# Oxidation-Reduction of Ti-6 Al-4V in Direct Energy Deposition Subject to Minimum Argon Consumption
## 1 Introduction
In DED processes, this flow can range from 30 L/min to 90 L/min for Ti-6 Al-4V, depending on the parameters used [18]. Such overuse of shielding gas not only increases the cost of deposition but is also wasteful and has a negative environmental impact [22]. [PERSON] et al. [23] studied the influence of shield gas by local shielding on the deposition in an AM process, finding that process by-products depend on the shield gas flow and velocity. To maintain a laminar flow in shielding the substrate in the based LMD process, [PERSON] made a shielding gas device that adapted to the depositional path. This was further sealed with aluminum foil. The process was successful in reducing the shield gas consumption but was not suitable for flexible deposition paths or with frequent changes to it [24]. [PERSON] et al. [25] observed that reducing the cross-flow rate of the shielding gas below a certain threshold decreased the melt pool width and increased the melt pool instability during an AM process. [PERSON] et al. [22] showed that the shielding gas flow had a convective cooling effect, resulting in a higher cooling rate near the top surface than in the lower part of the sample. In a study on depositing wire arc additive manufacturing (WAAM) samples under five trailing configurations, [PERSON] et al. [26] found that discoloration mainly occurred in the molten pool. More recent studies, such as those by [PERSON] et al. [27], have also highlighted the importance of controlling gas flow dynamics, emphasizing that local shielding can significantly reduce oxidation in reactive metals like titanium by optimizing flow rates and nozzle configurations. These findings are supported by newer research conducted by [PERSON] et al. [28], who demonstrated that using advanced gas flow control techniques, such as adaptive shielding, could stabilize the melt pool and improve deposition quality in Ti-6 Al-4V DED processes. [PERSON] et al. [29], in their work, demonstrated a local shielding device used in wire + arc additive layer manufacturing that reduced oxygen contamination levels by more than three orders of magnitude below 2000 parts per million while maintaining significant mechanical properties (hardness) at levels below 4000 parts per million. More recently, [PERSON] et al. [30] extended this work by developing a multi-zone local shielding system that dynamically adjusts argon flow to different sections of the deposition path, further enhancing protection against oxidation and improving mechanical properties. In line with these findings, recent research by [PERSON] et al. [31] indicated that controlled gas flow could also influence microstructural evolution by modifying the cooling rates during solidification, thus affecting the hardness and residual stress distribution in the deposited material. Recent advances in WAAM, such as the use of directed gas jets or multi-nozzle shielding configurations [32], have shown promise in further reducing oxidation and improving the surface finish by controlling the shielding environment more precisely. Despite these advancements, there are still very few studies available on the Laser Metal Deposition (LMD) of Ti-6 Al-4V alloy focusing on local shielding gas rather than using an inert gas chamber. Furthermore, systemic studies on optimizing shield gas usage remain scarce, with only a few recent works addressing comprehensive strategies for gas consumption reduction and process efficiency in DED [33]. The laser beam in the DED process leaves behind a newly formed layer of deposited material, which remains vulnerable to oxidation due to its high temperature. It wastes shield gas to create a shielding environment around the deposition since only this newly laid path requires shielding, covering only a fraction of the surrounding environment. Shielding only this newly laid path can drastically cut down argon consumption. The objective of this study is to systematically investigate the minimum flow conditions required to adequately shield critical areas using a modeling approach.