Materials Moments: Arthur C—Food Containers Lewis & Ray—Al Composites.
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Transcript of Materials Moments: Arthur C—Food Containers Lewis & Ray—Al Composites.
Materials Moments:
Arthur C—Food Containers
Lewis & Ray—Al Composites
Exam I
Friday 21 FebruaryCovers Chapters 1 – 7
Review Questions posted on Canvas
Strengthening Mechanisms
Sections 7.8 – 7.13
Strengthening Metals
Underlying Principle for Strengthening Metals
–Dislocations facilitate plastic deformation
–Inhibiting (binding, stopping, slowing) dislocation motion makes metals stronger
Strengthening Metals:(Ways to restrict dislocation motion)
Composition change:1. Solid-solution strengthening (Diffusion)
a) Case hardeningb) Alloying
1. Solid-solution strengthening (Diffusion)2. Alloying
Carburizing furnace
City Steel Heat Treating Co.
Case Hardening – Hard Case w/ tough core
Low-C Steels (> 0.30% C):
Carburizing,Nitriding,Carbonitriding
Carburized depth of 0.030” to 0.050” in 4 hours @ 1700°F
Alloying
http://tankiialloy.en.made-in-china.com/offer/AqCnWidOrYcV/Sell-Copper-Nickel-Alloy-Strip.html
Cu-Ni Alloy
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Atoms diffuse to a location that reduces strain energy
Underlying principle:
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Fig. 7.17
Tensile strains
Solid-Solution Strengthening:Smaller Substitutional Impurity
Solid-Solution Strengthening:Larger Substitutional Impurity
Fig. 7.18
Compressive strains
2. Solid-Solution Strengthening:
Interstital Impurity
Fig. 7.18
Compressive strains
Fits in interstitial sites
2. Solid-Solution Strengthening:
Interstital Impurity
Fig. 7.18
Compressive strains
Fits in interstitial sites
Strengthening metals:How are dislocations bound in:Solid-solution strengthening?
They seek sites near dislocations to reduce lattice strains.
This stabilizes the lattice and discourages plastic deformation.
YouTube: Dislocation motion is analogous to the movement of caterpillar
How Solid-Solution strengthening
binds dislocations
f16_07_pg190
Cu-Ni alloy:Strength & Elongation Variation with Ni content
Fig. 7.16
Strengthening Metals
No Composition change:
1.Grain-size Reduction— Polycrystalline metals
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Grain size reduction:Dislocation motion at a grain boundary
Fig. 7.14
Grain-size reductionDislocation Pile-ups at grain boundaries
Young Modulus and Yield Strength 2:11
How do we reduce grain size?
Strengthening metals:How are dislocations bound in:
Grain-size reduction?
It’s difficult for dislocations to move past a grain boundary
The more grain boundaries, the more difficult for dislocations to move metal is strengthened
Strengthening Metals:
(Ways to restrict dislocation motion)
1. Solid-solution strengthening (Diffusion)
2. Grain-size reduction
3. Strain Hardening a.k.a. Work Hardening
a.k.a. Cold Working
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3. Strain Hardening (Work Hardening) (Cold Working)
Includes (but not limited to)
Drawing
Rolling
Peening—Strain hardened on surface only
Strain hardened throughout
No composition change
Strain Hardening in Copper
Cold WorkingExample: Wire Drawing
YouTube: Wire Drawing“2.Combined Drawing Machine SH-1” 0:20 - 0:45
YouTube: Drawing Process in Manufacturing / Aluminium tube Production
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Cold WorkingExample: Drawing
2. Deep drawing of sheet metal, Tiefziehen von Metallblechen
1. Deep drawing of sheet metal, Tiefziehen von Metallblechen
YouTube:
Strain Hardening:Example: Rolling
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Cold WorkingExample: Shot peening
Cold WorkingExample: Shot peened surface
DislocationDensities
PlasticDeformation:
Stainless Steel
Strengthening due to Cold Work
Fig. 7.19
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Strengthening metals:
How are dislocations bound in:
Strain hardening?
f05_07_pg179
Increasing the dislocation density increases the number of dislocations which can repel each other.
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Plastic Deformation difficult
Dislocations can’t easily move
Metal is Strengthened
Strain Hardening
Recovery, Recrystallization, &
Grain Growth
Sections 7.10 – 7.13
Reverse of Strengthening
Annealing:Eliminates dislocations
1) Recovery
2) Recrystallization
3) Grain Growth
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Recrystallization 580ºC
Stages of Recrystallization and grain growth33% Cold-worked brass (Tm = 900-940ºC)
t = 3 sect = 0 t = 4 sec
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Grain size increases
Stages of Recrystallization and grain growthCold-worked brass
t = 8 sec (580ºC) t = 15 min (580ºC) t = 10 min (700ºC)
Recovery followed by grain growth in polycrystalline camphor-ethanol mixture
YouTube Video:
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Plastic Deformation:Polycrystalline Cold-worked Nickel
Before deformation After deformation
Fig
. 7.1
1--1
70
x p
hoto
mic
rog
rap
h
Controlled annealing
Strain-relaxed buffers due to annealing in Silicon
f16_07_pg190
Recovery, Recrystallization, and Grain Growth
Recovery (grains recover slightly from cold-working)
Recrystal-lization (new grains form)
Grain Growth (larger grains grow at expense of smaller)
See Fig. 7.22
YouTube: Tensile Test on Work-Hardened Copper: necking effect
YouTube: Tensile Test on Annealed Copper
Compare these videos:Take note of the knurled knob on the RHS
How do we
restore ductility to work hardened metals?
Eliminate Dislocations!
Some little study aids follow
Review on your own:When Strengthening metals:
How are dislocations bound in these cases?
1) Grain-size reduction
2) Solid Solution Strengthening
3) Strain hardening
Element Crystal structure Atomic radius
Fe BCC 0.124 nm
Cr BCC 0.125 nm
Al FCC 0.125 nm
N HCP 0.065 nm
a) N in Fe at 700°C b) N in Fe at 900°C
c) Cr in Fe at 700°C d) Cr in Fe at 900°C
e) Al in Fe at 700°C f) Al in Fe at 900°C
1. For which combination of metals do you expect solid solution strengthening to occur?
2. For which combination of metals do you expect diffusion to be the fastest?
Metallic xl Structures1) Face-Centered Cubic (FCC)
Cu, Al, Ag, Au, Pb, Ni, Pt
2) Body-Centered Cubic (BCC)Na, Fe, Cr, Mo, W
§ Hexagonal Close-Packed (HCP)Ti, Zn, Cd, Co, Mg