MSE 220 EXAM 1 QUESTIONS WITH VERIFIED
ANSWERS
Slip System - System with combination of slip plane and slip direction, along which
dislocation motion occurs. The system depends on the crystal structure of the metal,
and is such that the atomic distortion that accompanies the motion of the dislocation is
the minimum.
BCC Crystal Structure - List slip plane (and how many), number of independent
directions, and the number of slip systems? - - { 1 1 0 } (most dense plane), 6
independent ways
- 2 independent directions
- 12 slip systems in every BCC unit cell (6*2)
FCC Crystal Structure - List slip plane (and how many), number of independent
directions, and the number of slip systems? - - { 1 1 1 } (most dense plane), 4
independent ways
- 3 independent directions
- 12 slip systems in every FCC unit cell (4*3)
In a bond energy curve, where is the equilibrium bond length for any material? - When
m = 0; the lowest point on the graph.
The more shallow the slope of a bond energy curve, _______ - The higher the thermal
expansion coefficient.
The deeper the well of a bond energy curve, ______ - The higher the bond strength.
What is the value of a and n for FCC? - a = 2(root(2))*R
n = 4 atoms / unit cell
What is the value of a and n for BCC? - a = (4*R)/(root(3))
n = 2 atoms / unit cell
What is the value of a and n for HCP? - a = 2R
n = 6 atoms / unit cell
Gibb's Free Energy - If a group of atoms can be arranged in two different ways, the
arrangement with a lower g value will be thermodynamically favored.
Enthalpy - Measure of internal energy of a system (material).
, Entropy - Randomness (atom arrangment)
If G increases, what happens to enthalpy and entropy? - Enthalpy increases, and
entropy decreases.
What effect does defects have on enthalpy and entropy? - Enthalpy and entropy both
increase with number of defects
Increase in entropy trumps ______ - The increase in enthalpy.
Defect energy is - A function of the number of defects in a unit cell. As number of
defects increase, defect energy also increases. Increases with number of unsatisfied
bonds.
Types of point defects - 1) Substitutional: atom is substituted by another (an atom of a
different size than the host is called a substitutional dopant).
2) Interstitial: atom squeezes in between other atoms.
3) Vacancy: missing an atom.
Defects are more likely with a higher temp: T or F - True
Hume-Rothery Rules for complete solubility - 1) Same crystal structure
2) Atomic size < 15% difference
* IF atom is >50% smaller than host, then interstitial solid.
3) Similar electroneg. ~0.4
4) Same valence (BUT if host < 1 from other, ok)
Burgers Vector - Describes the magnitude and direction of lattice distortion associated
with dislocation.
In metals, b will point in a close packed crystallographic direction, and will be the
magnitude of 2R.
Screw Dislocation - Dislocation goes out from a flat surface, in a screw motion - sort of
like driving up a parking structure.
b is parallel to the dislocation line.
Screw dislocations exist and create local stress fields.
Edge Dislocation - Dislocation along edge of atoms.
b is perpendicular to the dislocation line.
Planar Dislocation - Presence of line defects cause planar defects.
*Grain boundary is a planar defect: where grains meet and do not align - unsatisfied
bonds.
Isotropic - Properties independent of direction.
ANSWERS
Slip System - System with combination of slip plane and slip direction, along which
dislocation motion occurs. The system depends on the crystal structure of the metal,
and is such that the atomic distortion that accompanies the motion of the dislocation is
the minimum.
BCC Crystal Structure - List slip plane (and how many), number of independent
directions, and the number of slip systems? - - { 1 1 0 } (most dense plane), 6
independent ways
- 2 independent directions
- 12 slip systems in every BCC unit cell (6*2)
FCC Crystal Structure - List slip plane (and how many), number of independent
directions, and the number of slip systems? - - { 1 1 1 } (most dense plane), 4
independent ways
- 3 independent directions
- 12 slip systems in every FCC unit cell (4*3)
In a bond energy curve, where is the equilibrium bond length for any material? - When
m = 0; the lowest point on the graph.
The more shallow the slope of a bond energy curve, _______ - The higher the thermal
expansion coefficient.
The deeper the well of a bond energy curve, ______ - The higher the bond strength.
What is the value of a and n for FCC? - a = 2(root(2))*R
n = 4 atoms / unit cell
What is the value of a and n for BCC? - a = (4*R)/(root(3))
n = 2 atoms / unit cell
What is the value of a and n for HCP? - a = 2R
n = 6 atoms / unit cell
Gibb's Free Energy - If a group of atoms can be arranged in two different ways, the
arrangement with a lower g value will be thermodynamically favored.
Enthalpy - Measure of internal energy of a system (material).
, Entropy - Randomness (atom arrangment)
If G increases, what happens to enthalpy and entropy? - Enthalpy increases, and
entropy decreases.
What effect does defects have on enthalpy and entropy? - Enthalpy and entropy both
increase with number of defects
Increase in entropy trumps ______ - The increase in enthalpy.
Defect energy is - A function of the number of defects in a unit cell. As number of
defects increase, defect energy also increases. Increases with number of unsatisfied
bonds.
Types of point defects - 1) Substitutional: atom is substituted by another (an atom of a
different size than the host is called a substitutional dopant).
2) Interstitial: atom squeezes in between other atoms.
3) Vacancy: missing an atom.
Defects are more likely with a higher temp: T or F - True
Hume-Rothery Rules for complete solubility - 1) Same crystal structure
2) Atomic size < 15% difference
* IF atom is >50% smaller than host, then interstitial solid.
3) Similar electroneg. ~0.4
4) Same valence (BUT if host < 1 from other, ok)
Burgers Vector - Describes the magnitude and direction of lattice distortion associated
with dislocation.
In metals, b will point in a close packed crystallographic direction, and will be the
magnitude of 2R.
Screw Dislocation - Dislocation goes out from a flat surface, in a screw motion - sort of
like driving up a parking structure.
b is parallel to the dislocation line.
Screw dislocations exist and create local stress fields.
Edge Dislocation - Dislocation along edge of atoms.
b is perpendicular to the dislocation line.
Planar Dislocation - Presence of line defects cause planar defects.
*Grain boundary is a planar defect: where grains meet and do not align - unsatisfied
bonds.
Isotropic - Properties independent of direction.
