Slip Systems and Hardening Materials

FCC Slip

Phi = angle from force to normal of the slip plane

Lambda= angle from force to slip direction

Use Miller indices to find these angles

Critical resolved shear stress

depends on material only

it's maximised when both angles are 45 degrees

calculated by yield stress* cos of the angles above

policrystal

Stops slipping at a grain boundary

material is stronger because slip does not propagate throughout the whole material

Hardening Materials

Grain size reduction

higher misorientation, higher resistance to slips⁉ ⚠

Solid solution strengthening

Uses substitutional impurity to relieve tension from the slip

Material becomes brittle

Cold working

improves yield strength, and tensile strength, but makes material more brittle

Changes size of sample

%CW = ( (A0 - Ad) / A0)*100

Annealing (heat treatment)

decreases numbers of dislocations

brings back original characteristics without changing shape

3 steps

Recovery

Grain growth

dislocations will get closer and cancel each other out

Recrystallization

formation of more grains, making material stronger

new grains grow

Dislocations will move if Tcrss<Tr