Exam review

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Materials Moments:

Materials Moments:

Aaron L—Fiber-reinforced plastics

Troy/Micah–Erasers

Background image: http://images.iop.org/objects/ntw/news/10/4/9/image1.jpg

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Figure: http://matse1.matse.illinois.edu/metals/11.gif

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Photo: Shows what looks like triple junction from one viewpoint is actually 4-point junction when viewed from different angle.

https://www.llnl.gov/str/November05/gifs/Bulatov7.jpg

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Dislocation Densities

Range:

103 mm-2 1010 mm-2

Carefully
solidified

Metals

Highly
deformed

Metals

Many opportunities to accommodate slip

SEM {100} planes

SEM single crystal of cadmium deforming by dislocation slip on {100} planes.

Image: http://www.doitpoms.ac.uk/tlplib/miller_indices/uses.php?printable=1

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f09_07_pg183

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Fig. 7.9

Slip in a single

zinc crystal

YouTube: SEM study of slip in deformed cadmium single crystal

f09_07_pg183.jpg

Slip Systems:

{ x y z } < a b c >

f06_07_pg180

Fig. 7.6

FCC Slip Systems

f06_07_pg180.jpg

Table 7.1

t01_07_pg180

t01_07_pg180.jpg

(1 0 1 0)

(1 1 0 0)

(0 1 1 0)

(1 0 1 0)

(1 1 0 0)

(0 1 1 0)

Plastic Deformation

Section 7.5:

Single Crystals

f07_07_pg182

f07_07_pg182

Max. shear stress

is on a plane 45º from the

tensile stress

f07_07_pg182.jpg

f08_07_pg182

f08_07_pg182

Slip in a

single crystal

Free to move at
critical SS

Fig. 7.8

f08_07_pg182.jpg

Table 7.1

t01_07_pg180

Table 7.1

t01_07_pg180.jpg

Plastic Deformation

Section 7.6:

Polycrystalline Materials

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f10_07_pg186

Plastic Deformation:

Slip in

Polycrystalline Copper

Fig. 7.1 (173x photomicrograph)

f10_07_pg186.jpg

f11_07_pg186

Plastic Deformation:
Polycrystalline
Cold-worked Nickel

Before deformation After deformation

Fig. 7.11--170x photomicrograph

f11_07_pg186.jpg

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:

  • Grain-size Reduction—

Polycrystalline metals

f14_07_pg188

Grain size reduction:
Dislocation motion at a grain boundary

Fig. 7.14

f14_07_pg188.jpg

Grain-size reduction

Dislocation Pile-ups at grain boundaries

Young Modulus and Yield Strength 2:11

Strengthening metals:

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

The key to strengthening metals…

Bind Dislocations!

Sorry, I can’t move right now. I’m kinda tied up

Strengthening Metals:

(Ways to restrict dislocation motion)

  • Grain-size reduction

  • Solid-solution strengthening (Diffusion)
  • Case hardening
  • Alloying

City Steel Heat Treating Co.

f16_07_pg190

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

f16_07_pg190.jpg

Alloy

http://tankiialloy.en.made-in-china.com/offer/AqCnWidOrYcV/Sell-Copper-Nickel-Alloy-Strip.html

Cu-Ni Alloy

Cu-Ni Alloy

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f04_07_pg178

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Atoms diffuse to a location that reduces strain energy

f04_07_pg178.jpg

f16_07_pg190

f16_07_pg190

Fig. 7.17

Tensile strains

Solid-Solution Strengthening:
Smaller Substitutional Impurity

f16_07_pg190.jpg

f16_07_pg190

Solid-Solution Strengthening:
Larger Substitutional Impurity

Fig. 7.18

Compressive strains

f16_07_pg190.jpg

f16_07_pg190

2. Solid-Solution Strengthening:

Interstital Impurity

Fig. 7.18

Compressive strains

Fits in interstitial sites

f16_07_pg190.jpg

f16_07_pg190

2. Solid-Solution Strengthening:

Interstital Impurity

Fig. 7.18

Compressive strains

Fits in interstitial sites

f16_07_pg190.jpg

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

f16_07_pg190

Cu-Ni alloy:

Strength & Elongation Variation with

Ni content

Fig. 7.16

f16_07_pg190.jpg

The SECRET to strengthening metals…

Bind Dislocations!