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