## 2 Materials and Methods  
Ti6 Al4V is widely used in a broad range of different applications, ranging from use as turbine blades in the aerospace industry, to prostheses in the biomedical industry. The employed samples were fabricated via an EOS M290 machine equipped with an Ytterbium laser with a maximum power of 400 W and a building space of 250\(\times\)250\(\times\)325 mm\({}^{3}\). The SLM technology implies that a laser scans the surface of a powder bed, locally melting the powder alloy, realizing a solid layer when cooling down. The building plate that contains the powder bed shifts down, and a new layer of metallic powder is spread on the top of the just-solidified metal, and the process goes on, building the component in a bottom-up manner, layer upon layer. The employed Ti6 Al4V powder was supplied by EOS GmbH, and its chemical composition is reported in Table 1.  
In Figure 1, a SEM image of the used powders and the granulometry distribution measured by the laser diffraction granulometer Mastersizer 2000 are reported. The particles have a spheroidal shape, and d\({}_{10}\), d\({}_{50}\) and d\({}_{90}\) are 23.62, 37.69 and 59.11 \(\upmu\)m, respectively, according to the material datasheet [29]. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Al** & **V** & **O** & **N** & **C** & **H** & **Fe** & **Y** & **Ti** & **Other** \\ \hline
5.50–6.75 & 3.50–4.50 & 0.20 & 0.05 & 0.08 & 0.015 & 0.30 & 0.005 & Bal & 0.10 Max \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of Ti6 Al4V powder (wt.%). All the samples were fabricated by adopting the standard process parameters provided by EOS for this alloy. They are summarized in Table 2.  
The samples geometry employed for the present study is dog-bone, with a square cross-section. Nominal dimensions were chosen according to the standard [30], referring to sintered parts, not being available at present a specific standard for additive manufactured components. The selected geometry has a nominal gauge length of 25.40 mm and a cross-section of 5.72 x 4.00 mm\({}^{2}\) (Figure 2). The first batch of nine specimens was fabricated with three different orientations: vertical, horizontal and inclined of 45\({}^{\circ}\), with respect to the building plate. Out of them, 2 sets of 3 specimens (each one with the three different orientations) were processed by 2 different BF conditions; meanwhile, the remaining 3 samples were not postprocessed at all. Indeed, the tests along different orientations were also intended to provide a verification of a substantial isotropy of the alloy, coherently with what is reported by the EOS Ti6 Al4V datasheet [31], in which very similar yield stresses (945 and 965 MPa) and ultimate tensile strengths (1055 and 1075 MPa) are declared for the horizontal and vertical building directions, with the percentage differences falling below 2%. Analogous properties were also found by other authors [32; 33; 34; 35], who used recent EOS SLM machines, as the one of this research. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Process Parameters**} \\ \hline Layer thickness & 30 \(\mu\)m \\ Laser power & 340 W \\ Focal spot dimension & 0.1 mm \\ Scanning speed & 1250 mm/s \\ Table temperature & 160 \({}^{\circ}\)C \\ Hatch spacing & 0.12 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Process parameters employed for all samples. Figure 1: (**a**) SEM image of Ti6 Al4V powders; (**b**) granulometry distribution of the powders. Figure 2: Dog-bone specimen geometry according to the ASTM E8/E8M-04 standard. In these studies, the differences in terms of ultimate strength between the different orientations were within 4%. More marked differences can be observed if less-modern machines are used for specimen production, instead, as documented by other works in the literature.