## 2 _Introduction and State of Research_  
Laser cladding is becoming increasingly widely used, especially with today's push for additive manufacturing capabilities as well as life cycle improvements of products. With the increase in applications, the number of newly developed materials for laser cladding has also increased. These new materials also increase the need for a more detailed process understanding to be able to deliver their best performance after being clad. One additive manufacturing technique is powder-blown laser direct metal deposition, which is part of the scope of this publication. Investigation of process parameters such as laser power, feed rate, mass flow rate and spot diameter for iron- and nickel-based alloys on metallurgical bonding, microstructure, porosity and cracking tendency have been the main focus of research in additive manufacturing technology so far [1; 2; 3; 4; 5]. This is sufficient in most cases for the above-mentioned iron- and nickel-based alloys. For materials with an affinity for oxidation, such as titanium or aluminum alloys, consideration of the usual process parameters, which are intended to ensure sufficient energy input for the build-up, is not sufficient. The present gas dynamics have a significant impact on the oxidation. Oxidation leads to unfavorable material properties such as the embrittlement of titanium. In powder-based direct metal deposition (DMD), the melt pool is protected against oxidation by the shield gas flow. In powder-based DMD, the gas dynamics are adjusted by the two machine parameters shielding gas volume flow and carrier gas volume flow. In the following, the state of research is presented which deals with the shielding gas atmosphere of the powder-based DMD process. [PERSON] and [PERSON] [6] investigated the impact of the ambient oxygen concentration in the resulting material deposition quality regarding WC-12 Co coatings. In this investigation, a shielding gas chamber was used, in which a precise ambient oxygen concentration could be set and held during a normal cladding run. Furthermore, the laser power was changed during the experiments to see the impact of the laser power combined with the oxygen concentration. Single tracks were deposited at different laser powers and oxygen concentrations. The cross sections were analyzed using optical microscopy as well as X-ray diffraction (XRD) to obtain an impression of pores and their size as well as the material composition. As main result of this study, the increase in the pore size in the build-up with increasing oxygen concentration is revealed. The main issue of this study is that no element analysis was performed. Thus, no reliable statement can be made whether the pores resulted from the change in oxygen concentration. Furthermore, it is also not possible to explain the contrary behavior that the porosity increase is due to exceeding a certain limit power. One possibility is that the increasing melt pool dynamics at higher temperatures and the decomposition of the hard-phase particles creates additional pores. Whether the porosity is ultimately determined by the oxygen concentration cannot be clearly concluded from this study. Furthermore, the influence of the nozzle geometry and the influence of the carrier gas and shield gas volume flow on the present oxygen concentration is not investigated. This will be investigated in more detail within the scope of the present study. [PERSON] et al. [7] have investigated the impact of process gases on Stellite 6 coatings onto a cylindrical steel substrate. The influence of carrier gas and shielding gas variation on the following coating properties were investigated: coating height, depth of the heat affected zone, roughness and microhardness. The study demonstrates that by increasing the carrier gas flow, the roughness of the surface decreases, thus reducing the formation of surface discontinuities. Furthermore, with increasing carrier gas flow, the depth of the heat affected zone, the height of the layer and the dilution increases.