## 3 Results and Discussion
### Analysis of Schmid Factor for a Load Applied along the Build Direction  
The orientation maps of various forms of DMLS Ti6 Al4V(ELI) shown in Figure 5 may not necessarily indicate the ease of slip for different deformation systems in the material under load. The Schmid law is commonly used to predict the ease of slip of different slip systems in a material depending on the direction of applied load. For further details on the Schmid law, different deformation mechanisms in \(\alpha\)- and \(\beta\)-phases in Ti6 Al4V and the use of the MTEX toolbox for statistical analysis of the global Schmid factor, the reader is referred to the authors' work published in ref. [34]. In this study, the statistical analysis of the global Schmid factor for the three main slip mechanisms of the \(\alpha\)-phase in the three different microstructures of LPBF Ti6 Al4V(ELI) was conducted based on the loading axis of quasi-static test compression specimens.  
The loading axis of the test samples was the same as the build direction during the DMLS process and, together with the second rank stress tensor acting on this axis, is illustrated in Figure 7. Since the volume fraction of the retained \(\beta\)-phase in samples C, D and E is very small (<7%), as stated in Section 3.2, its effect on the deformation of the alloy was ignored, and only the global Schmid factor for the common slip systems in the \(\alpha\)-phase was evaluated in this study. Figures 8-10 show the statistical distribution of the global Schmid factor for prismatic, basal and pyramidal <\(\alpha\)> slip systems in different forms of LPBF Ti6 Al4V(ELI) alloy.  
Figure 6: The area fraction distribution of different grain sizes determined from EBSD maps of (**a**) samples C, (**b**) samples D and (**c**) samples E.  
Figure 7: Schematic diagram illustrating the specimen loading axis and corresponding second-rank stress tensor.  
Figure 8: Typical values of the global Schmid factor for basal slip systems of the \(\alpha\)-phase for the load applied along the build orientation in samples (**a**) C, (**b**) D and (**c**) E, while (**d**) shows the statistical distribution of the values obtained in each form of material.  
Figure 9: Typical values of the global Schmid factor for prismatic slip systems of the \(\alpha\)-phase for the load applied along the build orientation in samples (**a**) C, (**b**) D and (**c**) E, while (**d**) shows the statistical distribution of the values obtained in each form of material.  
It is seen in Figure 8 that 66%, 63% and 43% of \(\alpha\)-grains in samples C, D and E, respectively, have their global Schmid factor higher at values in the range of 0.4-0.5 for the basal slip system. Only 33% of grains in samples C and D, and 39% of grains in sample E, have their values of global Schmid factor in the range of 0.4-0.5 for the prismatic slip system, as seen in Figure 9. Moreover, 57% of the grains in the three different groups of DMLS Ti6 Al4V(ELI) samples have their global Schmid factor in the upper range for the pyramidal <\(\infty\)> slip system. The difference in the values of critical resolved shear stress (CRSS) between the basal, prismatic and pyramidal <\(\infty\)> slip systems is comparatively small [34]. However, the sequence of ranking for these deformation mechanisms in terms of CRSS from low to high was seen in [34] to be basal, prismatic and pyramidal <\(\infty\)>. The observation made in Figures 8-10 and proceeding discussions suggest that the \(\alpha\)-grains with high values of Schmid factor in either of the deformation systems are likely to be activated during plastic deformation.