Lecture 03/24 Flashcards
What is slip?
Process by which plastic deformation is produced by dislocation motion
What is a slip plane?
Crystallographic plane along which the dislocation line travels
Where are dislocations introduced?
During solidification, plastic deformation, consequence of thermal stress that result from rapid cooling?
How can we define density?
Total dislocation length per unit vol or number of dislocations per unit area
When metals are plastically deformed, 5% of what is retained internally?
Strain energy
Why does lattice distortion exist?
Extra half-plane of atoms
Lattice strains are imposed on?
Neighboring atoms
What is a slip system?
Slip plane and slip direction
The slip plane will be along?
The greatest planar density
Slip direction will be in the direction of?
Highest linear density
What is the difference between elastic and plastic deformation?
- Elastic is nonpermanent, temporarily stretching interatomic bonds
- Plastic interatomic bonds are ruptured
What are the 2 fundamental dislocation types?
Edge and screw
Describe an edge dislocation
Localized lattice distortion response to a shear stress applied perpendicular to it’s line
Dislocation motion is analagous to?
Caterpillar motion
For a screw dislocation, the dislocation line is?
Perpendicular to the stress direction
What is attractive force?
Dislocations of opposite sign and some slip plane
What is resolved shear stress?
Shear stress component when slip plane oriented is neither perpendicular nor parallel to the direction of stress
What are the two types of plastic deformation?
Slip and twinning
What are the three mechanisms for strengthening metals?
- Grain size reduction
- Solid solution strengthening
- Strain hardening
The atomic disorder within a grain boundary results in?
Discontinuity of slip planes
What is solid solution strengthening?
Alloying with impurity atoms that go into either substitutional or interstitial solid solution
What is strain hardening?
Cold working resulting in reduction in cross sectional area
Explain strain-hardening
Dislocation density increases with cold working, the distance between dislocations decreases, dislocation motion is hindered
Restoration of plastically deformed specimens results from?
Recovery and recrystallization
How does recovery work?
Internal strain energy is relieved by virtue of dislocation motion, reduction in dislocations, electrical and thermal conductivities recover to their pre-cowrked states
How does recrystallization work?
Formation of new strain-free grains that have low dislocation densities, are small, and consume and replace parent grains
What happens if strain-free grains are left at an elevated temperature?
Grain size increases, small grains shrink, large grains continue to grow
Strength is increased by?
Decreasing dislocation mobility
