CH 4 - Imperfections in Solids Flashcards
What are the different types of imperfections?
point, line & area defects
What are the two types of point defects in metals?
vacancies & self-interstitials
What is a vacancy?
vacant atomic sites in a structure
What is a self-interstitial point defect?
extra atoms positioned between atomic sites
What are the possible outcomes when an impurity is added to a host metal?
substitutional or interstitial solid solution
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
What is an example of a line defect?
dislocations
What is a dislocation?
- slip between crystal planes result when dislocations move
- produce permanent dislocation
- only seen for single crystals
What are the two types of dislocations?
edge & screw
What is an edge dislocation?
- extra half-plane of atoms inserted in a crystal structure
- b vector perpendicular to dislocation line
What is a screw dislocation?
- spiral planar ramp resulting from shear deformation
- b vector parallel to dislocation line
What is a burger’s vector?
measure of lattice distortion
What are two examples of planar defects in solids?
twin boundary & stacking faults
What is a twin boundary planar defect?
reflection of atom positions across the twin plane
What is a stacking fault planar defect?
-for FCC metals, an error in ABCABC packing sequence
EX: ABCABABC
