glossary材料术语 英文版.pdf

GlossaryAAbrasive.A hard and wear-resis-tantmaterial(commonlyaceramic)that is used to wear,grind,or cutaway other material.Absorption.The optical phenome-nonwherebytheenergyofaphotonof light is assimilated within asubstance,normally by electronicpolarization or by an electron exci-tation event.Acceptor level.For a semiconduc-tor or insulator,an energy level ly-ing within yet near the bottom ofthe energy band gap,which may ac-cept electrons from the valenceband,leaving behind holes.Thelevel is normally introduced by animpurity atom.Activation energy(Q).The energyrequired to initiate a reaction,suchas diffusion.Activation polarization.The con-dition wherein the rate of an elec-trochemical reaction is controlledby the one slowest step in a se-quence of steps that occur in series.Addition(or chain reaction)poly-merization.The process by whichbifunctional monomer units areattached one at a time,in chainlikefashion,to form a linear polymermacromolecule.Adhesive.A substance that bondstogether the surfaces of two othermaterials(termed adherends).Age hardening.See Precipitationhardening.Allotropy.The possibility of exis-tence of two or more differentcrystal structures for a substance(generally an elemental solid).Alloy.A metallic substance that iscomposed of two or more elements.480Alloy steel.A ferrous(or iron-based)alloy that contains appre-ciable concentrations of alloyingelements(otherthanCandresidualamounts of Mn,Si,S,and P).Thesealloying elements are usually addedto improve mechanical and corro-sion resistance properties.Alternating copolymer.A copoly-merinwhichtwodifferentmerunitsalternate positions alongthe molec-ular chain.Amorphous.Having a noncrystal-line structure.Anelasticdeformation.Time-de-pendentelastic(nonpermanent)de-formation.Anion.A negatively charged,non-metallic ion.Anisotropic.Exhibitingdifferentvalues of a property in differentcrystallographic directions.Annealing.A generic term used todenote a heat treatment whereinthemicrostructureand,conse-quently,thepropertiesofamaterialarealtered.Annealingfre-quently refers to a heat treatmentwhereby a previously cold-workedmetal is softened by allowing it torecrystallize.Annealing point(glass).That tem-perature at which residual stressesin a glass are eliminated withinabout 15 min;this corresponds toa glass viscosity of about 1012Pa-s(1013P).Anode.The electrode in an elec-trochemical cell or galvanic couplethat experiences oxidation,or givesup electrons.Antiferromagnetism.A phenome-non observed in some materials(e.g.,MnO);complete magneticmoment cancellation occurs as aresult of antiparallel coupling ofadjacent atoms or ions.The macro-scopic solid possesses no net mag-netic moment.Artificial aging.For precipitationhardening,aging above room tem-perature.Atactic.A type of polymer chainconfiguration wherein side groupsare randomly positioned on oneside of the chain or the other.Athermal transformation.A reac-tion that is not thermally activated,andusuallydiffusionless,aswiththemartensitictransformation.Nor-mally,thetransformationtakesplace with great speed(i.e.,is inde-pendent of time),and the extent ofreaction depends on temperature.Atomic mass unit(amu).A mea-sure of atomic mass;one twelfth ofthe mass of an atom of C12.Atomic number(Z).For a chemi-cal element,the number of protonswithin the atomic nucleus.Atomic packing factor(APF).Thefraction of the volume of a unit cellthat is occupied by hard sphereatoms or ions.Atomic vibration.The vibration ofan atom about its normal positionin a substance.Atomic weight(A).The weightedaverage of the atomic masses of anatoms naturally occurring isotopes.It may be expressed in terms ofatomic mass units(on an atomicbasis),or the mass per mole ofatoms.Atom percent(at%).Concentra-tion specification on the basis of thenumber of moles(or atoms)of aparticular element relative to theGlossary481total number of moles(or atoms)of all elements within an alloy.Austenite.Face-centeredcubiciron;also iron and steel alloys that havethe FCC crystal structure.Austenitizing.Formingausteniteby heating a ferrous alloy above itsuppercriticaltemperaturetowithin the austenite phase regionfrom the phase diagram.BBainite.An austenitic transforma-tion product found in some steelsand cast irons.It forms at tempera-tures between those at which pearl-ite and martensite transformationsoccur.The microstructure consistsof?-ferrite and a fine dispersionof cementite.Band gap energy(Eg).For semi-conductorsandinsulators,theener-gies that lie between the valenceand conduction bands;for intrinsicmaterials,electrons are forbiddento have energies within this range.Bifunctional.Designatingmono-merunitsthathavetwoactivebond-ing positions.Block copolymer.A linear copoly-mer in which identical mer units areclustered in blocksalong the molec-ular chain.Body-centeredcubic(BCC).Acommon crystal structure found insome elemental metals.Within thecubic unit cell,atoms are located atcorner and cell center positions.Bohratomicmodel.Anearlyatomic model,in which electronsare assumed to revolve around thenucleus in discrete orbitals.Bohr magneton(?B).The mostfundamental magnetic moment,ofmagnitude 9.27?10?24A-m2.Boltzmanns constant(k).A ther-mal energy constant having thevalue of 1.38?10?23J/atom-K(8.62?10?5eV/atom-K).See alsoGas constant.Bonding energy.The energy re-quired to separate two atoms thatare chemically bonded to eachother.It may beexpressed on a per-atom basis,or per mole of atoms.Braggs law.A relationship?(Equa-tion 3.10)?which stipulates the con-ditionfordiffractionbyasetofcrys-tallographic planes.Branchedpolymer.Apolymerhaving a molecular structure of sec-ondary chains that extend from theprimary main chains.Brass.A copper-rich copperzincalloy.Brazing.A metal joining techniquethat uses a molten filler metal alloyhavingameltingtemperaturegreater than about 425?C(800?F).Brittle fracture.Fracture that oc-cursbyrapidcrackpropagationandwithout appreciable macroscopicdeformation.Bronze.A copper-rich coppertinalloy;aluminum,silicon,and nickelbronzes are also possible.Burgers vector(b).A vector thatdenotes the magnitude and direc-tion of lattice distortion associatedwith a dislocation.CCalcination.Ahigh-temperaturereactionwherebyonesolidmaterialdissociates to form a gas and an-other solid.It is one step in the pro-duction of cement.Capacitance(C).The charge-stor-ing ability of a capacitor,defined asthe magnitude of charge stored oneither plate divided by the appliedvoltage.Carbon-carbon composite.A com-posite that is composed of continu-ous fibers of carbon that are imbed-ded in a carbon matrix.The matrixwas originally a polymer resin thatwassubsequentlypyrolyzedtoform carbon.Carburizing.The process by whichthe surface carbon concentration ofa ferrous alloy is increased by diffu-sion from the surrounding envi-ronment.Case hardening.Hardening of theouter surface(or case)of a steelcomponent by a carburizing or ni-triding process;used to improvewear and fatigue resistance.Cast iron.Generically,a ferrousalloy,the carbon content of whichis greater than the maximum solu-bility in austenite at the eutectictemperature.Most commercial castirons contain between 3.0 and 4.5wt%C,andbetween1and 3wt%Si.Cathode.The electrode in an elec-trochemical cell or galvanic coupleat which a reduction reaction oc-curs;thus the electrode that re-ceives electrons from an externalcircuit.Cathodic protection.A means ofcorrosion prevention whereby elec-trons are supplied to the structureto be protected from an externalsource such as another more reac-tive metal or a dc power supply.Cation.A positively charged me-tallic ion.Cement.A substance(often a ce-ramic)that by chemical reactionbinds particulate aggregates into acohesive structure.With hydrauliccements the chemical reaction isone of hydration,involving water.Cementite.Iron carbide(Fe3C).Ceramic.A compound of metallicandnonmetallicelements,forwhich the interatomic bonding ispredominantly ionic.Ceramic-matrix composite(CMC).A composite for which both matrixand dispersed phases are ceramicmaterials.The dispersed phase isnormally added to improve frac-ture toughness.Cermet.Acompositematerialcon-sisting of a combination of ceramicand metallic materials.The mostcommon cermets are the cementedcarbides,composed ofanextremelyhardceramic(e.g.,WC,TiC),bonded together by a ductile metalsuch as cobalt or nickel.Chain-folded model.For crystal-line polymers,a model that de-scribes the structure of plateletcrystallites.Molecular alignment isaccomplished by chain folding thatoccurs at the crystallite faces.Charpy test.One of two tests(seealso Izod test)that may be used tomeasuretheimpactenergyornotchtoughness of a standard notched482Glossaryspecimen.An impact blow is im-parted to the specimen by means ofa weighted pendulum.Cis.For polymers,a prefix denot-ing a type of molecular structure.For some unsaturated carbon chainatomswithinamerunit,asideatomor group may be situated on onesideofthechainordirectlyoppositeat a 180?rotation position.In a cisstructure,two such side groupswithin the same mer reside on thesame side(e.g.,cis-isoprene).Coarse pearlite.Pearlite for whichthe alternating ferrite and cement-ite layers are relatively thick.Coercivity(orcoercivefield,Hc).The applied magnetic fieldnecessarytoreducetozerothemag-netic flux density of a magnetizedferromagnetic or ferrimagnetic ma-terial.Cold working.The plastic defor-mation of a metal at a temperaturebelow that at which it recrystallizes.Color.Visual perception that isstimulated by the combination ofwavelengths of light that are trans-mitted to the eye.Colorant.An additive that impartsa specific color to a polymer.Component.Achemicalconsti-tuent(element or compound)of analloy,which may be used to specifyits composition.Composition(Ci).Therelativecontent of a particular element orconstituent(i)within an alloy,usu-ally expressed in weight percent oratom percent.Concentration.See Composition.Concentration gradient(dC/dx).The slope of the concentration pro-file at a specific position.Concentrationpolarization.Thecondition wherein the rate of anelectrochemical reaction is limitedby the rate of diffusion in the so-lution.Concentration profile.The curvethat results when the concentrationof a chemical species is plotted ver-sus position in a material.Concrete.Acompositematerialconsisting of aggregate particlesbound together in a solid body bya cement.Condensation(orstepreaction)po-lymerization.Theformationofpolymer macromolecules by an in-termolecular reaction involving atleast two monomer species,usuallywith the production of a by-productof low molecular weight,such aswater.Conduction band.For electrical in-sulators and semiconductors,thelowest lying electron energy bandthat is empty of electrons at 0 K.Conduction electrons arethose thathave been excited to states withinthis band.Conductivity,electrical(?).Theproportionality constant betweencurrent density and applied electricfield;alsoameasureoftheeasewithwhich a material is capable of con-ducting an electric current.Congruenttransformation.Atrans-formation of one phase to anotherof the same composition.Continuous cooling transformation(CCT)diagram.Aplotoftempera-tureversusthelogarithmoftimeforasteelalloyofdefinitecomposition.Used to indicate when transforma-tions occur as the initially austenit-ized material iscontinuously cooledat a specified rate;in addition,thefinalmicrostructureandmechanicalcharacteristics may be predicted.Coordination number.The num-ber of atomic or ionic nearestneighbors.Copolymer.A polymer that con-sists of two or more dissimilar merunits in combination along its mo-lecular chains.Corrosion.Deteriorative loss of ametal as a result of dissolution envi-ronmental reactions.Corrosionfatigue.Atypeoffailurethat results from the simultaneousaction of a cyclic stress and chemi-cal attack.Corrosion penetration rate(CPR).Thickness loss of material per unitof time as a result of corrosion;usu-ally expressed in terms of mils peryear or millimeters per year.Coulombic force.A force betweencharged particles such as ions;theforceisattractivewhentheparticlesare of opposite charge.Covalentbond.Aprimaryin-teratomic bond that is formed bythe sharing of electrons betweenneighboring atoms.Creep.The time-dependent per-manentdeformationthatoccursun-der stress;for most materials it isimportantonlyatelevatedtempera-tures.Crevice corrosion.A form of cor-rosion that occurs within narrowcrevices and under deposits of dirtor corrosion products(i.e.,in re-gions of localized depletion of oxy-gen in the solution).Criticalresolvedshearstress(?crss).That shear stress,resolvedwithin a slip plane and direction,which is required to initiate slip.Crosslinkedpolymer.Apolymerinwhich adjacent linear molecularchains are joined at various posi-tions by covalent bonds.Crystalline.Thestateofasolidma-terial characterized by a periodicandrepeatingthree-dimensionalarray of atoms,ions,or molecules.Crystallinity.Forpolymers,thestate wherein a periodic and re-peatingatomicarrangementisachievedbymolecularchainalignment.Crystallite.A region within a crys-talline polymer in which all the mo-lecularchains areordered andaligned.Crystal structure.For crystallinematerials,the manner in whichatoms or ions are arrayed in space.It is defined in terms of the unit cellgeometry and the atom positionswithin the unit cell.Crystal system.A scheme by whichcrystal structures are classified ac-cording to unit cell geometry.Thisgeometryis specifiedinterms oftherelationships between edge lengthsand interaxial angles.There areseven different crystal systems.Curie temperature(Tc).That tem-perature above which a ferromag-Glossary483netic or ferrimagnetic material be-comes paramagnetic.DDefect structure.Relating to thekinds and concentrations of vacan-cies and interstitials in a ceramiccompound.Degradation.A term used to de-note the deteriorative processesthatoccurwithpolymericmaterials.These processes include swelling,dissolution,and chain scission.Degree of polymerization.The av-eragenumberofmerunitsperpoly-mer chain molecule.Design stress(?d).Product of thecalculated stress level(on the basisof estimated maximum load)and adesign factor(which has a valuegreater than unity).Used to protectagainst unanticipated failure.Devitrification.Theprocessinwhich a glass(noncrystalline or vit-reous solid)transforms to a crystal-line solid.Diamagnetism.A weak form of in-duced or nonpermanent magnetismfor which the magnetic susceptibil-ity is negative.Dielectric.Any materialthat iselectrically insulating.Dielectric constant(?r).The ratioof the permittivity of a medium tothat of a vacuum.Often called therelative dielectric constant or rela-tive permittivity.Dielectric displacement(D).Themagnitude of charge per unit areaof capacitor plate.Dielectric(breakdown)strength.The magnitude of an electric fieldnecessary to cause significant cur-rent passage through a dielectricmaterial.Diffraction(x-ray).Constructiveinterference of x-ray beams that arescattered by atoms of a crystal.Diffusion.Masstransportbyatomic motion.Diffusion coeff