Dislocation
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Transcript of Dislocation
METALLURGY AND MATERIAL SCIENCES
Cross- Slip and Climb
Dislocation MotionDislocation Motion
Glide (for edge, screw or mixed)
Cross-slip (for screw only)
Climb (or edge only)
Cross- Slip - Screw Dislocation
1 2
3
b
Cross-slip of a screw
dislocation
Change in slip plane of a screw
dislocation is called cross-slip
Slip plane 1
Slip p
lane
2
Slip p
lane
2
Climb - Edge Dislocation
Atomistic mechanism of climb
Climb of an edge dislocation
The motion of an edge dislocation from its slip plane to an adjacent parallel slip plane is called CLIMB
Obstacle
climbglide
glide
Slip plane 1
Slip plane 2
1 2
3 4?
Mar Athanasius College of Engineering - /Mechanical/Dr.Binu
C.Yeldose
Climb of an edge dislocation
Climb up
Climb down
Half plane shrinks Half plane stretches
Atoms move away from the edge to nearby
vacancies
Atoms move toward the edge
from nearby lattice sites
Vacancyconcentration
goes down
Vacancyconcentration
goes up
Jogs and Kinks Defect in a defect!
A straight dislocation line can have a break in it of two types: A jog moves it out of the current slip plane (→ to a parallel one) A kink leaves the dislocation on the slip plane The Jog and the Kink can be considered as a defect in a dislocation line
(which itself is a defect → hence these are defects in a defect) Jogs and Kinks can be produced by intersection of straight dislocations
JogsJogs
The presence of a jog in a dislocation line increases the energy of the crystal
The energy of a jog per unit length is less than that for the dislocation (as this lies in the distorted region near the core of the dislocation)
This energy is about 0.5 - 1.0 eV (~1019 J) for metals
22
1 bbGEJog b1 → Burgers vector of the dislocation
b2 → Length of the jog
→ Constant with value (0.5-1.0)
Geometric properties of dislocations
Dislocation PropertyType of dislocation
Edge Screw
Relation between dislocation line (t) and b
||
Slip direction || to b || to b
Direction of dislocation line movement relative to b
||
Process by which dislocation may leave slip plane
climb Cross-slip