# Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
## 4 Industrial Case Studies  
In principle, different industries intend to repair the components that need to withstand severe working conditions and are also vital to the whole process. Thus, the quality of repair is highly considered and evaluated after the process to achieve in the repaired part final properties equal to the base components. Table 4 resumes the most common industrial applications of DED to repair various components. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Component** & **Material** & **Ref.** \\ \hline Mold, Die, Tools & Steel & [78, 81, 82] \\ Rails & Steel & [83, 84] \\ Vessels & Steel & [85] \\ Crankshaft & Steel & [86] \\ Driveshaft & Steel & [87] \\ Marin piston & Steel & [88] \\ Gas turbine compressor seal & Ni-based superalloy & [87] \\ Low-pressure turbine blades & Ni-based superalloy & [89] \\ Turbine airfoils & Ni-based superalloys & [18] \\ High-pressure single-crystal & Ni-based superalloys & [90] \\ turbine blades & Ni-based superalloys & [91] \\ Thin-curved compressor blade & Ni-based superalloys & [91] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Application of DED in repairing the various components. Figure 6: Processing strategies and sample cross-section. (**a**) Different build directions. (**b**) rectangular, (**c**) trapezoidal, milled slots. (**d**) LENS(tm) deposition schematic. (**e**) Void inclusion on rectangular and (**f**) Smooth transition on trapezoidal, milled slots [80]. One of the most important steps in the manufacturing of dies and molds is materials selection that is also very important from the economic point of view. Indeed, it is found that materials selection has a direct effect on the life and cost of molds and dies. Nonetheless, in the production of dies and molds, both design aspects, such as ductility, fatigue strength toughness, wear, and corrosion resistance, and aspects related to the manufacturing like hardness, polishability, machinability, dimensional stability should be also considered [92]. Different materials under different working environments behave differently and have multiple types of failure. Substantially, change in the dimensions, geometry, and materials properties of the dies during the working condition would negatively affect their performance and lead to failure. Different sorts of defects in dies and molds are shown in Figure 7. It has been revealed that the lifetime of these components are shorter than the expected life, and many of these defects appear in a shorter time than the anticipated period. Therefore, from the economic point of view, it is believed that restoration and remanufacturing is an interesting solution to recover the dies and molds [93]. There are several techniques to be employed for repairing die and molds. In Table 5, these technologies are compared, in terms of deposition rate, post repairing metallurgical characteristics, and necessity of post heat treatment. As can be seen in Table 5, repair with traditional techniques, such as TIG/Plasma and GTAW, has higher deposition rates and poor metallurgical characteristics, which is not desirable. On the contrary, it is clear that advanced methods, like DED, provide sharper, smaller deposition with focused and concentrated high laser energy and consequently lead to good metallurgical properties after deposition. Figure 7: Different types of defects in dies and molds [94]. Rail maintenance and substitution is a significant fraction of expenses of running a rail network. Wear and rolling contact fatigue (RCF) are the main defects that can reduce the lifetime of rail tracks. Switches and crossing are the main parts that can undergo wear, and it is found that their maintenance costs are 330 times higher than straight tracks on a per meter basis [97]. It is known that their wear and RCF properties can be improved via some surface treatments like case hardening, peening, or surface coating. For this reason, DED is of great interest to be used as a coating method to weld different materials on the top of the running surface of the substrate.