The design of new alloys by and for metal additive manufacturing (AM) is an emerging field of research. Currently, pre-alloyed powders are used in metal AM, which are expensive and inflexible in terms of varying chemical composition. The present study describes the adaption of rapid alloy development in laser powder bed fusion (LPBF) by using elemental powder blends. This enables an agile and resource-efficient approach to designing and screening new alloys through fast generation of alloys with varying chemical compositions. This method was evaluated on the new and chemically complex materials group of multi-principal element alloys (MPEAs), also known as high-entropy alloys (HEAs). MPEAs constitute ideal candidates for the introduced methodology due to the large space for possible alloys. First, process parameters for LPBF with powder blends containing at least five different elemental powders were developed. Secondly, the influence of processing parameters and the resulting energy density input on the homogeneity of the manufactured parts were investigated. Microstructural characterization was carried out by optical microscopy, electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS), while mechanical properties were evaluated using tensile testing. Finally, the applicability of powder blends in LPBF was demonstrated through the manufacture of geometrically complex lattice structures with energy absorption functionality.

Density functional theory (DFT) calculations were performed on Al x C y CoFeMnNi multi-principal element alloys (MPEAs) to understand the influence of Al and C on the stacking-fault energy (SFE). C addition to CoFeMnNi resulted in increased SFE, while it decreased in Al-alloyed CoFeMnNi. For experimental verification, Al 0.26 C y CoFeMnNi with 0, 1.37 and 2.70 at% C were designed by computational thermodynamics, produced by additive manufacturing (AM) and characterized by tensile tests and microstructure analysis. Twinning-induced plasticity (TWIP) was enhanced with increased C, which confirmed a decreased SFE. The combination of these methods provides a promising toolset for mechanism-oriented design of MPEAs with advanced mechanical properties.

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The development of novel alloys specifically designed for additive manufacturing (AM) is a key factor in using the full potential of AM. This study addresses the design of advanced high strength steels (AHSS) that take advantage of the processing conditions during AM by laser powder bed fusion (LPBF). The alloy screening was guided by computational alloy selection (combined CALPHAD, Scheil-Gulliver, and phase-field simulations) and by rapid processing using powder blends (X30Mn21 steel and Al). Increasing Al contents, ranging from 0 to 5.4 wt. %, promoted bcc-fcc solidification, and allowed for tailoring the stacking fault energy (SFE). On the one hand, the transition from fcc to bcc-fcc solidification enabled controlling the microstructure and texture evolution during AM. On the other hand, the wide SFE range between 8 J/m² (0 wt. % Al) and 44 J/m² (5.4 wt. % Al) promoted flexible adjustment of the active deformation mechanisms, including transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), to govern the work-hardening behavior. The microstructure after LPBF and after plastic deformation was analyzed by XRD, SEM, EDX, EBSD, EPMA, and TEM. Mechanical properties of bulk specimens and lattice structures were analyzed using tensile and compression testing with a focus on energy absorption capacity. The influence of the chemical composition and the solidification conditions during LPBF on the microstructure evolution and the related microstructure-property-relationships of bulk and lattice structure specimens will be discussed.

Hot working tool steels (HWTS) are popular for industrial applications such as injection molding tools, and casting dies because of their high wear resistance, fatigue, strength, and toughness properties, even at elevated temperatures. Conventionally, they go through multi-stage heat treatments in order to attain targeted microstructures. Achieving such microstructures with a laser powder bed fusion (LPBF) process will require tailor-made process parameters since it is characterized by non-equilibrium conditions, non-uniform temperature distribution, and metastable phase formation. Recent advances in the LPBF qualification of 1.2343/4 HWTS have shown commendable results but are still fraught with the limitations of poor ductility or extra post-heat treatment steps. For the industrial competitiveness of LPBF HWTS, the enhancement of strength and ductility and elimination of post processing is critical. Therefore, minimizing retained austenite in the as-built samples through pre-heat treatment or alloying to reduce post heat treatments without sacrificing strength will be economically important for industry. In this work, 1.2343 HWTS and its modified form were LPBF printed both in the as-built, pre- and post-heat-treated conditions. The results are discussed based on the correlations of the powder properties with LPBF—part density, microstructure, and mechanical properties.