Materials Science and Engineering
Intro to MSE: Defect Classification
Homogenous Point Defects
- Point Defects (0D)
- Missing atoms (vacancies) or extra atoms (self-interstitial) in a structure
- Vacancies are easier to form because it requires more energy to compress bonds than to spread them apart
Heterogenous Point Defects
- Point Defects (0D)
- Interstitials- impurity atoms are between the lattice
- Substitutions- impurity atom where substance atom is expected
Linear Defects
- One Dimensional
- Edge dislocation- an extra plane of atoms is inserted into the lattice
- denoted by an upside down "T" below plane of extra atoms
- Burger's vector, b, denotes magnitude and direction of lattice distortion
- Burger's vector is perpendicular to plane of extra atoms
- On the side of the extra atoms, there will be compression, and on the side without the extra plane of atoms, there will be tension.
- Screw dislocation- atoms are one unit away from where they should be
- Burger's vector, b, denotes magnitude and direction of lattice distortion
- Burger's vector is parallel to extra plane of atoms
- Mixed dislocations- combinations of both edge and screw dislocations
Surface Defects
- Occur at surfaces, since the atoms on the surface are not bonded to as many atoms as they could be
- Interfaces- grain boundaries
- Low angle grain boundaries
- High angle grain boundaries
- Twins: Mechanical and annealing
- Stacking faults- where more than one defect is stacked on top of another
- Phase boundaries
- Ferromagnetic domain walls: where the magnetic field varies from grain to grain
Volumetric Defects
- Pores
- Cracks
- Inclusions
- Amorphous material
- Phase regions