CH 4 - Imperfections in Solids Flashcards Preview

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Flashcards in CH 4 - Imperfections in Solids Deck (17):
1

What are the different types of imperfections?

point, line & area defects

2

What are the two types of point defects in metals?

vacancies & self-interstitials

3

What is a vacancy?

vacant atomic sites in a structure

4

What is a self-interstitial point defect?

extra atoms positioned between atomic sites

5

What are the possible outcomes when an impurity is added to a host metal?

substitutional or interstitial solid solution

6

What are the conditions for a substitutonal solid solution? (Hume-Rothery rules)

(1) atomic radii within +/- 15%
(2) similar electronegativities
(3) same crystal structure for pure metals
(4) similar valencies
*all else equal, a metal will have a greater tendency to dissolve a metal of higher valency than one of lower valency

7

What is an example of a line defect?

dislocations

8

What is a dislocation?

-slip between crystal planes result when dislocations move
-produce permanent dislocation
-only seen for single crystals

9

What are the two types of dislocations?

edge & screw

10

What is an edge dislocation?

-extra half-plane of atoms inserted in a crystal structure
-b vector perpendicular to dislocation line

11

What is a screw dislocation?

-spiral planar ramp resulting from shear deformation
-b vector parallel to dislocation line

12

What is a burger's vector?

measure of lattice distortion

13

What are two examples of planar defects in solids?

twin boundary & stacking faults

14

What is a twin boundary planar defect?

reflection of atom positions across the twin plane

15

What is a stacking fault planar defect?

-for FCC metals, an error in ABCABC packing sequence
EX: ABCABABC

16

What is a grain boundary?

-regions between crystals
-transition from lattice of one region to that of the other
-slightly disordered
-low density in grain boundaries

17

What is solidification?

result of casting of molten material