## 4 Conclusions  
The three different microstructures of Ti6 Al4V(ELI) produced by DMLS technology followed by heat treatment and their corresponding properties at high strain rate and temperature have been presented and discussed in this paper, with the following conclusions deduced:  
* The DMLS Ti6 Al4V(ELI) showed a wide range of microstructures dependent on heat treatment regime. The average \(\alpha\)-lath thickness increased from 2.5 to 6 \(\upmu\)m and 9 \(\upmu\)m for heat treatment temperatures of 800, 940 and 1020 \({}^{\circ}\)C, respectively.
* Samples C and D exhibited a random \(\alpha\)-lathe texture, however, some \(\alpha\)-lathe crystal-lographic orientations were repeated within the same prior \(\beta\)-grains. The colonies of \(\alpha\)-lathes within the equiaxed and semi-equiaxed morphologies in samples E, consisted of crystals with a similar orientation.
* Samples C (heat treated at 800 \({}^{\circ}\)C) recorded the highest value of Vickers microhardness. A decline in hardness was noted upon heat treatment at 940 \({}^{\circ}\)C for samples D which was attributed to coarsening of \(\alpha\)-lathes. Surprisingly, a gain in hardness was then seen to occur in samples E that were heat treated just above the \(\alpha\)\(\rightarrow\)\(\beta\) transformation temperature, even though these samples recorded a higher average size of the \(\alpha\)-lathes.
* It was shown that the microstructures of samples C, D and E are sensitive to strain rate and temperature, with the flow stress increasing with increase in strain rate and decreasing with the increase in temperature.
* Samples C and E yielded at the highest and lowest value of stress at most of the test conditions, respectively. This was attributed to variation in microstructure where samples C with smaller grain sizes resulted in higher dynamic strength and samples E yielded at lower stress due to the presence of coarse \(\alpha\)-lathes in the microstructure.
* The strain rate sensitivity of these samples varied, with samples D showing the highest value followed by samples E, while samples C showed the lowest values, at any given temperature. This difference was also ascribed to microstructure, in particular, the grain sizes and the texture.
* For all three different samples of DMLS Ti6 Al4V(ELI), the deformation surfaces were characterised by the formation of ASBs running across the cut surfaces.
* The thickness of these ASBs increased with strain rate and temperature.
* The thickness of these ASBs also varied in different samples due to variation of hardness and strength of the samples as a result variation in heat treatment.
* Micrographs of the fracture surfaces of samples C, D and E were characterised by elongated dimples in all conditions of testing, and these dimples were elongated along the directions of shear, with their sizes increasing for deformation at high temperature.  
Conceptualization, A.M., M.M. and W.d.P.; methodology, A.M.; formal analysis, A.M.; writing--original draft preparation, A.M.; writing--review and editing, A.M., M.M. and W.d.P.; supervision, M.M. and W.d.P.; funding acquisition, W.d.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the South African Department of Science and Innovation (DSI) through the Council for Scientific and Industrial Research (CSIR), for the Collaborative Program in Additive Manufacturing, Contract No.: CSIR -NLC-CPAM-18-MOA-CUT-01.  
Not applicable.