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Controlling microstructure and mechanical properties of additively manufactured high-strength steels by tailored solidification

: Köhnen, Patrick; Ewald, Simon; Schleifenbaum, Johannes Henrich; Belyakov, Andrey; Haase, Christian


Additive manufacturing 35 (2020), Art. 101389, 15 pp.
ISSN: 2214-8604
Journal Article
Fraunhofer ILT ()
Additive Manufacturing; Laser Powder Bed Fusion; Solidification; Simulation; Lattice structure

The development of novel alloys specifically designed for additive manufacturing (AM) is a key factor in usingthe full potential of AM. This study addresses the design of advanced high strength steels (AHSS) that takeadvantage of the processing conditions during AM by laser powder bed fusion (LPBF). The alloy screening wasguided by computational alloy selection (combined CALPHAD, Scheil-Gulliver, and phase-field simulations) andby rapid processing using powder blends (X30Mn21 steel and Al). Increasing Al contents, ranging from 0 to 5.4wt. %, promoted bcc-fcc solidification, and allowed for tailoring the stacking fault energy (SFE). On the onehand, the transition from fcc to bcc-fcc solidification enabled controlling the microstructure and texture evolutionduring 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-inducedplasticity (TRIP) and twinning-induced plasticity (TWIP), to govern the work-hardening behavior. The microstructureafter 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 compressiontesting with a focus on energy absorption capacity. The influence of the chemical composition and the solidificationconditions during LPBF on the microstructure evolution and the related microstructure-property-relationshipsof bulk and lattice structure specimens will be discussed.