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The laser-based powder bed fusion of metals (PBF-LB/M) offers a variety of advantages over conventional processing techniques and the possibility to recycle and reuse powder increases its sustainability. However, the process and resulting part properties are influenced by a variety of factors including powder recycling grade and residual oxygen content of the process atmosphere. Especially in terms of reactive materials like Ti-6Al-4V, oxidation during processing and recycling determines process stability and reproducibility. This work therefore focusses on the influence of the conventionally varied processing parameters as well as atmosphere residual oxygen content process and powder recycling on the microstructure and mechanical properties. For this purpose, the design of experiments approach is used and by evaluation of regression models, effect sizes and interactions are given. Additionally, two different etching techniques were employed to reveal different aspects of the microstructure. While no significant influence of powder recycling and residual oxygen on the microstructure could be observed, they both significantly influence the mechanical properties. A maximum hardness of 470 HV0.1, a maximum ultimate tensile strength of 1252.3 MPa, and a maximum elongation at break of 17.8 % were obtained. The results demonstrate the importance of the processing atmosphere’s residual oxygen content and of taking into account the changing powder characteristics during recycling as well as its effect on the part properties.

In laser-based powder bed fusion of metals (PBF-LB/M), residual oxygen in the processing atmosphere is regarded as disruptive and disadvantageous for the manufacturing process and the resulting component properties. A novel approach to eliminate residual oxygen is to add small amounts of silane to the argon process gas. Silane eliminates residual oxygen and forms SiO2 nanoparticles, which in turn can be incorporated into the powder during the process. It is therefore necessary to evaluate the influence of these nanoparticles admixed to the metal powder. In this work, Ti-6Al-4V powder was modified with pyrogenic SiO2 nanoparticles generated by the reaction of a silane argon gas mixture with ambient air. Modified and unmodified powder was analyzed and processed using statistically designed experiments. An improvement of the flow rate according to DIN EN ISO 4490 (from 33.3 to 32.5 s/50 g) and increase of apparent density according to DIN EN ISO 3923 (from 2.52 to 2.58 g/cm3) could be observed after powder modification. No statistically significant effects of the modification on roughness, porosity, and hardness were found. The results demonstrate that powder modification using silane can lead to enhanced flowability without affecting the PBF-LB processing window of Ti-6Al-4V.

This work follows up on the influence of the processing parameters and a subsequent heat treatment on the resulting properties of magnetizable neodymium-iron-boron (NdFeB) parts produced by Laser Powder Bed Fusion. Highly dense (> 95 %) cubes were built up and an uneven distribution of neodymium- and iron-rich phases was observed. It could be shown that internal stresses leading to crack development represent the main challenge. According to the experimental results, this can be approached more effectively through successive optimization of the processing parameters and therefore adjustment of the energy input rather than heat treatment of the built parts.

A promising approach to address the mismatch of bone and implant stiffness, leading to the stress-shielding phenomenon, is the application of functionally graded materials with adjusted porosity. Although defect formation and porosity in laser-based powder bed fusion of metals (PBF-LB/M) are already widely investigated, so far there is little research on the influences and parameter interactions regarding the pore characteristics. This work therefore aims to provide an empirical process model for the generation of gas porosity in the PBF-LB process of Ti-6Al-4V. Parts with closed locally adjusted porosity of $\sim $ ∼ 6 % achieved through gaseous pores instead of lack of fusion defects or lattice structures were built by PBF-LB. Parameter variation and evaluation of relative density, pore size and sphericity was done in accordance with the design of experiments approach. A parameter set for maximum gas porosity (laser power of 189 W, scanning speed of 375 mm/s, hatch spacing of 150 μm) was determined for a constant layer thickness of 30 μm and a spot diameter of 35 μm. Tensile tests were conducted with specimens consisting of a core with maximum gas porosity or lack of fusion porosity, respectively, and a dense skin as well as fully dense specimens. Whereas lack of fusion defects can lead to significant reduction of stiffness of 32.2 %, the elastic modulus remained unchanged at 110.0 GPa when implementing spherical pores. Nevertheless, the found superior strength and ductility of specimens with gas porous core (> 1100 MPa and > 0.05 mm/mm, respectively) underline the advantages of adjusted porosity for the application in functionally graded materials and lightweight applications.

Die Anwesenheit von Sauerstoff bewirkt beim Laser Powder Bed Fusion (LPBF) eine Bauteilversprodung und fuhrt zu Oxidschichten mit verschlechterten Benetzungseigenschaften des Grundwerkstoffes. Zur Inertisierung der Prozessatmosphare wird deshalb beim LPBF herkommlicherweise Argon eingesetzt, wobei der Restsauerstoffgehalt bei Normaldruck weiterhin kritische Oxidationen bewirkt.

The PBF-LB/M (laser-based powder bed fusion of metals) process is associated with high as-built surface roughness and surface texturing caused by a variety of process inherent effects. It is well known that surface roughness is influenced by the applied processing parameters and correlates with porosity. In terms of reactive materials like Ti-6Al-4V, also the powder recycling grade and especially the residual oxygen content within the processing atmosphere play important roles regarding process stability, reproducibility and part properties. Therefore, this study investigated the influence of the residual oxygen content on porosity and surface roughness for virgin as well as recycled powder by employing DoE techniques. Within the examined range, unlike for the roughness, no significant influence of residual oxygen content and powder constitution on porosity could be detected. It could be shown that the reproducibility of relative density mainly depends on the processing parameter combination. Furthermore, powder recycling led to higher top and side surface roughness and a dependence of surface texture on processing parameters could be demonstrated.

In laser-based powder bed fusion of metals (PBF-LB/M) the presence of oxygen is known to encourage embrittlement and impair the wetting properties of the substrate and solidified material. Conventionally, inert gases like argon are used to reduce the residual oxygen content within the processing atmosphere. However, especially in terms of reactive materials like titanium the remaining oxygen still causes critical oxidations.In this publication, a new approach for obtaining an oxygen-free processing atmosphere is presented. Thereby the argon shielding gas is doped with reactive monosilane to reduce the residual oxygen content to a range comparable to XHV (Extreme High Vacuum, thermodynamic oxygen activity