Lecture 4 Flashcards
what are the close packed planes in a HCP? how many are there?
the hexagonal layers of close-packed spheres (basal planes)
1
what are the close packed planes in a CCP? how many are there?
the (111) planes (think about them being across the X/s of the tops and bottoms), which are perpendicular to a cube’s body diagonal
4
how many close-packed directions are in one close-packed plane for hcp and ccp?
3 in both
What is the difference in the images of HCP versus simple hexagonal
HCP vs. SH
atoms/unit cell
a = ___
CN =
APF =
HCP
6 atoms
a = 2r
CN = 12
AFP = 0.74
SH
3 atoms
a = 2r
CN = 8
APF = 0.605
In the calculation of the simple hexagonal, what do we use in atoms/unit cell?
we use 1 atom bc it’s a primitive unit cell
what does layer construction look like for hexagonal versus square
how do you form ccp or simple cublic structure with layering
lay a cubic layer of atoms
CCP: next layer on the square interstices
SC: next layer on top of the first
is the simple cubic a common or uncommon crystal structure
uncommon
what is the one element that crystalizes in the simple cubic structure?
𝛼-polonium
SC
what is the closest packed direction?
CN?
a = ?
atoms/unit cell?
APF:
closest packed direction: (100) (along the cube’s edges)
CN = 6
a = 2r
atoms/unit cell = 1
APF = 0.52
What does the APF > to be close-packed?
0.74
What are 6 elements that commonly have the BCC structure?
Fe, Cr, W, V, Nb, Mo
can the BCC be constructed from hexagonal close packed or square packed layers of atoms?
no
what is the only direction in which atoms are in contact along in BCC?
the body-diagonal
4r = sqrt(3)*a
how many atoms are in the unit cell of a BCC
2
what is the plane in the BCC that atoms are the most (not fully) close-packed?
110 (the face diagonal plane)
what is the atomic packing factor for BCC
PD = (vol occupied by atoms)/(total volume of unit cell) = 0.68 = 68%
what are the different lattice constant formulas for SC, BCC, FCC, HCP
SC: a = 2r
BCC: a = 4/(sqrt(3))r
FCC: a = 2 sqrt(2)*r
HCP: a = 2r
how do you calculate the planar density of a certain plane?
PD = (area of total atoms on the plane) / (area of the plane)
what are the close packed planes and directions for CCP
{111} and <110>
what are the close packed planes and directions for BBC
{110} and <111>
what are the close packed planes and directions for SC
{100} and <100>
what are the close packed planes and directions for HCP
{001} and <100>
When doing calculations for planar density, when there’s only a portion of the atom in the plane, what do you do?
use the fraction of the actual atom in the plane
for example, it may be 1/8 of a whole atom in the cube, but 1/4 of a circle in a plane. use the 1/4
where does deformation in metals occur
on the closest packed planes and in the closest-packed directions
what is a slip system
the combo of slip plane and direction
