# Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
## 3 Identified DED Capabilities in Repair
This variation of phase composition and microstructure, as a consequence of maximum reached temperature and cooling rate, resulted in a decreasing trend of microhardness from the deposition zone to HAZ. Moreover, it was found that compressive residual stresses in the normal direction were generated during the DED process. These residual stresses would be beneficial for dies that are exposed to cyclic thermomechanical loading. Figure 4: Tensile stress-strain curve of a cast-iron repaired via a traditional welding and DED process (AMD in the figure) [77]. Figure 3: The hardness of cast iron parts repaired by using (**a**) traditional welding process and (**b**) Additive Metal Layer Deposition (AMD) process [77]. [PERSON] et al. studied the effect of building strategy on the microstructure and hardness of Ti-6 Al-4V component repaired by DED process [79]. In their work, the effects of deposition strategy (decreasing track length and constant track length) and laser energy density (LED) on the metallurgical characteristics of the deposited layer had been investigated. It was revealed that with a decreasing track length deposition strategy, the microstructure could be rather homogeneous with respect to the constant. On the other hand, it was found that at LED, the microstructure seemed to be more homogeneous and composed of martensite, whereas for high LED, the microstructure was very heterogeneous and the majority of the microstructure composed of Widmanstadtten. Finally, it could be concluded that the nature of obtained microstructure and the hardness ranges of Ti-6 Al-4V alloy linked to the cooling rates during the laser processing, and so this technique could be taken into account as a proper technology for repairing of this alloy. It is also reported that on the contrary to the repair of surface defects via DED, which is very simple, repair of sub-surface defects is still challenging. For instance, some internal cracks have been repaired by milling different slots like rectangular, triangular, and U-grooved, followed by filling them using DED. However, it is found that large porosities and voids are apparent at sharp transition areas, and consequently, the strategy for preparation of different damaged zones would be different. Recently, [PERSON] et al. used LENS\({}^{\text{TM}}\) technology to repair the internal cracks in IN 718 alloy [80]. In this work, the different strategy, like varying deposition orientation, to repair the Inconel 718 parts with different damaged zones, was investigated. This work indicated that in comparison with rectangular cross-section, trapezoidal shape cross-section had a better furroin and smoother transition of deposit material along the sidewall without void inclusion (Figure 6) [80]. Figure 5: SEM images of CPM 9V: (**a**) deposition zone, (**b**) interface zone, (**c**) HAZ [78]. In parallel to the efforts that have been paid to the capability of DED as repair, a large amount of work has also been carried out to explore the quality and repeatability of repair by this technology [12]. For instance, [PERSON] et al. indicated that after repairing a component, the required dimensional specification and tolerances should be controlled and then the performance of the part under the working condition should be tested via simulation [12].