# Oxidation-Reduction of Ti-6 Al-4V in Direct Energy Deposition Subject to Minimum Argon Consumption
## 2 Material and Methods
### Conformal Shielding Nozzle Attachment System  
This paper presents a novel nozzle attachment system specifically designed and assembled for the DMG-MORI Laser-Tech 650 coaxial nozzle to provide an enhanced shielding environment during the DED process. In conventional DED machines, a carrier gas is used to transport powder particles into the melt pool, while a built-in shield gas flow provides coverage for the newly laid path to protect it from atmospheric gases. However, as Ti-6 Al-4V is highly reactive at temperatures above 600 \({}^{\circ}\)C, this standard shield gas coverage may not be sufficient to prevent oxidation. Therefore, a completely new nozzle attachment system, as shown in Figure 2, was developed to deliver additional shield gas precisely to cover critical areas with optimized argon consumption.  
The system features eight individual attachments, each connected to a solenoid valve that controls the delivery of the shielding gas based on the deposition path. In this system, only one segment of the attachment is activated at any given time to deliver the shield gas specifically to the newly deposited path, as depicted in Figure 3. For example, at position A, attachment 5 is engaged because it is located directly above the deposition path. This targeted approach significantly reduces argon consumption while ensuring a higher concentration of shielding gas in the critical areas, thereby improving protection against oxidation.  
As discussed above, the 85 mm long chamber filled with steel wool, as shown in Figure 4, serves not only as a diffuser but also as a reservoir that traps argon gas, making it readily available when the attachment is activated. To support the wool and further diffuse the gas, a 304 stainless steel Dutch weave mesh is used at the outlet. While selecting the mesh, it was ensured that the mesh would be able to withstand high temperatures during the deposition process. For this reason, a 304 stainless steel mesh was considered instead of plastic mesh, as it offers more thermal resistance and durability. Results from Ansys Fluent determined that a porosity value of 60% through porous media ensured adequate back pressure to distribute argon gas within the attachment. Hence, a 12 \(\times\) 64 Dutch Woven mesh, as shown in Figure 5, of 61% was considered for the experiment [35]. The mesh has a horizontal wire diameter of 0.58 mm and a vertical wire diameter of 0.41 mm.  
Figure 2: (**a**) AM nozzle during deposition. (**b**) AM nozzle with a specially built attachment system for conformal shielding. (**c**) Attachments with increased transparency for better understanding.  
Figure 4: Cross-sectional view of a coax nozzle with one of the attachments.  
Figure 5: Mesh size of 12 \(\times\) 64.  
Figure 3: (**a**) Top view of the system with one of the eight attachments in use during the deposition process. (**b**) Example of working the nozzle attachment system while depositing a rectangular-shaped component at four different locations: A, B, C, and D. The attachment in use is highlighted. Different attachment number is highlighted depending on the deposition path.  
The attachment provides additional shielding coverage up to 85 mm and covers a surface area of 60 mm\({}^{2}\). While the attachment is designed to shield the trailing path, there are scenarios where the path may not lie directly under the attachment, such as when printing cylindrical components. In such cases, the triangular shape of the attachment allows for a flexible shielding approach, providing a protective gas curtain along non-linear deposition paths. Additionally, multiple nozzles can be activated simultaneously for extra shielding when necessary.