Seite - 112 - in 3D Printing of Metals

Metals 2016,6, 286 3.ResultsandDiscussion 3.1. PhasesandComposition Identification Figure2depicts the typicalXRDspectrumofSLM-processedcomposites. Itwasevident that thepeakscharacterizedwithrelativelystrongdiffraction intensitieswere identifiedas thealuminum matrix, i.e., theAlSi10Mgphase.Meanwhile, theprimaryphaseofSiwasalsogeneratedduringSLM, whichwasmainlyconsistentwith thepreviousreports. Thediffractionpeakswithrelativelyweak intensitycorrespondingto thenewsilica-richphase (aluminumsilicate, i.e.,Al2Si4O10)was identified, revealingthegeneral formationof the insitusynthesizedAl2Si4O10 reinforcedAMCs. Figure2.XRDspectrum(a)andthefieldemissionscanningelectronicmicroscope(FE-SEM)images showingthecharacteristicmicrostructure(b)of theSLM-processedcompositesat150Wand400mm/s. ThemicrostructureofSLM-processedcomposites is showninFigure2b. Itwasclearlyobserved that thequitefinecellularmicrostructurewasobtainedwithanellipseshape. EDXspectraof the two differentphasesabovewereobtainedtodeterminetheirrespectivechemicalcompositionquantitatively, andtherelevantresultsare illustratedinTable1. Itwasrevealedthat thephase(Point1,Figure2b)was richinAlelementswithasmallamountofSiandOelementsdissolvedinthealuminummatrix,which wasconsideredthealuminummatrix. Thehigherconcentrationofoxygencouldhavebeenascribed to thediffusionof theAl2O3 reinforcement.Ontheotherhand, themolten liquidaluminumtended tooxidizeduringSLMdue to the residualoxygenwithin theoperatingchamber [11],whereas the phase (Point 2, Figure2b)wasmainly composedofAl, Si, andOelementswithanatomic ratioof approximate2:4:10,whichrevealedthat thenewphaseof insitusynthesizedAl2Si4O10 reinforcements weregenerated.Moreover,asseenfromtheEDXresults, thehighcoolingrate inducedbySLMcan effectivelyextendthesolidsolubilityofSi in thealuminummatrix, leadingtoasupersaturatedsolid solutionof6.07%. Furtheranalysisof theEDXresultof thealuminummatrix indicatedSLMcould largelyextendthesolidsolubilityofSi inα-Al, leading toasupersaturatedsolidsolutionof6.07%. Thus, it is reasonable toconcludethat the insituAl2Si4O10phasewasgenerated,andtheattendant in situAl2Si4O10/AlSi10MgcompositesweresuccessfullypreparedbySLMcombinedwith theXRDand EDXresults. Table1.EDXelementanalysisofPoint1andPoint2 inFigure2bshowingthechemical compositions in theSLM-processedAl2Si4O10/AlSi10Mgcomposites. Position Elements (at.%) Al Si O Mg Point1 89.1 5.75 4.74 0.41 Point2 12.56 24.98 62.46 - 112