The Science and Engineering of Materials PDF

 Performance...

 Performance What is Materials Science and Engineering? Cost Synthesis and Composition Processing Structure Macro-Scale Structure Engine Block ≡ up to 1 meter Unit Cell Performance Criteria Microstructure Power generated - Grains Efficiency ≡ 1–10 millimeters Durability Cost Properties affected Microstructure High cycle fatigue - Dendrites and Phases Ductility ≡ 50–500 micrometers Nano-structure Properties affected - Precipitates Yield strength ≡ 3–100 nanometers Ultimate tensile strength Properties affected High cycle fatigue Yield strength Atomic-scale structure Low cycle fatigue Ultimate tensile strength ≅ 1–100 Angstroms Thermal growth Low cycle fatigue Properties affected Ductility Ductility Young’s modulus Thermal growth A real-world example of important microstructural features at different length-scales resulting from the sophisticated synthesis and processing used, and the properties they influence. The atomic, nano, micro, and macro-scale structures of cast aluminum alloys (for engine blocks) in relation to the properties affected and performance are shown. The materials science and engineering (MSE) tetrahedron that represents this approach is shown in the upper right corner. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. (Illustrations Courtesy of John Allison and William Donlon, Ford Motor Company.)  Units and conversion factors 1 pound (lb) ⫽ 4.448 Newtons (N) 1 psi ⫽ pounds per square inch 1 MPa ⫽ MegaPascal ⫽ MegaNewtons per square meter (MN/m2) ⫽ Newtons per square millimeter (N/mm2) ⫽ 1,000,000 Pa 1 GPa ⫽ 1000 MPa ⫽ GigaPascal 1 ksi ⫽ 1000 psi ⫽ 6.895 MPa 1 psi ⫽ 0.006895 MPa 1 MPa ⫽ 0.145 ksi ⫽ 145 psi Some useful relationships, constants, and units Electron volt ⫽ 1 eV ⫽ 1.6 ⫻ 10⫺19 Joule ⫽ 1.6 ⫻ 10⫺12 erg 1 amp ⫽ 1 coulomb/second 1 volt ⫽ 1 amp ⭈ ohm kBT at room temperature (300 K) ⫽ 0.0259 eV c ⫽ speed of light 2.998 ⫻ 108 m/s eo ⫽ permittivity of free space ⫽ 8.85 ⫻ 10⫺12 F/m q ⫽ charge on electron ⫽ 1.6 ⫻ 10⫺19 C Avogadro constant NA ⫽ 6.022 ⫻ 1023 kB ⫽ Boltzmann constant ⫽ 8.63 ⫻ 10⫺5 eV/K ⫽ 1.38 ⫻ 10⫺23 J/K h ⫽ Planck’s constant 6.63 ⫻ 10⫺34 J-s ⫽ 4.14 ⫻ 10⫺15 eV-s Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  The Science and Engineering of Materials Sixth Edition Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  The Science and Engineering of Materials Sixth Edition Donald R. Askeland University of Missouri—Rolla, Emeritus Pradeep P. Fulay University of Pittsburgh Wendelin J. Wright Bucknell University Australia Brazil Japan Korea Mexico Singapore Spain United Kingdom United States Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  This is an electronic sample of the print textbook. The publisher reserves the right to remove content from this title at any time if subsequent rights restrictions require it. For valuable information on pricing, previous editions, changes to current editions and alternate formats, please visit www.cengage.com/highered to search by ISBN#, author, title, or keyword for materials in your areas of interest. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  The Science and Engineering of Materials, © 2011, 2006 Cengage Learning Sixth Edition Authors Donald R. Askeland, Pradeep ALL RIGHTS RESERVED. No part of this work covered by the P. Fulay, Wendelin J. Wright copyright herein may be reproduced, transmitted, stored, or used in any form or by any means graphic, electronic, or Publisher, Global Engineering: mechanical, including but not limited to photocopying, Christopher M. 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For your course and learning solutions, visit www.cengage.com/engineering. Purchase any of our products at your local college store or at our preferred online store www.CengageBrain.com. Printed in the United States of America 1 2 3 4 5 6 7 13 12 11 10 09 Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  To Mary Sue and Tyler –Donald R. Askeland To Jyotsna, Aarohee, and Suyash –Pradeep P. Fulay To John, as we begin the next wonderful chapter in our life together –Wendelin J. Wright Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  Contents Chapter 1 Introduction to Materials Science and Engineering 3 1-1 What is Materials Science and Engineering? 4 1-2 Classification of Materials 7 1-3 Functional Classification of Materials 11 1-4 Classification of Materials Based on Structure 13 1-5 Environmental and Other Effects 13 1-6 Materials Design and Selection 16 Summary 17 | Glossary 18 | Problems 19 Chapter 2 Atomic Structure 23 2-1 The Structure of Materials: Technological Relevance 24 2-2 The Structure of the Atom 27 2-3 The Electronic Structure of the Atom 29 2-4 The Periodic Table 32 2-5 Atomic Bonding 34 2-6 Binding Energy and Interatomic Spacing 41 2-7 The Many Forms of Carbon: Relationships Between Arrangements of Atoms and Materials Properties 44 Summary 48 | Glossary 50 | Problems 52 Chapter 3 Atomic and Ionic Arrangements 55 3-1 Short-Range Order versus Long-Range Order 56 3-2 Amorphous Materials 58 3-3 Lattice, Basis, Unit Cells, and Crystal Structures 60 3-4 Allotropic or Polymorphic Transformations 72 3-5 Points, Directions, and Planes in the Unit Cell 73 3-6 Interstitial Sites 84 3-7 Crystal Structures of Ionic Materials 86 3-8 Covalent Structures 92 3-9 Diffraction Techniques for Crystal Structure Analysis 96 Summary 100 | Glossary 102 | Problems 104 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part. viii CONTENTS Chapter 4 Imperfections in the Atomic and lonic Arrangements 113 4-1 Point Defects 114 4-2 Other Point Defects 120 4-3 Dislocations 122 4-4 Significance of Dislocations 130 4-5 Schmid’s Law 131 4-6 Influence of Crystal Structure 134 4-7 Surface Defects 135 4-8 Importance of Defects 141 Summary 144 | Glossary 145 | Problems 147 Chapter 5 Atom and Ion Movements in Materials 155 5-1 Applications of Diffusion 156 5-2 Stability of Atoms and Ions 159 5-3 Mechanisms for Diffusion 161 5-4 Activation Energy for Diffusion 163 5-5 Rate of Diffusion [Fick’s First Law] 164 5-6 Factors Affecting Diffusion 168 5-7 Permeability of Polymers 176 5-8 Composition Profile [Fick’s Second Law] 177 5-9 Diffusion and Materials Processing 182 Summary 187 | Glossary 188 | Problems 190 Chapter 6 Mechanical Properties: Part One 197 6-1 Technological Significance 198 6-2 Terminology for Mechanical Properties 199 6-3 The Tensile Test: Use of the Stress–Strain Diagram 204 6-4 Properties Obtained from the Tensile Test 208 6-5 True Stress and True Strain 216 6-6 The Bend Test for Brittle Materials 218 6-7 Hardness of Materials 221 6-8 Nanoindentation 223 6-9 Strain Rate Effects and Impact Behavior 227 6-10 Properties Obtained from the Impact Test 228 6-11 Bulk Metallic Glasses and Their Mechanical Behavior 231 6-12 Mechanical Behavior at Small Length Scales 233 Summary 235 | Glossary 236 | Problems 239 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part.  CONTENTS ix (a) Chapter 7 Mechanical Properties: Part Two 247 (b) 7-1 Fracture Mechanics 248 7-2 The Importance of Fracture Mechanics 250 (c) 7-3 Microstructural Features of Fracture in Metallic Materials 254 7-4 Microstructural Features of Fracture in Ceramics, Glasses, and Composites 258 7-5 Weibull Statistics for Failure Strength Analysis 260 7-6 Fatigue 265 7-7 Results of the Fatigue Test 268 7-8 Application of Fatigue Testing 270 7-9 Creep, Stress Rupture, and Stress Corrosion 274 7-10 Evaluation of Creep Behavior 276 7-11 Use of Creep Data 278 Summary 280 | Glossary 280 | Problems 282 Chapter 8 Strain Hardening and Annealing 291 8-1 Relationship of Cold Working to the Stress-Strain Curve 292 8-2 Strain-Hardening Mechanisms 297 8-3 Properties versus Percent Cold Work 299 8-4 Microstructure, Texture Strengthening, and Residual Stresses 301 8-5 Characteristics of Cold Working 306 8-6 The Three Stages of Annealing 308 8-7 Control of Annealing 311 8-8 Annealing and Materials Processing 313 8-9 Hot Working 315 Summary 317 | Glossary 318 | Problems 320 Chapter 9 Principles of Solidification 329 9-1 Technological Significance 330 9-2 Nucleation 330 9-3 Applications of Controlled Nucleation 335 9-4 Growth Mechanisms 336 9-5 Solidification Time and Dendrite Size 338 9-6 Cooling Curves 343 9-7 Cast Structure 344 9-8 Solidification Defects 346 9-9 Casting Processes for Manufacturing Components 351 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part. x CONTENTS 9-10 Continuous Casting and Ingot Casting 353 9-11 Directional Solidification [DS], Single Crystal Growth, and Epitaxial Growth 357 9-12 Solidification of Polymers and Inorganic Glasses 359 9-13 Joining of Metallic Materials 360 Summary 362 | Glossary 363 | Problems 365 Chapter 10 Solid Solutions and Phase Equilibrium 375 10-1 Phases and the Phase Diagram 376 10-2 Solubility and Solid Solutions 380 10-3 Conditions for Unlimited Solid Solubility 382 10-4 Solid-Solution Strengthening 384 10-5 Isomorphous Phase Diagrams 387 10-6 Relationship Between Properties and the Phase Diagram 395 10-7 Solidification of a Solid-Solution Alloy 397 10-8 Nonequilibrium Solidification and Segregation 399 Summary 403 | Glossary 404 | Problems 405 Chapter 11 Dispersion Strengthening and Eutectic Phase Diagrams 413 11-1 Principles and Examples of Dispersion Strengthening 414 11-2 Intermetallic Compounds 414 11-3 Phase Diagrams Containing Three-Phase Reactions 417 11-4 The Eutectic Phase Diagram 420 11-5 Strength of Eutectic Alloys 430 11-6 Eutectics and Materials Processing 436 11-7 Nonequilibrium Freezing in the Eutectic System 438 11-8 Nanowires and the Eutectic Phase Diagram 438 Summary 441 | Glossary 441 | Problems 443 Chapter 12 Dispersion Strengthening by Phase Transformations and Heat Treatment 451 12-1 Nucleation and Growth in Solid-State Reactions 452 12-2 Alloys Strengthened by Exceeding the Solubility Limit 456 12-3 Age or Precipitation Hardening 458 12-4 Applications of Age-Hardened Alloys 459 12-5 Microstructural Evolution in Age or Precipitation Hardening 459 12-6 Effects of Aging Temperature and Time 462 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part.  CONTENTS xi 12-7 Requirements for Age Hardening 464 12-8 Use of Age-Hardenable Alloys at High Temperatures 464 12-9 The Eutectoid Reaction 465 12-10 Controlling the Eutectoid Reaction 470 12-11 The Martensitic Reaction and Tempering 475 12-12 The Shape-Memory Alloys [SMAs] 479 Summary 480 | Glossary 482 | Problems 483 Chapter 13 Heat Treatment of Steels and Cast Irons 493 13-1 Designations and Classification of Steels 494 13-2 Simple Heat Treatments 498 13-3 Isothermal Heat Treatments 500 13-4 Quench and Temper Heat Treatments 504 13-5 Effect of Alloying Elements 509 13-6 Application of Hardenability 511 13-7 Specialty Steels 514 13-8 Surface Treatments 516 13-9 Weldability of Steel 518 13-10 Stainless Steels 519 13-11 Cast Irons 523 Summary 529 | Glossary 529 | Problems 532 Chapter 14 Nonferrous Alloys 539 14-1 Aluminum Alloys 540 14-2 Magnesium and Beryllium Alloys 547 14-3 Copper Alloys 548 14-4 Nickel and Cobalt Alloys 552 14-5 Titanium Alloys 556 14-6 Refractory and Precious Metals 562 Summary 564 | Glossary 564 | Problems 565 Chapter 15 Ceramic Materials 571 15-1 Applications of Ceramics 572 15-2 Properties of Ceramics 574 15-3 Synthesis and Processing of Ceramic Powders 575 15-4 Characteristics of Sintered Ceramics 580 15-5 Inorganic Glasses 582 15-6 Glass-Ceramics 588 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part. xii CONTENTS 15-7 Processing and Applications of Clay Products 590 15-8 Refractories 591 15-9 Other Ceramic Materials 593 Summary 595 | Glossary 596 | Problems 597 Chapter 16 Polymers 601 16-1 Classification of Polymers 602 16-2 Addition and Condensation Polymerization 605 16-3 Degree of Polymerization 610 16-4 Typical Thermoplastics 612 16-5 Structure—Property Relationships in Thermoplastics 615 16-6 Effect of Temperature on Thermoplastics 619 16-7 Mechanical Properties of Thermoplastics 624 16-8 Elastomers [Rubbers] 630 16-9 Thermosetting Polymers 635 16-10 Adhesives 637 16-11 Polymer Processing and Recycling 638 Summary 643 | Glossary 644 | Problems 645 Chapter 17 Composites: Teamwork and Synergy in Materials 651 17-1 Dispersion-Strengthened Composites 653 17-2 Particulate Composites 655 17-3 Fiber-Reinforced Composites 661 17-4 Characteristics of Fiber-Reinforced Composites 665 17-5 Manufacturing Fibers and Composites 672 17-6 Fiber-Reinforced Systems and Applications 677 17-7 Laminar Composite Materials 684 17-8 Examples and Applications of Laminar Composites 686 17-9 Sandwich Structures 687 Summary 689 | Glossary 689 | Problems 691 Chapter 18 Construction Materials 697 18-1 The Structure of Wood 698 18-2 Moisture Content and Density of Wood 700 18-3 Mechanical Properties of Wood 702 18-4 Expansion and Contraction of Wood 704 18-5 Plywood 705 18-6 Concrete Materials 705 Copyright 2010 Cengage Learning, Inc. 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May not be copied, scanned, or duplicated, in whole or in part.  CONTENTS xiii 18-7 Properties of Concrete 707 18-8 Reinforced and Prestressed Concrete 712 18-9 Asphalt 713 Summary 714 | Glossary 714 | Problems 715 Chapter 19 Electronic Materials 719 19-1 Ohm’s Law and Electrical Conductivity 720 19-2 Band Structure of Solids 725 19-3 Conductivity of Metals and Alloys 729 19-4 Semiconductors 733 19-5 Applications of Semiconductors 741 19-6 General Overview of Integrated Circuit Processing 743 19-7 Deposition of Thin Films 746 19-8 Conductivity in Other Materials 748 19-9 Insulators and Dielectric Properties 750 19-10 Polarization in Dielectrics 751 19-11 Electrostriction, Piezoelectricity, and Ferroelectricity 755 Summary 758 | Glossary 759 | Problems 761 Chapter 20 Magnetic Materials 767 20-1 Classification of Magnetic Materials 768 20-2 Magnetic Dipoles and Magnetic Moments 768 20-3 Magnetization, Permeability, and the Magnetic Field 770 20-4 Diamagnetic, Paramagnetic, Ferromagnetic, Ferrimagnetic, and Superparamagnetic Materials 773 20-5 Domain Structure and the Hysteresis Loop 776 20-6 The Curie Temperature 779 20-7 Applications of Magnetic Materials 780 20-8 Metallic and Ceramic Magnetic Materials 786 Summary 792 | Glossary 793 | Problems 794 Chapter 21 Photonic Materials 799 21-1 The Electromagnetic Spectrum 800 21-2 Refraction, Reflection, Absorption, and Transmission 800 21-3 Selective Absorption, Transmission, or Reflection 813 21-4 Examples and Use of Emission Phenomena 814 21-5 Fiber-Optic Communication System 823 Summary 824 | Glossary 824 | Problems 825 Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. xiv CONTENTS Chapter 22 Thermal Properties of Materials 831 22-1 Heat Capacity and Specific Heat 832 22-2 Thermal Expansion 834 22-3 Thermal Conductivity 839 22-4 Thermal Shock 843 Summary 845 | Glossary 846 | Problems 846 Chapter 23 Corrosion and Wear 851 23-1 Chemical Corrosion 852 23-2 Electrochemical Corrosion 854 23-3 The Electrode Potential in Electrochemical Cells 857 23-4 The Corrosion Current and Polarization 861 23-5 Types of Electrochemical Corrosion 862 23-6 Protection Against Electrochemical Corrosion 868 23-7 Microbial Degradation and Biodegradable Polymers 874 23-8 Oxidation and Other Gas Reactions 875 23-9 Wear and Erosion 879 Summary 881 | Glossary 882 | Problems 883 Appendix A: Selected Physical Properties of Metals 888 Appendix B: The Atomic and lonic Radii of Selected Elements 891 Answers to Selected Problems 893 Index 901 Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  Preface When the relationships between the structure, properties, and processing of materials are fully understood and exploited, materials become enabling—they are transformed from stuff, the raw materials that nature gives us, to things, the products and technologies that we develop as engineers. Any technologist can find materials properties in a book or search databases for a material that meets design specifications, but the ability to innovate and to incorporate materials safely in a design is rooted in an understanding of how to manipu- late materials properties and functionality through the control of materials structure and processing techniques. The objective of this textbook, then, is to describe the foundations and applications of materials science for college-level engineering students as predicated upon the structure-processing-properties paradigm. The challenge of any textbook is to provide the proper balance of breadth and depth for the subject at hand, to provide rigor at the appropriate level, to provide mean- ingful examples and up to date content, and to stimulate the intellectual excitement of the reader. Our goal here is to provide enough science so that the reader may understand basic materials phenomena, and enough engineering to prepare a wide range of students for competent professional practice. Cover Art The cover art for the sixth edition of the text is a compilation of two micrographs obtained using an instrument known as a scanning tunneling microscope (STM). An STM scans a sharp tip over the surface of a sample. A voltage is applied to the tip. Electrons from the tip are said to “tunnel” or “leak” to the sample when the tip is in proximity to the atoms of the sample. The resulting current is a function of the tip to sample distance, and measurements of the current can be used to map the sample surface. The image on the cover is entitled “Red Planet.” The “land” in the cover art is a three-dimensional image of a single layer of the molecule hexaazatrinaphthylene (HATNA) deposited on a single crystal of gold, and the “sky” is a skewed two-dimensional image of several layers of a hexaazatriphenylene deriv- ative (THAP), also deposited on single crystal gold and exposed to a high background pres- sure of cobaltocene. Both HATNA and THAP are organic semiconductors. They belong to a class of disc-shaped molecules, which preferentially stack into columns. In such a config- uration, charge carrier transport along the molecular cores is enhanced, which in turn increases electrical conductivity and improves device performance. The color is false; it has been added for artistic effect. Sieu Ha of Princeton University acquired these images. Audience and Prerequisites This text is intended for an introductory science of materials class taught at the sophomore or junior level. A first course in college level chemistry is assumed, as is some coverage of first year college physics. A calculus course is helpful, but certainly not required. The text does not presume that students have taken other introductory engineering courses such as statics, dynamics, or mechanics of materials. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. xvi P R E FA C E Changes to the Sixth Edition Particular attention has been paid to revising the text for clarity and accuracy. New con- tent has been added as described below. New to this Edition New content has been added to the text including enhanced crystallography descriptions and sections about the allotropes of carbon, nanoindentation, mechanical properties of bulk metallic glasses, mechanical behavior at small length scales, integrated circuit manufacturing, and thin film deposition. New prob- lems have been added to the end of each chapter. New instructor supplements are also provided. At the conclusion of the end-of-chapter problems, you will find a special section with problems that require the use of Knovel (www.knovel.com). Knovel is an online aggregator of engineering references including handbooks, encyclopedias, dictionaries, textbooks, and databases from leading technical publishers and engineering societies such as the American Society of Mechanical Engineers (ASME) and the American Institute of Chemical Engineers (AIChE.) The Knovel problems build on material found in the textbook and require famil- iarity with online information retrieval. The problems are also available online at www.cen- gage.com/engineering. In addition, the solutions are accessible by registered instructors. If your institution does not have a subscription to Knovel or if you have any questions about Knovel, please contact [email protected] (866) 240-8174 (866) 324-5163 The Knovel problems were created by a team of engineers led by Sasha Gurke, senior vice president and co-founder of Knovel. Supplements for the Instructor Supplements to the text include the Instructor’s Solutions Manual that provides complete solutions to selected problems, annotated Powerpoint™ slides, and an online Test Bank of potential exam questions. Acknowledgements We thank all those who have contributed to the success of past editions and also the reviewers who provided detailed and constructive feedback on the fifth edition: Deborah Chung, State University of New York, at Buffalo Derrick R. Dean, University of Alabama at Birmingham Angela L. Moran, U.S. Naval Academy John R. Schlup, Kansas State University Jeffrey Schott, University of Minnesota Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  P R E FA C E xvii We are grateful to the team at Cengage Learning who has carefully guided this sixth edition through all stages of the publishing process. In particular, we thank Christopher Carson, Executive Director of the Global Publishing Program at Cengage Learning, Christopher Shortt, Publisher for Global Engineering at Cengage Learning, Hilda Gowans, the Developmental Editor, Rose Kernan, the Production Editor, Kristiina Paul, the Permissions and Photo Researcher, and Lauren Betsos, the Marketing Manager. We also thank Jeffrey Florando of the Lawrence Livermore National Laboratory for input regarding portions of the manuscript and Venkat Balu for some of the new end-of- chapter problems in this edition. Wendelin Wright thanks Particia Wright for assistance during the proofreading process and John Bravman for his feedback, contributed illustrations, patience, and constant support. Donald R. Askeland University of Missouri – Rolla, Emeritus Pradeep P. Fulay University of Pittsburgh Wendelin J. Wright Santa Clara University Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  About the Authors Donald R. Askeland is a Distinguished Teaching Professor Emeritus of Metallurgical Engineering at the University of Missouri–Rolla. He received his degrees from the Thayer School of Engineering at Dartmouth College and the University of Michigan prior to joining the faculty at the University of Missouri–Rolla in 1970. Dr. Askeland taught a number of courses in materials and manufacturing engineering to students in a variety of engineering and science curricula. He received a number of awards for excellence in teach- ing and advising at UMR. He served as a Key Professor for the Foundry Educational Foundation and received several awards for his service to that organization. His teaching and research were directed primarily to metals casting and joining, in particular lost foam casting, and resulted in over 50 publications and a number of awards for service and best papers from the American Foundry Society. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. xx ABOUT THE AUTHORS Pradeep P. Fulay is a Professor of Materials Science and Engineering at the University of Pittsburgh. He joined the University of Pittsburgh in 1989, was promoted to Associate Professor in 1994, and then to full professor in 1999. Dr. Fulay received a Ph.D. in Materials Science and Engineering from the University of Arizona (1989) and a B. Tech (1983) and M. Tech (1984) in Metallurgical Engineering from the Indian Institute of Technology Bombay (Mumbai) India. He has authored close to 60 publications and has two U.S. patents issued. He has received the Alcoa Foundation and Ford Foundation research awards. He has been an outstanding teacher and educator and was listed on the Faculty Honor Roll at the University of Pittsburgh (2001) for outstanding services and assistance. From 1992–1999, he was the William Kepler Whiteford Faculty Fellow at the University of Pittsburgh. From August to December 2002, Dr. Fulay was a visiting scientist at the Ford Scientific Research Laboratory in Dearborn, MI. Dr. Fulay’s primary research areas are chemical synthesis and processing of ceramics, electronic ceramics and magnetic materials, and development of smart materials and systems. Part of the MR fluids technology Dr. Fulay has developed is being transferred to industry. He was the Vice President (2001–2002) and President (2002–2003) of the Ceramic Educational Council and has been a Member of the Program Committee for the Electronics Division of the American Ceramic Society since 1996. He has also served as an Associate Editor for the Journal of the American Ceramic Society (1994–2000). He has been the lead organizer for symposia on ceramics for sol-gel processing, wireless communications, and smart structures and sensors. In 2002, Dr. Fulay was elected as a Fellow of the American Ceramic Society. Dr. Fulay’s research has been supported by National Science Foundation (NSF) and many other organizations. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  ABOUT THE AUTHORS xxi Wendelin Wright will be appointed as an assistant professor of Mechanical Engineering at Bucknell University in the fall of 2010. At the time of publication, she is the Clare Boothe Luce Assistant Professor of Mechanical Engineering at Santa Clara University. She received her B.S., M.S., and Ph.D. (2003) in Materials Science and Engineering from Stanford University. Following graduation, she served a post–doctoral term at the Lawrence Livermore National Laboratory in the Manufacturing and Materials Engineering Division and returned to Stanford as an Acting Assistant Professor in 2005. She joined the Santa Clara University faculty in 2006. Professor Wright’s research interests focus on the mechanical behavior of mate- rials, particularly of metallic glasses. She is the recipient of the 2003 Walter J. Gores Award for Excellence in Teaching, which is Stanford University’s highest teaching honor, a 2005 Presidential Early Career Award for Scientists and Engineers, and a 2010 National Science Foundation CAREER Award. In the fall of 2009, Professor Wright used The Science and Engineering of Materials as her primary reference text while taking and passing the Principles and Practices of Metallurgy exam to become a licensed Professional Engineer in California. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  The Science and Engineering of Materials Sixth Edition Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  The principal goals of a materials scientist and engineer are to (1) make existing materials better and (2) invent or discover new phenomena, materials, devices, and applications. Breakthroughs in the materi- als science and engineering field are applied to many other fields of study such as biomedical engineering, physics, chemistry, environmental engineering, and information technology. The materials science and engi- neering tetrahedron shown here represents the heart and soul of this field. As shown in this diagram, a materials scientist and engineer’s main objective is to develop materials or devices that have the best per- formance for a particular application. In most cases, the performance-to-cost ratio, as opposed to the per- formance alone, is of utmost importance. This concept is shown as the apex of the tetrahedron and the three corners are representative of A—the composition, B—the microstructure, and C—the synthesis and pro- cessing of materials. These are all interconnected and ultimately affect the performance-to-cost ratio of a material or a device. The accompanying micrograph shows the microstructure of stainless steel. For materials scientists and engineers, materials are like a palette of colors to an artist. Just as an artist can create different paintings using different colors, materials scientists create and improve upon different materials using different elements of the periodic table, and different synthesis and processing routes. (Car image courtesy of Ford Motor Company. Steel manufacturing image and car chassis image courtesy of Digital Vision/Getty Images. Micrograph courtesy of Dr. A.J. Deardo, Dr. M. Hua, and Dr. J. Garcia.) Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  Introduction to Materials Chapter 1 Science and Engineering Have You Ever Wondered? What do materials scientists and engineers study? How can steel sheet metal be processed to produce a high strength, lightweight, energy absorbing, malleable material used in the manufacture of car chassis? Can we make flexible and lightweight electronic circuits using plastics? What is a “smart material?” I n this chapter, we will first introduce you to the field of materials science and engi- neering (MSE) using different real-world examples. We will then provide an introduc- tion to the classification of materials. Although most engineering programs require students to take a materials science course, you should approach your study of materi- als science as more than a mere requirement. A thorough knowledge of materials sci- ence and engineering will make you a better engineer and designer. Materials science underlies all technological advances and an understanding of the basics of materials and their applications will not only make you a better engineer, but will help you during the design process. In order to be a good designer, you must learn what materials will be appropriate to use in different applications. You need to be capable of choosing the right material for your application based on its properties, and you must recognize how and why these properties might change over time and due to processing. Any engineer can look up materials properties in a book or search databases for a material that meets design specifications, but the ability to innovate and to incorporate materials safely in a design is rooted in an understanding of how to manipulate materials properties and functionality through the control of the material’s structure and processing techniques. The most important aspect of materials is that they are enabling; materials make things happen. For example, in the history of civilization, materials such as stone, iron, and bronze played a key role in mankind’s development. In today’s fast-paced world, the discovery of silicon single crystals and an understanding of their properties have enabled the information age. 3 Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 4 CHAPTER 1 Introduction to Materials Science and Engineering In this book, we provide compelling examples of real-world applications of engineered materials. The diversity of applications and the unique uses of materials illustrate why a good engineer needs to understand and know how to apply the prin- ciples of materials science and engineering. 1-1 What is Materials Science and Engineering? Materials science and engineering (MSE) is an interdisciplinary field of science and engi- neering that studies and manipulates the composition and structure of materials across length scales to control materials properties through synthesis and processing. The term composition means the chemical make-up of a material. The term structure means a description of the arrangement of atoms, as seen at different levels of detail. Materials sci- entists and engineers not only deal with the development of materials, but also with the synthesis and processing of materials and manufacturing processes related to the produc- tion of components. The term “synthesis” refers to how materials are made from naturally occurring or man-made chemicals. The term “processing” means how materials are shaped into useful components to cause changes in the properties of different materials. One of the most important functions of materials scientists and engineers is to establish the rela- tionships between a material or a device’s properties and performance and the microstruc- ture of that material, its composition, and the way the material or the device was synthesized and processed. In materials science, the emphasis is on the underlying relation- ships between the synthesis and processing, structure, and properties of materials. In materials engineering, the focus is on how to translate or transform materials into useful devices or structures. One of the most fascinating aspects of materials science involves the investiga- tion of a material’s structure. The structure of materials has a profound influence on many properties of materials, even if the overall composition does not change! For exam- ple, if you take a pure copper wire and bend it repeatedly, the wire not only becomes harder but also becomes increasingly brittle! Eventually, the pure copper wire becomes so hard and brittle that it will break! The electrical resistivity of the wire will also increase as we bend it repeatedly. In this simple example, take note that we did not change the material’s composition (i.e., its chemical make-up). The changes in the material’s prop- erties are due to a change in its internal structure. If you look at the wire after bending, it will look the same as before; however, its structure has been changed at the microscopic scale. The structure at the microscopic scale is known as the microstructure. If we can understand what has changed microscopically, we can begin to discover ways to control the material’s properties. Let’s examine one example using the materials science and engineering tetrahe- dron presented on the chapter opening page. Let’s look at “sheet steels” used in the manufacture of car chassis (Figure 1-1). Steels, as you may know, have been used in man- ufacturing for more than a hundred years, but they probably existed in a crude form dur- ing the Iron Age, thousands of years ago. In the manufacture of automobile chassis, a material is needed that possesses extremely high strength but is formed easily into aero- dynamic contours. Another consideration is fuel efficiency, so the sheet steel must also be thin and lightweight. The sheet steels also should be able to absorb significant amounts of energy in the event of a crash, thereby increasing vehicle safety. These are somewhat contradictory requirements. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 1 What is Materials Science and Engineering? 5 Figure 1-1 Application of the tetrahedron of materials science and engineering to sheet steels for automotive chassis. Note that the composition, microstructure, and synthesis-processing are all interconnected and affect the performance-to-cost ratio. (Car image courtesy of Ford Motor Company. Steel manufacturing image and car chassis image courtesy of Digital Vision/Getty Images. Micrograph courtesy of Dr. A.J. Deardo, Dr. M. Hua, and Dr. J. Garcia.) Thus, in this case, materials scientists are concerned with the sheet steel’s composition; strength; weight; energy absorption properties; and malleability (formability). Materials scientists would examine steel at a microscopic level to determine if its properties can be altered to meet all of these requirements. They also would have to Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 6 CHAPTER 1 Introduction to Materials Science and Engineering consider the cost of processing this steel along with other considerations. How can we shape such steel into a car chassis in a cost-effective way? Will the shaping process itself affect the mechanical properties of the steel? What kind of coatings can be developed to make the steel corrosion resistant? In some applications, we need to know if these steels could be welded easily. From this discussion, you can see that many issues need to be con- sidered during the design and materials selection for any product. Let’s look at one more example of a class of materials known as semiconducting polymers (Figure 1-2). Many semiconducting polymers have been processed into light emit- ting diodes (LEDs). You have seen LEDs in alarm clocks, watches, and other displays. These displays often use inorganic compounds based on gallium arsenide (GaAs) and other materials. The advantage of using plastics for microelectronics is that they are lightweight and flexible. The questions materials scientists and engineers must answer with applica- tions of semiconducting polymers are What are the relationships between the structure of polymers and their electrical properties? How can devices be made using these plastics? Will these devices be compatible with existing silicon chip technology? Figure 1-2 Application of the tetrahedron of materials science and engineering to semiconducting polymers for microelectronics. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 2 Classification of Materials 7 How robust are these devices? How will the performance and cost of these devices compare with traditional devices? These are just a few of the factors that engineers and scientists must consider during the development, design, and manufacture of semiconducting polymer devices. 1-2 Classification of Materials There are different ways of classifying materials. One way is to describe five groups (Table 1-1): TABLE 1-1 Representative examples, applications, and properties for each category of materials Examples of Applications Properties Metals and Alloys Copper Electrical conductor wire High electrical conductivity, good formability Gray cast iron Automobile engine blocks Castable, machinable, vibration-damping Alloy steels Wrenches, automobile chassis Significantly strengthened by heat treatment Ceramics and Glasses SiO2–Na2O–CaO Window glass Optically transparent, thermally insulating Al2O3, MgO, SiO2 Refractories (i.e., heat-resistant lining Thermally insulating, withstand of furnaces) for containing molten high temperatures, relatively metal inert to molten metal Barium titanate Capacitors for microelectronics High ability to store charge Silica Optical fibers for information Refractive index, low optical technology losses Polymers Polyethylene Food packaging Easily formed into thin, flexible, airtight film Epoxy Encapsulation of integrated circuits Electrically insulating and moisture-resistant Phenolics Adhesives for joining plies in plywood Strong, moisture resistant Semiconductors Silicon Transistors and integrated circuits Unique electrical behavior GaAs Optoelectronic systems Converts electrical signals to light, lasers, laser diodes, etc. Composites Graphite-epoxy Aircraft components High strength-to-weight ratio Tungsten carbide-cobalt Carbide cutting tools for machining High hardness, yet good (WC-Co) shock resistance Titanium-clad steel Reactor vessels Low cost and high strength of steel with the corrosion resistance of titanium Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 8 CHAPTER 1 Introduction to Materials Science and Engineering 1. metals and alloys; 2. ceramics, glasses, and glass-ceramics; 3. polymers (plastics); 4. semiconductors; and 5. composite materials. Materials in each of these groups possess different structures and properties. The differences in strength, which are compared in Figure 1-3, illustrate the wide range of prop- erties from which engineers can select. Since metallic materials are extensively used for load-bearing applications, their mechanical properties are of great practical interest. We briefly introduce these here. The term “stress” refers to load or force per unit area. “Strain” refers to elongation or change in dimension divided by the original dimension. Application of “stress” causes “strain.” If the strain goes away after the load or applied stress is removed, the strain is said to be “elastic.” If the strain remains after the stress is removed, the strain is said to be “plastic.” When the deformation is elastic, stress and strain are lin- early related; the slope of the stress-strain diagram is known as the elastic or Young’s mod- ulus. The level of stress needed to initiate plastic deformation is known as the “yield strength.” The maximum percent deformation that can be achieved is a measure of the ductility of a metallic material. These concepts are discussed further in Chapters 6 and 7. Metals and Alloys Metals and alloys include steels, aluminum, magnesium, zinc, cast iron, titanium, copper, and nickel. An alloy is a metal that contains additions of one or more metals or non-metals. In general, metals have good electrical and thermal con- ductivity. Metals and alloys have relatively high strength, high stiffness, ductility or forma- bility, and shock resistance. They are particularly useful for structural or load-bearing applications. Although pure metals are occasionally used, alloys provide improvement in a particular desirable property or permit better combinations of properties. Figure 1-3 Representative strengths of various categories of materials. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 2 Classification of Materials 9 Ceramics Ceramics can be defined as inorganic crystalline materials. Beach sand and rocks are examples of naturally occurring ceramics. Advanced ceramics are materials made by refining naturally occurring ceramics and other special processes. Advanced ceram- ics are used in substrates that house computer chips, sensors and actuators, capacitors, wire- less communications, spark plugs, inductors, and electrical insulation. Some ceramics are used as barrier coatings to protect metallic substrates in turbine engines. Ceramics are also used in such consumer products as paints, plastics, and tires, and for industrial applications such as the tiles for the space shuttle, a catalyst support, and the oxygen sensors used in cars. Traditional ceramics are used to make bricks, tableware, toilets, bathroom sinks, refractories (heat-resistant material), and abrasives. In general, due to the presence of porosity (small holes), ceramics do not conduct heat well; they must be heated to very high temperatures before melting. Ceramics are strong and hard, but also very brittle. We normally prepare fine powders of ceramics and convert these into different shapes. New processing techniques make ceramics sufficiently resistant to fracture that they can be used in load-bearing applications, such as impellers in turbine engines. Ceramics have exceptional strength under compression. Can you believe that an entire fire truck can be supported using four ceramic coffee cups? Glasses and Glass-Ceramics Glass is an amorphous material, often, but not always, derived from a molten liquid. The term “amorphous” refers to materials that do not have a regular, periodic arrangement of atoms. Amorphous materials will be discussed in Chapter 3. The fiber optics industry is founded on optical fibers based on high- purity silica glass. Glasses are also used in houses, cars, computer and television screens, and hundreds of other applications. Glasses can be thermally treated (tempered) to make them stronger. Forming glasses and nucleating (forming) small crystals within them by a special thermal process creates materials that are known as glass-ceramics. Zerodur™ is an exam- ple of a glass-ceramic material that is used to make the mirror substrates for large tele- scopes (e.g., the Chandra and Hubble telescopes). Glasses and glass-ceramics are usually processed by melting and casting. Polymers Polymers are typically organic materials. They are produced using a process known as polymerization. Polymeric materials include rubber (elastomers) and many types of adhesives. Polymers typically are good electrical and thermal insulators although there are exceptions such as the semiconducting polymers discussed earlier in this chapter. Although they have lower strength, polymers have a very good strength-to-weight ratio. They are typically not suitable for use at high temperatures. Many polymers have very good resist- ance to corrosive chemicals. Polymers have thousands of applications ranging from bullet- proof vests, compact disks (CDs), ropes, and liquid crystal displays (LCDs) to clothes and coffee cups. Thermoplastic polymers, in which the long molecular chains are not rigidly con- nected, have good ductility and formability; thermosetting polymers are stronger but more brittle because the molecular chains are tightly linked (Figure 1-4). Polymers are used in many applications, including electronic devices. Thermoplastics are made by shaping their molten form. Thermosets are typically cast into molds. Plastics contain additives that enhance the properties of polymers. Semiconductors Silicon, germanium, and gallium arsenide-based semicon- ductors such as those used in computers and electronics are part of a broader class of materials known as electronic materials. The electrical conductivity of semiconducting materials is between that of ceramic insulators and metallic conductors. Semiconductors have enabled the information age. In some semiconductors, the level of conductivity can Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 10 CHAPTER 1 Introduction to Materials Science and Engineering Figure 1-4 Polymerization occurs when small molecules, represented by the circles, combine to produce larger molecules, or polymers. The polymer molecules can have a structure that consists of many chains that are entangled but not connected (thermoplastics) or can form three-dimensional networks in which chains are cross-linked (thermosets). be controlled to enable electronic devices such as transistors, diodes, etc., that are used to build integrated circuits. In many applications, we need large single crystals of semicon- ductors. These are grown from molten materials. Often, thin films of semiconducting materials are also made using specialized processes. Composite Materials The main idea in developing composites is to blend the properties of different materials. These are formed from two or more materials, produc- ing properties not found in any single material. Concrete, plywood, and fiberglass are exam- ples of composite materials. Fiberglass is made by dispersing glass fibers in a polymer matrix. The glass fibers make the polymer stiffer, without significantly increasing its density. With composites, we can produce lightweight, strong, ductile, temperature-resistant materials or we can produce hard, yet shock-resistant, cutting tools that would otherwise shatter. Advanced aircraft and aerospace vehicles rely heavily on composites such as carbon fiber-reinforced polymers (Figure 1-5). Sports equipment such as bicycles, golf clubs, tennis rackets, and the like also make use of different kinds of composite materials that are light and stiff. Figure 1-5 The X-wing for advanced helicopters relies on a material composed of a carbon fiber- reinforced polymer. (Courtesy of Sikorsky Aircraft Division – United Technologies Corporation.) Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 3 Functional Classification of Materials 11 1-3 Functional Classification of Materials We can classify materials based on whether the most important function they perform is mechanical (structural), biological, electrical, magnetic, or optical. This classification of materials is shown in Figure 1-6. Some examples of each category are shown. These cat- egories can be broken down further into subcategories. Figure 1-6 Functional classification of materials. Notice that metals, plastics, and ceramics occur in different categories. A limited number of examples in each category are provided. Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 12 CHAPTER 1 Introduction to Materials Science and Engineering Aerospace Light materials such as wood and an aluminum alloy (that acci- dentally strengthened the engine even more by picking up copper from the mold used for casting) were used in the Wright brothers’ historic flight. Today, NASA’s space shuttle makes use of aluminum powder for booster rockets. Aluminum alloys, plastics, silica for space shuttle tiles, and many other materials belong to this category. Biomedical Our bones and teeth are made, in part, from a naturally formed ceramic known as hydroxyapatite. A number of artificial organs, bone replacement parts, cardiovascular stents, orthodontic braces, and other components are made using differ- ent plastics, titanium alloys, and nonmagnetic stainless steels. Ultrasonic imaging systems make use of ceramics known as PZT (lead zirconium titanate). Magnets used for magnetic resonance imaging make use of metallic niobium tin-based superconductors. Electronic Materials As mentioned before, semiconductors, such as those made from silicon, are used to make integrated circuits for computer chips. Barium titanate (BaTiO3), tantalum oxide (Ta2O5), and many other dielectric materials are used to make ceramic capacitors and other devices. Superconductors are used in making pow- erful magnets. Copper, aluminum, and other metals are used as conductors in power trans- mission and in microelectronics. Energy Technology and Environmental Technology The nuclear industry uses materials such as uranium dioxide and plutonium as fuel. Numerous other materials, such as glasses and stainless steels, are used in handling nuclear materials and managing radioactive waste. New technologies related to batteries and fuel cells make use of many ceramic materials such as zirconia (ZrO2) and polymers. Battery technology has gained significant importance owing to the need for many electronic devices that require longer lasting and portable power. Fuel cells will also be used in elec- tric cars. The oil and petroleum industry widely uses zeolites, alumina, and other materi- als as catalyst substrates. They use Pt, Pt/Rh and many other metals as catalysts. Many membrane technologies for purification of liquids and gases make use of ceramics and plastics. Solar power is generated using materials such as amorphous silicon (a:Si:H). Magnetic Materials Computer hard disks make use of many ceramic, metallic, and polymeric materials. Computer hard disks are made using alloys based on cobalt-platinum-tantalum-chromium (Co-Pt-Ta-Cr) alloys. Many magnetic ferrites are used to make inductors and components for wireless communications. Steels based on iron and silicon are used to make transformer cores. Photonic or Optical Materials Silica is used widely for making opti- cal fibers. More than ten million kilometers of optical fiber have been installed around the world. Optical materials are used for making semiconductor detectors and lasers used in fiber optic communications systems and other applications. Similarly, alumina (Al2O3) and yttrium aluminum garnets (YAG) are used for making lasers. Amorphous silicon is used to make solar cells and photovoltaic modules. Polymers are used to make liquid crystal displays (LCDs). Smart Materials A smart material can sense and respond to an external stimulus such as a change in temperature, the application of a stress, or a change in humid- ity or chemical environment. Usually a smart material-based system consists of sensors Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 5 Environmental and Other Effects 13 and actuators that read changes and initiate an action. An example of a passively smart material is lead zirconium titanate (PZT) and shape-memory alloys. When properly processed, PZT can be subjected to a stress, and a voltage is generated. This effect is used to make such devices as spark generators for gas grills and sensors that can detect under- water objects such as fish and submarines. Other examples of smart materials include magnetorheological or MR fluids. These are magnetic paints that respond to magnetic fields. These materials are being used in suspension systems of automobiles, including models by General Motors, Ferrari, and Audi. Still other examples of smart materials and systems are photochromic glasses and automatic dimming mirrors. Structural Materials These materials are designed for carrying some type of stress. Steels, concrete, and composites are used to make buildings and bridges. Steels, glasses, plastics, and composites also are used widely to make automotives. Often in these applications, combinations of strength, stiffness, and toughness are needed under different conditions of temperature and loading. 1-4 Classification of Materials Based on Structure As mentioned before, the term “structure” means the arrangement of a material’s atoms; the structure at a microscopic scale is known as “microstructure.” We can view these arrangements at different scales, ranging from a few angstrom units to a millimeter. We will learn in Chapter 3 that some materials may be crystalline (the material’s atoms are arranged in a periodic fashion) or they may be amorphous (the arrangement of the material’s atoms does not have long-range order). Some crystalline materials may be in the form of one crystal and are known as single crystals. Others consist of many crys- tals or grains and are known as polycrystalline. The characteristics of crystals or grains (size, shape, etc.) and that of the regions between them, known as the grain boundaries, also affect the properties of materials. We will further discuss these concepts in later chapters. A micrograph of stainless steel showing grains and grain boundaries is shown in Figure 1-1. 1-5 Environmental and Other Effects The structure-property relationships in materials fabricated into components are often influenced by the surroundings to which the material is subjected during use. This can include exposure to high or low temperatures, cyclical stresses, sudden impact, corrosion, or oxidation. These effects must be accounted for in design to ensure that components do not fail unexpectedly. Temperature Changes in temperature dramatically alter the properties of materials (Figure 1-7). Metals and alloys that have been strengthened by certain heat treatments or forming techniques may suddenly lose their strength when heated. A tragic reminder of this is the collapse of the World Trade Center towers on Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 14 CHAPTER 1 Introduction to Materials Science and Engineering Figure 1-7 Increasing temperature normally reduces the strength of a material. Polymers are suitable only at low temperatures. Some composites, such as carbon-carbon composites, special alloys, and ceramics, have excellent properties at high temperatures. September 11, 2001. Although the towers sustained the initial impact of the collisions, their steel structures were weakened by elevated temperatures caused by fire, ultimately leading to the collapse. High temperatures change the structure of ceramics and cause polymers to melt or char. Very low temperatures, at the other extreme, may cause a metal or polymer to fail in a brittle manner, even though the applied loads are low. This low-temperature embrit- tlement was a factor that caused the Titanic to fracture and sink. Similarly, the 1986 Challenger accident, in part, was due to embrittlement of rubber O-rings. The reasons why some polymers and metallic materials become brittle are different. We will discuss these concepts in later chapters. The design of materials with improved resistance to temperature extremes is essential in many technologies, as illustrated by the increase in operating temperatures of aircraft and aerospace vehicles (Figure 1-8). As higher speeds are attained, more heating of the vehicle skin occurs because of friction with the air. Also, engines operate more effi- ciently at higher temperatures. In order to achieve higher speed and better fuel economy, Figure 1-8 Skin operating temperatures for aircraft have increased with the development of improved materials. (After M. Steinberg, Scientific American, October 1986.) National aerospace plane Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.  1 - 5 Environmental and Other Effects 15 Figure 1-9 NASA’s X-43A unmanned aircraft is an example of an advanced hypersonic vehicle. (Courtesy of NASA Dryden Flight Research Center (NASA-DFRC).) new materials have gradually increased allowable skin and engine temperatures. NASA’s X-43A unmanned aircraft is an example of an advanced hypersonic vehicle (Figure 1-9). It sustained a speed of approximately Mach 10 (7500 miles/h or 12,000 km/h) in 2004. Materials used include refractory tiles in a thermal protection system designed by Boeing and carbon-carbon composites. Corrosion Most metals and polymers react with oxygen or other gases, partic- ularly at elevated temperatures. Metals and ceramics may disintegrate and polymers and non-oxide ceramics may oxidize. Materials also are attacked by corrosive liquids, leading to premature failure. The engineer faces the challenge of selecting materials or coatings that prevent these reactions and permit operation in extreme environments. In space appli- cations, we may have to consider the effect of radiation. Fatigue In many applications, components must be designed such that the load on the material may not be enough to cause permanent deformation. When we load and