## 2 Metals Used in WDED and Types of Microstructure and Mechanical Properties
### Titanium-Based Alloys
[78], investigated the microstructure of the top-to-bottom regions of the Ti-6 Al-4V alloy at low magnification. The columnar prior \(\beta\) grains are shown from the top to bottom of the build direction, as shown in Figure 7a-c. This microstructure was achieved because of the different temperatures during the solidification in the direction of the heat flow. In addition, a small amount of the micro and macro-pores is observed in the cross-section. The microstructure in the layer bond and HAZ has low changes due to thermal cycles and intrinsic heat treatment of neighboring weld bead deposition. Moreover, Figure 7d shows that the substrate of the AM after fabricating the sample on that has equiaxed prior \(\beta\) grains. The microstructure of the Ti-6 Al-4V alloy fabricated by the WDED at the high magnification shows the mixture of the thinner \(\alpha\) and \(\alpha^{\prime}\) (martensite) with the prior \(\beta\) grains, but after annealing treatment (710 \({}^{\circ}\)C for 2 h) the microstructure is changed to the \(\alpha+\beta\) structure, as shown in Figure 8 [78]. Figure 8: Microstructure of the Ti-6 Al-4V alloy fabricated by WDED (**a**) as-deposited and (**b**) annealing treatment [78]. Figure 7: Macro and Microstructure of the Ti-6 Al-4V alloy fabricated by WDED, (**a**) macrostructure, microstructure (**b**) top, (**c**) middle and (**d**) bottom [78]. [PERSON] et al. [79], investigated the microstructure of the top and bottom regions of Ti-6 Al-4V alloy and found two different microstructures with and without water quenching fabricated by the EBDED method. The microstructure of the Ti-6 Al-4V alloy with water quenching has a lamellar structure containing \(\alpha^{\prime}\)-\(\alpha\)-\(\beta\) phases, and the bottom position of the sample has \(\alpha^{\prime}\) structure [79]. The microstructure of the Ti-6 Al-4V alloy without quenching changes in the top from a lamellar structure to a basket-weave structure containing \(\alpha^{\prime}\) phases and in the bottom, the same structure is absorbed with the \(\alpha\) phase [79]. The structure of the TiAlNb alloys printed by the EBDED is changed by the heat treatment as shown in Figure 9 [74]. The printed sample with the EBDED has a mixed structure of the B\({}_{2}\) + O structure after doing the heat treatment at 960 \({}^{\circ}\)C, 1040 \({}^{\circ}\)C and 1100 \({}^{\circ}\)C can be seen that the structure of the TiAlNb alloy in 960 \({}^{\circ}\)C is turned to the B\({}_{2}\) + O + \(\alpha_{2}\) structure with the precipitation of the \(\alpha_{2}\), after increasing the temperature of the heat treatment to 1040 \({}^{\circ}\)C the structure of the alloy is turned to the B\({}_{2}\) + \(\alpha_{2}\) structure and the O structure is solved at this temperature and has a discontinuous grain boundary. In addition, by increasing the heat treatment temperature to 1040 \({}^{\circ}\)C the structure changes to the B\({}_{2}\) structure and the grain grows [74]. [PERSON] et al. [80] checked the effect of the heat treatment on the mechanical properties and microstructure of the Ti-6 Al-4V alloy fabricated by the EBDED method. The microstructure of the Ti-6 Al-4V alloy annealed at 690 \({}^{\circ}\)C and 750 \({}^{\circ}\)C has a continuous \(\alpha\) grain boundary with the prior \(\beta\) grain boundary and because the \(\alpha^{\prime}\) martensite at those annealing temperatures has low atomic force for the diffusion driving and a slow rate of redistribution solubility, the \(\beta\) prior grains are contained in the \(\alpha^{\prime}\) martensite structure. Above 800 \({}^{\circ}\)C for the annealing treatment all the \(\alpha^{\prime}\) martensitic structure is soluble in the \(\alpha\) and \(\beta\) structures.