MSE 170 Midterm review - University of...
Transcript of MSE 170 Midterm review - University of...
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Chapter 2 -
MSE 170 Midterm review
• Exam date: 11/2/2008 Mon, lecture time • Place: Here! • Close book, notes and no collaborations • A sheet of letter-sized paper with double-sided
notes is allowed • Material on the exam will be taken from the text
book reading, lecture notes, homework, and lab • Bring a calculator and straight edge/triangle • The review materials are not comprehensive,
there may be questions on the exam on topics not listed here
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Chapter 2 - 2
A few pointers • Eat a good (light) breakfast. Bring some food if you get hungry, with less glucose your brain won’t work as well.
• Take a few minutes to read the entire exam first and make sure you are clear on how many points each question is worth.
• Bring a watch! Taking 20 minutes to answer perfectly a 5 point question is still going to get you only 5 points
• Read the question carefully……Read the question carefully again! Make sure you are answering the right question. If not clear, ask! On average, 20% of the points are lost because of not reading the question carefully.
• Write clearly and explain your steps, you will be more likely to get partial credit if things go wrong at the end.
• Remember Occam’s Razor: the explanation of any phenomenon should make as few assumptions as possible, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory.
All other things being equal, the simplest solution is the best.
• When you are done, make sure to put your name and number and PLEASE hand in your work.
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Chapter 2 -
Bonding and atomic forces
• The periodic table
• What types of bonding are there?
• How does bonding affect materials properties?
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Chapter 2 - 4
The Periodic Table • Columns: Similar Valence Structure
Adapted from Fig. 2.6, Callister 7e.
Electropositive elements: Readily donate electrons
to become + ions.
Electronegative elements: Readily acquire electrons to become - ions.
give
up
1e
give
up
2e
give
up
3e
iner
t gas
es
acce
pt 1
e ac
cept
2e
O
Se Te Po At
I Br
He Ne Ar Kr Xe Rn
F Cl S
Li Be H
Na Mg
Ba Cs Ra Fr
Ca K Sc Sr Rb Y
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Chapter 2 -
Bonding and atomic forces (continued)
• Atomic forces & potential vs interatomic distance
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Chapter 2 -
Atomic bonding in solids
Bonding forces and energies
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Chapter 2 -
Crystal structure
• Determine #atoms/unit cell, CN#, APF and density
• Draw and index crystallographic direction and planes
• Close-packed plane and stacking sequence
• Crystal systems
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Chapter 2 -
Crystal Structures
8
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Chapter 2 -
Crystal structures (ceramics)
• Know the types of ceramic structures and identify their unit cells
• Determine coordination number for ceramic structures based on ionic radii and charge
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Chapter 2 - 10
Crystallographic Directions
1. Vector repositioned (if necessary) to pass through origin. 2. Read off projections in terms of unit cell dimensions a, b, and c 3. Adjust to smallest integer values 4. Enclose in square brackets, no commas
[uvw]
ex: 1, 0, ½ => 2, 0, 1 => [ 201 ]
-1, 1, 1
families of directions <uvw>
z
x
Algorithm
where overbar represents a negative index
[ 111 ] =>
y
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Chapter 2 - 11
Crystallographic Planes • Miller Indices: Reciprocals of the (three) axial
intercepts for a plane, cleared of fractions & common multiples. All parallel planes have same Miller indices.
• Algorithm 1. Read off intercepts of plane with axes in terms of a, b, c 2. Take reciprocals of intercepts 3. Reduce to smallest integer values (no always) 4. Enclose in parentheses, no commas i.e., (hkl)
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Chapter 2 -
Defects
• Distinguish point, linear (dislocation 1D), interfacial(2D), volume(3D) defects
• Draw and describe edge and screw dislocations
• Burgers circuits and vectors
• Understand equilibrium of vacancies and effect of T
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Chapter 2 - 13
• Vacancies: -vacant atomic sites in a structure.
• Self-Interstitials: -"extra" atoms positioned between atomic sites.
Point Defects
Vacancy distortion of planes
self- interstitial
distortion of planes
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Chapter 2 - 14
Two outcomes if impurity (B) added to host (A): • Solid solution of B in A (i.e., random dist. of point defects)
OR
Substitutional solid soln. (e.g., Cu in Ni) Interstitial solid soln.
(e.g., C in Fe)
Point Defects in Alloys
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Chapter 2 - 15
Imperfections in Solids
Fig. 4.3, Callister 7e.
Edge Dislocation – extra half-plane of atoms inserted in a crystal structure – b ⊥ to dislocation line
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Chapter 2 -
Diffusion
• Mechanisms, concentration gradients, diffusion coefficient
• Ficks laws
• Effects of T on diffusion coefficients
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Chapter 2 - 17
• Interdiffusion: In an alloy, atoms tend to migrate from regions of high conc. to regions of low conc.
Initially
Adapted from Figs. 5.1 and 5.2, Callister 7e.
Diffusion
After some time
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Chapter 2 - 18
Steady-State Diffusion
Fick’s first law of diffusion C1
C2
x
C1
C2
x1 x2
D ≡ diffusion coefficient
Rate of diffusion independent of time Flux proportional to concentration gradient =
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Chapter 2 - 19
Non-steady State Diffusion
• The concentration of diffusing species is a function of both time and position C = C(x,t)
• In this case Fick’s Second Law is used
Fick’s Second Law
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Chapter 2 -
Mechanical properties
• Definition of stress, strain, elastic modulus
• Analysis of stress-strain curves
• Yield strength, tensile strength, Poisson's ratio, ductility, resilience, and toughness
• Hardness
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Chapter 2 - 21
Elastic means reversible!
Elastic Deformation 1. Initial 2. Small load 3. Unload
F
δ
bonds stretch
return to initial
F
δ
Linear- elastic
Non-Linear- elastic
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Chapter 2 -
Concepts of stress and strain
• Tension tests – engineering stress
– engineering strain
• Compression tests
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Chapter 2 - 23
Linear Elastic Properties • Modulus of Elasticity, E: (also known as Young's modulus)
• Hooke's Law: σ = E ε σ
Linear- elastic
E
ε
F
F simple tension test
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Chapter 2 -
Plastic deformation
• Slip plane, direction and system, resolved shear stress
• Mechanism of plastic deformation
• Strengthening mechanisms
• Recovery, recrystallization, and grain growth
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Chapter 2 - 25
Plastic means permanent!
Plastic Deformation (Metals)
F
δ linear elastic
linear elastic
δ plastic
1. Initial 2. Small load 3. Unload
p lanes still sheared
F
δ elastic + plastic
bonds stretch & planes shear
δ plastic
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Chapter 2 - 26
Dislocation Motion Dislocations & plastic deformation • Cubic & hexagonal metals - plastic deformation by
plastic shear or slip where one plane of atoms slides over adjacent plane by defect motion (dislocations).
• If dislocations don't move, deformation doesn't occur!
Adapted from Fig. 7.1, Callister 7e.
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Chapter 2 -
Remember to THINK! and
GOOD LUCK
27