Electron beam melting (EBM) is an established powder bed-based additive manufacturing process for the fabrication of complex-shaped metallic components. For metastable austenitic Cr-Mn-Ni TRIP steel, the formation of a homogeneous fine-grained microstructure and outstanding damage tolerance have been reported. However, depending on the process parameters, a certain fraction of Mn evaporates. This can have a significant impact on deformation mechanisms as well as kinetics, as was previously shown for as-cast material. Production of chemically graded and, thus, mechanically tailored parts can allow for further advances in terms of freedom of design. The current study presents results on the characterization of the deformation and strain-hardening behavior of chemically tailored Cr-Mn-Ni TRIP steel processed by EBM. Specimens were manufactured with distinct scan strategies, resulting in varying Mn contents, and subsequently tensile tested. Microstructure evolution has been thoroughly examined. Starting from one initial powder, an appropriate scan strategy can be applied to purposefully evaporate Mn and, therefore, adjust strain hardening as well as martensite formation kinetics and ultimate tensile strength.

Material-and energy-saving lightweight constructions are of particular interest to the industry since decades, especially for vehicle and aircraft production. One of the ways of reducing the weight in components is to replace a solid matrix by periodically recurring cell or truss structure. Cellular materials such as metallic foams, truss, or honeycomb structures are characterized by high specific energy absorption and rigidness. Due to their high specific stiffness and compressive strength, square honeycomb structures are well suited for energy dissipating stiffeners, such as sandwich panels and bumpers. [1][2][3] However, the production of honeycomb structures using conventional manufacturing methods is very complex. Metallic square-celled honeycomb structures are often produced in two ways: either slotted metal strips are inserted into each other and joined together by soldering, or they are produced by metal extrusion using complex dies. [4,5] Another recently developed technology is the extrusion of powders with a binder and subsequent debinding and sintering. [6,7] In contrast, additive manufacturing (AM) allows producing most of the complex lightweight structures in a single manufacturing step. All of the AM methods are based on the computer-aided design (CAD), taking a model of a component and building it up layer by layer. One of the most advanced AM methods for the fabrication of metallic components is the electron beam powder-bed fusion (EB-PBF) technology, which is called electron beam melting (EBM) in the following. This process belongs to the group of powderbed AM technologies in which powder particles are fused layer by layer. [8,9] The EBM process is somewhat similar to the widely used selective laser melting (SLM) process, although there are principal differences between laser and electron beam. [10] The microstructure of EBM-manufactured materials is often characterized by columnar and epitaxial grain morphology. Continuous melt crystallization through the multiple layers results in the formation of a strong texture and anisotropy. [8,[11][12][13] This phenomenon can even be utilized to produce single crystalline superalloys by adapting EBM scanning strategy. [14,15] However, in case of materials which can undergo phase transformation in the solid state during cooling (Ti-6Al-4V, Ti-6Al-4V doped with Cu or La, titanium aluminide, and so on), the mentioned columnar and textured structure can be avoided.

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The fatigue lives of additively manufactured (AM) Inconel 718 (IN718) produced by selective electron beam melting and conventional wrought material as reference conditions were studied in the very high cycle fatigue regime under fully reversed loading (R = −1) at the elevated temperature of 873 K using an ultrasonic fatigue testing system. The fatigue lives of the AM material were significantly reduced compared to the wrought material, which is discussed in relation to the microstructure and a fractographical analysis. The additively manufactured material showed large columnar grains with a favoured orientation to the building direction and porosity, whereas the wrought material showed a fine-grained structure with no significant texture, but had Nb- and Ti-rich non-metallic inclusions. Crystallographic crack initiation as well as crack initiation from the surface or internal defects were observed for the AM and the wrought IN718, respectively.

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