Metallic Crystal Structures and Properties

Flashcards covering primary metallic crystal structures, lattice types, and material properties based on the lecture notes.

When atoms arrange themselves into crystals, what happens to their free energy?

Atoms arrange themselves into crystals in order to minimize their free energy.

What is the result of structures that deviate from the crystalline ideal regarding energy?

Structures that deviate from the crystalline ideal will result in higher energies in the atoms.

What are the lattice constants found in a crystal structure?

Lattice constants include a, b, c (lattice vectors) and alpha, beta, gamma (interaxial angles).

What does FCC stand for?

Face Centered Cubic

How many atoms are in an FCC unit cell?

4

What is the Atomic Packing Factor (APF) for FCC?

0.74

Name two common metals that exhibit an FCC crystal structure.

Aluminum (Al), Copper (Cu), Gold (Au), Lead (Pb), Nickel (Ni), Platinum (Pt), Silver (Ag) (Any two are acceptable, e.g., Al, Cu)

Describe the general characteristics of FCC metals.

Fairly soft, malleable (easily formed), do not harden much as they deform, and will deform a great deal before failure.

For FCC, what is the relationship between the lattice parameter 'a' and the atomic radius 'R'?

a = 4R

What does BCC stand for?

Body Centered Cubic

Name two common metals that exhibit a BCC crystal structure.

Chromium (Cr), Iron (Fe), Molybdenum (Mo), Phosphorous (P), Sodium (Na), Tantalum (Ta), Tungsten (W), Vanadium (V) (Any two are acceptable, e.g., Cr, Fe)

Describe the general characteristics of BCC metals.

Generally harder than FCC metals, will not deform as much before failure, and tend to get harder as they deform.

What does HCP stand for?

Hexagonal Close Packed

Name two common metals that exhibit an HCP crystal structure.

Cadmium (Cd), Zinc (Zn), Magnesium (Mg), Cobalt (Co), Zirconium (Zr) (Any two are acceptable, e.g., Cd, Mg)

Describe the general deformation characteristics of HCP metals.

Generally will harden rapidly as they deform and cannot usually deform a lot without failure.

Define Anisotropic.

Anisotropic means properties depend on orientation.

How do properties relate to orientation in an isotropic material?

In an isotropic material, properties are independent of orientation.

Define Polycrystalline.

Polycrystalline means containing many crystals.

Define Polymorphic and provide an example.

Polymorphic means having different crystal structures. For example, Iron (Fe) transforms from BCC to FCC and back to BCC upon cooling from liquid to room temperature.

What is the difference between Polymorphic and Allotropic?

Polymorphic refers to having different crystal structures, while Allotropic is the same concept but specifically for an elemental solid.

Define an Amorphous structure.

Amorphous refers to having no crystal structure.

What do BCC, FCC, and HCP stand for?

BCC stands for Body Centered Cubic, FCC stands for Face Centered Cubic, and HCP stands for Hexagonal Close Packed.

If a metal turns from a BCC to an HCP structure as it is heated, is this an example of polymorphism or polycrystallinity?

Polymorphism.

If a metal turns from BCC to FCC, what generally happens to its volume per atom?

Since FCC (APF = 0.74) is more densely packed than BCC (APF = 0.68), the volume per atom would generally decrease (the metal would contract).