YouTube: Diffusion posted by smcblackburn - PowerPoint PPT Presentation

Title: YouTube: Diffusion posted by smcblackburn


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Diffusion videos
YouTube Diffusion posted by smcblackburn
YouTube Slide Puzzle Physics, Leiden University
http//www.yale.edu/yaleche/chemeng/eia/eia.htm
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Materials Moments Abdelrhman A. Paper
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Principles of Materials

• Are everywhere

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Section 5.1-5.3, 5.5-5.6Diffusion
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YouTube Diffusion posted by
smcblackburn 016-110 View the rest of this
video if you have trouble understanding the
concept of diffusion.
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Diffusion

• Gases
• Liquids
• Solids

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Diffusion

• Connect 2 gas tanks Ar He
• Assume equal T P
• Gasses diffuse?reach uniform comp.

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Diffusion

• 2 gases Ar He
• 2 liquids water alcohol
• Diffuse until uniform composition

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Diffusion

• 2 gases Ar He
• 2 liquids water alcohol
• 2 solids Blocks of Cu Ni
• Heat at elevated T (below Tm)
• Leave for days
• Eventually reaches uniform composition

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Diffusion
In all cases, diffusion rate increases as T
increases.

• Rate
• 2 gases Ar He Fastest
• 2 liquids water alcohol
• 2 solids Blocks of Cu Ni Slowest

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f03_05_pg112
Vacancy Diffusion
Interstitial Diffusion
Fig. 5.3
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f03_05_pg112
Vacancy Diffusion
Interstitial Diffusion
Fig. 5.3
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f03_05_pg112

• Interdiffusion
• Example Cu, Ni
• Vacancy diffusion or interstitial diffusion?

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Metallic xl Structures

• Face-Centered Cubic (FCC)
• Cu, Al, Ag, Au, Pb, Ni, Pt
• Body-Centered Cubic (BCC)
• Na, Fe, Cr, Mo, W
• Hexagonal Close-Packed (HCP)
• Ti, Zn, Cd, Co, Mg

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Example Cu, Ni
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f03_05_pg112

• Interdiffusion
• Vacancy diffusion
• Example Cu, Ni

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Interdiffusion
Initially
See Figs. 5.1 and 5.2
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YouTube Slide Puzzle Physics, Leiden
University
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http//www.yale.edu/yaleche/chemeng/eia/eia.htmE
ric I. Altman Vacancy diffusion in a layer of
adsorbed Br atoms on Cu(100)
Whats Cu(100)?
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f03_05_pg112

• Interdiffusion

• Vacancy diffusion
• Interstitial diffusion
• Other paths
• Dislocations
• Grain boundaries
• Free surfaces

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f03_05_pg112

• Two conditions for diffusion
• Empty site near the diffusing atom
• Diffusing atom needs enough energy to break
  existing bonds.

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Ficks First Law Steady-State Diffusion
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Ficks First LawSteady-state diffusion
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Factors affecting diffusion rates

1. Diffusing species host material
2. Temperature
3. Concentration Gradient

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t02_05_pg119
Table 5.2
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t02_05_pg119
Diffusing Host Metal T(oC) D
(m2/s) species Fe a-Fe (BCC) 500 3.0 x
10-21 Fe a-Fe (BCC) 900 1.8 x 10-15 Fe g-Fe
(FCC) 500 1.1 x 10-17 Fe g-Fe (FCC) 900 7.8 x
10-16

• Which diffuses faster?
• Fe through a-Fe at 500oC
• Fe through a-Fe at 900oC
• Fe through g-Fe at 500oC
• Fe through g-Fe at 900oC

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The question thats kept you up late at night
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How does diffusion affect material properties?
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f16_07_pg190
Case Hardening Hard Case w/ tough core
Low-C Steels (gt 0.30 C) Carburizing, Nitriding
, Carbonitriding Carburized depth of 0.030 to
0.050 in 4 hours _at_ 1700F
City Steel Heat Treating Co.
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Steel C Fe

• Interstitial C imposes lattice strains in Fe

• Strains near dislocations can bind atoms and
  reduce deformation

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CarburizingSolid Diffusion process
Composition processing affect material
properties
YouTube Vacuum Carburizing and Heat treating
Begin at 135240
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Section 6.1-6.3Mechanical Properties of Metals
Elastic Deformation Stress-Strain behavior
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t02_05_pg119
Material Properties Mechanical Properties

• Stiffness
• Ductility
• Strength
• Toughness
• Hardness

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t02_05_pg119
Tensile Test
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t02_05_pg119
Tensile Test
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t02_05_pg119
Tensile Test
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t02_05_pg119
Strain gages

• Metal-foil gage
• Bond to testing material using epoxy
• Variations in electrical resistance converted to
  strain measurements.
• Grid shape maximizes resistance while keeping
  gage small

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fig_06_11
Brittle Failure Tensile test of Nodular Graphite
Cast Iron
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t02_05_pg119
Tensile Test
AlMgSi alloy ductile fracture
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Principles of Stress and Strain