Week 5: Defects Flashcards
Why are the number of dislocations present greatest in metals?
Because metallic bonding is non-directional
How are strength and dislocation motion related?
The less dislocation motion there is, the stronger a material will be.
Why does heating alter strength and other properties?
Heating causes the bonds to expand and allows more dislocation motion. This makes the material more ductile and able to plastically deform more easily.
What are the Hume-Rothery rules used for?
This will tell us if two metals can form a solid solution/alloy or not.
It’s used only for substitutional atoms
What are the 2 types of dislocations?
Edge and screw dislocations
Slip
The dislocation of atoms due to a force.
When slip occurs, plastic deformation occurs
Slip plane
Plane on which easiest slippage occurs
Slip directions
Direction of movement of the slip
Grain boundaries
The 2D interface between adjacent grains in a polycrystalline material
What happens when dislocations can’t move?
Plastic deformation doesn’t occur
What are the 4 Hume-Rothery rules for determining solid solutions?
- Atomic radius is < 15%
- Crystal structure of atoms has to be the same
- Proximity in the periodic table -> similar electronegativities
- Similar valencies
What are methods to increase the dislocation density of metals?
Cold rolling and cold forging
Slip systems
Where a metal will deform most easily on the most packed slip planes
