Chapter 4 Flashcards
grain size
n=2^(G-1)
n = grains/inch^2
G = ASTM grain size
grain size with magnification
n*(M/100)^2=2^(G-1)
M = magnification
for naked eye, M=1
imperfection types
point, line and area
types of point defects
vacancy atoms, interstitial atoms, substitutional atoms
type of line defect
dislocations
type of area defect
grain boundaries
substitutional atom
an atom of a different size replaces one atom in the lattice
vacancy atom
an atom is missing in the lattice
interstitial atom
an extra atom is in the lattice where there should not be an atom
equilibrium for number of vacancies
needed because it increases the entropy of the crystal
N(v) = N * exp(-Q(v)/kT)
N(v) = number of defects
N = total number of atom sites
Q(v) = activation energy
k = Boltzmann’s constant
T = temp in kelvin
two types of alloys
solid solution of B in A
solid solution of B in A and particles of a new phase with different composition, structures and properties
types of alloy of solid solution of B in A
interstitial - B is much smaller atom so fills in gaps between A atoms
substitutional - B is similar size to A so replaces A in some locations
When does a second phase form in an alloy?
when these 4 conditions are not met:
1. atomic size should be +/- 15%
2. crystal structure should be the same
3. stronger electronegativities are better for mixing
4. higher valency metal can dissolve quicker
edge dislocations
one line of atoms ends before the end of the material at an edge dislocation line - creates some lattice distortion. Above line, atoms are squeezed together and below line atoms are spread apart
screw dislocations
formed by shear stress where a plane of atoms and all above it are shifted
twin boundary
reflection of atom positions across a twin plane
what does a larger grain size number mean?
higher grain density
grain size linear intercept method
draw a line down a photo of grains, lbar = L(T)/PM
L(T) = total length of all lines
P = total number of intersections
M = magnification
lbar = mean grain size
