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The additive manufacturing technique selective laser melting (SLM) is the most common process for metallic powders. The layer‐by‐layer process allows construction of components with high complex designs compared with conventional process routes. However, the orientation of parts related to the build platform and later to different loading conditions should be taken into account as the process‐induced microstructure and defects creating anisotropic mechanical behavior. To evaluate this influence of the building orientation as well as the process‐induced defects, different fatigue tests were performed on the SLM‐processed austenitic steel AISI 316 L (X2CrNiMo17‐12‐2). The distribution of the process‐induced porosity and, thus, the fatigue behavior is strongly related to the building direction, leading to a reduction of fatigue life for the tested 90° specimens of more than 90%.

The laser-based fusion of metallic powder allows construction of components with arbitrary complexity. In selective laser melting, the rapid cooling of melt pools in the direction of the component building causes significant anisotropy of the microstructure and properties. The objective of this work is to investigate the influence of build anisotropy on the microstructure and mechanical properties in selective laser melted AlSi10Mg. The alloy is comprehensively used in the automotive industry and has been one of the most frequently investigated Al alloys in additive manufacturing. Using specimens produced in three different building orientations with respect to the build platform, the anisotropy of the microstructure and defects will be investigated using scanning electron microscopy and microcomputed tomography. The analysis showed a seven-times higher pore density for the 90°-specimen compared to the 0°-specimen. The scanning electron microscopy revealed the influence of the direction of the cooling gradient on the constitution of the eutectic phase. Mechanical properties are produced in quasi-static and fatigue tests of variable and constant loading amplitudes. Specimens of 0° showed 8% higher tensile strength compared to 90°-specimens, while fracture strain was reduced almost 30% for the 45°-specimen. The correlation between structural anisotropy and mechanical properties illustrates the influence of the building orientation during selective laser melting on foreseen fields of application.

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Additive manufacturing allows for the production of highly complex structures due to its layer-wise local melting of powder material. For this reason, this technique has a high potential for manufacturing extremely lightweight components potential. However, laser based additive manufacturing is still restricted due to the limited amount of processable alloys, especially Fe-based materials. A main object in current research is to expand the varieties for steel that may be used. Additionally, the modification and optimization of steel powder is seen as an interesting aspect for improving the material properties of additively manufactured parts. In this work, secondary hardenable martensitic tool steel X30CrMo7-2 is investigated, starting from the raw powder which is enriched with nitrogen by gas nitriding and subsequently characterized to ensure the usability of the modified powder for laser-powder bed fusion. In a next step, the raw and nitrided powder are used to generate cylindrical specimens to allow for further analysis of the microstructure and for a mechanical characterization of compression behavior. Moreover, a variety of heat treatments is carried out. The higher content of nitrogen leads to an increase in porosity. However, the addition of nitrogen causes an increase in hardness and in the compressive yield point, especially after heat treatment. After tempering, compressive yield stress is increased from 1,111 MPa to 1990 MPa, while for conventional material it is slightly reduced from 1,316 MPa to 1225 MPa.