铁基粉末冶金材料

铁基粉末冶金材料内容提要•概述•工艺过程•产品种类•混料、成型、烧结及后处理•发展趋势粉末冶金简介粉末冶金是：通过对所需基础粉末，合金粉末及添加剂混合，然后将混粉填充在具有要求形状的模腔内进行压制成形，再将成型坯体在保护气氛下进行烧结使各种颗粒形成冶金结合，经过后续处理后得到最终产品。由于精确的成型技术，粉末冶金产品具有以下特点：近净成型形状复杂优良的尺寸精度.粉末冶金简介粉末冶金技术发展迅速：其原料涵盖了近乎所有技术元素产品形状复杂程度日益提高粉末冶金产业主要分为两个领域：铁基粉末冶金非铁基粉末冶金铁基粉末冶金材料•自润滑制品•结构件•软磁材料自润滑零件结构件零件软磁零件粉末冶金产品优势•近净成型•期望的力学性能•大规模的生产和重复性好•表面光洁度•高尺寸精度•允许不同材料组合•多孔及孔隙度可控（自润滑材料）•良好的磁性能（软磁材料）粉末冶金基本工艺过程后续处理粉末原料•基粉类型•合金体系•合金化方式基粉的选择混料•混料要求•混合方式•均匀性与偏析•松装密度与流动性混粉及装粉过程中产生的细粉团聚压制•压制方式•生坯密度与密度均匀性•生坯强度•生坯缺陷充模过程•Caremustbetakenwhenfillingthinsectionsasbridgesmayoccur.Themin.crosssectionsizeisabout1mm.装粉高度与模冲进入量的计算DieCRUPLOPLIPt1t2H2LOPLIPUPDieH1FD=3.2g/cm3GD=7.2g/cm3Example:t1=10mmt2=25mmH1=22.5mmH2=56mmUPentry=31mmH1=GD/FD*t1H2=GD/FD*t2UPentry=H2-t2粉末压制摩擦力•Betweenpowderparticles•Betweenpunchesandthedie-wall•Betweenpunchesandpowderparticles•Betweenpowderparticlesandthedie-wall摩擦力导致的后果•Lossesoftheappliedforce•Variationofpressureandgreendensity•Higherejectionforces•(Wearofthetool-set)密度分布双向压制示意图a)Stationarydie,twomovingpunches.b)Stationarylowerpunchandfloatingdie.c)Stationarylowerpunch,andthediebeingwithdrawnathalfthespeedofthetoppunch.如何减小摩擦力•加入润滑剂•模壁润滑•优化压制工艺-压制速度-压制温度-滑动距离-润滑剂含量对生坯理论密度的影响ASC100.29Amountoflubricant不同润滑剂对生坯理论密度的影响ASC100.29脱模力的变化过程•Duetoresidualradialstressesasignificantforceisrequiredtoejectcompactsfromthedie.•RRS’sshouldbekepttoaminimumtoavoidhighejectionforces,henceavoidtoolingproblems.模具润滑状况对脱模力的影响Goodlubrication模具润滑状况对脱模力的影响•Excessivediewallwearorinsufficientlubricationmayresultincoldweldingofthecompacttothediewall.GoodlubricationBadlubrication•Resultsinincreasedejectionforceandstick-slipbehaviour(squeakynoise)压制缺陷SEMimageofacracknosinteringnecks过压分层烧结•烧结的作用脱除润滑剂冶金粘结元素扩散尺寸变化微观结构防止氧化与还原氧化物•烧结温度、烧结时间、烧结气氛烧结过程MetalpowdercompactPorousmetalSinteredstate(bondingbetweenparticles)Greenstate(coldwelding)生坯与烧结件AftercompactionAftersintering烧结工艺示意图Temp.TimeRTDelubrication(300-700C)C-dissolution(800-950C)4321Sintering(1100-1300C)Cooling(CoolingRate)1234影响烧结的因素•Temperature•Time•Atmosphere•Materialcomposition•Alloyingmethod•Lubricantcontent•Sinteringcycle烧结过程的实质•Particlebonding•Microstructure•DimensionalchangeSinteringnecksPoresPhases/structuresSizeShapeAlloyingHomogenization烧结驱动力V1+V2=V3E1+E2E3123E1+E2E3ΔEHighenergystateLowenergystateDrivingForce:Surfaceenergy固态烧结•BytheDiffusionofthemetalatomsCuspheres孔隙变化FromsharpcornerstoflatterpartsoftheporesurfaceFromsmallporestonear-bylargerporesandgrainboundaries均匀化过程NiinFe-base影响均匀化的因素Niparticlesize:5um,10umTemperature:1000-1300CWeighingfactor:•Temperature•Niparticlesize•TimeTime:0.5-500h烧结的分类•Temperature(1150C,1150C)•Furnace(batch,pusher,belt,walkingbeam)•Atmosphere(“vacuum”,Endo,N2/H2)•State(liquid,solid)•Pressure(atmospheric,pressure-assisted)高温烧结•Acceleratestheatomicmotion(bettersinteringnecks)•Improvesthesurfacereductionofparticles(activatessintering)•Increasesthesintereddensity•Improvesthehomogenization•Improvesporerounding•Improvesmechanicalproperties瞬时液相烧结SecondaryporeFe–Cu系膨胀机理90%Fe10%Cu1150CFe-Cu系与Fe-Cu-C系的尺寸变化CuCu+1%C烧结常见的问题•Achievesufficientlytighttolerances•Oxidation(alloyingelements,sinteringatmosphere)•Carburisation(temperature,sinteringatmosphere)•Decarburisation(temperature,sinteringatmosphere)•Poorsurfacefinish(delubrification)影响尺寸变化的因素•Particlesize•Alloyingelement•Unevenfillingandcompaction•Unevendistributionofalloyingelementsinthecomponent•Liquidphaseformation•Sinteringtemperatureandtime•Uneventemperaturedistributionofthesinteringfurnace•Poorcontrolofgasflowinthesinteringfurnace脱蜡缺陷(Blistering)Fe+2.5%Ni+0.4%C烧结缺陷Poorsinteringnecks(sponge)Poorsinteringnecks(atomised)Oxidationduringsintering弱烧结颈和游离石墨烧结脱碳NC100.24+Cu+Ni+1%CD.AB+0.6%CAstaloyCrM+0.3%C烧结渗碳PASC30+0%CD.HP-1+0.5%C过低的烧结温度FreeCuinDistaloymaterial后续处理TreatmentDefinitionExamplesCoatings-adepositionofalayerofaseparatematerialontothesurfaceofthesubstratewithoutanychemicalreactionElectroplatingPaintingmetallizingChemicalconversiontreatmentsAchemicalreactionbetweenthesurfacelayersoftheoriginalsubstrateandanexternalreactantSteamtreatmentPhosphatising,etcThermochemicaltreatmentsDiffusionofotherspecies,suchasC,N,intothesurfacelayersoftheoriginalsubstrateCarburisingCarbonitridingNitrocarburisingNitridingPlasmatreatments,etc后续处理TreatmentDefinitionExamplesThermaltreatmentsChangeinmicrostructureofthesurfacelayersoftheoriginalsubstratebythermallycyclingthroughaphasetransformationInductionhardeningLaserhardeningMechanicaldeformationMechanicaldeformationinthesurfacelayersoftheoriginalsubstrate,mainlytoinducecompressivestresses,butalsotoprovidedensificationofthesurfacelayerSurfacecoldrolling,etc发展趋势•高密度•高性能•高尺寸精度•低单位成本•新工艺•新材料发展趋势HighMediumLowVerylowVerypoorPoorMediumGoodVerygoodPlasticsCasting+ForgingPMTolerances粉末冶金关注领域高中低中高低Fe-Cr-Mo-Ni-CLiquidphaseFe-Cr-Mo-Ni-CMixAstaloyCrMD.HP-1Fe-Cu-Mo-Ni-CFe-Cu-Mo-Ni-CStarmixDistaloyAEAstaloyCrLFe-Cu-CCu–met.Fe-Cu-CDistaloyACuFe-Cu-CDist.ACu,Starmix尺寸公差