MATERIAL SCIENCE AND ENGINEERING GLOSSARY TERMS
abrasion a process where hard particles are forced against and moved along a solid surface.
abrasive a hard and wear-resistant material (commonly a ceramic) that is used to wear, grind, or cut away other material.
abrasive wheel a grinding wheel composed of an abrasive grit and bonding agent.
acid a chemical substance that yields hydrogen ions when dissolved in water.
acoustic emission a measure of integrity of a material determined by sound emission when a material is stressed.
acrylic synthetic resin made from acrylic acid or a derivative thereof; acrylics possess the property of transparency and offer flame resistance.
activated rosin flux mixture of rosin and small amounts of organic-halide activators or organic-acid activators.
activation energy the energy required to initiate a reaction, such as diffusion.
activator substance that enhances the ability of a flux to remove oxides and other contaminants from surfaces being joined.
adhesion (1) the attractive force between adjacent surfaces in a frictional contact; (2) the state in which two surfaces are held together by interfacial forces.
aging a change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working, heat treatment, or a cold working operation.
air-lock an intermediate enclosed chamber of a vacuum or pressure system through which an object may be passed without materially changing the vacuum or pressure of the system.
alclad composite wrought product comprised of an aluminum alloy core having one or both surfaces as metallurgically bonded aluminum or aluminum alloy coating that is anodic to the core, and thus electrochemically protects the core against corrosion.
alkali metal a metal in group IA of the periodic table that form strongly alkaline hydroxides (lithium, sodium, potassium, rubidium, cesium, francium).
alkaline earth metal a metal in group IIA of the periodic table (beryllium, magnesium, calcium, strontium, barium, radium).
allotriomorphic crystal a crystal having a normal lattice structure, but with an imperfect outward shape due to the influence of its surroudings.
allotropy the possibility of existence of two or more different crystal structures for a substance (generally an elemental solid).
alloy a metallic substance that is composed of two or more elements.
alpha iron the body-centered cubic (BCC) form of pure iron, stable below 910 C (1670 F).
amorphous non-crystalline, without long-range order.
analog circuit electrical circuit that provides a continuous relationship between its input and output.
anion a negatively charged non-metallic ion.
anisotropy material characteristic of exhibiting different values of a property in different crystallographic directions.
annealing a generic term used to denote a heat treatment where the microstructure and properties of a material are altered; it frequently refers to a heat treatment where a previously cold-worked metal is softened by allowing it to recrystallize.
annealing twin a twin formed in a crystal during recrystallization.
anode the electrode of an electrolyte cell at which oxidation occurs; electrons flow away from the anode in the external circuit; it is usually at the electrode that corrosion occurs and metal ions enter solution.
anodic protection a technique to reduce the corrosion rate of a metal by polarizing it into its passive region, where dissolution rates are low.
anodic reaction electrode reaction equivalent to a transfer of positive charge from the electronic to the ionic conductor; an anodic reaction is an oxidation process.
anodizing forming a conversion coating on a metal surface by anodic oxidation; most often applied to aluminum.
antiferromagnetism a phenomenon where complete magnetic moment cancellation occurs as a result of antiparallel coupling of adjacent atoms or ions; the macroscopic solid possesses no net magnetic moment.
atactic a type of polymer chain configuration where side groups are randomly positioned on one side of the chain or the other.
atom percent (at%) concentration specification on the basis of the number of moles (or atoms) of a particular element relative to the total number of moles (or atoms) of all elements within an alloy.
atomic packing factor (APF) the fraction of the volume of a unit cell that is occupied by "hard sphere" atoms or ions.
austenite face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure.
austenitizing forming austenite by heating a ferrous alloy above its upper critical temperature - to within the austenite phase region from the phase diagram.
bainite an austenitic transformation product found in some steels and cast irons; it forms at temperatures between those at which pearlite and martensite transformations occur; the microstructure consists of alpha-ferrite and a fine dispersion of cementite.
band gap energy for semiconductors and insulators, the energies that lie between the valence and conduction bands; for intrinsic materials electrons are forbidden to have energies within this range.
bauxite an ore of aluminum consisting of moderately pure hydrated alumina - Al2O3× 2H2O.
block copolymer a linear copolymer in which identical mer units are clustered in blocks along the molecular chain.
body-centered cubic (BCC) within the cubic unit cell atoms are located at corner and center cell positions (figure). more
bonding energy the energy required to separate two atoms that are chemically bonded to each other.
branched polymer a polymer having a molecular structure of secondary chains that extend from the primary main chains.
brass copper (Cu) based alloy with zinc (Zn) as the main alloying element.
brazing a metal joining technique that uses a molten filler metal alloy having a melting temperature greater than about 425 degrees C (800 F).
Brinell hardness test a test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter into it under a specified load; the result is expressed as the Brinell hardness number.
brittle crack propagation a very sudden propagation of a crack with the absorption of no energy except that stored elastically in the body.
brittle fracture separation of a solid with little or no macroscopic plastic deformation; fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture; brittle tensile fractures have a bright, granular appearance and exhibit little or no necking; typical fracture mode of a glass or ceramic.
brittleness the tendency of a material to fracture without first undergoing significant plastic deformation.
bronze copper (Cu) based alloy with tin (Sn) as the main alloying element.
Burgers vector (b) a vector that denotes the magnitude and direction of lattice distortion associated with a dislocation.
capacitance the charge-storing ability of a capacitor, defined as the magnitude of charge stored on either plate divided by the applied voltage.
carbon steel steel which owes its properties chiefly to various percentages of carbon without substantial amounts of other alloying elements; also known as ordinary, straight carbon, or plain carbon steel.
cast iron a ferrous alloy; the carbon content is greater than the maximum solubility in austenite at the eutectic temperature.
casting generic term referring to a process where a fluid material (usually a molten alloy) is made to flow into a shaped mold cavity where it solidifies; this method is used to produce complex component shapes and properties difficult to achieve otherwise. more
cation a positively charged metallic ion.
cementite iron carbide.
ceramic a compound of metallic and nonmetallic elements, for which the interatomic bonding is predominantly ionic.
Charpy test an impact test in which a V-notched, keyhole-notched, or U-notched specimen, supported at both ends horizontally, is struck behind the notch by a striker mounted at the lower end of a pendulum; the energy that is absorbed in fracture is calculated from the height to which the striker would have risen had there been no specimen and the height to which it actually rises after fracture of the specimen.
circuit interconnections of electrical elements and devices that perform a desired electrical function.
cleavage transcrystalline fracture along specific crystallographic planes; usually associated with low-energy fracture; may exhibit river patterns and/or tongues.
cold working plastic deformation of a metal at a temperature below that at which it recrystallizes; increasing the amount of cold work causes the dislocation density to rise in the material, making it more difficult to plastically deform the material and eventually cause brittle fracture.
columnar structure coarse structure of parallel columns of grains caused by highly directional solidification of molten metal resulting from sharp thermal gradients.
component an element or chemical compound that helps make up a material system; the composition of a phase or system can be described by giving the relative amounts of each component.
condensation polymerization the formation of polymer macromolecules by an intermolecular reaction involving at least two monomer species, usually with the production of a by-product of low molecular weight, such as water.
conductivity, electrical the proportionality constant between current density and applied electric field; a measure of the ease with which a material is capable of conducting an electric current.
conformal coating a thin nonconducting coating that is either plastic or inorganic; it is applied to a circuit for environmental and mechanical protection.
coordination number the number of atomic or ionic nearest neighbors.
cope the top half of a horizontally parted mold.
copolymer a polymer that consists of two or more dissimilar mer units in combination along its molecular chains.
coulombic force a force between charged particles, such as ions.
covalent bond a primary interatomic bond that is formed by the sharing of electrons between neighboring atoms.
creep the time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures.
critical resolved shear stress the shear stress, resolved within a slip plane and direction, which is required to initiate slip.
crosslinked polymer a polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.
crystal structure for crystalline materials, the manner in which atoms or ions are arrayed in space; it is defined in terms of the unit cell geometry and the atom positions within the unit cell.
crystalline the state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules.
crystallization act or process of forming crystals or bodies by elements or compounds solidifying so they are bounded by plane surfaces, symmetrically arranged, and are external expressions of definite internal structure.
cure to irreversibly polymerize a thermosetting plastic by subjecting it to a time-temperature profile.
Curie temperature the temperature above which a ferromagnetic or ferrimagnetic material becomes paramagnetic.
defect structure relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound.
degree of polymerization the average number of mer units per polymer chain molecule.
delta iron an allotropic (polymorphic) form of iron stable above 2550° F and crystallizing in the body centered cubic lattice.
diamagnetism a weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative.
die (1) a metal form used as a permanent mold for die casting or for a wax pattern in investment casting; (2) an integrated circuit chip as diced or cut from the finished wafer.
dielectric any material that is electrically insulating.
dielectric constant a relative measurement of the degree of polarization (shift of positive charge toward the negative electrode and negative charge toward the positive electrode) that occurs when a material is placed in an electric field.
diffraction (x-ray) constructive interference of x-ray beams that are scattered by atoms of a crystal.
diffusion motion of atoms, ions, or vacancies through a material.
diffusion coefficient (D) the constant of proportionality between the diffusion flux and the concentration gradient in Fick's first law; its magnitude is indicative of the rate of atomic diffusion.
diffusion flux (J) the quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time.
dipole a system or object whose one end has a negative charge and the other a positive charge.
dislocation a linear crystalline defect around which there is atomic misalignment; plastic deformation corresponds to the motion of dislocations in response to an applied shear stress; edge, screw, and mixed dislocations are possible.
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.
domain a volume region of a ferromagnetic or ferrimagnetic material in which all atomic or ionic magnetic moments are aligned in the same direction.
doping the intentional alloying of semiconducting materials with controlled concentrations of donor or acceptor impurities.
drag the bottom half of a horizontally parted mold.
ductile fracture a mode of fracture that is attended by extensive gross plastic deformation.
ductile-to-brittle transition the transition from ductile to brittle behavior with a decrease in temperature exhibited by BCC alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests.
ductility a measure of a material's ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation or percent area reduction from a tensile test.
edge dislocation a linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra half-plane of atoms within a crystal; the Burgers vector is perpendicular to the dislocation line.
elastic deformation nonpermanent deformation, totally recovered upon release of an applied stress.
elastomer a polymeric material that may experience large and reversible elastic deformations.
electrodeposition (1) the deposition of a conductive material from a plating solution by the application of electrical current; (2) the deposition of a substance on an electrode by passing electric current through an electrolyte; electroplating, electroforming, electrorefining, and electrotwinning result from electrodeposition.
electrolyte a solution through which an electric current may be carried by the motion of ions.
electromagnetic radiation energy propagated at the speed of light by an electromagnetic field.
electronegative for an atom, having a tendency to accept valence electrons; also a term to describe non-metallic elements.
electropositive for an atom, having a tendency to release valence electrons; also a term to describe metallic elements.
equiaxed powder or grain shapes with approximately equal dimensions.
equilibrium (phase) the state of a system where the phase characteristics remain constant over indefinite time periods; at equilibrium the free energy is a minimum.
etching chemical surface corrosion, usually conducted in a controlled fashion on a polished surface of a material sample to reveal details of the microstructure.
eutectic upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases; the lowest melting composition in a material system.
eutectoid upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed.
extrusion a forming technique whereby a material is forced, by compression, through a die orifice.
face-centered cubic (FCC) a crystal structure found in some of the common elemental metals; within the cubic unit cell atoms are located at all corner and face-centered positions (figure). more
feeder part of the gating system that forms the reservoir of molten metal necessary to compensate for losses due to shrinkage as the metal solidifies; sometimes referred to as a riser.
ferrimagnetism permanent and large magnetizations found in some ceramic materials; it results from antiparallel spin coupling and incomplete magnetic moment cancellation.
ferrite (ceramic) ceramic oxide materials composed of both divalent and trivalent cations, some of which are ferrimagnetic.
ferrite (iron) body-centered cubic iron; also iron and steel alloys that have the BCC crystal structure.
ferroelectricity spontaneous alignment of electric dipoles within a material under the influence of an electric field, resulting in a hysteresis loop when the direction of electric field is switched.
ferromagnetism spontaneous alignment of magnetic dipoles within a material under the influence of a magnetic field, resulting in a hysteresis loop when the direction of magnetic field is switched.
ferrous alloy a metal alloy for which iron is the prime constituent.
Fick's first law the diffusion flux is proportional to the concentration gradient; this relationship is employed for steady-state diffusion situations.
Fick's second law the time rate of change of concentration is proportional to the second derivative of concentration; this relationship is employed in nonsteady-state diffusion situations.
firing a high temperature heat treatment that increases the density and strength of a ceramic piece.
flux chemically or physically active formulation capable of cleaning oxides and enabling wetting of metals with solder.
foam a polymer that has been made porous (or spongelike) by the incorporation of gas bubbles.
forging mechanical forming of a metal by heating and hammering.
fracture toughness .
free energy a thermodynamic quantity that is a function of both the internal energy and entropy (or randomness) of a system; at equilibrium the free energy is at a minimum.
Frenkel defect in an ionic solid, a cation-vacancy and cation-interstitial pair.
gall to damage the surface of a powder metallurgy compact or die part through adhesion of powder to the die cavity wall or punch surface.
galling (1) a condition whereby excessive friction between mating parts results in localized welding; subsequent spalling and a further roughening of the rubbing surfaces may follow; (2) a severe form of scuffing associated with gross damage to the surfaces or failure.
galvanic cell (1) a cell in which chemical change is the source of electrical energy; it usually consists of two dissimilar conductors in contact with each other and with an electrolyte, or of two similar conductors in contact with each other and with dissimilar electrolytes; (2) a cell or system in which a spontaneous oxidation-reduction reaction occurs, the resulting flow of electrons being conducted in an external part of the circuit.
galvanic corrosion corrosion associated with the current of a galvanic cell consisting of two dissimilar conductors in an electrolyte or two similar conductors in dissimilar electrolytes; where the two dissimilar metals are in contact, the resulting reaction is referred to as couple action.
galvanic couple a pair of dissimilar conductors, commonly metals, in electrical contact.
galvanic current the electric current that flows between metals or conductive nonmetals in a galvanic couple.
galvanize to coat a metal surface with zinc using various processes.
gamma iron the face-centered cubic form of pure iron, stable from 910 to 1400 C (1670 to 2550 F).
gamma ray short-wavelength electromagnetic radiation, similar to x-rays but of nuclear origin, with a range of wavelength from about 10-14 10-10 m.
gas metal arc welding an arc welding process that produces coalescence of metals by heating them with an arc between a continuous filler metal electrode and the workpieces; shielding is obtained entirely from an externally supplied gas.
gate the portion of the runner where the molten metal enters the mold cavity.
Gibbs free energy determines the relative stability of a material system at constant temperature and pressure;G = H - TS, where H is enthalpy, T is absolute temperature, and S is entropy of the system.
glass an amorphous material with three-dimensional primary atomic bonding. more
glass transition temperature the temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid into a rigid glass.
grain an individual crystal in a polycrystalline metal or ceramic.
Griffith Crack Theory click here for info.
Guinier-Preston (G-P) zone a small precipitation domain in a supersaturated metallic solid solution; it has no well-defined crystalline structure of its own and contains an abnormally high concentration of solute atoms; the formation of G-P zones constitutes the first stage of precipitation and is usually accompanied by a change in properties of the solid solution in which they occur.
hardenability a measure of the depth to which a specific ferrous alloy may be hardened by the formation of martensite upon quenching from a temperature above the upper critical temperature.
hardness the measure of a material's resistance to deformation by surface indentation or by abrasion.
heat capacity the quantity of heat required to produce a unit temperature rise per mole of material.
hermetic sealing of an object so it is airtight.
hexagonal close-packed (HCP) the unit cell is of hexagonal geometry and is generated by the stacking of close-packed planes of atoms. more
hot isostatic pressing (1) a process for simultaneously heating and forming a compact in which the powder is contained in a sealed flexible sheet metal or glass enclosure and subjected to equal pressure from all directions at a temperature high enough to permit plastic deformation and sintering; (2) a process that subjects a component (casting, powder forgins, etc.) to both elevated temperature and isostatic gas pressure in an autoclave; simultaneous application of heat and pressure virtually eliminates internal voids and microporosity through a combination of plastic deformation, creep, and diffusion.
hot pressing a method used to densify a material, whereby heat and pressure are applied simultaneously, and the pressure is typically applied unidirectionally via rigid tooling.
hot working any metal forming operation that is performed above a metal's recrystallization temperature.
hypereutectoid alloy for an alloy system displaying a eutectoid, an alloy for which the concentration of solute is greater than the eutectoid composition.
hypoeutectoid alloy for an alloy system displaying a eutectoid, an alloy for which the concentration of solute is less than the eutectoid composition.
hysteresis (magnetic) the irreversible magnetic flux density-versus-magnetic field strength (B-versus-H) behavior found for ferromagnetic and ferrimagnetic materials; a closed B-H loop is formed upon field reversal.
inclusion foreign particle present as an undesirable impurity in a material.
infrared reflow technique in which long wavelength light (IR) serves as the heat source to reflow solder and form solder joints.
inorganic flux an aqueous flux solution of inorganic acids and halides.
insulator (electric) a nonmetallic material that has a filled valence band at 0 K and a relatively wide energy band gap; consequently the room-temperature electrical conductivity is very low.
integrated circuit a microcircuit that consists of interconnected elements inseparably associated and formed in-situ on or within a single substrate, usually silicon, to perform an electronic circuit function.
interdiffusion diffusion of atoms of one metal into another metal.
intergranular fracture fracture of polycrystalline materials by crack propagation along grain boundaries.
intermediate solid solution a solid solution or phase having a composition range that does not extend to either of the pure components of the system.
interstitial site octahedral and tetrahedral open spaces within a close-packed arrangment of atoms or ions in which a cation can fit.
interstitial solid solution a solid solution wherein relatively small solute atoms occupy interstitial positions between the solvent or host atoms.
investment casting this process is based on surrounding (investing) an expendable pattern, typically wax, with a ceramic mold and then removing (by melting or vaporizing) the pattern prior to pouring molten alloy into the mold; also known as lost wax and precision casting. more
ion an atom with a positive charge because it has had electrons removed or a negative charge because it has had electrons added.
ionic bonding a coulombic interatomic bond that exists between two adjacent and oppositely charged ions; one of the primary types of atomic bonding in ceramics.
isomerism the phenomenon whereby two or more polymer molecules or mer units have the same composition but different structural arrangements and properties.
isotactic a type of polymer chain configuration where all side groups are positioned on the same side of the chain molecule.
isothermal at a constant temperature.
isotropic having identical values of a property in all crystallographic directions.
Izod test a type of impact test in which a V-notched specimen, mounted vertically, is subjected to a sudden blow delivered by the weight at the end of a pendulum arm; the energy required to break off the free end is a measure of the impact strength or toughness of the material.
Jominy end quench test click here
killed steel steel treated with a strong deoxidizing agent, such as aluminum or silicon, in order to reduce the oxygen content to a level so no reaction occurs between carbon and oxygen during solidification.
kiln a furnace in which ceramics are fired.
Knoop hardness test an indentation hardness test using calibrated machines to force a rhombic-based pyramidal diamond indenter having specified edge angles, under specified conditions, into the surface of the test material and to measure the long diagonal after load removal.
lapping a surface finishing operation used to achieve a fine polish and close tolerances.
laser acronym for light amplification by stimulated emission of radiation; a source of concentrated coherent light generated by stimulating electronic or molecular transitions to lower energy levels.
laser soldering method of soldering in which the heat required to reflow a solder interconnection is provided by a laser (YAG or CO2); the solder joints are heated sequentially and cooled rapidly.
latent heat the thermal energy absorbed or released when a material experiences a phase change.
lattice the space arrangement of atoms in a crystal.
lattice parameter the length of any side in a crystal structure's unit cell.
leaching process of liquid solder dissolving a metal coating.
lead a wire that connects two points in a circuit; it is usually self-supporting.
lever rule in a phase diagram, the relative proportions of the conjugate phases, at a stated value of temperature and pressure, or both, is such that a state of mechanical balance would obtain, if the corresponding weight of each phase were placed upon its composition point upon the tie-element (tie-line, tie-triangle, etc.) and the fulcrum were located at the gross composition point of the mixture.
light metal one of the low-density metals, such as aluminum, magnesium, titanium, beryllium, or their alloys.
liquidus the line on the phase equilibrium diagram above which only liquids are stable and below which some solid is present; the lowest temperature at which a metal or alloy is completely liquid.
Luder bands elongated surface markings or depressions in sheet metal caused by discontinuous yielding.
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.
necking reduction of the cross-sectional area of a material in a localized area caused by uniaxial tension.
network polymer a polymer composed of trifunctional mer units that form three-dimensional molecules.
Neumann's Law the symmetry of the physical properties of a crystal must include the symmetry of the point group of the crystal.
noble metal a metal with high resistance to chemical reaction, especially oxidation and solution by organic acids; sometimes called a precious metal.
noncrystalline the solid state wherein there is no long-range atomic order; sometimes the terms amorphous, glassy, and vitreous are used synonymously.
nondestructive testing (NDT) a procedure for determining the quality or characteristics of a material, part, or assembly without permanently altering it or its properties; examples include ultrasonic and radiographic inspection.
nonsteady-state diffusion the diffusion condition for which there is some net accumulation or depletion of diffusing species; the diffusion flux is dependent on time.
normalizing for ferrous alloys, austenitizing above the upper critical temperature, then cooling in air; the objective of this heat treatment is to enhance toughness by refining the grain size.
nucleation the initial stage in a phase transformation; it is evidenced by the formation of small particles (nuclei) of the new phase which are capable of growing.
octahedral position the void space among close-packed, hard sphere atoms or ions for which there are six nearest neighbors; an octahedron (double pyramid) is circumscribed by the lines constructed from centers of adjacent spheres.
ordering positioning of host and substitution ions in an ordered, repetitious pattern rather than in a random arrangement.
ore a natural mineral mined and treated for extraction of its components.
orientation arrangements in space of the axes of a crystal lattice with respect to a coordinate system.
outgassing gaseous emission or de-aeration of a material.
oxidation a reaction in which there is an increase in valence resulting from a loss of electrons; often associated with the corrosion of metals, where the corroded metal forms an oxide; elevated temperatures increase the rate of oxidation.
paramagnetism property of a material that, when placed in a magnetic field, is magnetized parallel to the field to an extent proportional to the field; this does not apply at very low temperatures or in extremely large magnetic fields.
Peierls stress the stress required to move a dislocation.
peritectic an isothermal reversible reaction in metals where a liquid phase reacts with a solid phase to produce a single (and different) solid phase upon cooling. more
peritectoid an isothermal reversible reaction where a solid phase reacts with a second solid phase to produce a single (and different) solid phase upon cooling. more
permeability (1) passage or diffusion of a gas, vapor, liquid, or solid through a material without physically or chemically affecting it; (2) term used to express various relationships between magnetic induction and magnetizing force; either absolute permeability or specific (relative) permeability.
pewter tin-base white metal containing antimony and copper; 1 to 8% Sb and 0.25 to 3% Cu.
pH the negative logarithm of hydrogen-ion activity denoting the degree of acidity or basicity of a solution; at 25 degrees C 7.0 (on a scale of 0 to 14) is the neutral value, with decreasing values below 7.0 indicating increasing acidity, and increasing values above 7.0 indicating increasing basicity.
phase a portion of a material system whose properties and composition are homogeneous and which is physically distinct from other parts of the system. more
phase diagram graphical representation of the temperature and composition limits of phase fields in an alloy or ceramic system; it can be an equilibrium diagram, approximation to an equilibrium diagram, or a representation of metastable conditions or phases. more
phase rule this states that the maximum number of phases (P) that may coexist at equilibrium is two plus the number of components (C) in the mixture minus the number of degrees of freedom (F): P + F = C + 2.
phase transformation changes that can occur within a given material system; how one or more phases in an alloy change into a new phase or mixture of phases; transformation occurs because the initial state of the alloy is unstable relative to the final state; at constant temperature and pressure the relative stability of a system is determined by its Gibbs free energy.
photolithography science of replicating complex circuitry onto the surface of a specimen.
pickling the chemical removal of surface oxides and other contaminants from a material by immersion in an aqueous acid solution; sulfuric and hydrochloric acids are common pickling solutions.
piezoelectricity elastic strain caused when an electrical current is applied to a piezoelectric material and conversely, an electric current produced when pressure is applied to a piezoelectric material; these materials exhibit the Perovskite crystal structure.
pig a metal casting used in remelting.
plane strain thin plate and sz = 0; 2D strain / 3D stress. (see Griffith Crack Theory)
plane stress thick sections; 2D stress / 3D strain. (see Griffith Crack Theory)
plastic deformation the permanent (inelastic) distortion of a material under an applied stress that strains the material beyond its elastic limit; the ability of a material to be permanently deformed without fracture.
plating forming an adherent layer of metal on an object; often used as a shop term for electroplating.
Poisson's ratio the ratio of the transverse contracting strain to the longitudinal elongational strain when a tensile stress is applied to a material.
polarization displacement of the centers of positive and negative charge.
polyimide thermosetting ring chain polymer characterized by -NH group; it's increasingly used as dielectrics in high performance circuits.
polymorphism different crystal structures at different temperatures or pressures for a single compound.
porosity fine holes, voids, interstitials, or open spaces between grains or trapped in grains of a material's microstructure.
precipitation in metals, the separation of a new phase from solid or liquid solution, usually with changing conditions of temperature, pressure, or both.
precipitation hardening increase the hardness of a supersaturated solid solution by heat treating it to cause a second phase to precipitate out; coherency of the precipitate/matrix interface and how well the two lattices match up greatly influence the effect of precipitate.
precipitation heat treatment artificial aging of metals in which a constituent precipitates from a supersaturated solid solution.
quench rapidly cool a material; typically done to retain a structure at room temperature that otherwise is only stable at high temperature.
radioactivity spontaneous decay of some isotopes in nuclei.
radiography nondestructive method of internal examination in which metal objects are exposed to a beam of X-ray or gamma radiation; differences in thickness, density, or absorption caused by internal defects or inclusions are apparent in the shadow image produced on a fluorescent screen or photographic film placed behind the object.
reciprocal lattice a group of points arranged about a center in such a way that the line joining each point of the center is perpendicular to a family of planes in the crystal, and the length of this line is inversely proportional to their interplanar distance.
reflow soldering process of joining metallic surfaces through the mass heating of solder/solder paste to form solder fillets at metallized areas; it creates a mechanical and electrical connection between components and a PCB.
refractory a heat-resistant material.
residual stress internal stress in a material often resulting from thermal or mechanical straining.
resilience the tendency of a material to return to its original shape after the removal of a stress that has produced elastic strain.
resin an organic polymer that crosslinks to form a thermosetting plastic when mixed with a curing agent.
resin flux a resin and small amounts of organic activators in an organic solvent.
resistance welding type of welding process in which the work pieces are heated by the passage of an electric current through the contact; this includes spot welding, seam or line welding, and percussion welding; flash and butt welding are sometimes considered as resistance welding processes.
rheology study of flow characteristics.
rosin a hard, natural resin, consisting of abietic acid and pimaric acids and their isomers, some fatty acids, and terepene hydrocarbons; the resin is extracted from pine trees and subsequently refined.
rosin flux rosin in an organic solvent or rosin as a paste with activators.
saponifier an alkaline chemical added to water to improve its ability to dissolve rosin flux residues.
sintering densification of a particulate ceramic compact involving a removal of the pores between the starting particles (accompanied by equivalent shrinkage) combined with coalescence and strong bonding between adjacent particles.
solder a low melting point alloy, usually of lead (Pb) and tin (Sn), that can wet copper, conduct current, and mechanically join conductors.
solder balls small spheres of solder adhering to the laminate, mask, or conductor surfaces usually after wave or reflow soldering.
solder bridging when solder paste or solder on two or more adjacent pads come into contact to form a conductive path or bridge.
solder mask a dielectric material used to cover the entire surface (except where the joints are to be formed) of a PCB primarily to protect the circuitry from environmental damage; it also helps to reduce bridging.
solder paste mixture of minute spherical solder particles, activators, solvent, and a gelling or suspension agent.
soldering process of joining metallic surfaces with solder without melting the base material.
solid solution a single, solid, homogeneous crystalline phase containing two or more chemical species.
solidification the change from liquid state to solid state upon cooling through the melting temperature or melting range.
solidification range the temperature between the liquidus and solidus.
solidification shrinkage crack a crack that forms due to internal stresses developed from shrinkage during solidification of a metal casting; also called a hot crack.
solidus the temperature in a phase equilibrium diagram below which no liquids are present; the highest temperature at which a metal or alloy is completely solid.
solution heat treatment heating an alloy to a suitable temperature, holding at that temperature for enough time to allow one or more constituents to enter into solid solution, and then rapidly cooling to hold the consituents in solution.
solvent solution capable of dissolving a solute.
solvus the curve on a phase equilibrium diagram that defines the limits of solid solubility.
spinodal structure a fine homogeneous mixture of two phases that form by growth of composition waves in a solid solution during suitable heat treatment; the phases differ in composition from each other and the parent phase, but have the same crystal structure as the parent phase.
stainless steel any steel containing at least 10.5% Cr as the principal alloying element.
steel an iron-based alloy containing manganese, usually carbon, and other alloying elements.
stoichiometry refers generally to the composition of a material and specifically to the relative atomic proportions of cations and anions.
strain the unit of change in the size or shape of a body due to force; a dimensionless number that characterizes the change in dimensions of an object during a deformation or flow process.
stress (s) force per unit area.
stress intensity factor (K) a scale factor to define the magnitude of the crack-tip stress field; the functionality depends on the configuration of the cracked component and the manner in which the loads are applied. (see Griffith crack theory)
surface insulation resistance the electrical resistance of an insulating material between a pair of contacts or conductors; SIR is determined under specified environmental and electrical conditions.
surface mount technology method of assembling printed circuit boards where the components are mounted onto the surface of the board rather than being inserted into holes in the board.
thermal expansion change in dimensions of a material resulting from a change in temperature.
thermal shock stresses induced in a material because of a rapid temperature change or a thermal gradient.
toughness a measure of the energy absorbed before and during the fracture process; it is equal to the area under the tensile stress-strain curve.
transgranular through or across crystals or grains; also called intracrystalline or transcrystalline.
transition metal a metal having available electron energy levels occupied so that the d-band contains less than its maximum number of ten electrons per atom; the incompletely filled d-levels cause the unique properties of the transition metals; included in this class are iron, cobalt, nickel, and tungsten. more
transition temperature an arbitrarily defined temperature that lies within the temperature range where metal fracture characteristics change rapidly; an example is the ductile-to-brittle transition temperature (DBTT).
tribology the science and technology of interacting surfaces in relative motion and of the practices related thereto; the science concerned with the design, friction, lubrication, and wear of contacting surfaces that move relative to one another (e.g. bearings, cams, gears). more
triclinic having three axes of any length with none of the included angles being equal to one another or 90 degrees.
true strain the ratio of the change in dimension, resulting from a given load, to the magnitude of the dimension immediately prior to applying the load; the natural logarithm of the ratio of the gage length at the moment of observation to the original gage length.
true stress the load applied to a material divided by the cross sectional area over which it acts.
twin two portions of a crystal with a definite orientation relationship; the orientation of one portion is a mirror image of the orientation of the other portion across a twinning plane or an orientation derived by rotating one portion about a twinning axis.
twin bands bands across a crystal grain where crystallographic orientations have a mirror image relationship to the orientation of the matrix grain across a composition plane usually parallel to the sides of the band.
under-cooling cooling a material below the temperature of an equilibrium phase change fast enough to not allow the occurrence of the transformation.
unit cell the smallest repetitive volume that comprises the complete pattern of a crystal.
vacancy an unfilled lattice site in a crystal structure.
valence the charge on an ion based on the number of electrons transferred or shared within a specific structure.
virgin a metal made directly from ore by smelting.
viscosity coefficient of resistance to flow.
welding the joining of two metal surfaces that have been heated, melted, and fused together.
work angle in arc welding, the angle between the electrode and one of the joints.
work hardening (strain hardening) increase dislocation density in metals through straining a material with an applied stress; degree of hardening may be manipulated through recovery and recrystallization.
wrought alloy an alloy that is suitable for mechanical forming below melting-point temperatures.
wrought iron commercial iron that contains less than 0.3% carbon and 1.0 or 2.0% slag, giving it ductility and toughness.
X-radiation electromagnetic radiation of the same nature as visible light, but having a wavelength approximately one thousandth that of visible light.
X-ray tube a device that produces X-rays by the impact of high-speed electrons on a metal target.
zone any group of crystal planes that are all parallel to one line, called the zone axis.