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Materials/Processes

Selection of Materials
Specific Metals
  Metal Ores
  Iron and Steel
  Decarburization
  Aluminum/Aluminum Alloys
  Nickel and Nickel Alloys
  Titanium and Titanium Alloys


General Manufacturing Processes

Metallic Components
Ceramic and Glass Components
Polymers/Plastic Components
Composites

Manufacturing Defects
Metals
Polymers
Composites

Service Induced Damage
Metals
Polymers
Composites
Material Specifications

Component Design, Performance and NDE
Strength
Durability
Fracture Mechanics
Nondestructive Evaluation

Similarities and Difference Between the
FCC and HCP Structure

The face centered cubic and hexagonal close packed structures both have a packing factor of 0.74, consist of closely packed planes of atoms, and have a coordination number of 12. The difference between the fcc and hcp is the stacking sequence. The hcp layers cycle among the two equivalent shifted positions whereas the fcc layers cycle between three positions. As can be seen in the image, the hcp structure contains only two types of planes with an alternating ABAB arrangement. Notice how the atoms of the third plane are in exactly the same position as the atoms in the first plane. However, the fcc structure contains three types of planes with a ABCABC arrangement. Notice how the atoms in rows A and C are no longer aligned. Remember that cubic lattice structures allow slippage to occur more easily than non-cubic lattices, so hcp metals are not as ductile as the fcc metals.

The table below shows the stable room temperature crystal structures for several elemental metals.

Metal
Crystal Structure
Atomic Radius (nm)
Aluminum
FCC

0.1431

Cadmium
HCP
0.1490
Chromium
BCC
0.1249
Cobalt
HCP
0.1253
Copper
FCC
0.1278
Gold
FCC
0.1442
Iron (Alpha)
BCC
0.1241
Lead
FCC
0.1750
Magnesium
HCP
0.1599
Molybdenum
BCC
0.1363
Nickel
FCC
0.1246
Platinum
FCC
0.1387
Silver
FCC
0.1445
Tantalum
BCC
0.1430
Titanium (Alpha)
HCP
0.1445
Tungsten
BCC
0.1371
Zinc
HCP
0.1332

A nanometer (nm) equals 10-9 meter or 10 Angstrom units.