The ultimate tensile strength for nylon is 5.00 108n m2

An Introduction

MATERIALS SCIENCE and ENGINEERING

William D. Callister, Jr. David G. Rethwisch

9E

Characteristics of Selected Elements

Atomic Density of Crystal Atomic Ionic Most Melting Atomic Weight Solid, 20�C Structure, Radius Radius Common Point

Element Symbol Number (amu) (g/cm3) 20�C (nm) (nm) Valence (�C)

Aluminum Al 13 26.98 2.71 FCC 0.143 0.053 3� 660.4 Argon Ar 18 39.95 — — — — Inert �189.2 Barium Ba 56 137.33 3.5 BCC 0.217 0.136 2� 725 Beryllium Be 4 9.012 1.85 HCP 0.114 0.035 2� 1278 Boron B 5 10.81 2.34 Rhomb. — 0.023 3� 2300 Bromine Br 35 79.90 — — — 0.196 1� �7.2 Cadmium Cd 48 112.41 8.65 HCP 0.149 0.095 2� 321 Calcium Ca 20 40.08 1.55 FCC 0.197 0.100 2� 839 Carbon C 6 12.011 2.25 Hex. 0.071 �0.016 4� (sublimes at 3367) Cesium Cs 55 132.91 1.87 BCC 0.265 0.170 1� 28.4 Chlorine Cl 17 35.45 — — — 0.181 1� �101 Chromium Cr 24 52.00 7.19 BCC 0.125 0.063 3� 1875 Cobalt Co 27 58.93 8.9 HCP 0.125 0.072 2� 1495 Copper Cu 29 63.55 8.94 FCC 0.128 0.096 1� 1085 Fluorine F 9 19.00 — — — 0.133 1� �220 Gallium Ga 31 69.72 5.90 Ortho. 0.122 0.062 3� 29.8 Germanium Ge 32 72.64 5.32 Dia. cubic 0.122 0.053 4� 937 Gold Au 79 196.97 19.32 FCC 0.144 0.137 1� 1064 Helium He 2 4.003 — — — — Inert �272 (at 26 atm) Hydrogen H 1 1.008 — — — 0.154 1� �259 Iodine I 53 126.91 4.93 Ortho. 0.136 0.220 1� 114 Iron Fe 26 55.85 7.87 BCC 0.124 0.077 2� 1538 Lead Pb 82 207.2 11.35 FCC 0.175 0.120 2� 327 Lithium Li 3 6.94 0.534 BCC 0.152 0.068 1� 181 Magnesium Mg 12 24.31 1.74 HCP 0.160 0.072 2� 649 Manganese Mn 25 54.94 7.44 Cubic 0.112 0.067 2� 1244 Mercury Hg 80 200.59 — — — 0.110 2� �38.8 Molybdenum Mo 42 95.94 10.22 BCC 0.136 0.070 4� 2617 Neon Ne 10 20.18 — — — — Inert �248.7 Nickel Ni 28 58.69 8.90 FCC 0.125 0.069 2� 1455 Niobium Nb 41 92.91 8.57 BCC 0.143 0.069 5� 2468 Nitrogen N 7 14.007 — — — 0.01–0.02 5� �209.9 Oxygen O 8 16.00 — — — 0.140 2� �218.4 Phosphorus P 15 30.97 1.82 Ortho. 0.109 0.035 5� 44.1 Platinum Pt 78 195.08 21.45 FCC 0.139 0.080 2� 1772 Potassium K 19 39.10 0.862 BCC 0.231 0.138 1� 63 Silicon Si 14 28.09 2.33 Dia. cubic 0.118 0.040 4� 1410 Silver Ag 47 107.87 10.49 FCC 0.144 0.126 1� 962 Sodium Na 11 22.99 0.971 BCC 0.186 0.102 1� 98 Sulfur S 16 32.06 2.07 Ortho. 0.106 0.184 2� 113 Tin Sn 50 118.71 7.27 Tetra. 0.151 0.071 4� 232 Titanium Ti 22 47.87 4.51 HCP 0.145 0.068 4� 1668 Tungsten W 74 183.84 19.3 BCC 0.137 0.070 4� 3410 Vanadium V 23 50.94 6.1 BCC 0.132 0.059 5� 1890 Zinc Zn 30 65.41 7.13 HCP 0.133 0.074 2� 420 Zirconium Zr 40 91.22 6.51 HCP 0.159 0.079 4� 1852

Values of Selected Physical Constants

Quantity Symbol SI Units cgs Units

Avogadro’s number NA 6.022 � 10 23 6.022 � 1023

molecules/mol molecules/mol Boltzmann’s constant k 1.38 � 10�23 J/atom K 1.38 � 10�16 erg/atom K

8.62 � 10�5 eV/atom K Bohr magneton mB 9.27 � 10

�24 A m2 9.27 � 10�21 erg/gaussa

Electron charge e 1.602 � 10�19 C 4.8 � 10�10 statcoulb

Electron mass — 9.11 � 10�31 kg 9.11 � 10�28 g Gas constant R 8.31 J/mol K 1.987 cal/mol K Permeability of a vacuum m0 1.257 � 10

�6 henry/m unitya

Permittivity of a vacuum �0 8.85 � 10 �12 farad/m unityb

Planck’s constant h 6.63 � 10�34 J s 6.63 � 10�27 erg s 4.13 � 10�15 eV s

Velocity of light in a vacuum c 3 � 108 m/s 3 � 1010 cm/s a In cgs-emu units. b In cgs-esu units.

# ##

##

# # ##

Unit Abbreviations

A � ampere in. � inch N � newton � angstrom J � joule nm � nanometer

Btu � British thermal unit K � degrees Kelvin P � poise C � Coulomb kg � kilogram Pa � Pascal

�C � degrees Celsius lbf � pound force s � second cal � calorie (gram) lbm � pound mass T � temperature cm � centimeter m � meter �m � micrometer eV � electron volt Mg � megagram (micron) �F � degrees Fahrenheit mm � millimeter W � watt ft � foot mol � mole psi � pounds per square g � gram MPa � megapascal inch

Å

SI Multiple and Submultiple Prefixes

Factor by Which Multiplied Prefix Symbol

109 giga G 106 mega M 103 kilo k 10�2 centia c 10�3 milli m 10�6 micro � 10�9 nano n 10�12 pico p

a Avoided when possible.

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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

Front Cover: Depiction of a unit cell for iron carbide (Fe3C) from three different perspectives. Brown and blue spheres represent iron 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 EXECUTIVE EDITOR Daniel Sayre EDITORIAL PROGRAM ASSISTANT Jessica Knecht SENIOR CONTENT MANAGER Kevin Holm PRODUCTION EDITOR James Metzger EXECUTIVE MARKETING MANAGER Christopher Ruel DESIGN DIRECTOR Harry Nolan SENIOR DESIGNER Madelyn Lesure SENIOR PHOTO EDITOR MaryAnn Price COVER ART Roy Wiemann and William D. Callister, Jr.

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.

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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.

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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

viii • Preface

New/Revised Content Several important changes have been made with this Ninth Edition. One of the most signifi- 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.

Preface • ix

• Student Lecture PowerPoint® Slides. These slides (in both Adobe Acrobat® PDF and PowerPoint® formats) are virtually identical to the lecture slides provided to an instructor for use in the classroom. The student set has been designed to allow for note taking on printouts.

• 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.

x • Preface

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 assign- 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 on their achievement in the classroom and beyond. 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.

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• 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 materi- 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.

Feedback

Since we undertook the task of writing this and previous editions, instructors and stu- 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.

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 market- ing survey; their valuable contributions were driving forces for many of the changes and additions to this ninth edition.

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

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

William D. Callister, Jr. David G. Rethwisch

October 2013

Contents

LIST OF SYMBOLS xxi

1. Introduction 1

Learning Objectives 2 1.1 Historical Perspective 2 1.2 Materials Science and Engineering 2 1.3 Why Study Materials Science and

Engineering? 4 Case Study—Liberty Ship Failures 5 1.4 Classification of Materials 6 Case Study—Carbonated Beverage

Containers 11 1.5 Advanced Materials 12 1.6 Modern Materials’ Needs 14 1.7 Processing/Structure/Properties/

Performance Correlations 15 Summary 17 References 17 Questions 18

2. Atomic Structure and Interatomic Bonding 19

Learning Objectives 20 2.1 Introduction 20

ATOMIC STRUCTURE 20

2.2 Fundamental Concepts 20 2.3 Electrons in Atoms 22 2.4 The Periodic Table 28

ATOMIC BONDING IN SOLIDS 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 2.8 Mixed Bonding 43 2.9 Molecules 44 2.10 Bonding Type-Materials Classification

Correlations 44 Summary 45

Equation Summary 46 List of Symbols 46 Processing/Structure/Properties/Performance Summary 47 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 52 3.1 Introduction 52

CRYSTAL STRUCTURES 52

3.2 Fundamental Concepts 52 3.3 Unit Cells 53 3.4 Metallic Crystal Structures 54 3.5 Density Computations 60 3.6 Polymorphism and Allotropy 60 Materials of Importance—Tin (Its

Allotropic Transformation) 61 3.7 Crystal Systems 62

CRYSTALLOGRAPHIC POINTS, DIRECTIONS, AND PLANES 64

3.8 Point Coordinates 64 3.9 Crystallographic Directions 67 3.10 Crystallographic Planes 75 3.11 Linear and Planar Densities 81 3.12 Close-Packed Crystal Structures 82

CRYSTALLINE AND NONCRYSTALLINE MATERIALS 84

3.13 Single Crystals 84 3.14 Polycrystalline Materials 84 3.15 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

xiv • Contents

Processing/Structure/Properties/Performance Summary 96 Important Terms and Concepts 97 References 97 Questions and Problems 97 Fundamentals of Engineering Questions and Problems 104

4. Imperfections in Solids 105

Learning Objectives 106 4.1 Introduction 106

POINT DEFECTS 106

4.2 Vacancies and Self-Interstitials 106 4.3 Impurities in Solids 108 4.4 Specification of Composition 111

MISCELLANEOUS IMPERFECTIONS 115

4.5 Dislocations—Linear Defects 115 4.6 Interfacial Defects 118 Materials of Importance—Catalysts (and

Surface Defects) 121 4.7 Bulk or Volume Defects 122 4.8 Atomic Vibrations 122

MICROSCOPIC EXAMINATION 123

4.9 Basic Concepts of Microscopy 123 4.10 Microscopic Techniques 124 4.11 Grain-Size Determination 128

Summary 131 Equation Summary 132 List of Symbols 133 Processing/Structure/Properties/Performance Summary 134 Important Terms and Concepts 135 References 135 Questions and Problems 135 Design Problems 138 Fundamentals of Engineering Questions and Problems 139

5. Diffusion 140

Learning Objectives 141 5.1 Introduction 141 5.2 Diffusion Mechanisms 142 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 169 6.1 Introduction 169 6.2 Concepts of Stress and Strain 170

ELASTIC DEFORMATION 174

6.3 Stress–Strain Behavior 174 6.4 Anelasticity 177 6.5 Elastic Properties of Materials 177

PLASTIC DEFORMATION 180

6.6 Tensile Properties 180 6.7 True Stress and Strain 187 6.8 Elastic Recovery After Plastic

Deformation 190 6.9 Compressive, Shear, and Torsional

Deformation 191 6.10 Hardness 191

PROPERTY VARIABILITY AND DESIGN/SAFETY FACTORS 197

6.11 Variability of Material Properties 197 6.12 Design/Safety Factors 199

Summary 203 Equation Summary 205 List of Symbols 205 Processing/Structure/Properties/Performance Summary 206 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 217 7.1 Introduction 217

DISLOCATIONS AND PLASTIC DEFORMATION 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

MECHANISMS OF STRENGTHENING IN METALS 229

7.8 Strengthening by Grain Size Reduction 229 7.9 Solid-Solution Strengthening 231 7.10 Strain Hardening 232

RECOVERY, RECRYSTALLIZATION, AND GRAIN GROWTH 235

7.11 Recovery 235 7.12 Recrystallization 236 7.13 Grain Growth 240

Summary 242 Equation Summary 244 List of Symbols 244 Processing/Structure/Properties/Performance Summary 245 Important Terms and Concepts 246 References 246 Questions and Problems 246 Design Problems 250 Fundamentals of Engineering Questions and Problems 250

8. Failure 251

Learning Objectives 252 8.1 Introduction 252

FRACTURE 253

8.2 Fundamentals of Fracture 253 8.3 Ductile Fracture 253 8.4 Brittle Fracture 255 8.5 Principles of Fracture Mechanics 257 8.6 Fracture Toughness Testing 265

FATIGUE 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

CREEP 281

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 298 9.1 Introduction 298

DEFINITIONS AND BASIC CONCEPTS 298

9.2 Solubility Limit 299 9.3 Phases 300 9.4 Microstructure 300 9.5 Phase Equilibria 300 9.6 One-Component (or Unary) Phase

Diagrams 301

BINARY PHASE DIAGRAMS 302

9.7 Binary Isomorphous Systems 303 9.8 Interpretation of Phase Diagrams 305 9.9 Development of Microstructure in

Isomorphous Alloys 309 9.10 Mechanical Properties of Isomorphous

Alloys 312 9.11 Binary Eutectic Systems 312 9.12 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 328 9.15 Congruent Phase Transformations 329 9.16 Ceramic and Ternary Phase

Diagrams 330 9.17 The Gibbs Phase Rule 330

THE IRON–CARBON SYSTEM 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 Mechanical Properties 356

Learning Objectives 357 10.1 Introduction 357

PHASE TRANSFORMATIONS 357

10.2 Basic Concepts 357 10.3 The Kinetics of Phase Transformations 358 10.4 Metastable Versus Equilibrium States 369

MICROSTRUCTURAL AND PROPERTY CHANGES IN IRON–CARBON ALLOYS 370

10.5 Isothermal Transformation Diagrams 370 10.6 Continuous-Cooling Transformation

Diagrams 381 10.7 Mechanical Behavior of Iron–Carbon

Alloys 384 10.8 Tempered Martensite 388 10.9 Review of Phase Transformations and

Mechanical Properties for Iron–Carbon Alloys 391

Materials of Importance—Shape-Memory Alloys 394 Summary 397 Equation Summary 398 List of Symbols 399 Processing/Structure/Properties/Performance Summary 399 Important Terms and Concepts 401 References 402 Questions and Problems 402 Design Problems 406 Fundamentals of Engineering Questions and Problems 406

11. Applications and Processing of Metal Alloys 408

Learning Objectives 409 11.1 Introduction 409

TYPES OF METAL ALLOYS 410

11.2 Ferrous Alloys 410 11.3 Nonferrous Alloys 422 Materials of Importance—Metal Alloys

Used for Euro Coins 433

FABRICATION OF METALS 434

11.4 Forming Operations 434

11.5 Casting 436 11.6 Miscellaneous Techniques 437

THERMAL PROCESSING OF METALS 439

11.7 Annealing Processes 439 11.8 Heat Treatment of Steels 441 11.9 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 468 12.1 Introduction 468

CERAMIC STRUCTURES 468

12.2 Crystal Structures 469 12.3 Silicate Ceramics 477 12.4 Carbon 481 12.5 Imperfections in Ceramics 482 12.6 Diffusion in Ionic Materials 486 12.7 Ceramic Phase Diagrams 487

MECHANICAL PROPERTIES 490

12.8 Brittle Fracture of Ceramics 491 12.9 Stress–Strain Behavior 495 12.10 Mechanisms of Plastic Deformation 497 12.11 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 511 13.1 Introduction 511

TYPES AND APPLICATIONS OF CERAMICS 512

xvi • Contents

13.2 Glasses 512 13.3 Glass–Ceramics 512 13.4 Clay Products 514 13.5 Refractories 514 13.6 Abrasives 516 13.7 Cements 517 13.8 Carbons 518 13.9 Advanced Ceramics 521

FABRICATION AND PROCESSING OF CERAMICS 525

13.10 Fabrication and Processing of Glasses and Glass–Ceramics 526

13.11 Fabrication and Processing of Clay Products 531

13.12 Powder Pressing 535 13.13 Tape Casting 537

Summary 538 Processing/Structure/Properties/Performance Summary 540 Important Terms and Concepts 542 References 543 Questions and Problems 543 Design Problem 544 Fundamentals of Engineering Questions and Problems 544

14. Polymer Structures 545

Learning Objectives 546 14.1 Introduction 546 14.2 Hydrocarbon Molecules 546 14.3 Polymer Molecules 549 14.4 The Chemistry of Polymer Molecules 549 14.5 Molecular Weight 553 14.6 Molecular Shape 556 14.7 Molecular Structure 558 14.8 Molecular Configurations 559 14.9 Thermoplastic and Thermosetting

Polymers 562 14.10 Copolymers 563 14.11 Polymer Crystallinity 564 14.12 Polymer Crystals 568 14.13 Defects in Polymers 570 14.14 Diffusion in Polymeric Materials 571

Summary 573 Equation Summary 575 List of Symbols 575 Processing/Structure/Properties/Performance Summary 575 Important Terms and Concepts 576 References 576 Questions and Problems 577 Fundamentals of Engineering Questions and Problems 579

15. Characteristics, Applications, and Processing of Polymers 580

Learning Objectives 581 15.1 Introduction 581

MECHANICAL BEHAVIOR OF POLYMERS 581

15.2 Stress–Strain Behavior 581 15.3 Macroscopic Deformation 584 15.4 Viscoelastic Deformation 584 15.5 Fracture of Polymers 588 15.6 Miscellaneous Mechanical

Characteristics 590

MECHANISMS OF DEFORMATION AND FOR STRENGTHENING OF POLYMERS 591

15.7 Deformation of Semicrystalline Polymers 591

15.8 Factors That Influence the Mechanical Properties of Semicrystalline Polymers 593

Materials of Importance—Shrink-Wrap Polymer Films 597

15.9 Deformation of Elastomers 597

CRYSTALLIZATION, MELTING, AND GLASS- TRANSITION PHENOMENA IN POLYMERS 599

15.10 Crystallization 600 15.11 Melting 601 15.12 The Glass Transition 601 15.13 Melting and Glass Transition

Temperatures 601 15.14 Factors That Influence Melting and Glass

Transition Temperatures 603

POLYMER TYPES 605

15.15 Plastics 605 Materials of Importance—Phenolic

Billiard Balls 607 15.16 Elastomers 608 15.17 Fibers 610 15.18 Miscellaneous Applications 610 15.19 Advanced Polymeric Materials 612

POLYMER SYNTHESIS AND PROCESSING 616

15.20 Polymerization 616 15.21 Polymer Additives 618 15.22 Forming Techniques for Plastics 620 15.23 Fabrication of Elastomers 622 15.24 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 References 629 Questions and Problems 629 Design Questions 633 Fundamentals of Engineering Question 633

16. Composites 634

Learning Objectives 635 16.1 Introduction 635

PARTICLE-REINFORCED COMPOSITES 637

16.2 Large-Particle Composites 637 16.3 Dispersion-Strengthened Composites 641

FIBER-REINFORCED COMPOSITES 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 16.8 Polymer-Matrix Composites 653 16.9 Metal-Matrix Composites 659 16.10 Ceramic-Matrix Composites 660 16.11 Carbon–Carbon Composites 662 16.12 Hybrid Composites 662 16.13 Processing of Fiber-Reinforced

Composites 663

STRUCTURAL COMPOSITES 665

16.14 Laminar Composites 665 16.15 Sandwich Panels 667 Case Study—Use of Composites in the

Boeing 787 Dreamliner 669 16.16 Nanocomposites 670

Summary 673 Equation Summary 675 List of Symbols 676 Important Terms and Concepts 676 References 676 Questions and Problems 676 Design Problems 679 Fundamentals of Engineering Questions and Problems 680

17. Corrosion and Degradation of Materials 681

Learning Objectives 682 17.1 Introduction 682

CORROSION OF METALS 683

17.2 Electrochemical Considerations 683 17.3 Corrosion Rates 689 17.4 Prediction of Corrosion Rates 691

17.5 Passivity 698 17.6 Environmental Effects 699 17.7 Forms of Corrosion 699 17.8 Corrosion Environments 707 17.9 Corrosion Prevention 707 17.10 Oxidation 709

CORROSION OF CERAMIC MATERIALS 712

DEGRADATION OF POLYMERS 713

17.11 Swelling and Dissolution 713 17.12 Bond Rupture 715 17.13 Weathering 716

Summary 717 Equation Summary 719 List of Symbols 719 Important Terms and Concepts 720 References 720 Questions and Problems 721 Design Problems 723 Fundamentals of Engineering Questions and Problems 724

18. Electrical Properties 725

Learning Objectives 726 18.1 Introduction 726

ELECTRICAL CONDUCTION 726

18.2 Ohm’s Law 726 18.3 Electrical Conductivity 727 18.4 Electronic and Ionic Conduction 728 18.5 Energy Band Structures in

Solids 728 18.6 Conduction in Terms of Band and

Atomic Bonding Models 730 18.7 Electron Mobility 732 18.8 Electrical Resistivity of Metals 733 18.9 Electrical Characteristics of Commercial

Alloys 736 Materials of Importance—Aluminum

Electrical Wires 736

SEMICONDUCTIVITY 738

18.10 Intrinsic Semiconduction 738 18.11 Extrinsic Semiconduction 741 18.12 The Temperature Dependence of Carrier

Concentration 744 18.13 Factors That Affect Carrier

Mobility 745 18.14 The Hall Effect 749 18.15 Semiconductor Devices 751

ELECTRICAL CONDUCTION IN IONIC CERAMICS AND IN POLYMERS 757

18.16 Conduction in Ionic Materials 758

xviii • Contents

18.17 Electrical Properties of Polymers 758

DIELECTRIC BEHAVIOR 759

18.18 Capacitance 759 18.19 Field Vectors and Polarization 761 18.20 Types of Polarization 764 18.21 Frequency Dependence of the Dielectric

Constant 766 18.22 Dielectric Strength 767 18.23 Dielectric Materials 767

OTHER ELECTRICAL CHARACTERISTICS OF MATERIALS 767

18.24 Ferroelectricity 767 18.25 Piezoelectricity 768

Materials of Importance—Piezoelectric Ceramic Ink-Jet Printer Heads 769 Summary 770 Equation Summary 773 List of Symbols 774 Processing/Structure/Properties/Performance Summary 774 Important Terms and Concepts 778 References 778 Questions and Problems 778 Design Problems 782 Fundamentals of Engineering Questions and Problems 783

19. Thermal Properties 785

Learning Objectives 786 19.1 Introduction 786 19.2 Heat Capacity 786 19.3 Thermal Expansion 790 Materials of Importance—Invar

and Other Low-Expansion Alloys 792

19.4 Thermal Conductivity 793 19.5 Thermal Stresses 796

Summary 798 Equation Summary 799 List of Symbols 799 Important Terms and Concepts 800 References 800 Questions and Problems 800 Design Problems 802 Fundamentals of Engineering Questions and Problems 802

20. Magnetic Properties 803

Learning Objectives 804 20.1 Introduction 804 20.2 Basic Concepts 804

20.3 Diamagnetism and Paramagnetism 808 20.4 Ferromagnetism 810 20.5 Antiferromagnetism

and Ferrimagnetism 811 20.6 The Influence of Temperature on Magnetic

Behavior 815 20.7 Domains and Hysteresis 816 20.8 Magnetic Anisotropy 819 20.9 Soft Magnetic Materials 820 Materials of Importance—An

Iron–Silicon Alloy Used in Transformer Cores 821

20.10 Hard Magnetic Materials 822 20.11 Magnetic Storage 825 20.12 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 839 21.1 Introduction 839

BASIC CONCEPTS 839

21.2 Electromagnetic Radiation 839 21.3 Light Interactions with Solids 841 21.4 Atomic and Electronic

Interactions 842

OPTICAL PROPERTIES OF METALS 843

OPTICAL PROPERTIES OF NONMETALS 844

21.5 Refraction 844 21.6 Reflection 846 21.7 Absorption 846 21.8 Transmission 850 21.9 Color 850 21.10 Opacity and Translucency in

Insulators 852

APPLICATIONS OF OPTICAL PHENOMENA 853

21.11 Luminescence 853 21.12 Photoconductivity 853 Materials of Importance—Light-Emitting

Diodes 854 21.13 Lasers 856 21.14 Optical Fibers in Communications 860

Contents • xix

Summary 862 Equation Summary 864 List of Symbols 865 Important Terms and Concepts 865 References 865 Questions and Problems 866 Design Problem 867 Fundamentals of Engineering Questions and Problems 867

22. Economic, Environmental, and Societal Issues in Materials Science and Engineering 868

Learning Objectives 869 22.1 Introduction 869

ECONOMIC CONSIDERATIONS 869

22.2 Component Design 870 22.3 Materials 870 22.4 Manufacturing Techniques 870

ENVIRONMENTAL AND SOCIETAL CONSIDERATIONS 871

22.5 Recycling Issues in Materials Science and Engineering 873

Materials of Importance—Biodegradable and Biorenewable Polymers/ Plastics 876 Summary 878 References 879 Design Questions 879

Appendix A The International System of Units (SI) 880

Appendix B Properties of Selected Engineering Materials 882

B.1 Density 882 B.2 Modulus of Elasticity 885 B.3 Poisson’s Ratio 889 B.4 Strength and Ductility 890 B.5 Plane Strain Fracture Toughness 895 B.6 Linear Coefficient of Thermal

Expansion 897 B.7 Thermal Conductivity 900 B.8 Specific Heat 903 B.9 Electrical Resistivity 906 B.10 Metal Alloy Compositions 909

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

xx • Contents

List of Symbols

The number of the section in which a symbol is introduced or explained is given in parentheses.

A = area Å = angstrom unit Ai = atomic weight of

element i (2.2) 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

(induction) (20.2) Br = magnetic remanence (20.7) BCC = body-centered cubic crystal

structure (3.4) b = lattice parameter: unit cell

y-axial length (3.7) b = Burgers vector (4.5) C = capacitance (18.18) Ci = concentration (composition) of

component i in wt% (4.4) C¿i = concentration (composition) of

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

z-axial length (3.7) c = velocity of electromagnetic

radiation in a vacuum (21.2) D = diffusion coefficient (5.3) D = dielectric displacement (18.19) DP = degree of polymerization (14.5) d = diameter d = average grain diameter (7.8)

dhkl = interplanar spacing for planes of Miller indices h, k, and l (3.16)

E = energy (2.5) E = modulus of elasticity or

Young’s modulus (6.3) e = electric field intensity (18.3) Ef = Fermi energy (18.5) Eg = band gap energy (18.6) Er(t) = relaxation modulus (15.4) %EL = ductility, in percent elongation

(6.6) e = electric charge per electron

(18.7) e- = electron (17.2) erf = Gaussian error function (5.4) exp = e, the base for natural

logarithms F = force, interatomic or

mechanical (2.5, 6.2) f = Faraday constant (17.2) FCC = face-centered cubic crystal

structure (3.4) G = shear modulus (6.3) H = magnetic field strength (20.2) Hc = magnetic coercivity (20.7) HB = Brinell hardness (6.10) HCP = hexagonal close-packed 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

xxii • List of Symbols

(hkil) = Miller indices for a crystal- lographic plane, hexagonal crystals (3.10)

I = electric current (18.2) I = intensity of electromagnetic

radiation (21.3) i = current density (17.3) iC = corrosion current density (17.4) J = diffusion flux (5.3) J = electric current density (18.3) Kc = fracture toughness (8.5) KIc = plane strain fracture tough-

ness for mode I crack surface displacement (8.5)

k = Boltzmann’s constant (4.2) k = thermal conductivity (19.4) l = length lc = critical fiber length (16.4) ln = natural logarithm log = logarithm taken to base 10 M = magnetization (20.2) Mn = polymer number-average

molecular weight (14.5) Mw = polymer weight-average

molecular weight (14.5) mol% = mole percent N = number of fatigue cycles (8.8) NA = Avogadro’s number (3.5) Nf = 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)

ni = 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

meter (18.10) Q = activation energy Q = magnitude of charge stored

(18.18) R = atomic radius (3.4) R = gas constant %RA = ductility, in percent reduction

in area (6.6) r = interatomic distance (2.5)

r = reaction rate (17.3) rA, rC = anion and cation ionic radii

(12.2) S = fatigue stress amplitude (8.8) SEM = scanning electron microscopy

or microscope T = temperature Tc = Curie temperature (20.6) TC = superconducting critical

temperature (20.12) Tg = glass transition temperature

(13.10, 15.12) Tm = melting temperature TEM = transmission electron

microscopy or microscope TS = tensile strength (6.6) t = time tr = rupture lifetime (8.12) Ur = modulus of resilience (6.6) [uyw] = indices for a crystallographic

direction (3.9) [uvtw], [UVW] = indices for a crystallographic

direction, hexagonal crystals (3.9)

V = electrical potential difference (voltage) (17.2, 18.2) VC = unit cell volume (3.4) VC = corrosion potential (17.4) VH = Hall voltage (18.14) Vi = volume fraction of phase i (9.8) y = velocity vol% = volume percent Wi = mass fraction of phase i (9.8) wt% = weight percent (4.4) x = length x = space coordinate Y = dimensionless parameter or

function in fracture toughness expression (8.5)

y = space coordinate z = space coordinate a = lattice parameter: unit cell y–z

interaxial angle (3.7) a, b, g = phase designations al = linear coefficient of thermal

expansion (19.3) b = lattice parameter: unit cell x–z

interaxial angle (3.7) g = lattice parameter: unit cell x–y

interaxial angle (3.7) g = shear strain (6.2) ¢ = precedes the symbol of a pa-

rameter to denote finite change P = engineering strain (6.2) P = dielectric permittivity (18.18)

List of Symbols • xxiii

Pr = dielectric constant or relative permittivity (18.18)

P. s = steady-state creep rate (8.12) PT = true strain (6.7) h = viscosity (12.10) h = overvoltage (17.4) 2u = Bragg diffraction angle (3.16) uD = Debye temperature (19.2) l = wavelength of electromagnetic

radiation (3.16) m = magnetic permeability (20.2) mB = Bohr magneton (20.2) mr = relative magnetic permeability

(20.2) me = electron mobility (18.7) mh = hole mobility (18.10) n = Poisson’s ratio (6.5) n = frequency of electromagnetic

radiation (21.2) r = density (3.5) r = electrical resistivity (18.2) rt = radius of curvature at the tip of

a crack (8.5) s = engineering stress, tensile or

compressive (6.2) s = electrical conductivity (18.3) s* = longitudinal strength (compos-

ite) (16.5) sc = critical stress for crack propa-

gation (8.5) sfs = flexural strength (12.9) sm = maximum stress (8.5) sm = mean stress (8.7)

s¿m = stress in matrix at composite failure (16.5)

sT = true stress (6.7) sw = safe or working stress (6.12) sy = yield strength (6.6) t = shear stress (6.2) tc = fiber–matrix bond strength/

matrix shear yield strength (16.4)

tcrss = critical resolved shear stress (7.5)

xm = magnetic susceptibility (20.2)

Subscripts c = composite cd = discontinuous fibrous

composite cl = longitudinal direction (aligned

fibrous composite) ct = transverse direction (aligned

fibrous composite) f = final f = at fracture f = fiber i = instantaneous m = matrix m, max = maximum min = minimum 0 = original 0 = at equilibrium 0 = in a vacuum

• 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

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Learning Objectives 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 dif- ferent materials have evolved with rather specialized characteristics that meet the needs of our modern and complex society, including metals, plastics, glasses, and fibers.

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.

1.1 HISTORICAL PERSPECTIVE

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 using 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 differ- 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.

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

Processing Structure Properties Performance

4 • Chapter 1 / Introduction

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

1.3 WHY STUDY MATERIALS SCIENCE 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.

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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 Atlan- tic, where the once ductile metal experienced brit- tle fracture when temperatures dropped to below the transition temperature.6

• 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 inexperi- enced operators.

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)

6 • Chapter 1 / Introduction

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 cracks.

• Improving welding practices and establishing weld- ing codes.

In spite of these failures, the Liberty ship program was considered a success for several reasons, the pri- mary reason being that ships that survived failure were able to supply Allied Forces in the theater of operations and in all likelihood shortened the war. In addition, structural steels were developed with vastly improved resistances to catastrophic brittle fractures. Detailed analyses of these failures advanced the understand- ing of crack formation and growth, which ultimately evolved into the discipline of fracture mechanics.

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, ce- 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

Tutorial Video: What are the

Different Classes of Materials?

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.

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8 • Chapter 1 / Introduction

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(Figure 1.8) and heat, and are not transparent to visible light; a polished metal surface has a lustrous appearance. In addition, some of the metals (i.e., Fe, Co, and Ni) have desirable magnetic properties.

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

Tutorial Video: Ceramics

1.4 Classification of Materials • 9

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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

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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.

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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 recy- 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 as impervious to the passage of carbon dioxide 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

12 • Chapter 1 / Introduction

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, pi- ezoelectric ceramics, magnetostrictive materials, and electrorheological/magnetorheo- 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

1.5 ADVANCED MATERIALS

1.5 Advanced Materials • 13

magnetic fields. Also, electrorheological and magnetorheological fluids are liquids that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively.

Materials/devices employed as sensors include optical fibers (Section 21.14), piezoelec- tric materials (including some polymers), and microelectromechanical systems (MEMS; Section 13.9).

For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise created by the rotating rotor blades. Piezoelectric sensors inserted into the blades monitor blade stresses and deformations; feedback signals from these sensors are fed into a computer-controlled adaptive device that generates noise-canceling antinoise.

Nanomaterials One new material class that has fascinating properties and tremendous technological promise is the nanomaterials, which may be any one of the four basic types—metals, ceramics, polymers, or composites. However, unlike these other materials, they are not distinguished on the basis of their chemistry but rather their size; the nano prefix denotes that the dimensions of these structural entities are on the order of a nanometer (10-9 m)—as a rule, less than 100 nanometers (nm; equivalent to the diameter of ap- proximately 500 atoms).

Prior to the advent of nanomaterials, the general procedure scientists used to understand the chemistry and physics of materials was to begin by studying large and complex structures and then investigate the fundamental building blocks of these struc- tures that are smaller and simpler. This approach is sometimes termed top-down science. However, with the development of scanning probe microscopes (Section 4.10), which permit observation of individual atoms and molecules, it has become possible to design and build new structures from their atomic-level constituents, one atom or molecule at a time (i.e., “materials by design”). This ability to arrange atoms carefully provides op- portunities to develop mechanical, electrical, magnetic, and other properties that are not otherwise possible. We call this the bottom-up approach, and the study of the properties of these materials is termed nanotechnology.10

Some of the physical and chemical characteristics exhibited by matter may experi- ence dramatic changes as particle size approaches atomic dimensions. For example, materials that are opaque in the macroscopic domain may become transparent on the nanoscale; some solids become liquids, chemically stable materials become combustible, and electrical insulators become conductors. Furthermore, properties may depend on size in this nanoscale domain. Some of these effects are quantum mechanical in origin, whereas others are related to surface phenomena—the proportion of atoms located on surface sites of a particle increases dramatically as its size decreases.

Because of these unique and unusual properties, nanomaterials are finding niches in electronic, biomedical, sporting, energy production, and other industrial applications. Some are discussed in this text, including the following:

• Catalytic converters for automobiles (Materials of Importance box, Chapter 4)

• Nanocarbons—Fullerenes, carbon nanotubes, and graphene (Section 13.9)

• Particles of carbon black as reinforcement for automobile tires (Section 16.2)

• Nanocomposites (Section 16.16)

• Magnetic nanosize grains that are used for hard disk drives (Section 20.11)

• Magnetic particles that store data on magnetic tapes (Section 20.11)

10One legendary and prophetic suggestion as to the possibility of nanoengineered materials was offered by Richard Feynman in his 1959 American Physical Society lecture titled “There’s Plenty of Room at the Bottom.”

14 • Chapter 1 / Introduction

Whenever a new material is developed, its potential for harmful and toxicological interactions with humans and animals must be considered. Small nanoparticles have ex- ceedingly large surface area–to–volume ratios, which can lead to high chemical reactivi- ties. Although the safety of nanomaterials is relatively unexplored, there are concerns that they may be absorbed into the body through the skin, lungs, and digestive tract at relatively high rates, and that some, if present in sufficient concentrations, will pose health risks—such as damage to DNA or promotion of lung cancer.

In spite of the tremendous progress that has been made in the discipline of materials science and engineering within the past few years, technological challenges remain, in- cluding the development of even more sophisticated and specialized materials, as well as consideration of the environmental impact of materials production. Some comment is appropriate relative to these issues so as to round out this perspective.

Nuclear energy holds some promise, but the solutions to the many problems that remain necessarily involve materials, such as fuels, containment structures, and facilities for the disposal of radioactive waste.

Significant quantities of energy are involved in transportation. Reducing the weight of transportation vehicles (automobiles, aircraft, trains, etc.), as well as increasing engine op- erating temperatures, will enhance fuel efficiency. New high-strength, low-density struc- tural materials remain to be developed, as well as materials that have higher-temperature capabilities, for use in engine components.

Furthermore, there is a recognized need to find new and economical sources of energy and to use present resources more efficiently. Materials will undoubtedly play a significant role in these developments. For example, the direct conversion of solar power into electrical energy has been demonstrated. Solar cells employ some rather complex and expensive materials. To ensure a viable technology, materials that are highly efficient in this conversion process yet less costly must be developed.