## 3 Results and Discussion
### Analysis of Deformation Surfaces  
To determine failure mechanisms under quasi-static loads for different microstructures of LPBF Ti6 Al4V(ELI), microstructural analysis was carried out for samples tested at each strain rate. Figures 14-16 show the microstructures of deformed samples and corresponding failure mechanisms. The typical condition of the samples after testing at each strain rate is shown in (d) of each of these figures. Microstructural analysis of these deformed surfaces revealed that adiabatic shear bands (ASBs), shown in each micrograph in these figures, were the primary failure mechanism in the three microstructures of the LPBF Ti6 Al4V(ELI) alloy. The ASBs formed in all samples were tested at different strain rates. Adiabatic shear failure is generally thought to dominate the failure of materials loaded at high strain rate [41]. This is due to the fact that during the deformation of materials at high strain rates, inelastic work is transformed into heat, which cannot fully dissipate into the surrounding material during the short period of the plastic flow [42]. This raises the local temperature, causing thermal softening, which at some instance of plastic strain outweighs the flow hardening, and shear instability occurs. A shear localization occurs, forming a narrow shear band such as the ones shown in Figures 14-16, when the stress within the shear zone is exceeded by stress in other larger zones of the material [43]. Figure 14: Typical shear-deformed surfaces of samples C after tests at strain rates of (**a**) 0.001 s\({}^{-1}\), (**b**) 0.005 s\({}^{-1}\) and (**c**) 0.1 s\({}^{-1}\), while (**d**) shows the typical condition of the test samples after testing at the respective strain rates. reported in other studies on AM material [16,44]. However, the sizes of the ASBs were found to be thicker for the tests conducted at high strain rate for samples C, D and E reported in ref. [45] as compared with the ones reported in Figures 14-16 for tests conducted at quasi-static strain rate. The values of the thickness of the ASBs measured from Figures 14-16 and those obtained from [45] for tests conducted at two high strain rates for the three microstructures of LPBF Ti6 Al4V(ELI) are shown in Table 3.  
The results presented in Table 3 follow from the fact that at high strain rates, the peak stresses and corresponding plastic shear strain are higher, thus higher peak temperatures in localised zones are expected, and therefore a wider ASB formation is imminent. The deformed surfaces of samples C and D are characterised by narrow transformed shear bands with cracks propagating along them. The bifurcation of these narrow shear bands is evident in samples D. Both transformed and deformed shear zones are evident in samples E shown in Figure 16b,c. These different shear zones are an outcome of the extent of strain localization occurring during deformation. The transformed narrow zones (ASBs), such as those shown in Figures 14-16, are as a result of extensive localised flow, while the deformed shear zones seen in Figure 16b,c, characterised by shearing lamellar laths, are formed as a result of lesser localised flow due to higher ductility of the material. The presence of deformed shear zones in samples E were attributed to the ease of slip, and therefore plastic deformation aided by parallel \(\alpha\)-laths in the microstructure shown in Figures 4e and 5e. The thickness of the transformed ASBs in samples E is also seen to remain unchanged as the quasi-static strain rate increases. This was ascribed to earlier formation of deformed adiabatic shear zone in these samples, thus impeding formation of wider transformed ASBs within the tested plastic strain range. However, the difference in thickness of transformed ASBs is conspicuous at high strain rates because such levels of strain rate are known to cause large plastic deformation within a very short period.