Page - 49 - in 3D Printing of Metals

Metals 2016,6, 284 movementduringtheslidingprocessandthusactedasaprotection layerbetweenthecounterball andTi64sample, therebypreventingdirectmetal-metal contact, leadingtoa lowerwearrate. Figure12.Schematic road-maponthe formationof tribo-layerduringslidingwearofTi64samples. 4. Summary Duetothefastcoolingrate thatwasinherently involvedinatypicalEBMprocess, itwasobserved that the thinnerEBM-built Ti64 samples (0.5mmand1mmthick) hadmuchfinermicrostructure andhighermicrohardness as compared to the as-cast form. However, they showed similarwear characteristics, regardlessof thedifferentmicrostructureswithintheEBM-builtandtheas-castsamples. Thehigherhardnessof theEBM-built samplesresulted in theirhigherwearresistanceandintrinsically lowerwearrate. It isworthnotingthatallof thewearratesobtainedinourexperimentwere lower ascompared to the theoretical estimation. It couldbedue to themildwearconditions (e.g., avery lowslidingspeedof2 cm/s)and the formationof the tribo-layer that remainedon thewear track, actingasaprotectionbarrierbetweenthecounterballandtheTi64substrate.Wecanconcludethat the EBMprocess iscapableofmanufacturingTi64partswithsuperiorwearpropertiescomparedto the as-cast counterparts. Acknowledgments: The authors are grateful for financial support provided by A*Star Industrial Additive ManufacturingProgram: WorkPackage3. Weacknowledge theuseof resources inSingaporeCentre for 3D Printing(SC3DP) fundedbytheNationalResearchFoundation(NRF),Singapore. AuthorContributions:W.Q.T.examinedthespecimensandwrote themainpaper. X.T.designedtheexperiments andfabricated theTi64samplesusingEBM.W.Q.T.,X.T.,P.W.andM.L.S.N.performedspecimenpreparationand characterization. E.L.andS.B.T. supervisedtheproject.Allauthorsdiscussedtheresultsandfinalizedthepaper. Conflictsof Interest:Theauthorsdeclarenoconflictof interest. References 1. Frazier,W.E.Metal AdditiveManufacturing: AReview. J.Mater. Eng. Perform. 2014, 23, 1917–1928. [CrossRef] 2. Gibson, I.;Rosen,D.W.;Stucker,B.AdditiveManufacturingTechnologies; Springer: Berlin,Germany,2010. 3. Chua,C.K.;Leong,K.F.3DPrintingandAdditiveManufacturing: Principles andApplications;WorldScientific: Singapore,2015. 4. Boyer, R.; Welsch,G.; Collings, E.W.Materials PropertiesHandbook: TitaniumAlloys; ASM International: MaterialsPark,OH,USA,1994. 5. Tan, X.P.; Kok, Y.; Toh, W.Q.; Tan, Y.J.; Descoins, M.; Mangelinck, D.; Tor, S.B.; Leong, K.F.; Chua,C.K. Revealingmartensitic transformation andα/β interface evolution in electron beammelting three-dimensional-printedTi-6Al-4V.Sci. Rep. 2016,6, 26039. [CrossRef] [PubMed] 49