# Application of Directed Energy Deposition-Based Additive Manufacturing in Repair
## 4 Industrial Case Studies
In fact, through DED process, it would be possible to deposit a wide range of beneficial materials, i.e., alternative steels of hard facing alloys, on areas of the tracks prone to wear and/or RCF. [PERSON] et al. studied the wear properties of repaired rail disks with various materials and have found that wear behavior of rail track was not always improved after depositing a coating layer by DED. Figure 8 compares the wear rates of the repaired disks after 5000 cycles. As can be seen, stellite showed the lowest wear rate with an average of 0.18 ug/cycle in comparison with the as-built sample with 1.59 ug/cycle [97]. On the contrary, the least consistency in the wear rate and the highest wear rate was revealed with the Margining and Stainless steel coatings. Also, [PERSON] et al. and [PERSON] et al. investigated rail track repairing using DED process [83; 97]. According to their research, the expense for maintenance of some components, such as switches and crossings, is very low for the straight track parts, and therefore, it is highly recommended to repair those simple geometry components instead of replacing them. Figure 8: Comparison between the wear rate of repaired discs after 5000 wet cycles; R indicates wear rate of the rail disc, W indicates wear rate of wheel disc [97]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Criteria** & **TIG/Plasma** & **GTAW** & **Cold Spray** & **Thermal Coating** & **DED** \\ \hline Deposition rate & ** & *** & ** & **** & **** \\ \hline Portability & **** & **** & ** & ** & ** \\ \hline Metallurgical properties & ** & ** & ** & ** & **** \\ \hline Set up time & *** & ** & *** & ** & **** \\ \hline Post-heat treatment & *** & ** & *** & ** & ** \\ \hline Cost & ** & ** & ** & ** & ** \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison between different repair methods for dies and molds [94; 95; 96]. [PERSON] et al. used the DED process to repair the cracks in the austenitic stainless steel vessels that withstand internal water pressure up to 2 bar [85]. In this work, the DED process parameters for in-situ repairing of through-wall cracks in parts or vessels were developed. They found that crack sealing of 4.5 and 6.0 mm plate thickness underwater pressure could be successfully repaired under worst-case conditions with a rather high powder efficiency [85]. Over the last 100 years, diesel engines have undergone revolutionary improvements in their design and performance. The crankshaft is one of the most important parts that is heavily used in the engine. A crankshaft is a very critical component that needs very high precision production process and servicing requirements [98]. However, it is noticed that repairing this part via conventional technologies is faced with some challenges like bending stiffness and also is very expensive [86]. [PERSON] et al. have repaired marine diesel crankshaft using DED process (Figure 9). According to their microstructural observation, there was a very good interfacial bonding between the deposited layer and the base metal (Figure 10a). The Vickers hardness outcomes showed that there was a drop from 500 to 300 HV from HAZ to unaffected zone (Figure 10b). Finally, they concluded that the resulting component showed a high quality in terms of interfacial bonding and dilution [86]. A drive shaft, which is a mechanical part that transmits torque and rotation, is also repaired successfully by employing DED process. In principle, the high level of torsion and shear stresses that applied on the torque under the working condition damage the surface of this shaft. Traditionally, to repair theses shafts, thermal spry processes have been employed, but thereafter, in some cases, some defects, such as severe spalling, have been revealed on some repaired shafts (the top shaft in Figure 11). Afterward, more deep investigations have shown that DED can provide better metallurgical and mechanical bonding concerning the thermal spray processes and can be considered as a more reliable solution to repair the drive shafts.