Shear band formation
Limited non-homogeneous deformation
Very large localized strain ε~1 or 100%
Occurs especially under high strain
rates
Mechanism of deformation still unclear
1
Plastic deformation ⇔movement of dislocations
Strengthening methods
2
Cold working
Deformation at temperatures below 0.4
Tm
Dislocation density increases from
106/cm2 to 1010-12/cm2
High dislocation density results in a
large number of dislocation interactions
which results in high strength and
hardness
3
Solid solution strengthening
Interaction between stress fields of alloy
atoms and dislocations
This is the purpose of alloying
4
Grain size refinement
Small grains result in higher strength
Small grains is equivalent to a large
number of grain boundaries in the same
volume
Grain boundaries act as barriers to
dislocation motion
5
Mechanism
Strength is inversely proportional to grain size
σ = σ0 + kyd-1/2
Hall-Petch equation
Smaller grains have more boundary area and hence more
barriers to dislocation motion
6
Precipitation hardening
Precipitates are second-phase particles
Hard precipitates act as barriers to
dislocation motion
Applicable only to some alloy systems
7