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YouTube: Diffusion posted by smcblackburn
YouTube: Slide Puzzle Physics, Leiden University
http://www.yale.edu/yaleche/chemeng/eia/eia.htm
Diffusion videos
Materials Moments:
Abdelrhman A. – Paper
Principles of Materials
Are everywhere
Section 5.1-5.3, 5.5-
5.6
Diffusion
YouTube: Diffusion posted by smcblackburn
0:16-1:10
View the rest of this video if you have trouble understanding the concept of diffusion.
Diffusion
• Gases
• Liquids
• Solids
Diffusion
Connect 2 gas tanks: Ar & He• Assume equal T & P
• Gasses diffusereach uniform comp.
• 2 gases: Ar & He
• 2 liquids: water & alcohol• Diffuse until uniform composition
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
Diffusion
Rate
• 2 gases: Ar & He Fastest
• 2 liquids: water & alcohol
• 2 solids: Blocks of Cu & Ni Slowest
Diffusion In all cases, diffusion rate increases as T increases.
Fig. 5.3
Diffusion Mechanisms
VacancyDiffusion
InterstitialDiffusion
Fig. 5.3
Diffusion Mechanisms
VacancyDiffusion
InterstitialDiffusion
Interdiffusion
Example: Cu, Ni
Vacancy diffusion or interstitial diffusion?
Metallic xl Structures
1) Face-Centered Cubic (FCC)Cu, Al, Ag, Au, Pb, Ni, Pt
2) Body-Centered Cubic (BCC)Na, Fe, Cr, Mo, W
3) Hexagonal Close-Packed (HCP)Ti, Zn, Cd, Co, Mg
Example: Cu, Ni
Interdiffusion
1) Vacancy diffusion
Example: Cu, Ni
Initially
See Figs. 5.1 and 5.2
Interdiffusion
After some time
YouTube:
Slide Puzzle Physics, Leiden University
http://www.yale.edu/yaleche/chemeng/eia/eia.htm
Eric I. Altman
“Vacancy diffusion in a layer of adsorbed Br atoms on
Cu(100)”What’s Cu(100)?
Interdiffusion
1) Vacancy diffusion
2) Interstitial diffusion
3) Other paths
• Dislocations
• Grain boundaries
• Free surfaces
Two conditions for diffusion• Empty site near the diffusing atom
• Diffusing atom needs enough energy to break existing bonds.
Fick’s First Law:Steady-State Diffusion
Fick’s First Law—Steady-state diffusion
Factors affecting diffusion rates
1. Diffusing species & host material
2. Temperature
3. Concentration Gradient
Table 5.2
Diffusing Host Metal T(oC) D (m2/s)speciesFe -Fe (BCC) 500 3.0 x 10-21
Fe -Fe (BCC) 900 1.8 x 10-15
Fe -Fe (FCC) 500 1.1 x 10-17
Fe -Fe (FCC) 900 7.8 x 10-16
Which diffuses faster?A.Fe through -Fe at 500oCB.Fe through -Fe at 900oCC.Fe through -Fe at 500oCD.Fe through -Fe at 900oC
The question that’s kept you up late at night:
How does
diffusion affect material
properties?
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
Steel = C + Fe
• Interstitial C imposes lattice strains in Fe
• Strains near dislocations can bind atoms and reduce deformation
Carburizing—Solid Diffusion process
Begin at 1:35–2:40
YouTube: Vacuum Carburizing and Heat treating
Composition & processing affect material properties
Section 6.1-6.3Mechanical Properties of
Metals:
Elastic Deformation:
Stress-Strain behavior
Material Properties:
Mechanical Properties
• Stiffness
• Ductility
• Strength
• Toughness
• Hardness
Tensile Test
Tensile Test
Tensile Test
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
Brittle Failure: Tensile test of Nodular Graphite Cast Iron
Tensile Test
AlMgSi alloy ductile fracture
Principles of
Stress and Strain