Crystal defects
- Created by: smallbat123
- Created on: 07-12-17 10:27
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- Crystal Defects
- Point defects
- Atom missing or irregularly place in lattice
- Self-interstitial atoms
- Extra atom crowded into void of crystal
- Only in low concentrations
- Distort
- Highly stress lattice
- Only in low concentrations
- Extra atom crowded into void of crystal
- Self-interstitial atoms
- Atom missing or irregularly place in lattice
- Linear defects (dislocations)
- Movement
- Plastic deformation occurs
- Strain or work hardening
- Additional dislocations created
- Run into each other = hinders
- Force driven upwards = strengths
- Strengthened by making difficult
- Interstitial atoms or grain boundaries pin
- Strengthened by making difficult
- Force driven upwards = strengths
- Along densest planes of atoms
- Stress needed, increased with spacing between planes
- BCC and FCC have many
- Move easily
- High ductility
- Move easily
- Plastic deformation occurs
- Groups of atoms in irregular positions
- Generated and move when stress applied
- Edge dislocations
- Parallel to direction of stress
- Caterpillar movement
- Small number of bonds broken at one time
- To begin bonds significantly distorted in immediate vicinity of line
- Screw dislocations
- Perpendicular to stress
- Shear stress
- Applied across one end so metal begins to rip
- Only proportion of bonds broken at one given time
- Small amount of force
- Shear stress
- Perpendicular to stress
- Edge dislocations
- Ionic bonded
- Movement
- Planar defects
- Grain boundaries in polycrystals
- Limit lengths and motion of dislocations
- Smaller grain = more boundaries = strengthens
- Size controlled by cooling rate when cast or heat treated
- Limit lengths and motion of dislocations
- Grain boundaries in polycrystals
- Any defect disrupts motion of dislocations
- Slip and plastic deformation more difficult
- Bulk defects
- Voids
- Seen using SEM
- Causes
- Trapped air bubbles during solidification
- Porosity
- Shrinkage as solidifies
- Cavitation
- Trapped air bubbles during solidification
- Voids
- Deformation
- Sufficient load applied changing it's shape
- Elastic
- Temporary shape change
- Self reversing
- Low stress that stretches bonds
- Atoms don't slip past each other
- Plastic
- Significant stress
- Bond breakage
- Energy required to move occurs in densest plane
- Dislocations have preferred direction of travel
- Slip along parallel planes of grain
- Group = slip band
- Seen under microscope as single line
- Closely spaced slip planes
- Seen under microscope as single line
- Group = slip band
- Slip along parallel planes of grain
- Dislocations have preferred direction of travel
- Permanent change
- Significant stress
- Point defects
- Bulk defects
- Voids
- Seen using SEM
- Causes
- Trapped air bubbles during solidification
- Porosity
- Shrinkage as solidifies
- Cavitation
- Trapped air bubbles during solidification
- Voids
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