Diffusion videos YouTube: Diffusion posted by smcblackburn YouTube: Slide Puzzle Physics, Leiden University http://www.yale.edu/yaleche/chemeng/eia/eia.htm

Materials Moments: Abdelrhman A. – Paper Background image: http://images.iop.org/objects/ntw/news/10/4/9/image1.jpg

Principles of Materials Are everywhere Background image: http://www.genealogyintime.com/GenealogyResources/Wallpaper/Brick-Wall-Images/images/02%20-%201740%20Swedish%20brick%20wall.jpg

Section 5.1-5.3, 5.5-5.6 Diffusion

posted by smcblackburn 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 diffusereach uniform comp.

Diffusion 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 2 gases: Ar & He Fastest 2 liquids: water & alcohol 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

Diffusion Mechanisms f03_05_pg112 Vacancy Diffusion Interstitial f03_05_pg112.jpg Interstitial Diffusion Fig. 5.3

Diffusion Mechanisms f03_05_pg112 Vacancy Diffusion Interstitial f03_05_pg112.jpg Interstitial Diffusion Fig. 5.3

Interdiffusion f03_05_pg112 Example: Cu, Ni Vacancy diffusion or interstitial diffusion? f03_05_pg112 f03_05_pg112.jpg 13

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

Example: Cu, Ni Thermocouples and resistors whose resistance is stable across changes in temperature contain the 55% copper-45% nickel alloy (constantan). Monel metal is a nickel-copper alloy, containing a minimum of 63% nickel. Cupronickel or copper-nickel or "cupernickel" is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese.

Example: Cu, Ni Vacancy diffusion f03_05_pg112 Interdiffusion f03_05_pg112.jpg 16

Interdiffusion Initially After some time See Figs. 5.1 and 5.2 17

YouTube: Slide Puzzle Physics, Leiden University

http://www. yale. edu/yaleche/chemeng/eia/eia. htm Eric I 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 f03_05_pg112 Vacancy diffusion Interstitial diffusion Other paths Dislocations Grain boundaries Free surfaces f03_05_pg112.jpg 20

Two conditions for diffusion f03_05_pg112 Empty site near the diffusing atom Diffusing atom needs enough energy to break existing bonds. f03_05_pg112 f03_05_pg112.jpg 21

Fick’s First Law: Steady-State Diffusion

Fick’s First Law—Steady-state diffusion

Factors affecting diffusion rates Diffusing species & host material Temperature Concentration Gradient

t02_05_pg119 t02_05_pg119.jpg Table 5.2

t02_05_pg119 Which diffuses faster? Fe through a-Fe at 500oC 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 t02_05_pg119 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 t02_05_pg119.jpg

The question that’s kept you up late at night:

How does diffusion affect material properties? It strengthens

City Steel Heat Treating Co. Case Hardening – Hard Case w/ tough core f16_07_pg190 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 City Steel Heat Treating Co. 29

Steel = C + Fe Interstitial C imposes lattice strains in Fe Strains near dislocations can bind atoms and reduce deformation

Carburizing—Solid Diffusion process Composition & processing affect material properties YouTube: Vacuum Carburizing and Heat treating Begin at 1:35–2:40

Section 6.1-6.3 Mechanical Properties of Metals: Elastic Deformation: Stress-Strain behavior Image: http://images.iop.org/objects/phw/news/12/2/27/Fracture.jpg

Mechanical Properties Material Properties: Mechanical Properties t02_05_pg119 Stiffness Ductility Strength Toughness Hardness t02_05_pg119.jpg

Tensile Test t02_05_pg119 t02_05_pg119.jpg

Tensile Test t02_05_pg119 t02_05_pg119.jpg

Tensile Test t02_05_pg119 t02_05_pg119.jpg

Strain gages t02_05_pg119 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 t02_05_pg119.jpg

fig_06_11 Brittle Failure: Tensile test of Nodular Graphite Cast Iron

Tensile Test t02_05_pg119 AlMgSi alloy ductile fracture t02_05_pg119.jpg AlMgSi alloy ductile fracture

Principles of Stress and Strain