Materials Science And Engineering

Six Property classifications of materials

Mechanical, Electrical, Thermal, Magnetic, Optical, Deteriorative

Material Structure

How internal components of the materials is arranged

4 Elements of materials to consider

Processing, structure, properties, and performance

3 Important Criteria for materials selection

In-service conditions, deterioration of material properties, and cost of material

4 classifications of materials

metals, ceramics, polymers, composites

Advanced Materials

Semiconductors, biomaterials, smart materials, nanomaterials

atomic number (Z)

number of protons

isotope

Atoms of the same element that have different numbers of neutrons

atomic weight

Average of the mass numbers of all isotopes

4 Dimensions of structural elements

Subatomic, atomic, microscopic, and macroscopic

atomic mass unit (amu)

used to compute atomic weight

1 mole

6.02 x 10^23

quantum mechanics

Study of physics at the atomic level where energy is quantized in discrete, rather than continuous, levels.

Bohr atomic model

Atoms described as electrons orbiting the nucleus in well defined paths.

wave-mechanical model

the current model of the atom that deals with the wave-particle duality of nature.

quantum number

a number that specifies the properties of electrons

electron state

values of energy that are permitted for electrons

Pauli exclusion principle

An atomic orbital may describe at most two electrons, each with opposite spin direction

ground state

The lowest energy state of an atom

electron configuration

the arrangement of electrons in an atom

valence electron

Electrons on the outermost energy level of an atom

electropositive

When something is not at all electronegative, i. e. most metals

electronegative

Capable of receiving electrons, i. e. most non-metals

Force-potential energy relationship for two atoms

E=Integral (F dr)

bonding energy

energy required to separate two atoms to an infinite separation

primary bond

ionic, covalent, and metallic

ionic bond

Formed when one or more electrons are transferred from one atom to another

coulombic force

A force between charged particles such as ions

Attractive energy-interatomic separation relationship

Ea=-(A/r)

Repulsive energy-interatomic separation relationship

Er=(B/r^n)

covalent bonding

A bond formed when atoms share one or more pairs of electrons

metallic bonding

the chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons

secondary bond

Weak bonds, such as Van der Waals bonds, that typically join molecules to one another.

van der Waals bond

A type of secondary bond in which a temporary dipole induces another dipole in an adjacent atom

dipole

created by equal but opposite charges that are separated by a short distance

hydrogen bonding

secondary bond that exists between molecules that contain hydrogen

polar molecule

A molecule that has electrically charged areas.

crystalline

A solid that is made up of crystals in which particles are arranged in a regular, repeating pattern.

crystal structure

the arrangement of atoms, ions, or molecules in a regular way to form a crystal

lattice

The three-dimensional arrangement of atoms or ions in a crystal.

unit cell

the smallest group of particles within a crystal that retains the geometric shape of the crystal

face-centered cubic (FCC)

A unit cell of cubic geometry with atoms located at each of the corners and the centers of the faces

Unit cell edge length for FCC

coordination number

number of nearest neighbor or touching atoms

atomic packing factor (APF)

The volume of atoms in a selected unit cell divided by the volume of the unit cell.

body-centered cubic (BCC)

cubic unit cell with atoms located at all eight corners and a single atom at the cube center

Unit cell edge length for body-centered cubic

hexagonal closed-packed (HCP)

Theoretical density for metals

polymorphism

The ability of a solid material to exist in more than one form or crystal structure

allotropy

when polymorphism is found in elemental solids

lattice parameters

The combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry.

crystal system

A way in which the structures are classified. (BCC, FCC ...)

Miller indices

A shorthand for expressing directions and planes in crystals

Linear Density

The number of atoms centered on a crystallographic direction per unit length.

planar density

The number of atoms or ions centered on a crystallographic plane per unit area of the plane.

single crystal

A crystalline solid for which the periodic and repeated atomic pattern extends throughout its entirety without interruption

grain

a small crystal that composes most crystalline solids

polycrystalline

Describing a solid, usually isotropic, of joined crystals or grains.

grain boundary

region of mismatch between two adjacent grains in a polycrystalline microstructure

isotropic

properties of a material are independent of directions

diffraction

Occurs when an object causes a wave to change direction and bend around it

Bragg's law

Interplanar spacing for a plane having indices h, k, and l

noncrystalline

molecules do not arrange into repeating patterns

amorphous

Without definite form

imperfection

a type of defect in the perfect order of a crystalline material

point defect

A crystalline defect associated with one or, at most, several atomic sites

vacancy

A missing atom or ion at a lattice site that would normally be occupied

temperature dependence of the equilibrium number of vacancies

Nv=N^(-(Qv/k*T)

Boltzmann's constant

Kb=1.38 x 10^-23 K/K

self-interstitial

A host atom or ion positioned on an interstitial lattice site.

alloy

A mixture of two or more metals

solid solution

An alloy of two or more metals or a metal(s) and a nonmetal(s) which is a single-phase atomic mixture

solute

A substance that is dissolved in a solution.

solvent

A liquid substance capable of dissolving other substances

substitutional solid solution

A solution formed by substituting species B directly for species A on the lattice sites normally occupied by A.

interstitial solid solution

A solid solution in which atoms or ions of a foreign species are located in the interstitial positions.

composition

the nature of something's constituents

weight percent

A concentration specification on the basis of weight (or mass) of a particular relative to the total alloy weight (or mass)

atom percent

A concentration specification on the basis of the number of moles (or atoms) or a particular element relative to the total number of moles (or atoms) of all elements within an alloy

edge dislocation

an extra "half plane" of atoms inserted into a crystal

dislocation line

The line that extends along the end of the extra half-plane of atoms for an edge dislocation and along the center of the spiral of a screw dislocation

screw dislocation

result of shear forces on part of material that caused displacement of a portion of crystal

mixed dislocation

A dislocation that has both edge and screw components

Burgers vector

a vector that denotes the magnitude and direction of lattice distortion associated with a dislocation.

atomic vibration

The vibration of an atom about its normal position in a substance

microstructure

The structural features of an alloy subject to observation under a microscope

microscopy

investigation of minute objects through a microscope

photomicrograph

Photograph of an image produced by a microscope.

transmission electron microscope (TEM)

microscope where image is derived from electrons that have passed through it

scanning electron microscope (SEM)

An instrument that bounces electrons off objects to create a three-dimensional image that is more highly magnified than possible through a light microscope.

scanning probe microscope (SPM)

Microscope with a very sharp tip that is scanned over a surface to measure some property.

grain size

The average grain diameter as determined from a random cross section

relationship between ASTM grain size number and number of grains per square inch

n=2^(G-1)

diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

interdiffusion

atoms of one metal diffuse in another metal; in an alloy, atoms migrate from high to low concentration

impurity diffusion

when diffusion occurs by the movement of solute atoms in a dilute solution

self-diffusion

The mechanism by which a species diffuses in itself

vacancy diffusion

the diffusion mechanism in which net atomic migration is from a lattice site to an adjacent vacancy