鐵基粉末冶金資料內(nèi)容提要概述工藝過程產(chǎn)品種類混料、成型、燒結(jié)及后處置開展趨勢粉末冶金簡介粉末冶金是：經(jīng)過對所需根底粉末，合金粉末及添加劑混合，然后將混粉填充在具有要求外形的模腔內(nèi)進(jìn)展壓制成形，再將成型坯體在維護(hù)氣氛下進(jìn)展燒結(jié)使各種顆粒構(gòu)成冶金結(jié)合，經(jīng)過后續(xù)處置后得到最終產(chǎn)品。

由于準(zhǔn)確的成型技術(shù)，粉末冶金產(chǎn)品具有以下特點(diǎn)：近凈成型外形復(fù)雜優(yōu)良的尺寸精度.粉末冶金簡介粉末冶金技術(shù)開展迅速：其原料涵蓋了近乎一切技術(shù)元素產(chǎn)品外形復(fù)雜程度日益提高粉末冶金產(chǎn)業(yè)主要分為兩個(gè)領(lǐng)域：鐵基粉末冶金非鐵基粉末冶金鐵基粉末冶金資料自光滑制品構(gòu)造件軟磁資料自潤滑零件結(jié)構(gòu)件零件軟磁零件粉末冶金產(chǎn)品優(yōu)勢近凈成型期望的力學(xué)性能大規(guī)模的消費(fèi)和反復(fù)性好外表光潔度高尺寸精度允許不同資料組合多孔及孔隙度可控〔自光滑資料〕良好的磁性能〔軟磁資料〕粉末冶金根本工藝過程后續(xù)處理粉末原料基粉類型合金體系合金化方式基粉的選擇混料混料要求混合方式均勻性與偏析松裝密度與流動性混粉及裝粉過程中產(chǎn)生的細(xì)粉聚會壓制壓制方式生坯密度與密度均勻性生坯強(qiáng)度生坯缺陷充模過程Caremustbetakenwhenfillingthinsectionsasbridgesmayoccur. Themin.crosssectionsizeisabout1mm.裝粉高度與模沖進(jìn)入量的計(jì)算DieCRUPLOPLIPt1t2H2LOPLIPUPDieH1FD=3.2g/cm3GD=7.2g/cm3Example:t1=10mmt2=25mmH1=22.5mmH2=56mmUPentry=31mmH1=GD/FD*t1H2=GD/FD*t2UPentry=H2-t2粉末壓制摩擦力BetweenpowderparticlesBetweenpunchesandthedie-wallBetweenpunchesandpowderparticlesBetweenpowderparticlesandthedie-wall摩擦力導(dǎo)致的后果LossesoftheappliedforceVariationofpressureandgreendensityHigherejectionforces(Wearofthetool-set)密度分布雙向壓制表示圖Stationarydie,twomovingpunches.Stationarylowerpunchandfloatingdie.c) Stationarylowerpunch,andthediebeingwithdrawnathalfthespeedofthetoppunch.如何減小摩擦力參與光滑劑模壁光滑優(yōu)化壓制工藝 -壓制速度 -壓制溫度 -滑動間隔 -光滑劑含量對生坯實(shí)際密度的影響ASC100.29Amountoflubricant不同光滑劑對生坯實(shí)際密度的影響ASC100.29脫模力的變化過程Duetoresidualradialstressesasignificantforceisrequiredtoejectcompactsfromthedie.RRS’sshouldbekepttoaminimumtoavoidhighejectionforces,henceavoidtoolingproblems.模具光滑情況對脫模力的影響Goodlubrication模具光滑情況對脫模力的影響Excessivediewallwearorinsufficientlubricationmayresultincoldweldingofthecompacttothediewall.GoodlubricationBadlubricationResultsinincreasedejectionforceandstick-slipbehaviour(squeakynoise)壓制缺陷SEMimageofacracknosinteringnecks過壓分層燒結(jié)燒結(jié)的作用脫除光滑劑冶金粘結(jié)元素分散尺寸變化微觀構(gòu)造防止氧化與復(fù)原氧化物燒結(jié)溫度、燒結(jié)時(shí)間、燒結(jié)氣氛燒結(jié)過程MetalpowdercompactPorousmetalSinteredstate(bondingbetweenparticles)Greenstate(coldwelding)生坯與燒結(jié)件AftercompactionAftersintering燒結(jié)工藝表示圖Temp.TimeRTDelubrication(300-700C)C-dissolution(800-950C)4321Sintering(1100-1300C)Cooling(CoolingRate)1234影響燒結(jié)的要素TemperatureTimeAtmosphereMaterialcompositionAlloyingmethodLubricantcontentSinteringcycle燒結(jié)過程的本質(zhì)ParticlebondingMicrostructureDimensionalchangeSinteringnecksPoresPhases/structuresSizeShapeAlloyingHomogenization燒結(jié)驅(qū)動力V1+V2=V3E1+E2>E3123E1+E2E3ΔEHighenergystateLowenergystateDrivingForce:Surfaceenergy固態(tài)燒結(jié)BytheDiffusionofthemetalatomsCuspheres孔隙變化FromsharpcornerstoflatterpartsoftheporesurfaceFromsmallporestonear-bylargerporesandgrainboundaries均勻化過程N(yùn)iinFe-base影響均勻化的要素Niparticlesize:5um,10umTemperature:1000-1300CWeighingfactor:TemperatureNiparticlesizeTimeTime:0.5-500h燒結(jié)的分類Temperature(<1150C,>1150C)Furnace(batch,pusher,belt,walkingbeam)Atmosphere(“vacuum〞,Endo,N2/H2)State(liquid,solid)Pressure(atmospheric,pressure-assisted)高溫?zé)Y(jié)Acceleratestheatomicmotion(bettersinteringnecks)Improvesthesurfacereductionofparticles(activatessintering)IncreasesthesintereddensityImprovesthehomogenizationImprovesporeroundingImprovesmechanicalproperties瞬時(shí)液相燒結(jié)SecondaryporeFe–Cu系膨脹機(jī)理90%Fe10%Cu1150CFe-Cu系與Fe-Cu-C系的尺寸變化CuCu+1%C燒結(jié)常見的問題AchievesufficientlytighttolerancesOxidation(alloyingelements,sinteringatmosphere)Carburisation(temperature,sinteringatmosphere)Decarburisation(temperature,sinteringatmosphere)Poorsurfacefinish(delubrification)影響尺寸變化的要素ParticlesizeAlloyingelementUnevenfillingandcompactionUnevendistributionofalloyingelementsinthecomponentLiquidphaseformationSinteringtemperatureandtimeUneventemperaturedistributionofthesinteringfurnacePoorcontrolofgasflowinthesinteringfurnace脫蠟缺陷(Blistering)

Fe+2.5%Ni+0.4%C燒結(jié)缺陷Poorsinteringnecks(sponge)Poorsinteringnecks(atomised)Oxidationduringsintering弱燒結(jié)頸和游離石墨燒結(jié)脫碳NC100.24+Cu+Ni+1%C D.AB+0.6%CAstaloyCrM+0.3%C燒結(jié)滲碳PASC30+0%C D.HP-1+0.5%C過低的燒結(jié)溫度FreeCuinDistaloymaterial后續(xù)處理TreatmentDefinitionExamplesCoatings-adepositionofalayerofaseparatematerialontothesurfaceofthesubstratewithoutanychemicalreactionElectroplatingPaintingmetallizingChemicalconversiontreatmentsAchemicalreactionbetweenthesurfacelayersoftheoriginalsubstrateandanexternalreactantSteamtreatmentPhosphatising,etcThermochemicaltreatmentsDiffusionofotherspecies,suchasC,N,intothesurfacelayersoftheoriginalsubstrateCarburisingCarbonitridingNitrocarburisingNitridingPlasmatreatments,etc后續(xù)處理TreatmentDefinitionExamplesThermaltreatmentsChangeinmicrostructureofthesurfacelayersoftheoriginalsubstratebythermallycyclingthroughaphasetransformationInductionhardeningLaserhardeningMechanicaldeformationMechanicaldeformation