Seite - 44 - in 3D Printing of Metals

Metals 2016,6, 284 Figure5.XRDpatterns for1mmand20mmEBM-builtandas-castTi64samples. 3.2. SurfaceConditions Figure 6 shows3Dsurfacemappingsof theEBMas-built 20mmsample and the as-polished 20mmsample fordryslidingwear tests. Toourauthors’bestknowledge, theroughbuildsurfaceof AM-fabricatedpartsmaybe themainobstacle to theirdirectpractical applications. FromFigure6, it can be obtained that EBMas-built Ti64 samples have an average surface roughness of 34.4μm. Inordertoavoidtheinfluenceofroughsurfacesonwearproperties,allof thesampleswerepolishedto amirror-likefinishwithroughnessof~0.3μm.XPSsurveyspectra forboth theEBM-built20mmTi64 sampleandTi64powderusedforEBMfabricationareshowninFigure7. InbothXPSspectra, itwas dominatedbystrongsignalsof titanium(Ti), carbon(C),andoxygen(O).Ofparticular interest is that thesignal foraluminum(Al)wasdetectedontheTi64powdersurface. Butnotonthesamplesurface. Thismay suggest that the surface oxide formon theEBMsampleswerepredominatelyTi andO. Thepresenceof carbononboth instanceswerenotunusualbasedonprevious literatures [25] and thedetectionofcarbonismainlyaresultofadsorptionoforganicmolecules fromtheenvironment. Adetailed scan of the elements present on the surface of the Ti64 sampleswere carried out and illustratedinFigure8a,b,wheretheTi2pandO1speakof theEBM-built20mmsamplewererevealed, respectively. TheTi 2ppeakhas symmetrical peak shapes,which is in linewith the formationof titaniumdioxide (TiO2). Correspondingly, theasymmetrical shapeof theO1speakput forwardthat oxidewasformedwithmore thanonemetalelement. Followingthedecompositionof theO1speakin Figure8brevealedthatbothTiO2 andAl2O3were formed.However, sinceAl isnotdetectableviaXPS ontheEBM-built surface, it is stronglysuggestedthat thesurfacesofall theEBM-built samplesare mainlycomprisedofTiO2. The instantaneous formationofasurficialTiO2 layer is supposedtobe the influential factor inducingpoorwearresistanceofTi64. Figure 6. Representative surface profiles of the EBM Ti64 20 mm samples of (a) as-built and (b) as-polished. 44