Lecture 4 (BME 296)

Miller Index

A notation system in crystallography for identifying crystallographic planes and directions.

Defect

An imperfection in the crystal structure of a material which can affect its mechanical properties.

FCC (Face-Centered Cubic)

A crystal structure where atoms are located at each of the corners and the centers of all the cube faces.

BCC (Body-Centered Cubic)

A crystal structure where atoms are located at each of the eight corners of the cube and a single atom at the center.

Atomistic free energy

The energy associated with the positions and interactions of atoms in a material.

Vacancy

A type of point defect in a crystal structure where an atom is missing from its lattice site; in the opposite direction of atomic diffusion

Self-interstitial

A defect where an atom occupies a space in the crystal lattice not normally occupied by an atom.

Atomic Packing Factor (APF)

The fraction of volume in a crystal structure that is occupied by atoms.

Grain Boundary

The interface between two grains in a polycrystalline material.

Diffusion

The process by which atoms or molecules move from an area of high concentration to an area of low concentration.

Interstitial diffusion

A type of diffusion in which atoms migrate from one interstitial position to another.

Line defect (1D)

A defect associated with one-dimensional irregularities in a crystal structure, such as edge dislocations

Point defect (0D)

A type of defect characterized by a localized disruption of the lattice.

Planar defect (2D)

A defect that extends in two dimensions, such as grain boundaries.

Volume defect (3D)

A three-dimensional defect in a crystal structure where the regular arrangement of atoms is disrupted; good for biomaterials

Plastic deformation

A permanent change in shape or size of a material due to applied stress; occurs by slip where an edge dislocation slides over adjacent plane of half-line atoms

Elastic deformation

A temporary change in shape or size of a material that is reversible when the stress is removed.

Strain hardening

A process that increases the strength of a material by deforming it plastically.

Annealing

A heat treatment process that alters the microstructure of a material to reduce dislocations and relieve internal stresses.

Surface free energy

The excess energy at the surface of a material compared to the bulk, leading to higher reactivity of surface atoms.

Grain boundary energy

The energy associated with the boundary between two grains, which can be higher than that of the grain itself.

Precipitates

Clusters of atoms that form within a solid material, often as a result of phase changes.

Voids

Three-dimensional defects in a material where there are empty spaces or vacancies.

Diffusion mechanisms

Vacancy & interstitial diffusion

Strain hardening

Ductile materials are deformed below their melting point causing an increase in number of dislocations (increased density); distance between dislocations is reduced and this blocks motion

Annealing

Increase temperature causing increased diffusion which causes dislocations to start moving; relieves strain energy thereby reducing dislocations