There won’t be a crystal with 100% of perfect arrangement. Defects are advantages in materials most of the time.
Types of defects:
- Point defects
- Line defects / Dislocations
- Planar defects
- Bulk defects - Related to volumetric defects. Common for any materials. Example: crack, holes.
Point Defects
Related to a single atom.
- Vacancy - Missing parent atom
- Self-interstitial atom - A self atom entered into an interstitial site
- Interstitial impurity atom - A foreign atom entered into an interstitial site
- Substitutional impurity atom - A foreign atom replaced a parent atom or a vacancy
Line Defects
Related to a line of atoms. Three types:
- Edge dislocation - only covered in s1
- Screw dislocation
- Mixed dislocation (combination of above 2)
Edge Dislocation
Caused by removal of a half plane.
Half Plane
Remaining part of a plane of atoms after a set of planes are gone missing.
Slip Plane
Plane that is perpendicular to the half plane and on a boundary.
Dislocation Line
Intersecting line of half plane and slip plane.
Planar Defects
Related to a plane of atoms.
Solidification
The process of conversion liquid to solid. Occurs in 3 steps:
- Nucleation
- Growth of crystals
- Formation of grain structure
Tiny solid particles forms. Called as Nuclei (nothing related to atom’s nucleus). Each nucleus grows bigger and forms a crystal. And then forms grains.
Grain
A group of atoms packed in a particular orientation that is different from that of the neighbor ones.
Each grain is usually in micrometer in size. Grain structure can only be observed through a microscope after careful preparation of samples (microstructure).
Grain Boundaries
The boundary between 2 adjacent grains. These are the planar defects found in crystalline materials.