mG-2 Flashcards
Which materials are crystalline?
metals, many ceramics, some polymers
When are materials typically noncrystalline?
complex structures, rapid cooling
What does amorphous mean?
noncrystalline
Do most engineering applications use single or polycrystals?
polycrystals
What is the term for properties that vary with direction?
anisotropic
Are single crystals anisotropic or isotropic?
anisotropic
If the grains of a polycrystal are randomly oriented is it anisotropic or isotropic?
isotropic
If the grains of a polycrystal are textured is it anisotropic or isotropic?
anisotropic
What is polymorphism?
two or more distinct crystal structures for the same material
Describe how to find crystallographic directions
- find x,y,z change in positions
- clear fractions
- write as numbers without commas in brackets []
- express negative numbers with a bar over the number
equation for linear density
LD = number of atoms / unit length of direction vector
number of atoms refers to radius
What is the algorithm for finding crystallographic planes?
- Read off intercepts of plane with axes (if no intercept use infinity)
- Take reciprocals of intercepts
- Reduce to smallest integer values
- Enclose in parentheses, no
commas i.e., (hkl)
What is the name of the indices used for crystallographic planes?
Miller indices
equation for planar density
PD = number of atoms centered on the plane / area of the plane
(number of atoms refers to radius)
x-ray diffraction give us what information?
crystal structure and interplanar spacing determinations
What is solidification?
molten material cooling, crystals forming and growing unitl they meet. The result is a grain structure
What is the equation for the equilibrium number of vacancies in a material?
Nv/N=e^(-Q/kT) Nv: number of defects per unit volume N: number of potential defect sites per unit volume Q: activation energy k: boltzman constant T: temperature
N=pNa/A
p: density
Na: Avogadro’s number 6.02210^23
A: atomic weight (g/mol)
What are the conditions for a substitutional solid solution?
- difference in radius less than 15%
- Proximity in periodic table (similar electronegatives)
- Same crystal structure for pure metals
- Higher valency
What is the burger’s vector?
measure of lattice distortion
What are the types of point defects in solids?
vacancy, interstitial, substitutional
What are the types of 1D or line defects in solids?
edge and screw dislocations
What are types of 2D or area defects in solids?
grain boundaries, stacking faults
What measurement can you see with optical microscopy at 2000x magnification?
about 1 micron
Can you see unit cell edge lengths with optical microscopy?
no
What is diffusion?
Introducing a foreign atom into a host material
What are the two mechanisms of diffusion?
- vacancy/substitutional
2. interstitial
What is Fick’s first law?
Steady state diffusion:
J=M/(At)
J=-D*dC/dx
What is Fick’s second law?
Non steady state diffusion:
Cx-C0/(Cs-C0) = 1 - erf(x/(2sqrt(Dt))
What does diffusion equation reduce to if everything is constant except for time and temperature?
D1t1=D2t2
What is the modulus of steel?
200 GPa or 29 Msi
What is the yield stress of steel?
250 MPa or 36 Ksi
How many atoms (n) for SC?
1
How many atoms (n) for BCC?
2
How many atoms (n) for FCC?
4
SC side length?
2r
BCC side length?
4r/sqrt(3)
FCC side length?
2sqrt(2)r
