Page - 40 - in 3D Printing of Metals

Metals 2016,6, 284 particularly for tensilepropertiesofmetalAMTi64,arecomparable to thoseofwroughtmaterialand muchbetter than itsas-cast form[12,13].However, therearestillvery limitedstudies involved in their wearproperties thatarecritical forsomespecificapplicationsunderwearandfrictionconditions [14]. Asknown,Ti64possessespoorwear resistanceunderdryslidingdue to lowprotectionexertedby tribo-oxides formedat the surface [15,16]. Therefore, it is imperative to studyonwearbehaviorof AMTi64partsandknowtheirwearproperties incomparisonwith thecounterpartsmanufacturedvia conventionalmethods. Inourpreviousworkspublishedelsewhere [5,6,17–21], themicrostructureand mechanicalpropertiesof theEBM-builtTi64partshavebeensystematicallystudied. Thepresentwork aimsat investigating thewearpropertiesofEBM-builtTi64partswithvarious thicknessesandmaking a comparative studyagainst commercially as-cast Ti64 sample. It is supposed tobe an important supplementarystudytoachievebetterunderstandingforpracticalapplicationsofEBM-manufactured Ti64parts. 2. ExperimentalSection 2.1.Materials,Fabrication, andSamplePreparation All theEBM-built sampleswere fabricatedviaanArcamA2XX(ArcamAB,Mölndal,Sweden) EBMmachine,whichhasabuildchamberofΦ420mm×380mm.Aschematicdiagramofa typical EBMmachine is illustrated inFigure1. Thepowderused in thisprocesswasTi-6Al-4VELI (Grade23) (BatchNo. 877)suppliedbyArcamAB,andwasmainlyspherical inshape,asshowninFigure2a. The sphericalnatureof thepowderassuresgoodfollowabilityandthusconsistency in thespreadingof powderduringraking. Thepowderhadasizedistributionrangingfrom45to105μm,while themean particle sizewas61.8μm±23.8μm.AsummaryonthepowdersizedistributionofTi64usedduring fabrication is asdepicted inFigure2b. Thenominal compositionof theTi64powder is as follows: 6.0Al-4.0V-0.03C-0.1Fe-0.1O-0.01N-<0.003HandthebalancebeingTi (wt.%). TheEBM-built samples ofvarying thicknessesof0.5mm,1mm,5mm,10mm,and20mmby100mminlengthand30mmin heightareshowninFigure3a. Theywere termed0.5mm,1mm,5mm,10mm,and20mmsamples, respectively. Thebuildchamberwasunderacontrolledvacuumenvironmenthavingatemperature rangeof600 to650 ◦C.Thesampleswerebuiltona210mm×210mmstainlesssteel (SS)startplate. ThesamplesweresubsequentlyremovedfromtheSSstartplateviaknockingonthebacksideof the SSplateandcleanedwith theuseof thepowderrecoveringsystem(PRS).PRSprimarily functionedas agritblasterwhereblastingmedia (Ti64)wereacceleratedtowards thesamplesurfacewith theaidof highvelocitycompressedairwith theaimtoremoveanyresidualpartially-sinteredandunmelted powderparticlessurroundingthesamples’ surface. Theas-cast samplesweresupplied in theformofa rodbyTitanEngineeringPte. Ltd. (Singapore,Singapore), cast to thespecificationASEMB348GR5 andhadadimensionofΦ25.4mm×1500mm.TheEBM-built sampleswereslicedfromthemiddle section (X–Zplane) intosquaresof20mm×20mm,while theas-cast samplewassliced intoadiscof Φ25.4mm×5mm.All thesampleswere thenhotmountedwithphenolicpolymerandsubsequently polishedtoamirror-likefinish. 40