Outline Slip Systems BCC, FCC, HCP Cross Slip Partial
Dislocations Stacking Faults The Thompson Tetrahedron Fancy Stuff
Frank rule, Frank loop, Lomer lock, Lomer-Cotrell dislocations,
prismatic dislocations 22.71: Physical MetallurgyProf. Michael P.
Short, P. 2
Slide 3
Slip Systems Systems of planes and directions that make
dislocation movement easy 22.71: Physical MetallurgyProf. Michael
P. Short, P. 3 Different views of FCC supercell
http://ilan.schnell-web.net/physics/fcc/
Slide 4
Slip Systems Systems of planes and directions that make
dislocation movement easy 22.71: Physical MetallurgyProf. Michael
P. Short, P. 4 Different views of FCC supercell
http://ilan.schnell-web.net/physics/fcc/
Slide 5
Slip Systems Systems of planes and directions that make
dislocation movement easy 22.71: Physical MetallurgyProf. Michael
P. Short, P. 5 Different views of FCC supercell
http://ilan.schnell-web.net/physics/fcc/
Slide 6
Counting Slip Systems Multiply: Number of non-parallel planes
Number of close packed directions per plane 22.71: Physical
MetallurgyProf. Michael P. Short, P. 6 k h l Same slip planes!
Slide 7
In Class Draw primary slip systems for FCC, BCC, and HCP
crystal systems 22.71: Physical MetallurgyProf. Michael P. Short,
P. 7
Slide 8
Evidence of Slip Systems 22.71: Physical MetallurgyProf.
Michael P. Short, P. 8
http://www.doitpoms.ac.uk/tlplib/slip/printall.php
Slide 9
Side Note: Twinning Bands can flip to mirror image of
surrounding crystal 22.71: Physical MetallurgyProf. Michael P.
Short, P. 9 Annealing twins in brass
http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php
Slide 10
Side Note: Twinning 22.71: Physical MetallurgyProf. Michael P.
Short, P. 10 Alternate plastic deformation mechanism
http://moisespinedacaf.blogspot.com/
http://dcg.materials.drexel.edu/?page_id=14#nuclear Twinning
observed in irradiated reactor pressure vessel steel
Slide 11
22.71: Physical MetallurgyProf. Michael P. Short, P. 11
Twinning MIT Dept. of Nuclear Science & Engineering 22.74:
Radiation Damage & Effects in Nuclear Materials Prof. Michael
P. Short Page 11
http://dcg.materials.drexel.edu/?page_id=14#nuclear Differently
oriented dislocations inside/outside twin boundary!
Slide 12
Evidence of Slip Systems 22.71: Physical MetallurgyProf.
Michael P. Short, P. 12 A scanning electron micrograph of a single
crystal of cadmium deforming by dislocation slip on 100 planes,
forming steps on the surface
http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php
Slide 13
Evidence of Slip Systems 22.71: Physical MetallurgyProf.
Michael P. Short, P. 13 Nanopillar compression tests using a
diamond flat punch Clear 45 degree angles observed Slip systems
activated by shear N. Friedman et al. Phys. Rev. Lett. 109, 095507
(2012)
Slide 14
Evidence of Slip Systems 22.71: Physical MetallurgyProf.
Michael P. Short, P. 14 Nanopillar compression tests using a
diamond flat punch Clear 45 degree angles observed Slip systems
activated by shear S. Brinckmann et al. Phys. Rev. Lett. 100,
155502 (2008)
Slide 15
Secondary Slip Systems When something blocks a primary slip
system, a secondary slip system may activate Only if it is
energetically favorable to continue deforming What happens if a
secondary system cant activate? 22.71: Physical MetallurgyProf.
Michael P. Short, P. 15
Slide 16
Cross Slip Dislocation switches slip systems if it get stuck
Example: pinned screw dislocation 22.71: Physical MetallurgyProf.
Michael P. Short, P. 16 time Derek Hull and David J. Bacon,
Introduction to dislocations, 4th ed. (Butterworth-Heinemann,
Oxford, 2001).
Slide 17
Cross Slip 22.71: Physical MetallurgyProf. Michael P. Short, P.
17 Allen & Thomas, p. 100 k h l [101]
Slide 18
Slip Systems Slip directions partially or fully enclose slip
planes 22.71: Physical MetallurgyProf. Michael P. Short, P. 18
Allen & Thomas, The Structure of Materials, p. 116
Slide 19
HCP Slip Systems 22.71: Physical MetallurgyProf. Michael P.
Short, P. 19 Ideal c/a = 1.63299 a 1 c a2a2 1122 24 [0001]
1011
Slide 20
Partial Dislocations Look carefully at the (111) plane in FCC
How many ways can atom A move to location B? 22.71: Physical
MetallurgyProf. Michael P. Short, P. 20 A B A B
Slide 21
Partial Dislocations Look carefully at the (111) plane in FCC
How many ways can atom A move to location B? 22.71: Physical
MetallurgyProf. Michael P. Short, P. 21 A B A B
Slide 22
Partial Dislocations A perfect dislocation can split into two
partials 22.71: Physical MetallurgyProf. Michael P. Short, P. 22
Allen & Thomas, p. 119 These move in unison
Slide 23
Partial Dislocations A perfect dislocation can split into two
partials 22.71: Physical MetallurgyProf. Michael P. Short, P. 23
Allen & Thomas, p. 117
Slide 24
Partial Dislocation Separation After formation, the two
partials repel each other Why? 22.71: Physical MetallurgyProf.
Michael P. Short, P. 24 Opposite screw parts attract Parallel edge
parts repel
Slide 25
Stacking Faults The shifted portion of the partial dislocation
is a stacking fault Atomic stacking order into the screen has
changed Was ABCA / BCABCABC Now it is ABCA / CABCABC 22.71:
Physical MetallurgyProf. Michael P. Short, P. 25
Slide 26
Stacking Fault Energy (SFE) 22.71: Physical MetallurgyProf.
Michael P. Short, P. 26
Slide 27
The Thompson Tetrahedron 22.71: Physical MetallurgyProf.
Michael P. Short, P. 27
http://imechanica.org/files/Partial%20Dislocation%20Tutorial%20for%20FCC%20Metals.pdf
Slide 28
Lomer-Cottrell Dislocation Two partials hit at 60 degree angles
Each consists of a leading and trailing partial Leading partial
intersections will form a new full edge dislocation 22.71: Physical
MetallurgyProf. Michael P. Short, P. 28
http://imechanica.org/files/Partial%20Dislocation%20Tutorial%20for%20FCC%20Metals.pdf
Slide 29
Lomer-Cottrell Dislocation 22.71: Physical MetallurgyProf.
Michael P. Short, P. 29
http://imechanica.org/files/Partial%20Dislocation%20Tutorial%20for%20FCC%20Metals.pdf
Lomer-Cottrell Dislocation Determination
Slide 30
Lomer Lock Both original dislocations (BC and DB) were in slip
planes Is the new dislocation in any slip planes? What happens
next? 22.71: Physical MetallurgyProf. Michael P. Short, P. 30
Slide 31
What Happens When Dislocations Get Stuck? When bits get pinned,
they can bow out creating Frank-Read sources 22.71: Physical
MetallurgyProf. Michael P. Short, P. 31
http://youtu.be/Db85wOCWJkU
Slide 32
Dislocation Loops 22.71: Physical MetallurgyProf. Michael P.
Short, P. 32 Loops have mixed edge/screw character May be circular
planes of atoms between two planes
Slide 33
Frank-Read Loop Sources 22.71: Physical MetallurgyProf. Michael
P. Short, P. 33 Come from sessile sections of dislocations Old
strain direction
Slide 34
Frank-Read Loop Sources 22.71: Physical MetallurgyProf. Michael
P. Short, P. 34
http://virtualexplorer.com.au/special/meansvolume/contribs/wilson/Generation.html
http://www.numodis.fr/tridis/TEM/recordings/FR_loin_53.mpg
Slide 35
Forces Between Dislocations 22.71: Physical MetallurgyProf.
Michael P. Short, P. 35 X & Y forces, no Z-force Burgers vector
of dislocation (2) transposed Line vector of dislocation (2)
transposed Stress tensor induced by dislocation (1) Force vector on
dislocation (2) Peach-Kohler Equation
Slide 36
Forces Lead to Pileup 22.71: Physical MetallurgyProf. Michael
P. Short, P. 36 http://youtu.be/r-geDwE8Z5Y Dislocations moving
& piling up in Inconel 617 (Ni-based alloy) under in- situ
straining in the TEM
Slide 37
Forces Lead to Grain Boundaries 22.71: Physical MetallurgyProf.
Michael P. Short, P. 37
http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_7/backbone/r7_2_1.html
Tilt grain boundary in Al http://moisespinedacaf.blogspot.com/
