EET 106

1. CHAPTER 1 Introduction to Material Engineering EET 106

2. CO1: • Ability to describe and analyze the Mechanical, Electrical and Magnetic properties of materials.

3. THE MARS ROVERS; SPIRIT AND OPPORTUNITY Spirit and Opportunity are made up of materials such as * Metals * Ceramics * Composites * Polymers * Semiconductors

4. WHAT ARE MATERIALS? • Materials may be defined as substance of which something is composed or made. • Materials are obtained from earth crust and atmosphere. • Examples :- • Silicon and Iron constitute 27.72 and 5.00 percentage of weight of earths crust respectively. • Nitrogen and Oxygen constitute 78.08 and 20.95 percentage of dry air by volume respectively.

5. WHY THE STUDY OF MATERIALS ARE IMPORTANT? • Production and processing of materials constitute a large part of our economy. • Engineers choose materials to suite design. • New materials might be needed for some new applications. • Example:- High temperature resistant materials. • Space station and Mars Rovers should sustain conditions in space. * High speed, low temperature, strong but light. • Modification of properties might be needed for some applications. • Example :- Heat treatment to modify properties.

6. MATERIAL SCIENCE AND ENGINEERING? • Materials science deals with basic knowledge about the internal structure, properties and processing of materials. • Materials engineering deals with the application of knowledge gained by materials science to convert materials to products. Materials Science and Engineering Materials Science Materials Engineering Applied Knowledge of Materials Basic Knowledge of Materials Resultant Knowledge of Structure and Properties

7. TYPES OF MATERIALS • Metallic Materials • Composed of one or more metallic elements. Example:- Iron (Fe), Copper (Cu), Aluminum (Al) • Metallic element may combine with nonmetallic elements. Example:- Silicon Carbide, Iron Oxide. • Metals have crystalline structure. • Good thermal and electric conductors. Metal Alloys Ferrous (contain large % of Iron) Eg: Steel, Cast Iron Nonferrous (do not contain or only small amount of Iron) Eg: amalgam, Brass, Pewter

8. The aircraft turbine engine PW 4000 is made principally from metal alloys.

9. TYPES OF MATERIALS • Polymeric (Plastic) Materials • Consist of long molecular chains, and mostly noncrystalline. • Some consist of mixtures of crystalline and noncrystalline regions. • Poor conductors of electricity and hence used as insulators. • Strength and ductility vary greatly. • Low densities and low decomposition temperatures. Examples :- Poly vinyl Chloride (PVC), Polyester. Applications:- Appliances, DVDs, Fabrics etc.

11. TYPES OF MATERIALS • Ceramic Materials • Metallic and nonmetallic elements are chemically bonded together. • Inorganic but can be either crystalline, noncrystalline or mixture of both. • High hardness, strength and wear resistance. • Very good insulator. Hence used for furnace lining for heat treating and melting metals. • Also used in space shuttle to insulate it during exit and reentry into atmosphere. • Other applications : Abrasives, construction materials, utensils etc. • Example:- Porcelain, Glass, Silicon nitride.

13. TYPES OF MATERIALS • Composite Materials • Mixture of two or more materials. • Consists of a filler material and a binding material. • Materials only bond, will not dissolve in each other. • Mainly two types :- • Fibrous: Fibers in a matrix • Particulate: Particles in a matrix Matrix can be metals, ceramic or polymer Examples :- • Fiber Glass ( Reinforcing material in a polyester or epoxy matrix) • Concrete ( Gravels or steel rods reinforced in cement and sand) Applications:- Aircraft wings and engine, construction.

16. TYPES OF MATERIALS • Electronic Materials • Not Major by volume but very important. • Silicon is a common electronic material. • Its electrical characteristics are changed by adding impurities. Examples:- Silicon chips, transistors Applications :- Computers, Integrated Circuits, Satellites etc.

17. COMPETITION AMONG MATERIALS Example:- • Materials compete with each other to exist in new market • Over a period of time usage of different materials changes depending on cost and performance. • New, cheaper or better materials replace the old materials when there is a breakthrough in technology Figure 1.14 Predictions and use of materials in US automobiles.

18. FUTURE TRENDS • Metallic Materials • Production follows US economy closely. • Alloys may be improved by better chemistry and process control. • New aerospace alloys being constantly researched. • Aim: To improve temperature and corrosion resistance. • Example: Nickel based high temperature super alloys. • New processing techniques are investigated. • Aim: To improve product life and fatigue properties. • Example: Isothermal forging, Powder metallurgy. • Metals for biomedical applications

19. FUTURE TRENDS • Polymeric (Plastic Materials) • Fastest growing basic material (9% per year). • After 1995 growth rate decreased due to saturation. • Different polymeric materials can be blend together to produce new plastic alloys. • Search for new plastic continues.

20. FUTURE TRENDS • Ceramic Materials • New family of engineering ceramics are produced last decade • New materials and applications are constantly found. • Now used in Auto and Biomedical applications. • Processing of ceramics is expensive. • Easily damaged as they are highly brittle. • Better processing techniques and high-impact ceramics are to be found.

21. FUTURE TRENDS • Composite Materials • Fiber reinforced plastics are primary products. • On an average 3% annual growth from 1981 to 1987. • Annual growth rate of 5% is predicted for new composites such as Fiberglass-Epoxy and Graphite-Epoxy combinations. • Commercial aircrafts are expected to use more and more composite materials.

22. FUTURE TRENDS • Electronic Materials • Use of electronic materials such as silicon increased rapidly from 1970. • Electronic materials are expected to play vital role in “Factories of Future”. • Use of computers and robots will increase resulting in extensive growth in use of electronic materials. • Aluminum for interconnections in integrated circuits might be replaced by copper resulting in better conductivity.

23. FUTURE TRENDS • Smart Materials :Change their properties by sensing external stimulus. • Shape memory alloys: Strained material reverts back to its original shape above a critical temperature. • Used in heart valves and to expand arteries. • Piezoelectric materials: Produce electric field when exposed to force and vice versa. • Used in actuators and vibration reducers.

24. MEMS AND NANOMATERIALS • MEMS: Microelectromechanical systems. • Miniature devices • Micro-pumps, sensors • Nanomaterials:Characteristic length < 100 nm • Examples: ceramics powder and grain size < 100 nm • Nanomaterials are harder and stronger than bulk materials. • Have biocompatible characteristics ( as in Zirconia) • Transistors and diodes are developed on a nanowire.

25. CASE STUDY: MATERIAL SELECTION • Problem: Select suitable material for bicycle frame and fork. Steel and alloys Wood Carbon fiber Reinforced plastic Aluminum alloys Ti and Mg alloys Low cost but Heavy. Less Corrosion resistance Light and strong. But Cannot be shaped Very light and strong. No corrosion. Very expensive Light, moderately Strong. Corrosion Resistance. expensive Slightly better Than Al alloys. But much expensive Cost important? Select steel Properties important? Select CFRP

26. ATOMIC STRUCTURE Fundamental concept • Atom – electrons – 9.11 x 10-31 kg protonsneutrons • Atomic number = # of protons in nucleus of atom = # of electrons of neutral species } 1.67 x 10-27 kg

27. Isotopes - atoms of some elements have two or more different atomic masses (the number of protons is the same for all atoms of a given element, the number of neutrons (N) may be variable.) • A [=] atomic mass unit = amu = 1/12 mass of 12C • 1 mole = 6.023 x 1023 atoms • 1 amu/atom = 1g/mol • Quantum mechanical principle - A set of principles and laws that govern systems of atomic and subatomic entities

28. ATOMIC MODEL Bohr atomic model - Electrons are assumed to revolve around the atomic nucleus in discrete orbital and the position of any particular electron is more or less well defined in terms of its orbital. An electron may change energy, but in doing so it must make a quantum jump either to an allowed higher energy (with absorption of energy) or to a lower energy (with emission of energy).

29. ATOMIC STRUCTURE • Valence electrons determine all of the following properties • Chemical • Electrical • Thermal • Optical

30. ELECTRON ENERGY STATES Bohr’s model worked very well for simple atom such as hydrogen. However, it did not able to explain the behavior of more complex (multielectron) atoms and left many unanswered questions. Louis de Broglie (1892-1987) proposed that particles of matter such as electrons could be treated in terms of both particle and wave (as light). Schrodinger (1887-1961) proposed a modern quantum mechanics model toexplain the the behavior of more complex (multielectron) atoms. Light behaves both as a particle and as a wave. Since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time. Now, scientists at EPFL have succeeded in capturing the first-ever snapshot of this dual behavior. Read more at: http://phys.org/news/2015-03-particle.html#jCp

31. ELECTRON ENERGY STATES • The first three electron energy states for the Bohr’s model for hydrogen atom. (b) Electron energy states for the first three shells of the modern quantum mechanics model for hydrogen atom.

32. ELECTRONIC STRUCTURE • Electrons have wavelike and particle-like properties. • This means that electrons are in orbitals defined by a probability. • Each orbital at discrete energy level determined by quantum numbers.Quantum NumbersDesignation n = principal (energy level/shell) K, L, M, N, O (1, 2, 3, etc.) l = orbitals (subshells) s, p, d, f (0, 1, 2, 3,…, n-1) ml = magnetic 1, 3, 5, 7 (-l to +l) ms = spin ½, -½

33. ELECTRONS IN ATOMS In terms of electron distribution, comparison of the : • Bohr’s model • Modern quantum mechanics model

34. ELECTRON ENERGY STATES The relative energies of the electrons for the various shells and subshells.

36. 4d N-shell n = 4 4p 3d 4s 3p M-shell n = 3 Energy 3s 2p L-shell n = 2 2s 1s K-shell n = 1 ELECTRON ENERGY STATES Electrons... • have discrete energy states • tend to occupy lowest available energy state.

37. QUANTUM NUMBERS The number of available electron states in some of the electron shells and subshells

38. Element Atomic # Electron configuration Hydrogen 1 1s 1 Helium 2 (stable) 1s 2 Lithium 3 1s 2 2s 1 Beryllium 4 1s 2 2s 2 Boron 5 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 Carbon 6 ... ... Neon 10 1s 2 2s 2 2p 6 (stable) Sodium 11 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 Magnesium 12 1s 2 2s 2 2p 6 3s 2 3p 1 Aluminum 13 ... ... 1s 2 2s 2 2p 6 3s 2 3p 6 (stable) Argon 18 ... ... ... Krypton 36 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable) SURVEY OF ELEMENTS • Most elements: Electron configuration not stable.

39. valence electrons ELECTRON CONFIGURATION • Valence electrons– electrons that occupy the outermost shells. • Filled shells - stable valence electron shell • Valence electrons are most available for bonding and tend to control the chemical properties. • example: C (atomic number = 6) 1s22s2 2p2 Valance electron are extremely important. They participate in the bonding between atoms to form atomic and molecular aggregates. Many of the physical and chemical properties of solids are based on these valence electrons.

40. 1s2 2s2 2p6 3s2 3p6 3d6 4s2 valence electrons 4d N-shell n = 4 4p 3d 4s 3p M-shell n = 3 Energy 3s 2p L-shell n = 2 2s 1s K-shell n = 1 ELECTRON CONFIGURATION 26 ex: Fe - atomic # =

41. ELECTRON CONFIGURATION The electrons fill up the lowest possible energy states in the electron shells and subshells The filled and lowest unfilled energy states for a sodium atom.

45. THE PERIODIC TABLE Periodic table – Element classification according to electron configuration The periodic table of the elements. The numbers in parentheses are the atomic weights of the most stable or common isotopes.

46. inert gases give up 1e give up 2e accept 2e accept 1e give up 3e H He Li Be O F Ne Na Mg S Cl Ar K Ca Sc Se Br Kr Rb Sr Y Te I Xe Cs Ba Po At Rn Fr Ra THE PERIODIC TABLE • Columns: Similar Valence Structure Adapted from Fig. 2.6, Callister 7e. Electropositive elements: Readily give up electrons to become + ions. Electronegative elements: Readily acquire electrons to become - ions.

47. ELECTRONEGATIVITY • Ranges from 0.7 to 4.0 • Large values: tendency to acquire electrons. Smaller electronegativity Larger electronegativity

48. BONDING FORCES AND ENERGY FOR ION PAIR • Energy – minimum energy most stable (a) The dependence of repulsive, attractive, and net forces on interatomic separation for two isolated atoms. (b) The dependence of repulsive, attractive, and net potential energies on interatomic separation for two isolated atoms.

49. BONDING FORCES AND ENERGY • This typical curve has a minimum at equilibriumdistance R0 • R > R0 ; • the potential decreases gradually, approaching 0 as R∞. • the force is attractive. • R < R0; • the potential increases very rapidly, approaching ∞ at small separation. • the force is repulsive.