L4- Dislocations

In which direction is glide applied

perpendicular to direction of applied stress

Force on dislocation of unit length b

F = τb

Force on length of dislocation, dl

F = τbdl

Restoring force

• due to production of tension ( as dislocation increases in length), energy increases

• opposed by tension in dislocation

• restoring force = force on length of dislocation

Equation for Energy

Examples of stable dislocation arrays

Examples of edge dislocations:

1. Glide

2. Climb

How is a kink formed?

• via the intersection of 2 edge dislocations

• part of slip mechanism

• on same crystal glide plane as rest of dislocation

• sideways motion of kink can act as mechanism for glide of main dislocation

How is a jog formed?

• via the intersection of 2 screw dislocations

• on non-glide crystal plane

• can only move within with dislocation to which it’s attached by climb

When an edge + screw dislocation cross

• formation of jog on 1 dislocation

• 1 length section of edge dislocation

• on crystal glide plane

• can move with dislocation to which it’s attached by glide

Stress to bend a dislocation

R= radius

Difference between Jogs and kinks

• Jogs= thermally activated

• Kinks = part of slip mechanism