Flashcards for Chapter 1: Crystal Structures of Metals

Characteristics:
- Metals are typically hard, tough, ductile, deformable, and conductive (thermal and electrical).
- Conductivity hierarchy: Hardness: Polymer < Metal < Ceramic
- Toughness: Ceramic < Metal < Polymer
- Melting Point: Polymer < Metal < Ceramic
- Thermal Conductivity: Ceramic < Polymer < Metal
- Electrical Conductivity: Ceramic < Polymer < Metal
Atomic Arrangement:
- The properties of metals are significantly influenced by the arrangement of atoms in three-dimensional space.
- Certain metals exhibit soft-hard magnetic properties.

Components of Atoms:
- Consists of a nucleus (positively charged, made of protons and neutrons) and electrons (negatively charged, orbiting around the nucleus).
- Protons = Electrons in neutral atoms; different chemical elements have different proton counts.
Energy Levels:
- Electron configurations across various energy levels contribute to different physical properties.

Shapes of Electron Orbitals:
- s subshell: Spherical density distribution
- p subshell: Dumbbell-shaped
- d and f orbitals: More complex shapes
Electron Probability:
- Orbitals define the 3D regions where electrons are likely located, impacting bonding and material properties.

Electrons in metals are modeled as free-moving; they form a 'sea of electrons' that moves amongst fixed positive metal ions.
This electron behavior affects mechanical strength, ductility, thermal and electrical resistivity, and conductivity.

Crystal Lattice:
- Comprised of unit cells that repeat to create a 3D structure, determining the physical arrangement of atoms.
Unit Cell:
- Defined by principal axes (x, y, z) and characterized by 6 lattice parameters: lengths (a, b, c) and angles (α, β, γ).
- For cubic structures: a = b = c and eta = eta = eta = 90^{ ext{o}}.
Calculation of Lattice Parameters:
- Example of Iron (Fe): Given a = 0.287 ext{ nm}, the number of unit cells in 1 cm is calculated as follows:
  1 ext{ cm} = 10^{-2} ext{ m} = 3.48 imes 10^7 ext{ unit cells}.

Types of Structures:
- Body Centered Cubic (BCC)
- Face Centered Cubic (FCC)
- Hexagonal Close Packed (HCP)
Example Elements:
- BCC: a-Fe, Cr, Mo, W
- FCC: Al, Cu, Pb, Au, Ni
- HCP: a-Ti, Zn, Mg, Cd

Definition:
- APF = rac{ ext{Total sphere volume}}{ ext{Total unit cell volume}}
FCC Example:
- Total atom contribution: 1/8 at corners + 1/2 at faces = total 4 atoms.
- ext{Volume calculations:}
- Unit cell volume, V_c = a^3\
- Total sphere volume for FCC, V_s = rac{4}{3}
  ho^3 ext{pi} \
- APF Calculation: ext{APF} = 0.74.

Slip Plane:
- A plane with a high density of atoms (low-index planes) facilitates easier atomic movement during stress applications.
Number of Slip Systems:
- BCC: 12 slip systems (though not all active)
- FCC: 12 active slip systems (high ductility)
- HCP: 3 active slip systems (less ductile)
Ductility Significance:
- Metals that can undergo significant plastic deformation without failing are considered safer for engineering applications.

Crystal structures in metals primarily include BCC, FCC, and HCP, with FCC and HCP being close-packed structures.
Lattice configurations related to the number and arrangement of atoms directly influence the physical and mechanical attributes of the metal.
A higher number of active slip systems corresponds to greater ductility, making metals easier to deform without cracking.

Callister, W. D. Fundamental of Materials Science and Engineering/ an Interactive E. Text, 2001, John Wiley & Sons, Inc., New York.