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MAE 20 1Chapter 4: Imperfections in solids

Point Defects

MAE 20 2Chapter 4: Imperfections in solids

Impurities in solids

Substitutional solid solutionCu in Ni

Interstitial solid solutionC in Fe

A complete series of solid solutions

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MAE 20 3Chapter 4: Imperfections in solids

Element Atomic Crystal Electro- ValenceRadius Structure nega-

(nm) tivity

Cu 0.1278 FCC 1.9 +2C 0.071H 0.046O 0.060Ag 0.1445 FCC 1.9 +1Al 0.1431 FCC 1.5 +3Co 0.1253 HCP 1.8 +2Cr 0.1249 BCC 1.6 +3Fe 0.1241 BCC 1.8 +2Ni 0.1246 FCC 1.8 +2Pd 0.1376 FCC 2.2 +2Zn 0.1332 HCP 1.6 +2

MAE 20 4Chapter 4: Imperfections in solids

Interstitial solid solutions

C interstitial atom inBCC iron

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MAE 20 5Chapter 4: Imperfections in solids

Edge dislocations

MAE 20 6Chapter 4: Imperfections in solids

Dislocation movement

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MAE 20 7Chapter 4: Imperfections in solids

Burgers vector

MAE 20 8Chapter 4: Imperfections in solids

Screw dislocations

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MAE 20 9Chapter 4: Imperfections in solids

Edge, screw and mixed dislocations

Edge

Screw

Mixed

MAE 20 10Chapter 4: Imperfections in solids

Grain boundaries from solidification

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MAE 20 11Chapter 4: Imperfections in solids

Grain boundaries

250µm = 0.01”

MAE 20 12Chapter 4: Imperfections in solids

Optical microscopy

Micrograph ofbrass (a Cu-Zn alloy)

0.75mm Fe-Cr alloy(b)

grain boundarysurface groove

polished surface

(a)

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MAE 20 13Chapter 4: Imperfections in solids

Equation summary

MAE 20 14Chapter 4: Imperfections in solids

Dislocation movement

http://mrsec.wisc.edu/Edetc/SlideShow/slides/defects/bubble_defect_color_mov.htmlBubble raft model

http://mrsec.wisc.edu/Edetc/SlideShow/Ball and stick model of dislocation movement

http://mrsec.wisc.edu/Edetc/SlideShow/Caterpillar moving