《徐先生相变会议》PPT课件.ppt

相变研究及材料形态学,徐祖耀上海交通大学材料科学与工程学院,形核理论,除籍特殊条件下，直接由起伏长大的Spinodal分解外，材料相变均以形核为开端。在均匀形核理论中，对起伏形核，按统计热力学，(Landau和Lifshitz)获得n个原子组成新相集团的几率Pn，决定于形核集团的最低可逆功Gn，即PnexpGn/kT其中k为Boltzman常数。由此式得每摩尔平衡集团的大小分布，Nne：Nne=NAexpGn/kT其中NA为Avagadro常数。,固态相变一般以母相中的缺陷（晶界，位错等）形核，属非均匀（非均质）形核。经典形核理论在近百年来被广泛应用，颇见成效，但也频受质疑。其形核率的基本方程不但难于求解，所得结果也往往不符合实验数据。非均匀形核由于实验情况难于描述清楚，形核率的计算颇有难度。Kelton在1991年的论文（SolidStatePhysics）中瞻望研究“非稳态形核率”（按数学，形核率为时间的函数时即为非稳态形核）,上世纪末，欧洲兴起同步辐射强X射线衍射三维仪、以测定一个晶粒（亚晶）内的相变。Offerman等（Science,2002）以此设备测得钢中奥氏体铁素体相变非均匀形核（晶界形核）相界能要比经典理论预测的小二个数量级或以上，即小于经典理论中二倍数量级的驱动力即能晶界形核。本文作者对此及时给以关注（2004年全国相变及凝固学术会议的大会报告）,2007年他们又发表兼具理论分析和实验的论文（ActaMater）,阐明C35钢（0.364C-0.656Mn-0.305Si）中，当达一定过冷度（如30度）1003K时呈显无形核能垒的晶界形核,宜予重视。其他如相变热力学，新相长大理论，动力学（包括相场理论），晶体学和形态学等均有待深入、创新，衷心盼望我国学者多作贡献,RelativeGibbsfreeenergyc(n)=DG(n)/kBTforaclusteroftheferritephaseinC35steelasafunctionoftheclustersizenatseveraltemperatures.BoththemaximumrelativeGibbsfreeenergyc*andthecriticalclustersizen*significantlydecreaseforlargervaluesoftheundercoolingA3T,发展材料形态学,材料组织对性质的影响是材料科学与工程的核心。材料科学的发展和材料的实际应用都需要材料形态学（MaterialsMorphology）,其内容包括：材料中不同组织形态的归纳和表征不同组织形态的成因组织形态对性质的影响，这对应用紧密相关，宜制成软件供材料设计者参考运用。,钢中珠光体的形态对力学性质的影响,设珠光体的片间距为S，高度为，向长大方向推进距离dx时，形成珠光体体积应为Sdx,质量为Sdx（为密度）。设Fe3C/间的表面能为，形成珠光体时新增表面面积为2dx，则新增界面能2dx。,Zener（1946）假定相变驱动力用于所需的界面能，则可求得S与过冷度T之间的线性关系。结合Kramer等工作，拙著金属材料热力学（P.281-282）中列出：ST=610-4cm.(1)根据Marder和Bramfitt，得：ST=8.026104(2)由他们的实验，得珠光体钢的屈服强度ys和断裂强度fs为：ys（MPa）=139+46.4S-1（S：m）fs（MPa）=436.4+98.1S-1（S：m）代入（1）或（2）式则可算得T对ys和fs的影响。,马氏体形态对钢的力学性质的影响,R.A.Grange,Strengtheningsteelbyaustenitegrainrefinement,Trans.ASM.,1966,59(1):26-48对8650，4340和4310钢作出马氏体屈服强度和原奥氏体晶粒大小的-1/2方呈线性Hall-Petch关系，见拙著马氏体相变与马氏体第二版图3-99。,条状马氏体显微组织的示意图图录自H.Kitahara,R.Ueji,N.Tsuji,Y.Minamino，Crystallographicfeaturesoflathmartensiteinlow-carbonsteel，ActaMater.，2006,54:1276-1288中，P1283，Fig.4,图录自S.Morito,H.Tanaka,R.Konishi,T.Furuhara,T.Maki，ThemorphologyandcrystallographyoflathmartensiteinFe-Calloys，ActaMater.，2003，51：1789-1799，P1797.Fig.10,Marder和Krauss(A.R.Marder,G.Krauss,2ndInter.Conf.TheStrengthofMetalsandAlloys,Alisomar,1970,vol.3,ASM.,822,见马氏体相变与马氏体的图3-98)以及Swarr和Krauss（T.Swarr,G.Krauss,Theeffectofstructureonthedeformationofas-quenchedandtemperedmartensiteinanFe-0.2pctCalloy,Metall.Trans.1976,7A:41-48）对Fe-0.2C和Roberts(R.J.Roberts,Metall.Trans.1970,1:3287-3294)对Fe-Mn得到，马氏体屈服强度与马氏体领域直径的-1/2方呈线性关系，如图（图录自G.Krauss,Martensiteinsteel:strengthandstructure,Mater.Sci.Enger.A,1999,273-275:40-57,P.556,Fig.33）,Yieldstrengthasafunctionofpacketsize,D,oflathmartensiteinanFe0.2wt.%CFeCalloyandanFeMnalloy,Inoue等显示领域大小影响马氏体钢的韧性。T.Inoue,S.Matsuda,Y.Okamura,K.Aoki，TheFractureofaLowCarbonTemperedMartensiteTrans.JIM.,1970,11:36-43,ThepacketsizeaffectsthetoughnessofmartensiticsteelJ.L.Nilles和W.S.Owen,Deformationtwinningofmartensite，Metall.Trans.1972,3:1877-1883,显示温度及领域大小对Fe-25%Ni形变方式的影响。如77K时，领域较小，屈服应力小于孪生应力，以滑移进行形变；当4K时才全部以孪生形变。如马氏体相变与马氏体第二版图3-9及3-97,2005年ICOMAT上，Morito等提出马氏体领域内马氏体束（block）的大小为决定条状马氏体强度的主要因素。我国钢研总院先显示奥氏体晶粒及马氏体领域大小对马氏体力学性能的影响，后得出束(block)的宽度为强度的控制因素;并显示原奥氏体晶粒及马氏体领域细化更有利于韧性的提高.,S.Morito,H.Yoshida,T.Maki,X.Huang,Effectofblocksizeonthestrengthoflathmartensiteinlowcarbonsteels,Mater.Sci.Eng,A,2006,438-440:237-240Theblocksizeisthekeystructuralparametercontrollingthestrengthoflathmartensite(byusingopticalmicroscopy,SEM,electronbackscattereddiffraction(EBSD)andTEM),Fig.1RelationshipbetweentheprioraustenitegrainsizeandthepacketsizeinquenchedmartensiteintheFe0.2CandtheFe0.2C2Mnalloys.,Fig.2RelationshipbetweentheprioraustenitegrainsizeandtheblockwidthinquenchedmartensiteintheFe0.2CandtheFe0.2C2Mnalloys.,HallPetchtypeplotsofyieldstrengthvs.reciprocalsquarerootofthepacketsize,(b)similarplotintermsoftheblocksize,fortheFe0.2CandtheFe0.2C2Mnalloys,Prioraustenitegrainsize(dg),sub-blockwidth(ds),lathwidth(dl),meanmisorientationangleofsub-blockboundaries(s),meanmisorientationangleoflathboundaries(l),anddislocationdensitywithinlaths(0)measuredinFe0.2C2MnalloyFe-0.2C-2Mn:Fe-0.206C-0.011Si-2.017Mn-0.004P-0.0007SFe-0.2C:Fe-0.18C-0.006Si-0.02Mn-0.001P-0.004S,Prioraustenitegrainsizehasastrongeffectonthescaleofpacketsandblocksinthequenchedlathmartensite,butlittleeffectonthedependentofthesubstructurewithintheblocks,implyingthatthesubstructurehardeningisbasicallyindependentofthegrainsize.ComparisonofFig.1andFig.2showsthattheblockwidthismuchsmallerthanthepacketsize,indicatingthatthehighangleboundariesinthestructurearedominatedbytheblockboundaries.SimilarHall-Petchslopesareobtainedwhentheyieldstrengthisanalyzedintermsoftheblocksizefortwoalloyswith0.2CasshowninFig.3b,inconsistentwiththepresentshownthattheMnaddition,doesnotchangethattheHall-Petchslope,andtheblocksizedominatestheyieldstrength,惠卫军,董瀚,翁宇庆42CrMoVNb细晶高强度钢的力学行为材料热处理学报,2005,26(5):57-61,对0.43C-1.10Cr-0.52Mo-0.30V-0.03Nb钢，细化奥氏体晶粒及马氏体packet宽度、提高马氏体的屈服强度及韧性（脆性转变温度）细化奥氏体晶粒对马氏体条宽无影响,ChunfangWang,MaoqiuWang,JieSui,WeijunHuiandHanDong，EffectofMicrostructureRefinementontheStrengthandToughnessofLowAlloyMartensiticSteel,J.Mater.Sci.Technol.,2007,23(5):659-664,Theprioraustenitegrainsizeandmartensiticpacketsizeina0.17C-1.8Cr-1.58Ni-0.23MosteelfollowtheHall-Petchrelationshipwiththeyieldstrengthandthemicrostructurerefinementismoreeffectiveinimprovingtheresistancetocleavagefracturethaninincrementofthestrength,ChunfangWang,MaoqiuWang,JieShi,WeijunHui,HanDong,Effectofmicrostructuralrefinementonthetoughnessoflowcarbonmartensiticsteel,ScritpaMater.,2008,58:492-495,Electronbackscattereddiffraction(EBSD)analysisofthecleavagecrackpathinanas-quenchedandtempered0.17C-0.21Si-0.55Mn-1.80Cr-1.58Ni-0.25Mo-0.011P-0.002Ssteelshowsthatthepacketboundarycanstronglyhinderthefracturepropagation,implyingthatthepacketsizecontrolstheimpactenergyandfractionappearancetransitiontemperature(FATT)Table.1Microstructuralfeatures,LSE,meancleavagefacetsize,fracturestressandyieldstrengthforthesteelaustenitizedatvarioustemperatures,?,(a)VariationofCharpyimpactenergywithtesttemperatureintherange77373Kforspecimenswithvariouspacketsizesand(b)50%FATTasafunctionofthemartensiticpacketsizeforthesteel.,Theaveragelathwidthofvarioussamplesisabout0.3m,beingindependentoftheprioraustenitegrainsize.Lowershelfenergy(LSE)decreaseswiththeincrementofpacketsize.Fromtable1,itseemsthattheyieldstrengthofmartensiticsteelisnotsostronglyrelatedtothepriorgrainsizeratherthanthetoughnessdoes.,L.A.Norstrom,Scand.J.Metall.,1976,5:159-165,Anequationfortheyieldstrengthofthelowcarbonmartensiticstructurewasdevelopedas:y=0+1+kyD-1/2+KSd-1/2+Gb0+Kl%Cwhere0isthefrictionstressofthepureiron,1isthesolidsolutionstrengtheningfromMnandNi,disthelathwidth,Disthepacketsize,0isthedislocationdensityofmartensiticpureiron.,Y.TomitaandK.Okabayashi,EffectofMicrostructureonStrengthandToughnessofHeat-TreatedLowAlloyStructuralSteels.Metall.Trans.A.,1986,17A:1203-1209.,Thepacketdiameteristheprimarymicrostructuralparametercontrollingyieldstressandductile-brittletransitiontemperature.Themechanicalpropertiesarealsoimprovedtoalesserdegreewithdecreasingwidthofthelathwithinthepacket.,Table.1ValuesofiandkyintheRelation,0.2=i+1+kydp-1/2,forMartensiticSteels,0.2=i+1+kydp-1/2,EffectofthelathwidthonkyparameterintheHall-Petchequation.,D.W.SmithandR.F.Hehemann,InfluenceofStructuralParameterontheYieldStrengthofTemperedMartensiteandLowerBainite,J.IronandSteelInst.,1971,June,476-481Thechangeinyieldstrengththatoccurwhenmartensiteandbainitein4340steelaretemperedattemperaturesintherangefrom315-540(from1500MPato1200MPa)canbeattributedtocoarseningofcarbideprecipitatesandtoincreaseinsizeofthecellularsubstructure(lathwidth).TheLangford-Cohenmodelforcell-sizehardening,whichrelatestheyieldstrengthwiththereciprocaloftheaveragecellwidth,providingabettercorrelationoftheexperimentaldatathandoestheHall-Petchmodel,0.2=0+1.2610-2w-1+4.2110-3p-1,0:thesumofpeierlsstress,solutionharderning,workhardening,andtheeffectofdislocationsubstructure.W:Theaveragecellsize(lathwidth)p:Theaverageplanarinterparticlespacing,inmm,J.P.Naylor,TheInfluenceoftheLathMorphologyontheYieldStressandTransitionTemperatureofMartensitic-BainiticSteels,Metall.Trans.,1979,10A,861-73.In0.065C-0.97Mn-2.32Cr-0.83Ni-0.19Mo-0.31Sisteel,thetensilestrengthincreaseswiththereductionoflathwidth(l)ofmartenstie.,Andtheductitle-brittletransitiontemperature(DBTT)canberelatedtoalogarithmicfunctionoftheprod