Page - 122 - in 3D Printing of Metals

Metals 2017,7, 64 Figure2.Cross-sectionalviewsofSLMsampleson(a)x–yplane; (b)x–zplane;and(c)y–zplane. Afinecellular-dendriticmicrostructurecouldbeobservedintheSLM-fabricatedsamplesasshown inFigure3. This isacommoncharacteristic formetalmaterials fabricatedbyAMprocessesasaresult of therapidsolidificationrates in the locallymeltedareas (selectively laser-scannedregions)which wereexperiencedbecauseofshort laser-material interactiontimeduringthebuildprocess [25–27]. Figure3. (a)and(b) showfinecellular-dendriticmicrostructures inSLM-fabricated316LSSspecimens. It is well understood that the microstructures obtained in AM-processed metal parts, whichdependontheappliedprocessingparameters, strongly influence themechanicalpropertiesof theparts, e.g., thedensification levels,yieldandtensilestrengthsandmicrohardness. Furthermore, thefinemicrostructures obtainedviaAMprocesses lead to improvements in tensile strength and microhardnesscomparedtoconventionalmanufacturingtechniques [28,29]. 3.2. Porosity Figure4showstheaverageporesizedistribution in theAM316LSSsamplesobtainedbyoptical microscopy. Theporesizesrangedfrom~5μmto~45μm,where thesmallerpores (≤5μm)accounted for themajority (~60%)andthe largerpores (>30μm)accountedfor less than3%.Theaverageporosity of theSLMspecimenswascalculatedtobe0.82%±0.36%,whichmeans thatahighdensification level (≥99%)wasachieved. 122