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