Material Science Exam 2

Polycrystalline

Consisting of many crystals or  grains

Grains

Crystals in a polycrystalline material

Grain Boundary

the interface between two grains, or crystallites, in a polycrystalline material

Lattice parameter

the axial lengths or dimensions of the unit cell and are denoted by convention as a, b, and c

Lattice

A collection of points that divide space into smaller equally sized segments

Unit cell

A subdivision of the lattice that still retains the overall characteristics of the entire lattice

Basis

A group of atoms associated with a lattice point

Interstitial (solid solution)

A point defect produced when an atom is placed into the crystal at a site that is normally not a lattice point

Substitutional (solid solution)

A point defect produced when an atom is removed from a regular lattice point and replaced with a different atom, usually of a different size

Dislocations

line imperfections in a crystalline material

Edge dislocation

A line defect that can be envisioned as an “extra half plane of atoms” inserted into the crystal

Screw dislocation

A line defect that can be envisioned as a spiral ramp in the crystal that was produced by skewing the crystal by one atomic spacing

Dislocation density

total length of dislocations per unit volume, usually used to represent the amount of dislocations present

Diffusion

The net flux of atoms, ions, or other species within a material caused by temperature and a concentration gradient

Flux (per area)

The number of atoms or other diffusing species passing through a plane of unit area per unit time. This is related to the rate at which mass is transported by diffusion in a solid.

Total flux

Flux (per area) multiplied by Area

Diffusion coefficient

A temperature-dependent coefficient related to the rate at which atoms, ions, or other species diffuse. The diffusion coefficient depends on temperature, the composition and microstructure of the host material, and the concentration of the diffusing species

Strain/work/deformation hardening

Strengthening of a material by increasing the number of dislocations by deformation, or cold working. Also known as “work hardening” or “deformation hardening”

% CW

(Ai-Af)/Ai * 100

Mixed bond

bonding between atoms is a mixture of two or more types

Recovery (stress relief)

A low-temperature annealing heat treatment designed to eliminate residual stresses introduced during deformation without reducing the strength of the cold-worked material. This is the same as a stress-relief anneal

Recrystallization

A medium-temperature annealing heat treatment designed to eliminate all of the effects of strain hardening produced during cold working

Grain growth

Movement of grain boundaries by diffusion in order to reduce the amount of grain boundary area. As a result, small grains shrink and disappear and other grains become larger, similar to how some bubbles in soap froth become larger at the expense of smaller bubbles. In many situations, grain growth is not desirable

Annealing

In the context of metals, annealing is a heat treatment used to eliminate part or all of the effects of cold working. For glasses, annealing is a heat treatment that removes thermally induced stresses

Equi-axed (grains)

crystal grains in a material that have approximately the same dimensions in all directions