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Metals 2017,7, 64
energy is applied, resulting in spatter ejection [36]. In this study, spherical pores dominated the
non-spherical ones, where rectangular-shaped poreswere visible only near the edges of the cut
specimens. This indicates thatmostof theporositydefects in theSLMsampleswereduetogaspores
duringthegasatomisationofthe316LSSpowders,similartotheworkcarriedoutbyTammas-Williams
etal. [37]. Thegasporescouldbeproduceddueto thepresenceofmoistureorcontaminantsonthe
surfaceof thepowderparticles [38]. TheseporescouldalsobeformedbythereactionsbetweenO2
andCwhicharepresent insmallamountsduringSLMprocessing,causingCOorCO2gasentrapment
in theSLM-built parts [39]. Thenon-uniformporedistribution in thisprocess couldbe causedby
oneof the followingfactors: (i) thevariationofsurfaceroughness [40]; and(ii) the layer-wisebuild
manner of theAM[41]. Thevariation in surface roughness results in an inhomogeneouspowder
distribution that leads to an inconsistentmelt flowandanunstablemoltenpool in the successive
layers [42]. These, in turn, contribute to thediscontinuities in the scan track formation, andhence
the irregularporedistributionobtained in this study.Nevertheless, thesedefects (poresandvoids)
aredetrimental to thequality ofAM-fabricatedmetal parts, especially as they reducemechanical
propertiessuchasyieldandtensile strength.
3.3.Microhardness
Theresultsof theVickersmicrohardness (HV) testswereevaluatedby: (i) comparingHVvalues
ofSLMsamples fordifferentcutplanes (x–y,x–zandy–z)asshowninFigure10;and(ii) comparing
HVvaluesofSLMandWMsamples (Figure11).
Figure10.Averagemicrohardness (HV)values forSLMspecimens in thex–y,x–zandy–zplanes.
FromFigure10, it canbeobservedthat theaveragemicrohardnessvalues for theSLMspecimens
inx–y,x–zandy–zplanesare262HV,237HV,and239HV, respectively. Themicrohardnessof the
SLMsamplesat thex–yplane(scandirection)wasthehighestcomparedtotheother twoplaneswhich
hadsimilarbutconsiderably lowerHVvalues. Thediscrepancyof themicrohardness ineachplane
indicatesanisotropyinSLM,whichis typicalofAMprocesses formetalcomponents [28,43–45]. This is
becauseofthelayer-wisebuildapproachwiththe“island”scanstrategyinAMprocesses,whichmeans
localised melting of powder particles that often results in non-homogeneous morphologies and
anisotropicgrainstructures [46,47].However, thesimilaraverageHVvalues in thex–zandy–zplanes
indicatedamoreuniformmicrohardnessdistribution in thebuilddirection compared to the scan
directionfor theSLM-processedsamples. Figure11showstheaveragemicrohardnessvaluesof the
SLMsamples (228HV),whichwerehigher thanthoseof theWMsample (192HV).This is consistent
withvarious literature, inwhichthemicrohardnessofAM316LSSparts is typicallyhigher thanthat
ofconventionallymanufactured316LSSparts [28,48].Highermicrohardness inAM316LSSsamples
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book 3D Printing of Metals"
3D Printing of Metals
- Title
- 3D Printing of Metals
- Author
- Manoj Gupta
- Editor
- MDPI
- Location
- Basel
- Date
- 2017
- Language
- English
- License
- CC BY-NC-ND 4.0
- ISBN
- 978-3-03842-592-2
- Size
- 17.0 x 24.4 cm
- Pages
- 170
- Keywords
- 3D printing, additive manufacturing, electron beam melting, selective laser melting, laser metal deposition, aluminum, titanium, magnesium, composites
- Categories
- Naturwissenschaften Chemie