M

macromolecule

a huge molecule made up of thousands of atoms.

magnetic field strength (H)

the intensity of an externally applied magnetic field.

magnetic flux density (B)

the magnetic field produced in a substance by an external magnetic field.

magnetization

the total magnetic moment per unit volume of material; also, a measure of the contribution to the magnetic flux by some material within an H field.

malleable cast iron

white cast iron that has been heat treated to convert the cementite into graphite clusters; a relatively ductile cast iron.

martensite

a metastable iron phase supersaturated in carbon that is the product of a diffusionless (athermal) transformation from austenite.

matrix

the continuous phase in a composite or two-phase alloy microstructure in which a second phase is dispersed.

mer

the group of atoms that constitutes a polymer chain repeat unit.

metal

an opaque lustrous elemental chemical substance that is a good conductor of heat and electricity and, when polished, a good reflector of light; most elemental metals are malleable, ductile, and are generally denser than the other elemental substances; metals are structurally distinguished from nonmetals by their atomic bonding and electron availability; the electron band structure of metals is characterized by a partially filled valence band; the "free electrons" lost from the outer shells of metallic atoms are available to carry an electric current; the defining property of a metal is that it is an element with a positive thermal coefficient of resistivity, meaning the electrical resistivity of a metal continuously increases as temperature increases.

metallic bond

a primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons ("sea of electrons") which are mutually shared by all the atoms in the metallic solid.

metallurgy

the science and technology of metals and alloys.

metastable

(1) nonequilibrium state of a material with respect to some transition, conversion, or reaction but stabilized kinetically either by rapid cooling or by some molecular characteristics; (2) possessing a state of pseudoequilibrium that has a free energy higher than that of the true equilibrium state.

micron

one millionth of a meter (0.000001), and another term for micrometer (10^-6).

microscopy

the investigation of microstructural elements using some type of microscope, e.g. scanning electron microscopy (SEM), light optical microscopy (LOM).

microstructure

the microscopic assemblage of grains, grain boundaries, amorphous phases, pores, and inclusions, that make up a material.

microvoid coalescence (MVC)

occurs due to the nucleation of microvoids, followed by their growth and eventual coalescence; initiation is caused by particle cracking or interfacial failure between an inclusion or precipitate particle and the surrounding matrix.

Miller indices

a set of three integers (four for hexagonal) that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts.

mixed dislocation

a dislocation that has both edge and screw components.

modulus of elasticity (E)

the ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material.

modulus of rupture

breaking strength in a nonductile solid as measured by bending.

molecule

a group of atoms that are bound together by primary interatomic bonds.

monomer

a molecule consisting of a single mer.