Chapter 3 Flashcards
crystalline materials…….
atoms pack in ____
-typical of __________,_________,__________
pack in periodic 3D arrays
typical of metals, many ceramics, some polymers
noncrystalline materials…..
atoms have ____________
-occurs for __________,_______________
atoms have no periodic packing
occurs in complex structures, rapid cooling
“amorphous”=_____________
noncrystalline
unit cell is __________________________________
is the smallest repetitive volume which contains the complete lattice pattern of a crystal
there are _ crystal systems and ___ crystal lattices
7 crystal systems
14 crystal lattices
a,b, and c are __________
lattice constants
metallic crystal structures tend to be _____ packed
densly
what are the reasons for dense packing?
- typically, only one element is present, so all atomic radi are the same
- metallic bonding is not directional (it can bond in all directions)
- nearest neighbor distances tend to be small in order to lower bond energy
- electron cloud shields cores from each other
metallic crystal structures have the _____ crystal structures
simplest crystal structures
simple cubic structure (SC)
this structure is _______ due to the low packing density.
___ directions are the cube edges
whats its coordination number?????
APF=?
how many atoms/unit cell=?
this is rare
closed-packed direction
coordination number = 6
APF= .52
1 atom /unit cell
what is the coordination number for simple cubic structure?
6
APF=
volume of atoms in unit cell/volume of unit cell
Body center cubic structure (BCC)
atoms touch each other along __________
coordination number =____________
how many atoms per cell? ____
APF=?
along cube diagonals
coordination number =8
2 atoms/unit cell
APF= .68
face centered cubic structure (FCC)
atoms touch each other along ___________
what is the coordination number?
how many atoms/unit cell?
APF=???/
atoms touch each other along face diagonals
coordination number=12
4 atoms/unit cell
APF=.74
hexagonal close-packed structure (HCP)
what is the coordination number=
APF=
how many atoms per cell?
coordination number = 12
APF=.74
6 atoms/unit cell
density=p=?
mass of atoms in unit cell/total volume of unit cell
density of materials classes?
________>__________>___________
metals(most dense)>ceramics>polymers
why?
metals- have close-packing (metallic bonding), often large atomic masses
ceramics- have less dense packing, often lighter elements, polymers have low packing density (often amorphous), lighter elements
however, composites have intermediate values
_________________for unit cell CENTER are a/2, b/2, c/2:
1/2,1/2,1/2
point coordinates
point coordinates for unit cell _________ are 111
a,b,c
CELL CORNER
What is the algorithm to find the crystallographic directions
- find the head and tail point coordinates
- subtract tail point coordinates from head point coordinates
- adjust to smallest integer values
- enclose in square brackets, no commas {uvw]
what is the formula for linear density =LD
LD=number of atoms/unit length of direction vector
all parrallel planes have _____________________
same Miller indices
what is the algorithm of crystallographic planes?
- read off intercepts of plane with axes in terms of a, b,c
- take reciprocals of intercepts
- reduce to smallest integer value
- enclose in parentheses, no commas
some engineering applications require single crystals:
such as:
- _________________
- ___________________
diamond single crystals for abrasives
turbine blades
properties of crystalline materials often related to _________
crystal structure
most engineering materials are ____________-
polycrystals
each “_____” is a single crystal
grain
if grain are randomly oriented, overall component properties are not ___________.
grain size typ. range from 1nm to 2cm.
directional
single crystals??
vary with direction:anisotropic.
poly crystals??
- properties may/may not vary with direction
- if grains are randomly orientated: ISOTROPIC
- if grains are textured: ANISOTROPIC
atoms may assemble into ____ or ________ structures
crystalline or amorphous
common metallic crystal structures are _______,___________, and _________
FCC, BCC, HCP
we can predict the density of a material, provided we know the _________,_______,__________
atomic weight, atomic radius, and crystal geometry
_____________ points, directions and planes are specified in terms of indexing schemes. ___________ directions and planes are related to atomic linear densities and PLANAR DENSITIES
crystallographic directions
materials can be ________ or ___________. Material properties generally vary with single crystal orientation (they are ___________) but are generally non-directional (they are _________) in polycrystals with randomly oriented grains
can be single crystals or polycrystalline
single crystals=anisotropic
non-directional=isotropic
