Chapter 4 defects in solids Flashcards
why are defects important
defects have a huge impact on the various properties of materials
- defects are responsible for color and price of a diamond
- forging a metal tool introduces defects and increases the strength of the tool
defects can be introduced or removed during ________
Processing
point defects
are lattice defects of zero dimensionality, i.e., they do not possess lattice structure in any dimension. Typical point defects are impurity atoms in a pure metal, vacancies, and self-interstitials.
vacancies
is a type of point defect in a crystal where an atom is missing from one of the lattice sites.
interstitial defect
is a type of point crystallographic defect where an atom of the same or of a different type, occupies a normally unoccupied site in the crystal structure.
point defects in metals
equilibrium concentration
Equilibrium is when the rate of the forward reaction equals the rate of the reverse reaction. All reactant and product concentrations are constant at equilibrium.
Boltzmann’s constant
activation energy
the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction.
measuring activation energy
estimating vacancy concentration
observing vacancy ( continued )
impurities
are foreign atoms that replace some of the atoms making up the solid or that squeeze into the interstices
atoms that are different from the host
a homogeneous material
or system has the same properties at every point
solids with impurities
substitutional impurity
An atom or ion which is not normally found in a solid, but which resides at the position where an atom or ion would ordinarily be located in the lattice structure and replaces it.
three types of point defects
Vacancy - in crystal an atom is missing from one of the lattice sites (point defect)
Interstitial - in crystal an atom of the same or different type occupies a normally unoccupied site in the lattice
Substitutional- same as interstitial but a different type of atom resulting in strain
*quick reference *
imperfections in metals
W Hume Rothery rules
are a set of basic rules that describe the conditions under which an element could dissolve in a metal, forming a solid solution.
solubility
imperfections in metals
Dislocations ( dislocation lines )
are linear defects. the interatomic bonds are significantly distorted only in the immediate vicinity of the dislocation line. this area is called the dislocation core.
burgers vector
edge dislocation
is a defect where an extra half-plane of atoms is introduced midway through the crystal( burger vector is perpendicular to dislocation line)
Screw dislocation
a spiral planar ramp is inserted ( burger vector is parallel to dislocation line)
mixed / partial dislocations
where do dislocations come from
the number of dislocations in a material is expressed as the dislocation density ( the total dislocation length per unit volume or the number of dislocations intersecting a unit area )
plastic deformation
is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces.
dislocations and crystal structures/ plastic deformation
grain boundaries
is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the crystal structure and tend to decrease the electrical and thermal conductivity of the material.
solidification
result of casting of molten material
steps of solidification
grain boundaries properties
interaction between grain boundaries and dislocation
bulk or volume defects
Three-dimensional macroscopic defects. They generally occur on a much larger scale than the microscopic defects.
-these include cracks, pores, foreign inclusions, and other phases.
Summary of this chapter
