材料基础范文

材料基础范文材料基础范文 Materials Science 材料科学 involves investigatingthe relationshipsthat existbetween the structures andproperties of materials 研究结构与性能之间的关系 Materials Engineering 材料工程 designing orengineering thestructure of a material to produce a predeterminedset ofproperties based on these structure property correlations 设计材料结构以产生预定的性能 Structure 结构 r elates to the arrangementof itsinternal ponents 内部成分的组织排列 Property 性能 a materialtrait in terms of the kindand magnitudeof responseto a specific imposedstimulus 一种材料对外界刺激反应的类型和程度 The differentproperties betweensame classification of materialsare causedby theirCrystal Structure 同种类型材料之间的不同特性是由晶体机构不同引起的 The propertiesof materialsare related to theirposition 成分 crystal structures 晶体结构 and the processing 加工 材料的性能与成分 晶体结构 加工方法有关 加工工艺 结构 性能 四者的关系With regardto therelationships of these fourponents thestructureof materialswill depend on how it is processed Furthermore a materials performance will be a function of its properties Thus the interrelationshipbetween processing structure properties andperformance isliear as depictedin theschematic illustrationprocessing structure properties performances property Category 性能的分类 mechanical 机械性 eletrcical 电性 thermal 热性 magic 磁性 optical 光学性 and deteriorative 失效性 Mechanical Properties 机械性能 relate deformationto an applied loador force examples includeelastic modulusand strength Electrical Properties 电性能 the stimulusis anelectric field such aselectrical conductivity 电导率 and dielectrionstant 介电常数 Thermal Properties 热性 The thermalbehavior ofsolids canbe representedintermsof heatcapacity 热容 and thermalconductivity 导热系数 Magic Properties 磁性 Demonstrate theresponse of a material to theapplication of a magicfield Optical Properties 光学性 electromagic orlight radiation index ofrefraction 折射 and reflectivity 反射 are representativeoptical properties Deteriorative Characteristic 失效性 Indicate thechemical reactivityof materialsProcessing 处理 The structureof amaterial willdependonhowit isprocessed Performance 表现性能 A material sperformancewillbeafunctionofitsproperties classi ficationofsolid materials 材料分类 标准 特点 solid materialshave beenconveniently groupedinto threebasic classifications metal ceramics andpolymer This schemeis basedprimarily onchemical makeupand atomicstructure and mostmaterials fallinto onedistinct groupingor another although thereare someintermediates 特点metals 金属 pure orbination of metallic elements Non localised electrons good conductorsof electricityand heat strong deformable ceramics 陶器 pounds of metallic andnon metallic elements oxides nitrides carbides hard andresistant tohigh temperatureand chemicalattack polymers 聚合物 long chain like moleculespossed ofhydrogen andnon metallic elements low density very fiexible Basic metals ceramics polymers Engineering materials Composites Semiconductor biomaterials posites 复合 more than one typeofmaterialwith abination ofproperties semiconductors 半导体intermediate betweenmetals and insulators biomaterials 生物材料 all of the abovematerials may be used for replacementof diseaasedor damagedbody parts 晶体类型shown inThe stimulusis electrical propertiesFCC face centered cubic crystal structurehas aunit cellof cubicgeometry with atomslocated ateach of the cornersand centersof allthe cubeface 除8个顶点外 每个面心上有一个阵点 a 2 2R n 4 A PF 0 74配位数 12BCC body centered cubic crystal structurehas aunit cellof cubicgeometry with atomslocated ateight cornersand asingle atomat cubecenter 除8个顶点外 体心上还有一个阵点 a 4 3 R n 2 APF 0 68配位数 8HCP Hexagonal close packed The topand bottomfaces of the unit cell consistof sixatoms thatform regularhexagons andsurround asingle atomin thecenter Another planeprovides threeadditional atomsto theunitcellc 1 633a n 6 APF 0 74配位数 12Coordination number 配位数 For eachatom coordination numberis thenumber ofnearest neighbor or touching atoms Some typicalstructures ofceramic materialare discussedhere AB type crystal structures AB2type crystalstructuresA2B3type crystalstructures ABO3typecrystalstructures AB 1 Sodium Chloridestructure NaCl coordination numberRNa Rcl 0 097nm 0 181nm 0 536coordination number 6 Structure FCC Cl ions atFCC positions Na at thefour octahedralsites Other poundsmany ceramicsincluding magnesiumoxide MgO calcium oxide CaO iron oxide FeO have thisstructure 2 Cesium ChlorideStructure ZnS Coordination numberRzn Rs 0 074nm 0 184nm 0 402coordination number 4 Structure FCC S anionsat thenormal latticepoints Zn cationsat halfof thetetrahedral sites Because aommodatethe restrictionof bothcharge balanceand coordination number other poundsGaAs semiconductors AB2 Fluorite Structure CaF2 coordination numbercoordinationnumber 4 structure FCC Ca anionslocated at all eightof thetetrahedral positions other poundscubic zirconia ZrO2 UO2 ThO2 CeO2ABO3 Perovskite Structure CaTiO3 Structure Cacations oupy the cubecorner Ti cationsoupy cubecenter O anionsoupytheface centersof theperovskite unitcell Other poundsBaTiO3 capacitors forelectronic applications A2B3Corundum Structure Al2O3alpha alumina Structure Oxygenanions packin ahexagonal arrangement aluminum cationsoupy someof theavailable positions application mostwidely ceramicmaterial spark plugs refractories electronic packagingsubstrates and abrasives 高分子hydrocarbon碳氢化合物Hydrocarbons areposed ofhydrogen andcarbon The intramolecularbonds arecovalent macromolecules高分子a hugemolecule made up ofthousands ofatoms Macromolecules高分子 polymer Polymer wascoined tomean manymers A poundconsisting oflong chain molecules each moleculemadeupof repeatingunits connectedtogether Mer 单体单元 结构单元 Structural entities originates fromthe Greekword meros which meanspart Monomer 单体 A stablemolecule fromwhich apolymer issynthesized such asethylene Polymerization 聚合反应 The synthesisof thelarge molecularweight polymersis termedpolymerization Thermoplastics 热塑性聚合物 Thermoplastics softenwhen heated and eventuallyliquefy and hardenwhen cooled processes thatare totallyreversible andmay berepeated 加热变软冷却变硬可回收的 Thermosetting 热固 性聚合物 Thermosetting polymersbee permanentlyhard whenheat is applied anddo notsoften uponsubsequent heating 塑料形成方式The mostmon methodfor formingplastic polymers Include pression 压塑 transfer 传递模塑 blow 吹塑模塑法 inje ction 注塑模塑 and extrusionmolding 挤压模塑 The methodusedfor aspecificpolymer depends on severalfactors 形成特殊聚合物取决于以下因素 1 whether the material is thermoplastic orthermosetting 是热塑性还是热固性 2 if thermoplastic the temperature at whichit softens 热塑性的话 在那个温度开始变软 3 the atmosphericstability 耐候性 of thematerial beingformed and 4 the geometry 几何形状 and size 尺寸 of the finished product Processing ofPolymer 聚合物的加工 1 Thermoplastics 热塑 Thermoplastics areformed above their glass transition temperatures 玻璃化转变温度 if amorphous 无定形 or abovetheir meltingtemperatures 熔融温度 if semicrystalline 半结晶 anappliedpressure must be maintainedas the piece iscooled sothat theformed articlewill retainits shape 热塑性塑料的形成是在他们的玻璃化转变温度以上 如果 无定形或是在融化温度以上或是半结晶 则必须加一个压力才能使 形成部分保持它的形状 2 Thermosettings 热固 Fabrication of thermosetting polymersis ordinarilyaomplished intwo stages First esthe preparationofalinear polymer This secondstage termed curing 固化 may ourduring heatingand or by the additionof catalysts and oftenunder pressure During curing chemical andstructural changesour ona molecularlevel a crosslinkedorawork structureforms 大分子的形成过程Addition polymerization 加成聚合反应 Four Methods 四种方法 1Free radicalpolymerization 自由基聚合 2Cationic Polymerization 阳离子聚合 3Anionic Polymerization 阴离子聚合 4Coordination Polymerization 配位聚合 Three distinctstages Initiation 链引发 Propagation 链增长 an d Termination 链终止 Chain reactionpolymerization 连锁聚合反应 Condensation polymerization 缩合聚合反应 Condensation polymerizationis theformation ofpolymers bystepwise intermolecularchemical reactionsthat normallyinvolve morethanonemonomer species Step reactionpolymerization 逐步聚合反应 Mechanical properties力学性能Strength 强度 yielding strength 屈服强度 The stresscorresponding to the intersectionof thisline and the stress strain curveas itbends overin theplastic regionis defined as the yield strengthTensile strength 拉伸强度 engineering stress in tension that may be sustainedwithout fracture Hardness 硬度 Rockwell hardnesstests 洛氏硬度 Brinell hardnesstests 布氏硬度 Knoop andVickers hardnesstests 维氏硬度 Ductility 塑性 It is a measure of thedegree ofplastic deformationthat hasbeen sustainedat fracture Stiffness 刚度 Resilience 回弹性 Resilience isthe capacityofamaterialto absorb energywhen it is deformedelastically and then upon unloading to havethis energyrecovered Toughness 韧性 isameasureof the abilityofathe maximummaterialto absorb energyup tofracture 应力应变Engineering stress the instantaneous load applied to a specimen divided by itscross sectional areabefore anydeformation F Ao F isthe instantaneousloadapplied perpendiculartothespecimen cross section N Ao theoriginal cross sectional areabefore anyload isapplied m2 Engineering strain the changein gauge length ofaspecimendividedbyits originalgaugelength l lo lo original lengthbefore anyload isapplied li theinstantaneouslength l li lo deformation elongation True stress T isdefinedasthe loadF dividedbytheinstantaneous cross sectional areaAi overwhich deformation is ourring i e the neck past thetensile point or F Ai Truestrain T defined byln li lo 真应力应变与工程应力应变的关系If novolume changeours duringdeformation that is if Ai li Ao lo trueand engineeringstress andstrain arerelated aording to r 1 r ln 1 Hooke s law 胡克定律 E Poisson s ratio泊松比For isotropic materials the ratioof lateraland axialstrains iscalled thePoisson s ratiov v x z y z Forisotropicmaterials shear 剪切 and elasticmoduli arerelatedtoeach otherand topoisson s ratioaordingtoE 2G 1 v 几个概念Yield strength 屈服强度 the stresscorresponding tothe intersectionoftheline which parallelstotheelastic portionofthe stress strain curveat somespecified strainoffset andthestress strain curveas itbends overin theplastic region Tensile strength 抗拉强度 thestressat themaximum onthe engineeringstress strain curve Yielding 屈服 the phenomenonthat plastic deformation begins Proportional limit 比例极限 the pointoftheinitial departurefrom linearityofthestress strain curve The elastic plastic transitionis verywell definedand oursabruptly inwhat is termed ayield pointphenomenon At theupper yieldpoint plastic deformationis initiatedwith anactual decrease in stress Continued deformationfluctuates slightlyabout someconstant stressvalue termed thelower yieldpoint stress subsequentlyrises withincreasing strain For metals the yieldstrength istaken asthe averagestress that is associatedwith thelower yieldpoint Forming OperationsofmetalConcept Those in which theshape ofa metalpiece ischanged byplasticdeformation 塑性变形 example forging 锻造 rolli ng 轧制 Casting 铸造 Powder metallurgy 粉末冶金 Welding 焊接法 extrusion 挤压 and drawing 拉拔 are monforming techniques Deformation Conditions 变形条件 The deformationmustbeinduced by an external 外部的 force orstress the magnitudeof whichmust exceed 超过 theyieldstrength 屈服强度 ofthematerial 外力 作用且应力超过屈服强度 热加工 冷加工定义When deformationis achievedata temperature abovethat atwhich recrystallization 再结晶 ours theprocessistermedhot working otherwise itiscold working Hot working operationAdvantages 1 Large deformationsand repeat 2 requiring lessdeformation energy Disadvantages 1 Surface oxidation resulting inmaterial lossandapoor finalsurface finish Cold working operationAdvantages 1 An increasein strength 2 Higher qualitysurface finish 3 Better mechanicalproperties 4 Closer dimensionalcontrol ofthefinishedpiece Disadvantages 1 The decreasein ductility 2 The totaldeformationisaomplished in a seriesof stepsinwhich thepieceis suessivelycold worked a small amount andthen process annealed an expensivefor and inconvenient procedureExtrusion 挤压 a barofmetalis forcedthrough adie orifice 模孔 by apressive forcethat isappliedtoa ram 活塞 the extrudedpiece thatemerges hasthe desiredshape anda reducedcross sectional area Rolling 轧制 Consists ofpassing apiece ofmetal betweentwo rolls滚轴 a reductionin thicknessresults frompressive stressesexerted bythe rolls Why maywelding 焊接 be consideredto bea fabricationtechique 1In welding two ormore metalparts arejoined toform asingle piecewhen one part fabricationis expensiveor inconvenient 2Both similarand dissimilarmetals may be welded 3The joiningbond ismetallurgical ratherthan justmechanical as withriveting 铆接 and bolting 螺栓连接 workedasmallamountandthenprocessannealed an expensiveandinconvenientprocedure Three Stagesof annealingprocess 退火工艺的步骤 heating tothe desiredtemperature holding or soaking均热 处理 at thattemperature cooling usually to room temperature退火目的 1 relieve stress 消除应力 2 increase softness ductility and toughness 提高韧性 3 produce aspecific microstructure 产生特定的微观结构 Normalizing Aims 正火目的 Refine thegrains andproduceamore uniform and desirablesize distributionThe reasonsof spheroidizing 球化退火 treatment 进行球化退火的原因 Medi um and high carbon steels 中 高碳钢 having amicrostructure containingeven coarsepearlite 珠光体 may stillbe toohard toconveniently machineor plasticallydeform These steels andinfact anysteel maybeheat treatedor annealedto developthe spheroiditestructure 球状结构 Spheroidized steelshave amaximum softnessand ductilityand areeasily machinedor deformed 玻璃Specific volume 比容 one ofthe distinctionsbetween crystallineand noncrystallinematerials liesin thedependence ofspecific volumeViscosity 粘度 Upon cooling a glassbees moreand moreviscous 粘稠的 inacontinuous mannerwith decreasingtemperature There isno definitetemperatureatwhichtheliquid transformstoasolid aswith crystallinematerials fictive temperature Tg 玻璃化转变温度 A slightdecreaseinslope ofthe curveours atwhat iscalled the glasstransitiontemperature or fictivetemperature Tg Below thistemperature thematerialis consideredto bea glass above itisfirst asupercooled liquid 过冷液体 and finallya liquid Most glass forming operationsare carriedout within the workingrange between theworking and softening temperatures 加工步骤Four differentforming methodsare used to fabricate 加工 glass products 1 pressing 2 blowing 3 drawing Drawing isusedtoform longglass piecessuch assheet rod tubing and fibers which havea constantcrosssection 4 fiber forming Glass Tempering 回火 1 Definition Thestrength ofa glass piece maybe enhancedby intentionallyinducing pressiveresidual surfacestresses This canbe aomplishedbyaheat treatmentprocedure called thermal tempering 2 Environment Withthis technique the glasswareis heatedtoatemperature abovetheglasstransition regionyet below the softeningpoint It isthen cooledto roomtemperature ina jetof air or insome cases an oilbath The residualstresses arisefrom differencesin coolingrates forsurface andinterior regions Processing 回火加工 Initially the surfacecools morerapidly and once havingdropped toatemperaturebelowthestrain point bees rigid At thistime the interior having cooledless rapidly is ata highertemperature abovethestrain point and therefore is stillplastic With continuedcooling contract toa greaterdegree thanthe nowrigid exteriorwill allow Thus the insidetends todraw inthe outside ortoimpose inwardradial stresses After theglasspiecehas cooledtoroomtemperature it sustainspressive stressesonthesurface with tensilestresses atinterior regions The characteristicsof clay 粘土 1 Hydroplasticity 含水塑性 when wateris added they beevery plastic hydroplasticity 2 Fusion temperature range clayfuses ormelts overa range of temperatures thus a denseand strongceramic piecemaybeproduced duringfiring withoutplete meltingsuch thatthe desiredshape ismaintained This fusiontemperaturerange of course dependsonthe positionofthe clay 3 Composites Claysare alumin