Dislocations - Initial overview

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Dislocations - Initial overview
Material w/ NO dislocations is very strong
Dislocations weaken a material
But dislocations make plastic deformation possible
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Ease of disloc movement along slip planes is key
to ductility
Well-defined slip planes are best for easy motion
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Most metals exhibit one of three very simple
types of atom arrangements (crystal structures)

1. cubic close-packed (ccp)
2. hexagonal close-packed (hcp)

Stacking of layers different for cubic or
hexagonal
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Most metals exhibit one of three very simple
types of atom arrangements (crystal structures)

1. cubic close-packed (ccp)
2. hexagonal close-packed (hcp)
3. "body centered cubic metal structure" ("bcc")

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Just for funhere are several views of the
structure of a sodium silicate zeolite a
somewhat complicated crystal structure
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Where are mostly densely packed planes in these
three crystal structures?

1. cubic close-packed (ccp)
2. hexagonal close-packed (hcp)
3. "body centered cubic metal structure" ("bcc")

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Where are mostly densely packed planes in these
three crystal structures?

1. cubic close-packed (ccp)
2. hexagonal close-packed (hcp)
3. "body centered cubic metal structure" ("bcc")

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Where are mostly densely packed planes in these
three crystal structures?

1. cubic close-packed (ccp)
2. hexagonal close-packed (hcp)
3. "body centered cubic metal structure" ("bcc")

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Slip planes are most densely packed planes in
crystal structure
Disloc movement easier in simple crystal
structures cuz slip planes well-defined
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Metals are so useful in our society because they
have simple crystal structures
Metals are so useful in our society because
they can be plastically deformed
Can be plastically deformed because
dislocations can move easily
Can move easily because the slip planes are
well-defined
Slip planes well-defined because metals have
simple crystal structures
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Problem as material deforms, dislocs disappear -
at surface, at grain boundaries, elsewhere If
dislocs disappear completely, mat'l becomes
extremely strong no longer ductile
Never happens Instead, more dislocs produced
during deformation!! Highly deformed mat'l
contains BILLIONS of dislocs
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Dislocation generators at work! Internal
generators act to constantly generate new dislocs
during deformation