High entropy or multi principal element alloys are a promising and relatively young concept for designing alloys. The idea of creating alloys without a single main alloying element opens up a wide space for possible new alloy compositions. High entropy alloys based on refractory metals such as W, Mo, Ta or Nb are of interest for future high temperature applications e.g., in the aerospace or chemical industry. However, producing refractory metal high entropy alloys by conventional metallurgical methods remains challenging. For this reason, the feasibility of laser-based additive manufacturing of the refractory metal high entropy alloy W₂₀Mo₂₀Ta₂₀Nb₂₀V₂₀ by laser powder bed fusion (PBF-LB/M) is investigated in the present work. In-situ alloy formation from mixtures of easily available elemental powders is employed to avoid an expensive atomization of pre-alloyed powder. It is shown that PBF-LB/M of W₂₀Mo₂₀Ta₂₀Nb₂₀V₂₀ is in general possible and that a complete fusion of the powder mixture without a significant number of undissolved particles is achievable by in-situ alloy formation during PBF-LB/M when selecting favorable process parameter combinations. The relative density of the samples with a dimension of 6 × 6 × 6 mm³ reaches, in dependence of the PBF-LB/M parameter set, 99.8%. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) measurements confirm the presence of a single bcc-phase. Scanning electron microscopy (SEM) images show a dendritic and/or cellular microstructure that can, to some extent, be controlled by the PBF-LB/M parameters.

In-situ alloy formation by Laser Powder Bed Fusion (PBF-LB/M) from mixtures of easily available elemental powders is an appealing approach for developing and qualifying new alloys for laser based additive manufacturing of metals. However, especially when dealing with high-melting elements, like W, Ta, Mo, or Nb, it is difficult to achieve a homogeneous element distribution and a complete fusion of the powder particles. The aim of this work was to understand the effects of the PBF-LB/M process parameters (laser power, scan speed, laser spot diameter) and three different single- and double-exposure strategies on the fusion of high-melting W, Ta, Mo, and Nb particles in a Ti-matrix. For this purpose, 220 samples with 10 vol.% of the high-melting particle fraction were prepared and analyzed by optical light microscopy and automated image processing, as well as by scanning electron microscopy (SEM). The results are discussed in the context of current research on the process dynamics of PBF-LB/M. Based on that process strategies to support a complete fusion of high-melting particles during in-situ alloy formation are derived. It is shown that the number of unmolten particles can be at least decreased by a factor of ten compared to the most unfavorable parameter combination. For the lower melting elements, Nb and Mo, a complete fusion without any remaining particles visible in the microsections was achieved for certain parameter combinations. The results prove the feasibility of in-situ alloy formation with high-melting alloying elements, but they also demonstrate the necessity to adjust the PBF-LB/M process strategy to achieve a complete dissolution of the alloying elements.

Within the scope of the presented work the processing of AISI H11 (1.2343 or X37CrMoV5-1) tool steel powder modified by adding carbon black nanoparticles in varying concentrations by means of Laser Metal Deposition (LMD) is extensively investigated. On the basis of single weld track experiments, multi-layered cuboid-shaped samples made out of pure AISI H11 tool steel powder as well as modified tool steel powder mixtures were manufactured by applying various process parameters. The main scientific aim of the investigations was to achieve a basic understanding of the influence of the added carbon black nanoparticles on the resulting sample properties. For that purpose, the generated specimens were first analyzed with respect to relative density, inner defects, microstructure, Vickers hardness and chemical composition. Subsequently, the mechanical properties of post-heat-treated specimens were investigated, with the focus on the yield strength (Y_0.2%), by means of compression tests. We prove that by adding carbon black nanoparticles to the initial AISI H11 powder, the formation of martensitic and bainitic phases, as well as the precipitation of carbides at the grain boundaries, are enhanced. As a result, a significant increase of Vickers hardness and of the compression yield strength by up to 11% can be achieved in comparison to samples made out of the unmodified AISI H11 powder. Furthermore, it can be fundamentally demonstrated that the fabrication of parts with layer-specific variable hardness can be realized by the controlled changing of the powder mixtures used during the layer-by-layer manufacturing approach.

The aim of this work is to investigate the β-Ti-phase-stabilizing effect of vanadium and iron added to Ti-6Al-4V powder by means of heterogeneous powder mixtures and in situ alloy-formation during laser powder bed fusion (L-PBF). The resulting microstructure was analyzed by metallographic methods, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The mechanical properties were characterized by compression tests, both prior to and after heat-treating. Energy dispersive X-ray spectroscopy showed a homogeneous element distribution, proving the feasibility of in situ alloying by LPBF. Due to the β-phase-stabilizing effect of V and Fe added to Ti-6Al-4V, instead of an α’-martensitic microstructure, an α/β-microstructure containing at least 63.8% β-phase develops. Depending on the post L-PBF heat-treatment, either an increased upsetting at failure (33.9%) compared to unmodified Ti-6Al-4V (28.8%), or an exceptional high compressive yield strength (1857 ± 35 MPa compared to 1100 MPa) were measured. The hardness of the in situ alloyed material ranges from 336 ± 7 HV0.5, in as-built condition, to 543 ± 13 HV0.5 after precipitation-hardening. Hence, the range of achievable mechanical properties in dependence of the post-L-PBF heat-treatment can be significantly expanded in comparison to unmodified Ti-6Al-4V, thus providing increased flexibility for additive manufacturing of titanium parts.

Concerning rare-earth materials additive techniques like hollow cathode discharging or magnetron sputtering have been used to produce thin films, e.g. for the application in microelectromechanical systems (MEMS). In this paper our investigations in additively processing NdFeB-powder materials by means of laser beam melting in a powder bed (LBM) in order to produce macroscopic, three-dimensional specimens are presented. In this context we explain the advantages of additively manufactured magnets in comparison to conventional production methods. Furthermore different rare-earth-material powders were characterized with respect to their suitability for the LBM process. We describe a melting or sintering of the material at varying process parameters to obtain test cubes. Those specimens were magnetized and their magnetic field was analyzed. Additionally the density and microstructure of the samples was investigated. Subsequently we conclude this paper by presenting future steps of our research.