Page - 59 - in 3D Printing of Metals

Metals 2017,7, 91 Figure7.Sampleofcrosssectionareaandthemeasuredarea for thedeterminationof theequivalent diameter. In thispicture,a0◦orientedSLMpart is seen. (2)VickershardnessHV10(accordingtoDINstandard—DINENISO6507-1)wasmeasuredon bothsitesof thebackandtopareasof thespecimen(Figure8)usingthehardnesstester,Zwick3212.002 (ZwickGmbHCoKG,Ulm,Germany). Thepartswere testedwitha test loadof98.07Nwithina test timeofabout10seconds.Onaverage,10 indentspersurfacewere takenforeachcondition. Prior to themeasurementof thebackandtopareas, thepartwas facecut (between10and50μm)toachieve apractical referencesurface. Figure8.Test specimenforhardnessdetermination.Hardnesswasmeasuredonbothsides (n=10for eachcaseandside). 2.4. StatisticalAnalysis All data are expressed as means ± standard deviation (SD). The association between the geometrical influences (length and diameter of the strut as well as the slenderness ratio λ) and thecompressionstrengthwasassessedbylinearregression.All statisticalanalyseswereperformed usingSPSS, softwareversion22 forWindows(SPSS® Inc.Chicago, IL,USA).Atwo-sample t-testwas performedtostatisticallyexaminesignificantdifferencesbetweenthemeans. This testwasusedfor measuringthehardnessofmanufacturedpartsdependentonmanufacturingtypeandheat-treatment variation. Moreover, the testwasperformed fordetermining the surfacequalityof SLMandEBM parts.Differencesofp<0.05wereconsideredasstatisticallysignificant. 59