crystal structures notes
TRANSCRIPT
ObjectivesObjectives1.1. Identify and describe the three Identify and describe the three
primary metallic crystal structures.primary metallic crystal structures.2. Explain the terms:
Anisotropic, anisotropyPolycrystalline, polycrystallinityPolymorphic, polymorphismAllotropic, allotropy
Crystal StructuresCrystal StructuresCrystal:Crystal:
Lattice ConstantsLattice Constants
a,b,c – lattice vectorsa,b,c – lattice vectors
alpha, beta, gamma – interaxial anglesalpha, beta, gamma – interaxial angles
Why Crystals?Why Crystals?
Atoms arrange themselves into Atoms arrange themselves into crystals in order to _______ their free crystals in order to _______ their free energy. energy.
Structures that deviate from the Structures that deviate from the crystalline ideal will result in crystalline ideal will result in _________ energies in the atoms._________ energies in the atoms.
Bravais
Lattices
FCC: Face Centered CubicFCC: Face Centered Cubic
FCC: Face Centered CubicFCC Metals
Al
Cu
Au
Pb
Ni
Pt
Ag
Face Centered Cubic
2 a
2 a
General CharacteristicsGeneral CharacteristicsFCC MetalsFCC Metals
Fairly softFairly soft Malleable (easily formed) and do not Malleable (easily formed) and do not
harden much as they deformharden much as they deform Will deform a great deal before Will deform a great deal before
failurefailure
BCC: Body Centered Cubic BCC: Body Centered Cubic
BCC: Body Centered Cubic
BCC MetalsCrFeMoP
NaTaWV
Unit Cell:
APF:
Body Centered Cubic
2 a
3 a
Unit Cell:
APF:
General CharacteristicsGeneral CharacteristicsBCC MetalsBCC Metals
Generally harder than FCC metalsGenerally harder than FCC metals Will not deform as much before Will not deform as much before
failurefailure Tend to get harder as they deformTend to get harder as they deform
Hexagonal Close PackedHexagonal Close Packed
Hexagonal Close Packed
HCP Metals
Cd
Zn
Mg
Co
Zr
Unit Cell:
APF:
General CharacteristicsGeneral CharacteristicsHCP MetalsHCP Metals
Tend to be______Tend to be______
Generally will harden rapidly as they Generally will harden rapidly as they deformdeform
Cannot usually deform a lot without Cannot usually deform a lot without failurefailure
AnisotropicAnisotropic- “Not Isotropic”; - “Not Isotropic”; properties depend on ______properties depend on ______
Wood
IsotropyIsotropyIsotropic Particle Board: Properties Isotropic Particle Board: Properties are ________ of ___________ are ________ of ___________
PolycrystallinePolycrystalline – containing many – containing many crystals.crystals.
PolymorphicPolymorphic – having different – having different ________________. (eg Iron is BCC ________________. (eg Iron is BCC FCC FCC BCC upon cooling from liquid BCC upon cooling from liquid to room temperature)to room temperature)
PolymorphicPolymorphic – having different crystal – having different crystal structures.structures.
AllotropicAllotropic – same as polymorphic but an – same as polymorphic but an elemental solid (many alloys are elemental solid (many alloys are polymorphic, only a few elements are)polymorphic, only a few elements are)
AmorphousAmorphous – no structure – no structure
Self-TestSelf-Test
What do BCC, FCC and HCP stand What do BCC, FCC and HCP stand for?for?
If a metal turns from BCC to HCP If a metal turns from BCC to HCP structure as it is heated, is it structure as it is heated, is it polymorphic or polycrystalline?polymorphic or polycrystalline?
If a metal turns from BCC to FCC, If a metal turns from BCC to FCC, what happens to the volume of the what happens to the volume of the metal?metal?