## 4 Summary and Outlook  
LMD of Ti6 Al4V is becoming a well established process for producing parts with complex structures. The microstructure and mechanical properties have been relatively well studied. Direct after LMD, the material features a columnar grains with \(\alpha\) martensite inside. Laser metal deposited Ti6 Al4V presents higher strength, but lower ductility. By applying post heat treatment, a strength-ductility balance can be achieved. After appropriate heat treatment, the specifications for the static mechanical properties, such as the ultimate strength, the yield strength and the elongation, can be met. For further research, the heat treatment methods should be further developed to modify the microstructure, since the previous results show that the laser metal deposited Ti6 Al4V presents generally lower ductility, even after the heat treatment documented in the literature. Additionally, in order to increase the productivity, the deposition rate should be further improved. Currently, the deposition rates for the typical processes are generally smaller than 0.5 kg/h. In comparison to LMD, other materials such as Inconel 625, can achieve a deposition rate of more than 5 kg/h; the achievable deposition rate with Ti6 Al4V is quite low. For the increase of the deposition rate, the plant and system technologies must be adapted. For example, the powder feeding nozzle for higher powder feeding rate should be developed and laser source with high power should be applied. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Powder** & **Laser** & **Scanning** & **Tensile** & **Yield** & **Tensile** & **Elongation** \\  & **Feeding Rate** & **Power** & **Speed** & **Axis** & **Strength** & **Strength** & \(A_{5}\) \\  & **\(m_{p}\)** & **\(P_{L}\)** & **V** & **Orientation** & **R\({}_{p}\)0.2** & **R\({}_{m}\)** & **(\%)** \\  & **(kg/h)** & **(W)** & **(mm/min)** & & **(MPa)** & **(MPa)** & **(MPa)** \\ \hline Kelbassa [20] & 0.036 & 450 & 500 & vertical & 984.37 & 1094.2 & 4.2 \\  & & & horizontal & 1040.8 & 1151.7 & 2.2 \\  & & 955 \({}^{\circ}\)C, 1 h, helium quenching & vertical & 922.2 & 1038.3 & 11.49 \\  & +700 \({}^{\circ}\)C, 2 h, argon cooling & horizontal & 933.9 & 1035.6 & 7.11 \\  & 640 \({}^{\circ}\)C, 1 h, vacuum oven cooling & vertical & 1008.9 & 1112 & 9.5 \\  & & horizontal & 1050.5 & 1147.3 & 7.07 \\ \hline Qiu [29] & 0.39–0.45 & 1100–1200 & 750–850 & vertical & 950 \(\pm\) 2 & 1025 \(\pm\) 2 & 5 \(\pm\) 1 \\  & & horizontal & 950 \(\pm\) 2 & 1025 \(\pm\) 10 & 12 \(\pm\) 1 \\  & 920 \({}^{\circ}\)C, 100 MPa, 4 h, furnace cooling & – & 850 \(\pm\) 2 & 920 \(\pm\) 1 & 17 \(\pm\) 2 \\ \hline Carroll [30] & 0.48 & 2000 & 636 & vertical (top) & 945 \(\pm\) 13 & 1041 \(\pm\) 12 & 14.5 \(\pm\) 1.2 \\  & & vertical (bottom) & 970 \(\pm\) 17 & 1087 \(\pm\) 8 & 13.6 \(\pm\) 0.5 \\  & & horizontal & 960 \(\pm\) 26 & 1063 \(\pm\) 20 & 10.9 \(\pm\) 1.4 \\ \hline Sterling [31] & 0.576 & 350 & 1015.8 & horizontal & 908 & 1038 & 3.8 \\  & 704 \({}^{\circ}\)C, 1 h, furnace cooling & & 959 & 1049 & 3.7 \\  & 1050 \({}^{\circ}\)C, 2 h, furnace cooling & & 957 & 1097 & 3.4 \\ \hline Zhai [39] & 0.06 & 330 & 600 & horizontal & 1005 & 1103 & 4 \\  & 760 \(\pm\) 4 \({}^{\circ}\)C, 1 h, air cooling & & 1000 & 1073 & 9 \\  & 0.12 & 780 & 800 & 990 & 1042 & 7 \\  & 760 \(\pm\) 4 \({}^{\circ}\)C, 1 h, air cooling & & 991 & 1044 & 10 \\ \hline Keist [42] & 0.72 & 2000 & 600 & vertical & 916 \(\pm\) 34 & 1032 \(\pm\) 31 & 19 \(\pm\) 4 \\  & & horizontal & 961 \(\pm\) 40 & 1072 \(\pm\) 33 & 17 \(\pm\) 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical properties of specimens of Ti6 Al4V fabricated by LMD. Last but not least, it would be interesting for both research and industry, if the process could be conducted under an open atmosphere. As shown in the state of the art, it is difficult to process Ti6 Al4V by local shielding because of the high sensitivity to oxidation of the material.