Abstract
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.
Highlights
Electron beam melting (EBM) is an additive manufacturing (AM) technique applicable for the production of complex designed metallic components solely based on the specifications given by a computer-aided design model
For the specimens melted with a hatch of 75 lm, a clear trend towards more pronounced Mn loss can be deduced with decreasing scan speed, vs. an increase of the volume energy, Evol, as well as the line energy, El, decreases the Mn content of the alloy; e.g., the initial Mn content in the precursor powder is reduced from 6.4 wt.% to 6.2 wt.% for batch I melted with a scan speed of 4100 mmsÀ1, whereas the reduction of the scan speed to 1700 mmsÀ1 in batch V yields a significant reduction of the Mn content to approximately 3.3 wt.%
Evol and El cannot be considered as isolated values determining the vaporization of Mn, as can be seen for batch III, which is characterized by a nominal higher Evol and higher Mn content as compared to batch IV
Summary
Electron beam melting (EBM) is an additive manufacturing (AM) technique applicable for the production of complex designed metallic components solely based on the specifications given by a computer-aided design model. Similar to laser powder bed fusion (L-PBF), EBM is a powder bed-based process implementing consecutive local melting of thin powder layers on top of each other.[1,2,3,4] The advantages in terms of efficient production and unprecedented freedom of design resulting from this tool-free and flexible production technique have recently gained increased academic interest. Upon adequate post-treatment, AM-processed materials are usually characterized by good mechanical properties similar or occasionally even superior to conventionally manufactured counterparts. The static and especially cyclic mechanical behavior of AM parts are significantly influenced by process-induced voids and cavities.[10,11,12,13,14] In previous studies on the fatigue behavior of machined L-PBF- and EBM-manufactured Ti6Al-4V specimens, it has been demonstrated that (Published online January 24, 2020)
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