机械工程材料ch02-StructureofMaterials

MechanicalEngineeringMaterialsChapterTwo(BilingualCourse)Outline1、AtomicScaleStructureinMaterials2、CrystalStructureinMaterials3、Notificationofthecrystalplaneandcrystalorientationincubiccrystalsystem4、CrystalDefectsThesubstanceismadeupofatoms.Thecombinationandarrangementofatomsdeterminepropertiesofthesubstance.Bindingforcesamongatoms,ionsandmoleculesarecalledbonds.Theircombinationstatusiscalledstructure.C60AtomicScaleStructureinMaterialsAtomicScaleStructureinMaterialsTheatomsinmaterialsareheldtogetherbybonds,whichdictatethestructureofmaterials.Therearefourimportantbondingmechanismsfoundinsolids:ionic,covalent,metallicandvanderWaalsbonds.Thefirstthreebondsarerelativelystrongandareknownasprimarybonds.IonicBonding(离子键)-NaClsolidasanexampleAnionicbondiscreatedbetweentwounlikeatomswithdifferentelectronegativities.Whensodiumdonatesitsvalenceelectrontochlorine,eachbecomesanion;attractionoccurs,andtheionicbondisformed.Theyareexcellentinsulatorsandtheelectronsaresotightlyheldinsidethebondthattheycan’tparticipateintheconductionprocess.CovalentBonding(共价键)-SiliconsolidasanexampleThecovalentbodingistypicallyobservedbetweenatomswithsmalldifferencesintheirelectronegativities.Incovalentbonding,stableelectronconfigurationsareformedbythesharingofvalenceelectronsamongtwoormoreatoms.AtomicScaleStructureinMaterials©2003Brooks/ColePublishing/ThomsonLearning™Covalentbondingrequiresthatelectronsbesharedbetween.Insilicon,withavalenceoffour,fourcovalentbondsmustbeformedAtomicScaleStructureinMaterialsMetallicBonding(金属键)-Fesolidasanexample©2003Brooks/ColePublishing/ThomsonLearning™Themetallicbondformswhenatomsgiveuptheirvalenceelectrons,whichthenformanelectronsea.Thepositivelychargedatomcoresarebondedbymutualattractiontothenegativelychargedelectrons.AtomicScaleStructureinMaterials©2003Brooks/ColePublishing/ThomsonLearning™VanderWaalsBonding(金属键)-PVCsolidasanexampleTheVanderWaalsbondingisakindofphysicalbonding,whicharerelativelyweakerthantheotherbonding.Thedrivingforceforthebondistheattractionoftheatomicormoleculardipoles.HydrogenbondingisaspecialcaseofVanderWaalsbond.AtomicScaleStructureinMaterialsCrystalStructureinMaterialsArrangementsofatomsandionsplayanimportantroleindeterminingthepropertiesofamaterials.Themannerinwhichatoms,ions,ormoleculesarespatiallyarrangedisnamedcrystalstructure.金属的结构晶态非晶态SiO2的结构1.LatticesandUnitCells(晶格和晶胞)Crystals:Atomsarearrangedregularlyinsolidstate.Metalsexistintheformofcrystalsundernormalconditions.Crystalsareanisotropic.Non-crystals:Atomsarearrangedindisorderinsolidstate.Crystalsandnon-crystalscouldconvertintoeachothercertaincircumstances.Isotropic晶体是指原子呈规则排列的固体。常态下金属主要以晶体形式存在。晶体具有各向异性。非晶体是指原子呈无序排列的固体。在一定条件下晶体和非晶体可互相转化。CrystalStructureinMaterialscrystallattice:three-dimensionalframeworksbylinkingcenteroftheatomswithimaginarylines.crossingpointsofthelinesarecallednodes.Arrayformedbythenodesiscalledspacelattice.CrystalStructureinMaterials晶胞(unitcell):能完全反映晶格特征的最小几何单元。晶格常数（点阵参数）latticeconstants/parameters：反映晶胞形状的参量。CrystalStructureinMaterialsCrystalStructureinMaterialsCrystalStructureinMaterialsCrystalsystemCrystalscouldbeclassifiedinto7crystalsystemsbasingonthedifferentcrystallattice.Morethan90%metalbelongstocubiccrystallatticeorhexagonalcrystallattice.Cubiccrystallattice:a=b=c，===90Hexagonalcrystallattice:a1=a2=a3c，==90，=120Crystallatticeconstants:sidelengthofthecrystallatticea,b,c.Cornerdimensionbetweenthecrystallatticesides,,.XZYOαβγbcCrystalStructureinMaterials布拉菲点阵(Bravaislattice)与晶系(CrystalSystem)布拉菲点阵晶系点阵参数简单立方体心立方面心立方立方a=b=c;α=β=γ=90o简单四方体心四方四方a=b≠c;α=β=γ=90o简单菱方菱方a=b=c;α=β=γ≠90o简单六方六方a=b;α=β=90o;γ=120o简单正交底心正交体心正交面心正交正交a≠b≠c;α=β=γ=90o简单单斜底心单斜单斜a≠b≠c;α=β=90o≠γ简单三斜三斜a≠b≠c;α≠β≠γ≠90oCrystalStructureinMaterials14种空间晶格CrystalStructureinMaterialsCrystalStructureinMaterialsCrystalStructureinMaterialsAtomradius(原子半径):halfthedistancebetweentheadjacentatomsinthecrystalcellalongthedirectionmostatomslie.Crystalcellatomicity(晶胞原子数):numberofatomsincludedinonecrystalcell.Coordinationnumber(配位数):thenumberofatomsnearestandwiththesamedistancetooneatom.是指晶格中与任一原子处于相等距离并相距最近的原子数目。Tightness(致密度):volumepercentageofatomsinthecrystalcell.CrystalStructureinMaterials（1）体心立方晶格(body-centercubiclattice)钠(Na);钾(K);铬(Cr);钼(Mo);钨(W);钒(V);钽(Ta);铌(Nb);α-铁(α-Fe)等。CrystalStructureinMaterials2.TypicalMetallicCrystalStructure*晶胞中的原子数:n=8×1／8＋1=2个*晶胞的特征参数:a=b=c,α=β=γ=90°;*原子的体积:v=4πR3／3*致密度:K=nV(原子)／V(晶体)=0.68=68%*配位数(N)：是指晶格中与任一原子处于相等距离并相距最近的原子数目。*原子的半径:4/3aN=8(原子间的最近距离d=)2/3aCrystalStructureinMaterialsCrystalStructureinMaterials（2）面心立方晶格(face-centercubiclattice)金(Au);银(Ag);铜(Cu);铝(Al);镍(Ni);铂(Pt);铅(Pb);γ-铁(γ-Fe)等。CrystalStructureinMaterials*晶胞中的原子数:n=8×1/8+6×1/2=4个*晶胞的特征参数:a=b=c,α=β=γ=90°;*原子的体积:v=4πR3／3*致密度:K=nV原子／V晶体=0.74=74%*配位数(N)：是指晶格中与任一原子处于相等距离并相距最近的原子数目。*原子的半径:R=4/2aN=12(原子间的最近距离d=)2/2aCrystalStructureinMaterials面心立方晶格（间隙及堆垛方式）（1）间隙:两种，为八面体和四面体间隙CrystalStructureinMaterialsCrystalStructureinMaterials（3）密排六方晶格(c/a=1.633close-packedhexagonallattice)镁(Mg);锌(Zn);镉(Cd);α–钛(α–Ti);铍(Be)等。Crys