Development of surface tailored metal powders for increased production efficiency at the laser powder-bed fusion additive manufacturing process

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The additive manufacturing technology powder bed fusion of metals using a laser based system (PBF-LB/M) is often confronted with the issue of high production lead times. To enable a more efficient process control, commercial materials will be tailored for PBF-LB/M. Typically, the process speed in terms of exposure is described by the ratio of laser power, track distance exposure speed and layer thickness. On one hand it is of great interest to influence absorption, wettability and thermal conductivity of the powder, and on the other hand to improve the flowability to accelerate the powder application. Accordingly, the overall goal of the research project is to develop a fundamental material and process understanding of the effects of surface functionalizations of commercially available starting materials and their influence on interparticle and laser-material interactions. To further deepen the research activities from the first funding period of SPP 2122, the metal powders (stainless steel 1.4404 and tool steel 1.2709) will be continuously considered for investigation. Based on the gained results, preliminary work and literature review, the following nanoparticle additives are used for surface tailoring: Silicon carbide and graphene (for which an increased production efficiency and mechanical properties have already been determined), silicon (Si) (to increase the wettability of the melt and to smooth the melt surfaces) and silicon nitride (to increase tensile properties). In addition, the particle surfaces of both original feedstock powder materials are treated mechanically and chemically to increase the specific surface, particle roughness, and hence to improve the flowability and absorption behavior. The commercially available additive materials in the micrometer size range are milled in stirred medial mills with grinding media down to the lower nanometer range and are applied by a wet fluidized bed process. In addition, dry intensive mixing processes are used to deposit existing nanoparticles onto the metal particles. The coating methods will be compared in terms of degree of agglomeration and homogeneity of the resulting coatings as well as resulting processing properties. In addition to the material combinations, particle sizes and loadings of the additives are systematically considered. Established measurement systems are used for the characterization of absorption, wettability, flowability as well as in-situ applications for the generation of µCT images of a powder bed, high-speed images of the powder application and the melting behavior as well as three-dimensional mappings of the powder bed. Samples produced from the functionalized powders are characterized with respect to microstructure and mechanical properties. The transfer of the obtained data into two simulative models of the powder application and the melt pool dynamics of different material combination represent a reasonable addition.