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The Unknown surrounds us at any given moment. That is where we seek knowledge
-Mother Superior Raquella Berto-Anirul
The Unknown surrounds us at any given moment. That is where we seek knowledge
-Mother Superior Raquella Berto-Anirul
Dislocations - Initial overviewDislocations - Initial overview
Material w/ NO dislocations is very strongMaterial w/ NO dislocations is very strong
Dislocations weaken a materialDislocations weaken a material
But it cannot be deformed plasticallyBut it cannot be deformed plastically
But dislocations make plastic deformation possibleBut dislocations make plastic deformation possible
Dislocations - need to control slipDislocations - need to control slip
Ease of disloc movement along slip planesis key to ductility
Ease of disloc movement along slip planesis key to ductility
Easier movement along slip planes meansgreater ductility
Easier movement along slip planes meansgreater ductility
Well-defined slip planes are best for easy motionWell-defined slip planes are best for easy motion
flat!!flat!!
Brief description of metal crystal structuresBrief description of metal crystal structures
Most metals exhibit one of three very simple types of atom arrangements (crystal structures):Most metals exhibit one of three very simple types of atom arrangements (crystal structures):
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)
close-packed structures built up of atom layers like this
close-packed structures built up of atom layers like this
Stacking of layers different for cubic or hexagonalStacking of layers different for cubic or hexagonal
Most metals exhibit one of three very simple types of atom arrangements (crystal structures):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")
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
No close-packed layers in "bcc"No close-packed layers in "bcc"
Brief description of metal crystal structuresBrief description of metal crystal structures
Just for fun……here are several views of the structure of a sodium silicate zeolite – a somewhat complicated crystal structure
Just for fun……here are several views of the structure of a sodium silicate zeolite – a somewhat complicated crystal structure
Brief description of metal crystal structuresBrief description of metal crystal structures
Where are mostly densely packed planesin these three crystal structures?
Where are mostly densely packed planesin these three crystal structures?
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
fourfour
Brief description of metal crystal structuresBrief description of metal crystal structures
Where are mostly densely packed planesin these three crystal structures?
Where are mostly densely packed planesin these three crystal structures?
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
fourfour oneone
Brief description of metal crystal structuresBrief description of metal crystal structures
Where are mostly densely packed planesin these three crystal structures?
Where are mostly densely packed planesin these three crystal structures?
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
1. cubic close-packed (ccp)2. hexagonal close-packed (hcp)3. "body centered cubic metal structure"
("bcc")
fourfour oneone sixsix
Brief description of metal crystal structuresBrief description of metal crystal structures
DislocationsDislocations
Slip planes are most densely packed planes in crystal structure
Slip planes are most densely packed planes in crystal structure
Disloc movement easier in simple crystal structures cuz slip planes well-definedDisloc movement easier in simple crystal structures cuz slip planes well-defined
DislocationsDislocations
Metals are so useful in our society becausethey have simple crystal structures
Metals are so useful in our society becausethey have simple crystal structures
Metals are so useful in our society because they can be plastically deformedMetals are so useful in our society because they can be plastically deformed
Can be plastically deformed because dislocations can move easilyCan be plastically deformed because dislocations can move easily
Can move easily because the slip planes are well-definedCan move easily because the slip planes are well-defined
Slip planes well-defined because metals have simple crystal structuresSlip planes well-defined because metals have simple crystal structures
DislocationsDislocations
Problem: as material deforms, dislocs disappear - at surface, at grain boundaries, elsewhere
If dislocs disappear completely, mat'l becomes extremely strong & no longer ductile
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
Never happens……Instead, more dislocs produced during deformation!!
Highly deformed mat'l contains BILLIONS of dislocs
Undeformed – 106 lines/cm2
Deformed – 1012 lines/cm2
Undeformed – 106 lines/cm2
Deformed – 1012 lines/cm2
Dislocation generatorsDislocation generators
Dislocation generators at work!
Internal generators act to constantly generate new dislocs during deformation
Dislocation generators at work!
Internal generators act to constantly generate new dislocs during deformation
Assignments for next class:
1. review today's classnotes
a. dislocations responsible for plastic flowb. need well-defined slip planesc. three metal crystal structures &
densely packed planesd. dislocation generatorse. coat hanger effect
2. Read text: sections 7.4-7.6, 7.10 Study diagrams in sections 3.4-3.6 (text has some errors here & is misleading)
Assignments for next class:
1. review today's classnotes
a. dislocations responsible for plastic flowb. need well-defined slip planesc. three metal crystal structures &
densely packed planesd. dislocation generatorse. coat hanger effect
2. Read text: sections 7.4-7.6, 7.10 Study diagrams in sections 3.4-3.6 (text has some errors here & is misleading)
