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