1 Material Science Structures and Properties of Metallic Materials Ceramics Polymers Composites Encompasses - Electronic, Magnetic, Optical, Mechanical, and Chemical Properties FE/EIT Exam - Two Major Areas - Fundamentals of 1. Strength, Deformation, Plasticity of Crystalline Solids 2. Phase Equilibrium in Metallic Systems
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1 Material Science Structures and Properties of Metallic Materials Ceramics Polymers Composites Encompasses - Electronic, Magnetic, Optical,
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Material Science Structures and Properties of
Metallic Materials Ceramics Polymers Composites
Encompasses - Electronic, Magnetic, Optical, Mechanical, and Chemical Properties
FE/EIT Exam - Two Major Areas - Fundamentals of 1. Strength, Deformation, Plasticity of Crystalline
Solids 2. Phase Equilibrium in Metallic Systems
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Mechanical Properties of Metals and Alloys
Experimental Techniques - Response to Applied Stress
Capacity to withstand static load (Tension / Compression)
Resistance to permanent deformation (Hardness)
Toughness under shock loading (Impact)
Useful life under cyclic loading (Fatigue)
Elevated temperature behavior (Creep and Stress Rupture)
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Tension Testing Two distinct stages of deformation Elastic Deformation (Reversible Change in
Elastic Deformation Hooke’s Law = E = Stress = Strain E = Young’s Modulus / Modulus of Elasticity
Plastic Deformation
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Plastic Deformation (Non-Linear)
Yield Stress = y
Off-Set Yield = 0.2%
Ultimate Tensile Strength = uts
Fracture Stress = f (f < uts)
Ductility
Work Hardening / Strain Hardening
Figure 3.1
Figure 3.2
Figure 3.3-4
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Nature of Plastic Flow For Crystalline Material (including metals and
alloys)
Plastic deformation involves sliding of atomic planes called slip deformation, analogous to shear.
Slip System - Combination of a close-packed plane and a close-packed direction.
Slip occurs along planes and are restricted in crystallographic directions that are the most densely packed. The greater the planes and directions, the easier it is to produce plastic slip without brittle fracture.
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Slip Deformation - continued
Slip occurs when the resolved component of
Shear Stress R = P/A cos cos exceeds the critical value
Rolling direction vs transverse direction affect mechanical properties, introduce anisotropy
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Effects of Heat Treatment Annealing - Softening, ductile behavior Quenching of Steel -
Martensite formation, strong but brittle Tempering of Martensite -
Hardness decreases, toughness increases Strength is sacrifice to avoid brittle failure
Age Hardening - Fine scale precipitation, increased strength
Case Hardening - Hard case, soft core by carburizing and nitriding Increased strength, better wear-resistance
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Effects of Processing Variables
Welding - Heat-affected zone, larger grain size, poorer mechanical properties. Local chemical changes, including loss of carbon in steel, quenching cracking due to rapid quenching.
Flame Cutting - Drastic changes of microstructure near the flame-cut surface, affects properties.
Machining and Grinding - Cold working results in stain hardening, may produce surface cracks.
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Effects of Service Conditions
Extreme Low Temperature Ductile-brittle transition occurs in steel.
Extreme High Temperature Causes corrosion and surface oxidation Surface cracks may form Results in corrosion fatigue, creep, and
rupture Impact Loading
Notch sensitivity, surface scratches, corrosion pits can initiate brittle failure
Phase - Bounded volume of material of uniform chemical composition, with fixed crystalline structure, and thermo-plastic properties at a given temperature.
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Equilibrium
Equilibrium between Phases Gibb’s Phase Rule P + F = C + 2 P = number of phases, C = number of
elements F = degrees of freedom, 2 = external
variables (temperature and pressure).
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Analysis of Phase Diagrams
Thermal Arrest (Freezing/Melting Point) Lever Rule Solid Solution Alloy Eutectic Notation = primarily A, small amount of dissolved
Molecules organized in distinct three dimensional patterns (motif = unit cell)
Atomic Bonding Ionic, Covalent, Metallic
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Electronic Structure of Atoms
Quantized = Orbiting (Shell) Electron Energy Levels
Quantum Numbers (Three Indicators) Quantum Number n = Energy Level
# of electrons per shell = 2n2
Sub-Levels l = 0, 1, … , n-1 l = 0, 1, 2, 3 = s, p, d, f for n=1, l =0 and shell = 1(s) for n=2, l =0,1 and shell = 2(s) and 2(p)
Magnetic Quantum Number m = -l to +l (0) Spin Quantum Number s = + 1/2 or -1/2
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Pauli’s Exclusion Principle
Each quantum state can accommodate 2 electrons
of opposite spin (- 1/2 & + 1/2 {up & down})
No more than 2 electrons per state Applies to states, not energy levels
Valence Electrons = Outermost s & p states
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Ionic Bonding
Electropositive and Electronegative Elements Example: Due to “exchanged” electrons
Sodium (Na+) and Chlorine (Cl-)
Opposite charges attract Electron clouds repel Potential energy minimum at balance
distance Potential Well = Preferred Site
Figure 3.26
Figure 3.27
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Covalent Bonding
Homopolar (Covalent) Bonding = Electron Sharing
Bonding Pairs = Number of Shared Electrons = 8 - N ( N=Valence)
Carbon (Atomic Number 6) Electron Configuration 1(s)22(s)22(p)2
Valence Electrons = 2 (from 2s) + 2 (from 2p) = 4
Bonding Pairs = 8 - 4 = 4
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Metallic Bonding
Metallic Elements (Valence = 1 or 2) Valence Electrons “free” to migrate and are
not “localized” to individual atoms in as in the case of ionic or covalent bonding.
The “sea” of migrating electrons and the attraction between positively charged atoms producing three-dimensional periodic lattices.
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Electrical Properties
Ionic and Covalent Bonding Localized Electrons = Insulators Conductivity increases with temperature
Metallic Bonding Free Migrating Electrons Collide with Oscillating Lattices Higher Mean Free Path = Higher
Conductivity Conductivity decreases with temperature
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Energy Bands
Pauli’s Exclusion Principle (2 per state) Energy bands have quasi-continuous levels Fill from lowest to highest energy levels Additional energy (thermal or electric field) Kinetic energy increases
Electrons move up an energy level but only at the highest level
Conduction Band - Valence Band - Energy Gap
Semiconductors
Figure 3.28
Energy Gap
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Crystalline State and Crystallography
Unit Cell Lattice with atoms at each corner (6
parameters) Parallelepiped (, a, b, c) Seven distinct shapes
Bravais Lattice Fourteen constructions are possible where
each atoms has an identical surrounding.
Figure 3.30
Table 3.2
Figure 3.33
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Body-Centered Cubic Lattice
Body-Centered Cubic Lattice BCC (9)
Face-Centered Unit Cell FCC (12) Closed Packed Plane
Hexagonal Closed Pack Lattice HCP (13)
Figure 3.34
Figure 3.35
Figure 3.37
Figure 3.36
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Miller Indices
System of notation used for denoting planes and directions in crystalline structures (hkl).
Note: All integers, without common factors.
Figure 3.38
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Primitive Cells
Only Corner Atoms Cubic Lattice, Hexagonal Lattice BCC, FCC, HCP are not primitive cells.
Number of Atoms per Cell Simple Cubic (1/8 * 8) = 1 per cell FCC (1/8 * 8 + 1/2 * 6) = 4 per cell BCC (1/* * * + 1) = 2 per cell
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Interplaner Spacing Interplaner Distance (dhkl) Perpendicular distance between equivalent planes Measured in Angstrom Units A = 10-8 cm
Atomic Packing Factor = Volume of Atoms Volume of Space
FCC APF = 0.74V BCC APF = 0.68
X-Ray Crystallography Bragg’s Law 2dhkl = sin = is X-Ray Wavelength and is Reflection