Test 2

grain growth

The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary.

ductile fracture

A mode of fracture attended by extensive gross plastic deformation.

brittle fracture

Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation.

transgranular fracture

Fracture of polycrystalline materials by crack propagation through the grains.

intergranular fracture

Fracture of polycrystalline materials by crack propagation along grain boundaries.

fracture mechanics

A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.

fracture toughness

The measure of a material's resistance to fracture when a crack is present.

Charpy test

One of two tests (see also Izod test) that may be used to measure the impact energy or notch toughness of a standard notched specimen.

Izod test

One of two tests (see also Charpy test) that may be used to measure the impact energy of a standard notched specimen.

impact energy (notch toughness)

A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading.

ductile-to-brittle transition

The transition from ductile to brittle behavior with a decrease in temperature exhibited by some low-strength steel (BCC) alloys.

fatigue

Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses.

fatigue limit

The maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles without failing.

fatigue strength

The maximum stress level that a material can sustain without failing for a specified number of cycles.

fatigue life

The total number of stress cycles that cause a fatigue failure at some specified stress amplitude.

case hardening

Hardening of the outer surface of a steel component by a carburizing or nitriding process.

thermal fatigue

A type of fatigue failure in which the cyclic stresses are introduced by fluctuating thermal stresses.

corrosion fatigue

A type of failure that results from the simultaneous action of a cyclic stress and chemical attack.

creep

The time-dependent permanent deformation that occurs under stress; important at elevated temperatures.

component

A chemical constituent (element or compound) of an alloy used to specify its composition.

system

A specific body of material or a series of possible alloys consisting of the same components.

solubility limit

The maximum concentration of solute that may be added without forming a new phase.

phase

A homogeneous portion of a system that has uniform physical and chemical characteristics.

equilibrium (phase)

The state of a system in which the phase characteristics remain constant over indefinite time periods.

free energy

A thermodynamic quantity that is a function of both internal energy and entropy of a system.

phase equilibrium

The state of a system at equilibrium regarding its phases.

metastable

A nonequilibrium state that may persist for a very long time.

phase diagram

A graphical representation of the relationships among environmental constraints, composition, and regions of phase stability.

isomorphous

Having the same structure; in the phase diagram sense, having the same crystal structure or complete solid solubility.

tie line

A horizontal line across a two-phase region of a binary phase diagram indicating equilibrium compositions.

lever rule

A mathematical expression to compute phase amounts in a two-phase alloy at equilibrium.

solvus line

The locus of points on a phase diagram representing the limit of solid solubility as a function of temperature.

solidus line

On a phase diagram, the locus of points at which solidification or melting begins during equilibrium cooling.

liquidus line

On a binary phase diagram, the line separating liquid and liquid + solid-phase regions.

eutectic reaction

A reaction where a liquid phase transforms isothermally and reversibly into two solid phases upon cooling.

eutectic structure

A two-phase microstructure resulting from the solidification of a liquid having the eutectic composition.

eutectic phase

One of the two phases found in the eutectic structure.

primary phase

A phase that exists in addition to the eutectic structure.

microconstituent

An element of the microstructure with identifiable structure, potentially consisting of more than one phase.

terminal solid solution

A solid solution that exists over a composition range extending to either composition extreme of a binary phase diagram.

intermetallic compound

A compound of two metals that has a distinct chemical formula, appearing as an intermediate phase on a phase diagram.

eutectoid reaction

A reaction where one solid phase transforms isothermally and reversibly into two new solid phases upon cooling.

peritectic reaction

A reaction in which a solid and a liquid phase transform into a different solid phase upon cooling.

congruent transformation

A transformation of one phase to another of the same composition.

Gibbs phase rule

An equation that expresses the relationship between the number of phases present and the number of externally controllable variables.

ferrite (ceramic)

Ceramic oxide materials composed of both divalent and trivalent cations.

austenite

Face-centered cubic iron; also iron and steel alloys that possess the FCC crystal structure.

cementite

Iron carbide (Fe3C).

pearlite

A two-phase microstructure found in steels and cast irons, consisting of alternating layers of ferrite and cementite.

hypoeutectoid alloy

An alloy for which the concentration of solute is less than the eutectoid composition.

proeutectoid ferrite

Primary ferrite that exists alongside pearlite for hypoeutectoid steels.

proeutectoid cementite

Primary cementite that exists alongside pearlite for hypereutectoid steels.

transformation rate

The reciprocal of the time necessary for a reaction to proceed halfway to completion.

phase transformation

A change in the number and/or character of the phases that constitute the microstructure of an alloy.

nucleation

The initial stage in a phase transformation indicated by the formation of small particles of the new phase.

growth (particle)

The increase in size of a particle of a new phase during a phase transformation.

kinetics

The study of reaction rates and the factors that affect them.

thermally activated transformation

A reaction that depends on atomic thermal fluctuations to occur.

supercooling

Cooling to below a phase transition temperature without the occurrence of the transformation.

superheating

Heating to above a phase transition temperature without the occurrence of the transformation.

isothermal transformation (TTT diagram)

A plot of temperature vs. the logarithm of time for a steel alloy used to determine when transformations begin and end.

coarse pearlite

Pearlite with relatively thick alternating ferrite and cementite layers.

fine pearlite

Pearlite with relatively thin alternating ferrite and cementite layers.

bainite

An austenitic transformation product found in steels and cast irons that forms between pearlite and martensite temperatures.

spheroidite

Microstructure consisting of spherelike cementite particles within a ferrite matrix.

martensite

A metastable iron phase supersaturated in carbon, resulting from a diffusionless transformation from austenite.

athermal transformation

A nonthermally activated reaction, typically diffusionless and occurring quickly.

plain carbon steel

A ferrous alloy where carbon is the primary alloying element.

alloy steel

A ferrous alloy containing appreciable concentrations of alloying elements to improve properties.

continuous-cooling transformation (CCT) diagram

A plot indicating when transformations occur during continuous cooling of a steel alloy.

tempered martensite

The product of tempering heat treatment of martensitic steel, consisting of small, uniformly dispersed cementite particles.

ferrous alloy

A metal alloy for which iron is the prime constituent.

high-strength, low-alloy (HSLA) steel

Strong, low-carbon steels with less than about 10 wt% total of alloying elements.

stainless steel

A steel alloy highly resistant to corrosion, predominantly alloyed with chromium.

cast iron

A ferrous alloy with carbon content greater than the maximum solubility in austenite at the eutectic temperature.

gray cast iron

A cast iron alloyed with silicon where graphite exists in the form of flakes.

ductile iron

A cast iron alloyed with silicon and magnesium/cerium, with free graphite in nodular form.

white cast iron

A low-silicon, very brittle cast iron where carbon is in a combined form as cementite.

malleable cast iron

White cast iron heat-treated to convert cementite into graphite clusters, resulting in a relatively ductile form.

compacted graphite iron

A cast iron with silicon and magnesium, where graphite exists as wormlike particles.

wrought alloy

A metal alloy that is ductile and can be worked during fabrication.

brass

A copper-rich copper-zinc alloy.

bronze

A copper-rich copper-tin alloy; can also include aluminum, silicon, and nickel bronzes.

temper designation

A letter-digit code designating the treatment of a metal alloy.

specific strength

The ratio of tensile strength to specific gravity for a material.

nonferrous alloys

Alloys in which iron is not the prime constituent.

hot working

Metal-forming operations performed above a metal's recrystallization temperature.

cold working

Plastic deformation of a metal at a temperature below that at which it recrystallizes.

forging

Mechanical forming of metal by heating and hammering.

rolling

Metal-forming operation that reduces thickness of sheet stock by using grooved rolls.

extrusion

A forming technique in which material is forced through a die orifice.

drawing (metals)

Technique to fabricate metal wire and tubing by pulling material through a die.

powder metallurgy (P/M)

Fabrication of metal pieces from compacted metal powders followed by heat treatment.

welding

A technique for joining metals by melting the pieces to be joined, possibly using filler metal.

annealing

A heat treatment process altering the microstructure and properties of a material.

process annealing

Annealing of previously cold-worked products below the lower critical temperature.

stress relief

A heat treatment to remove residual stresses in materials.

lower critical temperature

Temperature below which, under equilibrium conditions, all austenite transforms into ferrite and cementite.

upper critical temperature

Minimum temperature above which, under equilibrium conditions, only austenite is present.

normalizing

For ferrous alloys, austenitizing above the upper critical temperature, then cooling in air.