Workshop 2

Give examples of how dislocations interact to produce work hardening in metals and alloys?

• Kink - formed when 2 dislocations perp to each other- lies in glide plane

• jog - out of glide plane- hard for dislocation to move

• Twinning- plane = mirrored ∴ kinked ⇒ dislocations more difficult to move.

• Can form low angle grain boundaries

What effect does Taylor’s model for dislocation hardening predicting τ = τ₀ + A√ε have on ductility typically observed in a metal?

• As τ ↑, ductility decreases ⇒

• increases resistance for dislocations causing interactions with other grain boundaries/ dislocations.

Typically what increase in strength dτ/dC is produced by substitutional solute strengthening?

• Increase in strength

• diffusion = much slower

• must have empty vacant site for pinning ⇒ dislocations get stuck ⇒ more σ needed

Typically what increase in strength is produced by interstitial solute strengthening?

• Increase in strength

Why are interstitial solutes so much more effective strengtheners of metals?

• Interstitial atoms more mobile

• diffuse faster

• ⇒ finds low energy sites in lattice

• causing dislocations

Explain the effect of grain boundaries on hardening + hardening rate

• Reduced grain size

• grain boundaries (↑)

• different grains have different orientations

• increased difficulty for dislocations to move over grain boundaries

• so work hardening rate increases.

Explaining which precipitation parameters are dominant for each mechanism

• Cutting → strength

• bowing → spacing (↑) ⇒ σ needed for dislocations to bend through gap decreases