## 1 Introduction  
Additive manufacturing of metal components is currently becoming increasingly relevant for a wide range of industrial applications. Directed energy deposition (DED) processes are an essential driver for this development [1]. In these processes, a feedstock material in the form of powder or wire is melted by an energy source and deposited onto a substrate in layer-by-layer mode [2]. This approach typically enables significantly higher build rates than the widely used powder-bed fusion processes. Laser radiation is one of the most economically relevant of the different energy sources used for DED processes, as it allows for precise control of the energy input into the workpiece. This typically results in low thermal stresses and distortion. The corresponding processes are referred to as laser metal deposition (LMD). The use of wire as feedstock provides several advantages over the use of powder, such as low cost, good availability, ease of handling, and a low contamination of the process environment [3]. However, the wire is typically fed laterally to a solid laser beam, resulting in a strong directional dependence of the process. In order to overcome this directional dependence, laser processing heads that allow for coaxial wire feeding either in the center of several single beams [4; 5; 6] or inside an annular laser beam [7; 8; 9] are increasingly being utilized. A schematic representation of the process principle of laser metal deposition with coaxial wire feeding is illustrated in Figure 1.  
With regard to the industrial application of LMD processes, the resulting material properties are of crucial importance. Oxidation, which can occur during the process above a specific temperature depending on the material deposited, affects these properties significantly [10; 11]. In order to reduce the negative effects of oxidation, the concentration of oxygen in the high temperature process zone is typically decreased by displacing the atmospheric oxygen with inert gases, such as argon, nitrogen, or helium [12]. Regarding DED processes, numerous research papers exist on the effects of the atmospheric conditions on the resulting material properties. Besides the widely studied highly reactive materials (e.g., titanium alloys [13; 14; 15; 16]), nickel-based alloys [12], stainless steels [17], and zirconium alloys [18] have also been investigated. The results of these studies indicate that a low concentration of oxygen in the process zone is required for favorable part properties. However, a certain amount of oxygen may be tolerable depending on the material used [17]. The choice of the shielding gas itself is another factor that has a significant influence on the deposition process. For DED processes as well as for metal welding processes, mainly argon and helium are utilized. With regard to the stability of the gas flow, argon is preferable due to its robustness against external disturbances as well as reduced diffusion of the atmosphere [19]. In addition, argon is considerably less expensive than helium, resulting in a significant economic advantage. A common method for preventing atmospheric contamination during the process is to use a physical chamber filled with inert gas [20; 21; 22; 23; 24]. However, this method is highly cost-intensive due to the required equipment, the inert gas volume, and the time required for flooding the chamber [25]. In addition, the dimensions of the chamber limit the size of the components to be produced, modified, or repaired. Another approach to create an inert gas atmosphere in the process zone is to use a local shielding gas device. For this, a sufficiently large local shielding gas environment needs to be created to prevent oxidation of the melt pool and the deposited material during cooling. If this is not ensured, the deposited material typically includes oxide contaminations. For wire-based DED processes, these contaminations manifest themselves mainly in oxide layers on the surface of the deposited weld beads.