## 4 Discussion  
The XRD investigation showed that in the 3D-printed titanium sample, two phases were found, namely aluminum titanate (Al\({}_{0.15}\)Ti\({}_{0.85}\)) and less aluminum titanate vanadate (Ti\({}_{2}\)VAI). The established hexagonal phase of Al\({}_{0.15}\)Ti\({}_{0.85}\) has a crystallite size of 77 nm, and the cubic phase of Ti\({}_{2}\)VAI has a crystallite size of 18.5 nm. The diffractogram of a milled titanium sample showed two phases: mainly aluminum titanate (Al\({}_{0.15}\)Ti\({}_{0.85}\)) and less titanium vanadate (Ti\({}_{0.8}\)V\({}_{0.2}\)). A hexagonal phase of Al\({}_{0.15}\)Ti\({}_{0.85}\) with crystallite sizes of 106 nm and a cubic phase of Ti\({}_{0.8}\)V\({}_{0.2}\) with crystallite sizes of 22.8 nm were found. The nanoindentation experiments revealed significant differences in the indentation modulus and indentation hardness between the 3D-printed Ti-6 Al-4V specimens and the milled Ti-6 Al-4V specimens. Both parameters had higher values in the 3D-printed Ti-6 Al-4V sample. One reason for this result is that the 3D-printed Ti-6 Al-4V sample had smaller crystallite sizes than the milled one. The same tendency was obtained for the [PERSON]'s modulus of both samples, obtained by means of the tensile test (Table 3), but the values were smaller than those of the indentation modulus. This is because the indentation modulus is calculated in some sample volume, while the [PERSON]'s modulus is calculated in some direction [33]. The obtained results for the indentation hardness are in agreement with those obtained by [PERSON] [34]. The obtained from us mechanical properties are in good agreement also with these obtained from [PERSON] [35], [PERSON] [36], and [PERSON] [37]. We obtained higher mechanical properties than [PERSON] [38], but probably the reason is that we used different processing parameters. Moreover, she used a higher temperature of annealing heating and a different indentation method. We found that as indentation depth increased, the indentation hardness and modulus of both titanium alloys decreased slightly. The reason for different properties in the depth could be the layer-by-layer production method with several cycles of heating and cooling, which leads to structure changes in the depth, respectively, and changes in the mechanical properties. The slightly higher concentration of titanium in the composition of the 3D-printed sample, as well as the slightly lower concentration of aluminum, could be another reason for the higher indentation hardness obtained with the 3D-printed titanium sample. Nanoindentation is a method which determines the local mechanical properties at a point on the surface of the material, but the investigated samples have non-uniform surfaces, which can lead to higher experimental error when measuring the indentation hardness and indentation modulus. The results from the tensile test showed that the 3D-printed sample made by means of selective laser melting (SLM) technology had about 26% higher tensile strength and smaller elongation than the milled one. The same tendency for yield strength and elongation was obtained by [PERSON] and [PERSON] [39]. The results from the three-point bending test showed that the 3D-printed Ti-6 Al-4V sample had higher flexural strength than the milled one. Two different strain rates (1 mm/min and 60 mm/min) were used, and their influence on the obtained flexural strength was investigated as well. The strength achieved at different loading rates may be a function of the manufacturing method of the test specimens. For the milled Ti-6 Al-4V specimens, increasing speed causes a proportional increase in the recorded strength of \(\sim\)4.9%. As the roughness of the sample surface can have an influence on the nanoindentation results, AFM was used to study the surface topography and roughness of both titanium alloys. The AFM observation of the surface topography of the investigated samples showed that the milled Ti-6 Al-4V sample was characterized by a higher roughness than the 3D printed one.