Engineering Materials - Crystal Structures

Vocabulary flashcards based on lecture notes about crystal structures, imperfections, X-ray diffraction, and microscopy.

Crystal

An orderly array of atoms that have a repeating unit.

Non-crystalline

Solids that lack an ordered crystal structure; also known as amorphous.

Crystal lattice

Three-dimensional array of points coinciding with atom positions.

Unit cell

Smallest repetitive entity in the crystal; the basic structural unit or building block of the crystal structure.

Lattice parameters

Parameters (a, b, c, α, β, γ) that describe the size and shape of the unit cell.

Body Centred Cubic (BCC)

A cubic arrangement with an additional atom in the center of the cell.

Face Centred Cubic (FCC)

Atoms touch each other along face diagonals.

Hexagonal Close Packed (HCP)

The top and bottom faces of the unit cell consist of six atoms that form regular hexagons and surround a single atom in the center.

Isotropic materials

Materials having the same properties in all directions.

Anisotropic materials

Materials having properties that are direction dependent.

Crystallographic direction

A line between two poitns, or a vector.

Crystallographic planes

Read off the intercepts where the plane passes through each axis. If the plane is parallel to an axis, we call this infinite. The reciprocal of infinity is zero.

Polycrystalline materials

Grains of different orientations

Vacancy

A vacant lattice site where the atom is missing.

Self-interstitial

An atom pushed into the interstitial space that would not ordinarily be occupied.

Solid Solution

The addition of impurity atoms to a metal.

Solvent

Represents the element or compound that is present in the greatest amount.

Solute

Element or compound present in a minor concentration.

Linear Defects - Dislocations

One-dimensional defects around which atoms are misaligned.

Edge dislocation

Extra half-plane of atoms inserted in a crystal structure, b ⊥ to dislocation line.

Screw dislocation

Spiral planar ramp resulting from shear deformation, b || to dislocation line.

Grain Boundaries

Regions between crystals.

d

Spacing between crystal planes.

λ

Wavelength of X-rays.

θ

Angle of diffraction.

Microstructure

A structure with a length-scale in the micrometer range.