钨及钨合金的选择性激光熔化过程中微观组织演化分析-analysis of microstructure evolution during selective laser melting of tungsten and tungsten alloys.docx

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钨及钨合金的选择性激光熔化过程中微观组织演化分析-analysis of microstructure evolution during selective laser melting of tungsten and tungsten alloys.docx

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钨及钨合金的选择性激光熔化过程中微观组织演化分析-analysis of microstructure evolution during selective laser melting of tungsten and tungsten alloys

appearedtheaciculardendritegrowingalongthepreferredgrowthdirection.Withtheenlargementoflaserpowerimport,thedimensionofaciculardendritereducedaccordingly.Whenthelayernumberincreasedfromonetosix,themicrohardnessofSLMedspecimenswasdecreasedfrom826HVto353HV.TheeffectiveprincipleofaddingNielementduringSLMprocesswasstudied.TheformingmechanismsofW-Nialloysarecoexistedliquidphasesinteringandmelting/solidificationofpartWparticlesbylaserenergyinput.Undertheequallasercondition,themicrostructureofSLMedspecimenswiththeNielementcontentof10wt.%,20wt.%,40wt.%showedbarshape,dendritesandalveolar,separately.AddingNielementcandecreasethemeltviscosityandincreasethehomogenizemicrostructure.OnthebasisofthevariationofW-Nihardnessvalue,apowdershrinkagemodelcanbeestablishedaccordingtothethicknessofpowderlayershrinkageandforminglayernumber.Thevariationofreallayerthicknessandtherelevantmathematicalexplanationsarediscussed.Theresultsshowthatthetotalshrinkageofmetalpowderlayersharplyincreasesintheinitialfivelayers,andthenreachestoaplateauvaluewiththeincreasedprocessinglayers.Thisvalueisdefinedbytheratioofslicedlayerthickness(h)torelativedensity(k)duringselectivelasermeltingprocess.TheprocessingwindowwasestablishedaccordingtoexperimentsofW-Ni-CualloysBasedontheprocessingwindow,finalpartswasfabricatedshowingharmonioussinteringsurfacewithnocrackingandobviousporosity.ThesinteringmetallurgicalmechanismtransformfromLPStomelting/solidificationofWparticleswiththeenhancementoflaserenergyinput.Tofurtheroptimizethemicrostructureandformingproperty,rareearthoxideLa2O3wasaddedtoW-Ni-Cualloypowder.SuitablecontentofLa2O3(0.5wt.%-1.0wt.%)canenlargethelaserabsorptionofpowdersystem,refinethemicrostructure,decreaseroughnessofSLMedspecimens,reducemicrocrack,leadingtoabetterformingcharacteristicsandahighermicrohardnessvalue.Using90W-7Ni-3Feasrawmaterial,finiteelementanalysismethodwasappliedtoanalysisthethreedimensiontemperaturefieldofpowderbedunderdifferentformingparameters.Experimentsondifferentprocessingparametersw