Imperfections in Solids Chpt 4

Question 1

What are the types of defects explain

Answer 1

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

Question 2

How to calculate Equilibrium number of vacancies

Answer 2

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

Question 3

You can use the graph of temp. vs N_v / N

Answer 3

just multiply by ln

Question 4

What are self-Interstitials?

Answer 4

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

Question 5

What is substitutional type

Answer 5

impurity atoms replace the host atom

Question 6

Whats interstitial type

Answer 6

impurity atoms fill the voids among the host atoms

Question 7

Impurities vs alloys

Answer 7

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

Question 8

What are solid solutions?

Answer 8

host solvent dissolves the solute

solvent: in an alloy, the element present in greater amount

1. homogeneous
2. maintain crystal structure
3. contain randomly dispersed impurities

has substitutional solid solution
interstitial solid solution

Question 9

What are the factors for high solubility for substitutional solid solution?

Answer 9

1. radii of solute and solvent atoms <15%
2. crystal structures of solute and solvent should be the same
3. electro-negatives of solute and solvent should be comparable

Question 10

Factors for high solubility for interstitial solid solution?

Answer 10

1. for fcc, bcc, and hcp lattices, radius of solute should be significantly less than the solvent
2. sizes of voids compatible with radius of solute
3. normally, max solute concentration <10%

Question 11

Composition meaning

Answer 11

amount of impurity and host in the system

Question 12

What is weight percent and atom percent?

Answer 12

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

Question 13

COMPOSITION CONVERSION: LOOK UP THE CONVERSION WEIGHT AND VOLUME

Question 14

Line defects fall under what category

Answer 14

dislocations: cause slip between crystal plane when they move, produce permanent (plastic) deformation

Question 15

example of line defects

Answer 15

zinc after tensile elongation, forms slip steps

Question 16

What is edge dislocation

Answer 16

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.

Question 17

What is a dislocation

Answer 17

Is linear defect around which some of the atoms are misaligned.

Question 18

What is edge dislocation denoted as?

Answer 18

perpendicular symbol and always pointing at extra fucking crystal point lattici bRUH WHAT THE FUCK I SHOULD BE SLEEPING MOTHERFUCKING FUCK, FUCK.

Question 19

What happens to bonds in dislocation?

Answer 19

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

Question 20

Describe outloud the motion of edge dislocation.

Answer 20

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

Question 21

What is the burger’s vector?

Answer 21

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

Question 22

Whats the slip plane, step of slip and edge dislocation line?

Answer 22

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.

Question 23

What causes point defects?

Answer 23

response to chemical impurities, thermal vibration of atoms

Question 24

MAKE SURE YOU CAN DRAW A BURGER CIRCUIT AND VECTROR!!!

Question 25

Which half is the extra half plane?

Answer 25

the side where you see the atoms more condensed

Question 26

Whats the difference between edge dislocation line and burgers vector?

Answer 26

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.

Question 27

What are screw dislocations?

Answer 27

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

Question 28

in screw dislocation what are the burgers vectors and dislocation line vectors?

Answer 28

dislocation line vector is at base of cut shit and goes to through either side

burgers vector is parallel to the dlv

Question 29

Whats the difference between screw and edge dislocation?

Answer 29

edge: dislocation moves in direction of applied stress

screw: dislocation moves perpendicular in direction of applied stress

Question 30

is the net plastic deformatino for the screw and edge deformation?

Answer 30

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

Question 31

How are metallic materials introduced dislocations?

Answer 31

by solidification, plastic deformation and thermal stress

Question 32

What are interfacial defects

Answer 32

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.

Question 33

How are twin boundaries formed?

Answer 33

shear forces, annealing heat treatments following deformation

Annealing twins found in FCC metals

Mechanical twins in BCC and HCP metals