Abstract
Numerous factors, including variable grain structures and different inherent defects, impact the mechanical behavior of Ti6Al4V parts fabricated using metal Additive Manufacturing (AM) processes. This study focuses on an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain boundary misorientation angles, and inherent defects, as byproducts of the electron beam powder bed fusion (EB-PBF) AM process, impact its anisotropic mechanical behavior. Standard tensile testing, conducted on samples produced at different orientations relative to the build table, showed significant anisotropy in elastic-plastic constitutive characteristics. Furthermore, X-ray computed tomography (CT) and electron back-scattered diffraction (EBSD) analyses were conducted on as-built samples to assess the effects of inherent defects and microstructural anomalies on such behavior. The samples arranged vertically and parallel to build direction had an average porosity of 0.05%, while the horizontally built samples, which were perpendicular to the build direction, had an average porosity of 0.17%. Moreover, the vertical samples showed larger grain sizes, with an average of 6.6 µm, wider α lath sizes, a lower average misorientation angle, and subsequently lower strength values than the other two horizontal samples. Among the three strong preferred grain orientations of the α phases, <1 1 2¯ 1> and <1 1 2¯ 0> were dominant in the horizontally built samples, whereas the <0 0 0 1> orientation was dominant in vertically built samples. Finally, larger grain sizes and higher beta-phase volume ratios were observed in the areas located at distances further away from the build plate. This was possibly due to the change in thermal gradients, cooling rates, and some thermal annealing phenomena resultant from the elevated build chamber temperature.
Highlights
Ti6Al4V alloy is an α + β phase alloy, primarily used in the aerospace industry because of its high strength and lightweight
Powder bed fusion (PBF) additive manufacturing (AM)-processed Ti6Al4V parts are known to possess a distinctive microstructure, significant mechanical anisotropy, and various unwanted inherent defects such as a lack of fusion (LOF) porosity, keyhole porosity, and high surface roughness [8,9,10]. Some of these inherent issues of powder bed fusion (PBF) techniques are inhibiting them from being widely adopted in different manufacturing industries [11]. These intrinsic microstructural aspects of PBF processes are very crucial to the resultant mechanical behavior of AM parts, under various high-temperature applications
After the vibratory polishing, all samples were further cleaned in an ultrasound sonicator using acetone, metha4nofo2l0, and isopropyl alcohol (IPA), sequentially, before conducting electron back-scattered diffraction (EBSD) analysis on them
Summary
Ti6Al4V alloy is an α + β phase alloy, primarily used in the aerospace industry because of its high strength and lightweight. Powder bed fusion (PBF) AM-processed Ti6Al4V parts are known to possess a distinctive microstructure, significant mechanical anisotropy, and various unwanted inherent defects such as a lack of fusion (LOF) porosity, keyhole porosity, and high surface roughness [8,9,10] Some of these inherent issues of PBF techniques are inhibiting them from being widely adopted in different manufacturing industries [11]. A comprehensive analysis, including various microstructural features such as intrinsic defects, grain sizes, crystallographic texture, preferred grain orientation, and their effects on the mechanical anisotropic behaviors, was felt highly necessary by the authors to provide further insight and precaution for the users of EBM Ti6Al4V in various critical applications In this current study, an in-depth analysis of the variation of inherent defects, along with microstructural aspects and their contribution to the observed mechanical behaviors, has been conducted with the help of an X-ray computed tomography (CT) and electron back-scattered diffraction (EBSD) analysis
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