Seite - 127 - in 3D Printing of Metals

Metals 2017,7, 64 isattributed to thefine-grainmicrostructuresobtained in thecompletedparts resulting inahigher dislocationdensityofaustenitecells [49]. Thismakesslipmotionalongthegrainboundariesdifficult, thus increasing its strengthandresistance todeformation.Althoughthere is someporositycontent in theSLMsamples inthisstudy, thedefect isnotexpectedtohaveasignificant impactonthemechanical propertiesof thefinalpart since theSLMprocessingwasable toyieldhighdensification levels (>99%) and the average porositywas also very low (~0.33%). Nevertheless, the porosity-microhardness relationship isan importantaspect toconsiderwhenSLMisusedtomanufacture functionalpartssuch asbone implantsandindustrial tools. Figure11.Averagemicrohardness (HV)values forSLMandWMspecimens. 4.Conclusions TheSLM-built316LSSsampleswereable toachievehighdensification levels (>99%)witha low averageporositycontent (~0.82%). Eventhoughtheporositycontent in theSLM-builtpartswasvery low, theporeswerenotevenlydistributedthroughout thesamples. Thehighestporositycontent in theconcentratedregionswas foundtobe~1.68%whichwashigher thantheoverall average. Such lowporositycontentdoesnotshowanobvious impactonthemechanicalpropertiesof theAM316L SSsamplesproducedinthisstudy. Thehigheraveragemicrohardnessvaluesof theSLM-fabricated 316LSSpartscomparedto theirwroughtmanufacturedcounterpartwereprimarilyattributedto the localisedmeltingof thepowder layers, and the rapidheating/coolingcycle involvedduringSLM contributedto thefine-grainmicrostructures in thecompletedparts. AuthorContributions:ShahirMohdYusufanalysedthedataandwrote themanuscript;YifeiChencarriedout theexperimentsandanalysedthedata;RichardBoardmanpreparedandcarriedout theXCTscan;ShoufengYang andNongGaoareexperts inadditivemanufacturing(AM)andmetallurgy, respectively,andtheyalsomanaged andsupervisedtheproject. Conflictsof Interest:Theauthorsdeclarenoconflictof interest. References 1. Cherry, J.A.;Davies,H.M.;Mehmood,S.;Lavery,N.P.;Brown,S.G.R.; Sienz, J. Investigation into theeffectof processparametersonmicrostructuralandphysicalpropertiesof316Lstainlesssteelpartsbyselective laser melting. Int. J.Adv.Manuf. Technol. 2014,76, 869–879. [CrossRef] 2. Yusuf, S.M.; Gao, N. Influence of energy density on metallurgy and properties in metal additive manufacturing.Mater. Sci. Technol. 2017. [CrossRef] 3. Guo,N.;Leu,M.C.Additivemanufacturing: Technology,applicationsandresearchneeds.Front.Mech. Eng. 2013,8, 215–243. [CrossRef] 127