Imperfections in Solids Chpt 4 Flashcards
What are the types of defects explain
0-D: point defects: atoms missing or in irregular places in lattice (vacancies, interstitials [additional atoms occupy empty spaces betweeen regular lattice atoms], impurities)
1-D: linear defects: groups of atoms in irregular positions (edge and screw dislocations)
2-D: planar defects: the interfaces between homogeneous region of materials (grain boundaries, external surfaces) so aka area defects
How to calculate Equilibrium number of vacancies
N_v = N e ^ (- Q_v / k T )
N = number of atomic sites
Q_v = activation energy
k = boltzmann’s constant
= 1.38 x 10^-23 J/atom K
T = temperature
You can use the graph of temp. vs N_v / N
just multiply by ln
What are self-Interstitials?
extra atoms positioned between atomic sites.
self-interstitials in metals introduce large distortions in the surrounding lattice ; the energy for self-interstitial formation is 3 times larger as compared to vacancies
What is substitutional type
impurity atoms replace the host atom
Whats interstitial type
impurity atoms fill the voids among the host atoms
Impurities vs alloys
impurities:
atoms different from the host.
near all metals are impure
Alloy:
impurity atoms added intentionally for the characteristics that they impart
-like adding carbon to iron to make steel (stronger than pure iron)
-adding boron to silicon so it has electrical properties
What are solid solutions?
host solvent dissolves the solute
solvent: in an alloy, the element present in greater amount
- homogeneous
- maintain crystal structure
- contain randomly dispersed impurities
has substitutional solid solution
interstitial solid solution
What are the factors for high solubility for substitutional solid solution?
- radii of solute and solvent atoms <15%
- crystal structures of solute and solvent should be the same
- electro-negatives of solute and solvent should be comparable
Factors for high solubility for interstitial solid solution?
- for fcc, bcc, and hcp lattices, radius of solute should be significantly less than the solvent
- sizes of voids compatible with radius of solute
- normally, max solute concentration <10%
Composition meaning
amount of impurity and host in the system
What is weight percent and atom percent?
WP:
useful when making the solution
c_1 = (m_1 / [m_1 + m_2]) * 100
AP:
useful when trying to understand material at atomic level
c’_1 = (n_m1 / [n_m1 + n_m2]) * 100
n_m1 = m_1 / A_1,m1 is grams of element 1. A1 is atomic weight of element 1
COMPOSITION CONVERSION: LOOK UP THE CONVERSION WEIGHT AND VOLUME
Line defects fall under what category
dislocations: cause slip between crystal plane when they move, produce permanent (plastic) deformation
example of line defects
zinc after tensile elongation, forms slip steps
What is edge dislocation
extra portion of plane of atoms (half-plane) squeezed apart of the lattice. Its edge terminates with the crystal
an extra plane of atoms squeezed into a part of the lattice, resulting in that part of lattice containing extra atoms.
The part with extra atoms would therefore be under compressive stresses, while the part with the correct number of atoms would be under tensile (stretched) stress.
The dislocation line is the line connecting all the atoms at the end of the extra plane.
What is a dislocation
Is linear defect around which some of the atoms are misaligned.
What is edge dislocation denoted as?
perpendicular symbol and always pointing at extra fucking crystal point lattici bRUH WHAT THE FUCK I SHOULD BE SLEEPING MOTHERFUCKING FUCK, FUCK.
What happens to bonds in dislocation?
well, since the motion requires the successive bumping of half plane of atoms, the bonds acress the slipping planes are broken and remade in succession.
The interatomic bonds are significantly distorted only in the vicinity of dislocation line
Describe outloud the motion of edge dislocation.
well..ya konw.. AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
anyways, so, chile, “cheelay” hahahahhaahaha
as a shear force is applied (think of trying to create a moment or rotation), the atoms move into the right, leaving the half-plane (half the line of atoms) to be left un-bonded. then its like a chain affect, so if it started at the left, it would end at the right
What is the burger’s vector?
after all the deformation, the extra half-plane forms an edge that’s one unit step wide, its called this.
it describes the size and direction of the lattice distortion caused by dislocation
Whats the slip plane, step of slip and edge dislocation line?
slip plane:
the way the opposite side of where there first begins a break in structure after the force being applied.
- the part that curves inward first
step of slip:
after the deformation finished traversing the solid, it creates a step similar to in the first step but on the opposite side
Edge dislocation line:
the area where, after the step of slip starts moving the deformation back to its og place, but its stays in the middle, half plane.
What causes point defects?
response to chemical impurities, thermal vibration of atoms
MAKE SURE YOU CAN DRAW A BURGER CIRCUIT AND VECTROR!!!
Which half is the extra half plane?
the side where you see the atoms more condensed
Whats the difference between edge dislocation line and burgers vector?
edge dislocation line: perpendicular symbol that points parallel and colinearly to the extra half plane
burgers vector is a vector that goes from crystal point lattice to the next and points inward toward the extra half plane (also this vector is on the side with the extra FUCKING SHIT) FUCK.
What are screw dislocations?
When the crystal planes are stacked spirally around the dislocation line and the burger vector is parallel to the dislocation line. The upper front region is shifted one atomic distance to the right relative to bottom position
in screw dislocation what are the burgers vectors and dislocation line vectors?
dislocation line vector is at base of cut shit and goes to through either side
burgers vector is parallel to the dlv
Whats the difference between screw and edge dislocation?
edge: dislocation moves in direction of applied stress
screw: dislocation moves perpendicular in direction of applied stress
is the net plastic deformatino for the screw and edge deformation?
the SAME BROTHER I AM GOING INSANE. I AM GOING TO DIE I NEED LESS MOSNTER AND MORE GONSTER TO SLEEP OR IM GONNA KMS
How are metallic materials introduced dislocations?
by solidification, plastic deformation and thermal stress
What are interfacial defects
external surfaces: surface atoms are not fully bonded to maximum amount of nearest neighbors, have higher energy state. so materials try to minimize total surface are
Grain boundaries: more chemically reactive; impurity atoms segregate along these boundaries. Total interfacial energy lower in large or course-grained materials cuz less boundary area.
Twin boundaries: type of grain boundary where theres mirror lattice symmetry. each side of boundary looks identical.
How are twin boundaries formed?
shear forces, annealing heat treatments following deformation
Annealing twins found in FCC metals
Mechanical twins in BCC and HCP metals
