas plastic is relatively strong, may be made optically transparent, is inex-pensive and lightweight, and is recyclable, it is not

recy-as impervious to the precy-assage of carbon dioxide recy-as aluminum and glass For example, you may have no-ticed that beverages in aluminum and glass contain-ers retain their carbonization (i.e., “fizz”) for several years, whereas those in two-liter plastic bottles “go flat” within a few months

9Fiberglass is sometimes also termed a glass fiber–reinforced polymer composite (GFRP).

Tutorial Video:

Composites

Materials utilized in high-technology (or high-tech) applications are sometimes termed

advanced materials By high technology, we mean a device or product that operates or

functions using relatively intricate and sophisticated principles, including electronic equipment (camcorders, CD/DVD players), computers, fiber-optic systems, spacecraft, aircraft, and military rocketry These advanced materials are typically traditional mate-rials whose properties have been enhanced and also newly developed, high-performance materials Furthermore, they may be of all material types (e.g., metals, ceramics, polymers) and are normally expensive Advanced materials include semiconductors,

biomaterials, and what we may term materials of the future (i.e., smart materials and

nanoengineered materials), which we discuss next The properties and applications of

a number of these advanced materials—for example, materials that are used for lasers, integrated circuits, magnetic information storage, liquid crystal displays (LCDs), and fiber optics—are also discussed in subsequent chapters

Semiconductors

Semiconductors have electrical properties that are intermediate between those of

electrical conductors (i.e., metals and metal alloys) and insulators (i.e., ceramics and polymers)—see Figure 1.8 Furthermore, the electrical characteristics of these ma-terials are extremely sensitive to the presence of minute concentrations of impurity atoms, for which the concentrations may be controlled over very small spatial regions Semiconductors have made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries (not to mention our lives) over the past three decades

Biomaterials

Biomaterials are employed in components implanted into the human body to replace

dis-eased or damaged body parts These materials must not produce toxic substances and must

be compatible with body tissues (i.e., must not cause adverse biological reactions) All of the preceding materials—metals, ceramics, polymers, composites, and semiconductors—may be used as biomaterials

Smart Materials

Smart (or intelligent) materials are a group of new and state-of-the-art materials now

being developed that will have a significant influence on many of our technologies The

adjective smart implies that these materials are able to sense changes in their

environ-ment and then respond to these changes in predetermined manners—traits that are also

found in living organisms In addition, this smart concept is being extended to rather

sophisticated systems that consist of both smart and traditional materials

Components of a smart material (or system) include some type of sensor (which detects an input signal) and an actuator (which performs a responsive and adaptive function) Actuators may be called upon to change shape, position, natural frequency,

or mechanical characteristics in response to changes in temperature, electric fields, and/or magnetic fields

Four types of materials are commonly used for actuators: shape-memory alloys, ezoelectric ceramics, magnetostrictive materials, and electrorheological/magnetorheo-

pi-logical fluids Shape-memory alloys are metals that, after having been deformed, revert

to their original shape when temperature is changed (see the Materials of Importance

box following Section 10.9) Piezoelectric ceramics expand and contract in response to

an applied electric field (or voltage); conversely, they also generate an electric field

when their dimensions are altered (see Section 18.25) The behavior of magnetostrictive

materials is analogous to that of the piezoelectrics, except that they are responsive to