chapter 4 Flashcards
what is defect
defect refers to the lattice irregularity having one or more of its dimensions on the Oder of an atomic diameter.
1) Point defect associated with one or more atomic position
2) linear; one dimensional
3) interfacial defects which are two dimensional
What is vacancies
It is the simplest of the point defect which means atom is missing from its usual place where it is usually found. This atom is absent from the ordered structure of crystalline. Presence of vacancies increases entropy ( randomness)
Nv=N*exp(-Qv/kT)
Nv: total number of atomic sites per cubic meter atomic density
Qv: energy require for the formation of vacancy
T: temperature in kelvins
k: boltzman constant depend on units which one to pick
what is self Interstitial
an atom from crystal lattice which is crowded into an interstitial site a small void place under ordinary circumstances not occupied. self interstitial introduce large number of distortion
what is solid solution
due to the addition of the atoms to the metal results in a solid solution and/or a new second phase depending on the kind of impurities, their concentration and temp of alloy
what is solvent
a element or compound added in greatest
what is solute
a element or a compound present minor concentartion
Is solid solution not homogenous
No solid solution is homogenous that means that impurity atoms are uniformly distributed.
what is substitutional
solute or impurity atoms which replace host atoms.
What are humes Rothery rules
1) Atom size : Appreciable quantities of a solute may be accommodated in
this type of solid solution only when the difference in atomic radii between the
two atom types is less than about ±15%. Otherwise, the solute atoms create
substantial lattice distortions and a new phase forms.
2) crystal structure: should be the same
3) electronegativity: stronger e- negativity are better for mixing.
4) Valences. Other factors being equal, a metal has more of a tendency to dissolve
another metal of higher valency than to dissolve one of a lower valency
what is dislocation/ linear defects
one dimensional defect around which atoms are misaligned
what is edge dislocation
defect along the edges which is resulted by inserting and extra half plane that causes atoms to repel each other generating a distortion along the edges. Upside down T is postive edge dislocation and upward T is negative
what is screw dislocation
when stress is applied on the two opposite directions of crystal then there is a creation of screw dislocation. In this case dislocation line is axis of spiral deformation.
what is dislocation line
in edge it is where the plane ends and in screw is the axis of spiral deformation
What is the position of the burger vectors
burger vectors are same along the direction line even though the dislocation type can change burger remains the same in direction and magnitude throughout dislocation line
