Abstract
Additively manufactured (AM) materials and hot rolled materials are typically orthotropic, and exhibit anisotropic elastic properties. This paper elucidates the anisotropic elastic properties (Young’s modulus, shear modulus, and Poisson’s ratio) of Ti6Al4V alloy in four different conditions: three AM (by selective laser melting, SLM, electron beam melting, EBM, and directed energy deposition, DED, processes) and one wrought alloy (for comparison). A specially designed polygon sample allowed measurement of 12 sound wave velocities (SWVs), employing the dynamic pulse-echo ultrasonic technique. In conjunction with the measured density values, these SWVs enabled deriving of the tensor of elastic constants (Cij) and the three-dimensional (3D) Young’s moduli maps. Electron backscatter diffraction (EBSD) and micro-computed tomography (μCT) were employed to characterize the grain size and orientation as well as porosity and other defects which could explain the difference in the measured elastic constants of the four materials. All three types of AM materials showed only minor anisotropy. The wrought (hot rolled) alloy exhibited the highest density, virtually pore-free μCT images, and the highest ultrasonic anisotropy and polarity behavior. EBSD analysis revealed that a thin β-phase layer that formed along the elongated grain boundaries caused the ultrasonic polarity behavior. The finding that the elastic properties depend on the manufacturing process and on the angle relative to either the rolling direction or the AM build direction should be taken into account in the design of products. The data reported herein is valuable for materials selection and finite element analyses in mechanical design. The pulse-echo measurement procedure employed in this study may be further adapted and used for quality control of AM materials and parts.
Highlights
Ti6Al4V alloy was developed in the 1950s for the aerospace industry, which is still its largest consumer [1,2]
Electron backscatter diffraction (EBSD) and micro-computed tomography were employed to characterize the grain size and orientation as well as porosity and other defects which could explain the difference in the measured elastic constants of the four materials
Some differences in the density valPuroepsedrteyduced fromWrtohueghAt rchimedesEBmMeasurementsDvEsD. μCT haveSLM been reported befoDreentsoitoy,[ρ37(g]/. cHmo3)wever4,.4s2u3c±h0d.0i0ff0e5rence4.d42o1e±s n0.o00t0s5eem4t.4o28ex±p0l.a0i0n08the 4d.4if1-0 ± 0.0008 ference in the trendRPsoelroaoftsiivEtyeBd(M%en)asintyd(%D)ED vs. S90L9..2M800 in the curren909t..27s55tudy. It shou90l9.d.0991be borne in909..5500 mind that different Ti6Al4V powders were used for the three additive manufacturing (AM) processes, which differed in their size, oxyTgoeenlu, cainddatetrtahceeeeffleecmt oefntthelepvoerless.’μsiCzeT, sinhacplues, iaonndadnisatlryibsuetsioonf itnhtehDe sEaDmple on the and electron beam melting (EBM) samplesobrseevrevaeldedpomlaarintyyaenvdenthleymdeisapsuerreseddelhasigtihc-pdreonpseirttyiesd,eμfCecTtsi,mwaghiincghomf tahye sbaemples was related to iron conctoanmdiuncatetido.nT, whrheeic-dhicmoeunlsdioonraigl iμnCaTteifmroamgesthoef pthoewfdouerrss(asmeeplcehseamreicsahloawnnali-n Figure 5. yses results in SecTthioense2im.1)a.gSeus cwherceoanntaalmyziendatbiyonsecttoinugldthselipgrhotblaybilnitcyretharseeshthoelddaetn2s0i0tyμmin, iA.er.,only pores chimedes measurwemithenatds.iameter larger than 200 μm are taken into account in the analysis
Summary
Ti6Al4V alloy was developed in the 1950s for the aerospace industry, which is still its largest consumer [1,2]. Despite the abovementioned advantages of metal AM in general, and AM of Ti6Al4V the ability to fabricate fully dense, defect-free parts with homogeneous microstructure, good surface finish, and good mechanical properties are still considered to be a challenge [9,10,11]. Metal-based AM technologies are typically based on a layer-by-layer deposition approach and are classified according to the type of feedstock used (powder vs wire), the energy source (e.g., laser vs electron beam), and the methodology of printing (e.g., direct deposition vs powder bed). The two major metal AM processes are powder bed fusion (PBF) and directed energy deposition (DED). The former can further be divided into selective laser melting (SLM), electron beam melting (EBM), etc
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