Chapter 1 Introduction to Materials Science Engineering ISSUES

Chapter 1: Introduction to Materials Science & Engineering ISSUES TO ADDRESS. . . • What is materials science and engineering? • Why are materials important? • Why is it important for engineers to understand materials ? Chapter 1 - 1

What is Materials Science & Engineering? • Materials science – Investigate relationships between structures and properties of materials – Design/develop new materials • Materials engineering – Create products from existing materials – Develop materials processing techniques Chapter 1 - 2

Why Are Materials Important? • Materials drive advancements in our society – Stone Age – Bronze Age – Iron Age • What is today’s material age? – Silicon (Electronic Materials) Age? – Nanomaterials Age? – Polymer Age? Chapter 1 - 3

Why is it Important for Engineers to Understand Materials? • Products/devices/components that engineers design are all made of materials • To select appropriate materials and processing techniques for specific applications engineers must – have knowledge of material properties and – understand the structure-property relationships Chapter 1 - 4

Relationships Among Processing, Structure, & Properties • Processing (e. g. , cooling rate of steel from high temperature) affects structure (microstructure) • Structure in turn effects hardness (d) Structure Hardness (BHN) Property 600 500 400 (c) (a) (b) 4 μm 300 200 30 μm Data obtained from Figs. 11. 31(a) and 11. 32 with 4 wt% C composition, and from Fig. 11. 15, Callister & Rethwisch 5 e. Micrographs adapted from (a) Fig. 11. 19; (b) Fig. 10. 34; (c) Fig. 11. 34; and (d) Fig. 11. 21, Callister & Rethwisch 5 e. (Figures 11. 19, 11. 21, & 11. 34 copyright 1971 by United States Steel Corporation. Figure 10. 34 courtesy of Republic Steel Corporation. ) 100 0. 01 0. 1 1 10 1000 Cooling Rate (ºC/s) Processing Chapter 1 - 5

Types of Materials • Metals: – Strong, ductile – High thermal & electrical conductivities – Opaque, reflective • Polymers/plastics: compounds of non-metallic elements – Soft, ductile, low strengths, low densities – Low thermal & electrical conductivities – Opaque, translucent or transparent • Ceramics: compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides) – Hard, Brittle – Low thermal & electrical conductivities – Opaque, translucent, or transparent Chapter 1 - 6

Materials Selection Engineers often solve materials selection problems. Procedure: 1. For a Specific Application Determine Required Properties • Properties: mechanical, electrical, thermal, magnetic, optical, deteriorative. 2. From List of Properties Identify Candidate Material(s) 3. Best Candidate Material Specify Processing technique(s) • To provide required set of properties • To produce component having desired shape and size • Example techniques: casting, mechanical forming, welding, heat treating Chapter 1 - 7

Material Property Types Properties of materials fall into six categories as follows: • Mechanical • Electrical • Thermal • Magnetic • Optical • Deteriorative Chapter 1 - 8

Mechanical Properties Affect of carbon content on the hardness of a common steel: Fig. 11. 31, Callister & Rethwisch 5 e. [Data taken from Metals Handbook: Heat Treating, Vol. 4, 9 th edition, V. Masseria (Managing Editor), 1981. Reproduced by permission of ASM International, Materials Park, OH. ] Brinell hardness 320 240 160 80 0 0. 5 1 wt%C • Increasing carbon content increases hardness of steel. Chapter 1 - 9

Electrical Properties Factors that affect electrical resistivity – for copper: 5 (10 -8 Ohm-m) Resistivity, ρ 6 4 3 2 1 0 Fig. 12. 8, Callister & Rethwisch 5 e. Ni Cu + t% a 2 3. 3 Ni % t Ni 16 a. % t 2 a + 2 1. Cu +1 u C d e rm Ni % t defo 12 a. 1 + Cu Cu ” e r “Pu [Adapted from: J. O. Linde, Ann Physik 5, 219 (1932); and C. A. Wert and R. M. Thomson, Physics of Solids, 2 nd edition, Mc. Graw-Hill Company, New York, 1970. ] T (°C) • Increasing temperature increases resistivity. • Increasing impurity content (e. g. , Ni) increases resistivity. • Deformation increases resistivity. -200 -100 0 Chapter 1 - 10

Thermal Properties Thermal Conductivity (W/m-K) Thermal Conductivity – measure of a material’s ability to conduct heat 400 300 Fig. 17. 4, Callister & Rethwisch 5 e. [Adapted from Metals Handbook: Properties and Selection: Nonferrous alloys and Pure Metals, Vol. 2, 9 th ed. , H. Baker, (Managing Editor), ASM International, 1979, p. 315. ] 200 100 0 0 10 20 30 40 Composition (wt% Zinc) • Increasing impurity content (e. g. , Zn in Cu) decreases thermal conductivity. Chapter 1 - 11

Thermal Properties (continued) Material used for space shuttle Courtesy of Lockheed Missiles and Space Company, Inc. Courtesy of Lockheed Aerospace Ceramics Systems, Sunnyvale, CA Highly porous materials are poor conductors of heat 100 μm • Ceramic Fibers: – significant void space – low thermal conductivity • Demonstration: – low thermal conductivity of this material Chapter 1 - 12

Magnetic Properties • Magnetic Storage: -- Recording medium is magnetized by recording write head. • Magnetic Permeability vs. Composition: -- Adding 3 atomic % Si makes Fe a better recording medium! Magnetization Fe+3%Si Fe Magnetic Field Fig. 18. 23, Callister & Rethwisch 5 e. (Courtesy of HGST, a Western Digital Company. ) Adapted from C. R. Barrett, W. D. Nix, and A. S. Tetelman, The Principles of Engineering Materials, Fig. 1 -7(a), p. 9, 1973. (Electronically reproduced by permission of Pearson Education, Inc. , Upper Saddle River, New Jersey. ) Chapter 1 - 13

Optical Properties • The light transmittance of some materials depend on their structural characteristics: Aluminum oxide polycrystalline material (having many small grains)—is optically translucent Aluminum oxide polycrystalline material having some porosity—is optically opaque Specimen preparation, P. A. Lessing Aluminum oxide single crystal (high degree of perfection)—is optically transparent Chapter 1 - 14

Deteriorative Properties • Small cracks formed in steel bar that was simultaneously stressed and immersed in sea water - Form of stress-corrosion cracking Cracks Fig. 16. 21, Callister & Rethwisch 5 e. (from Marine Corrosion, Causes, and Prevention, John Wiley and Sons, Inc. , 1975. ) Chapter 1 - 15

Deteriorative Properties (cont. ) Crack Growth Rate (m/s) • For stress-corrosion cracking, rate of crack growth is diminished by heat treating 10 -8 “as-received” “heat treated” Adapted from Fig. 11. 20(b), R. W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials" (4 th ed. ), p. 505, John Wiley and Sons, 1996. (Original source: Markus O. Speidel, Brown Boveri Co. ) 10 -10 load For Aluminum alloy 7178 that is stressed while immersed in a saturated aqueous Na. Cl solution, crack growth rate is reduced by heat treating (160 C for 1 h prior to testing). Chapter 1 - 16

Example of Materials Selection: Artificial Hip Replacement • Anatomy of a human hip joint and adjacent skeletal features Chapter 1 - 17

Materials: Artificial Hip Replacement (cont. ) Hip joint problems can be painful and disabling • Joint deterioration (loss of cartilage) as one ages • Joint fracture arrows point to ends of fracture line X-ray of normal hip joint X-ray of fractured hip joint Chapter 1 - 18

Materials: Artificial Hip Replacement (cont. ) • Damaged and diseased hip joints can be replaced with artificial ones • Materials requirements for artificial joints – Biocompatible – minimum rejection by surrounding body tissues – Chemically inert to body fluids – Mechanical strength to support forces generated – Good lubricity and high wear resistance between articulating surfaces Chapter 1 - 19

Materials: Artificial Hip Replacement (cont. ) • Femoral stem — inserted into top of hip bone (femur) Head (Ball) • Head (Ball) — affixed to femoral stem • Shell — attached to pelvis • Liner — into which head fits Liner & Shell (Acetabular) Femoral Stem Photograph courtesy of Zimmer, Inc. , Warsaw, IN, USA. Chapter 1 - 20

Materials: Artificial Hip Replacement (cont. ) • Materials used - Femoral stem — titanium or Co. Cr. Mo alloy - Head (Ball) — Co. Cr. Mo alloy or Al 2 O 3 (ceramic) - Shell — titanium alloy - Liner — polyethylene (polymer) or Al 2 O 3 (ceramic) Chapter 1 - 21

Materials: Artificial Hip Replacement (continued) Head (Ball) Acetabular shell and liner Schematic diagram of an artificial hip X-ray of an implanted artificial hip Chapter 1 - 22

SUMMARY • Appropriate materials and processing decisions require engineers to understand materials and their properties. • Materials' properties depend on their structures; structures are determined by how materials are processed • In terms of chemistry the three classifications of materials are metals, ceramics, and polymers • Most properties of materials fall into the following six categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative. • An important role of engineers is that of materials selection. Chapter 1 - 23

ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 1 - 24