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Author: Kosiba, Konrad × Subject: laser powder bed fusion ×

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    Viscous Flow of Supercooled Liquid in a Zr-Based Bulk Metallic Glass Synthesized by Additive Manufacturing
    (Basel : MDPI, 2020) Kosiba, Konrad; Deng, Liang; Scudino, Sergio
    The constraint in sample size imposed by the critical cooling rate necessary for glass formation using conventional casting techniques is possibly the most critical limitation for the extensive use of bulk metallic glasses (BMGs) in structural applications. This drawback has been recently overcome by processing glass-forming systems via additive manufacturing, finally enabling the synthesis of BMGs with no size limitation. Although processing by additive manufacturing allows fabricating BMG objects with virtually no shape limitation, thermoplastic forming of additively manufactured BMGs may be necessary for materials optimization. Thermoplastic forming of BMGs is carried out above the glass transition temperature, where these materials behave as highly viscous liquids; the analysis of the viscosity is thus of primary importance. In this work, the temperature dependence of viscosity of the Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass fabricated by casting and laser powder bed fusion (LPBF) is investigated. We observed minor differences in the viscous flow of the specimens fabricated by the different techniques that can be ascribed to the higher porosity of the LPBF metallic glass. Nevertheless, the present results reveal a similar overall variation of viscosity in the cast and LPBF materials, which offers the opportunity to shape additively manufactured BMGs using already developed thermoplastic forming techniques.
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    Approach to Estimate the Phase Formation and the Mechanical Properties of Alloys Processed by Laser Powder Bed Fusion via Casting
    (Basel : MDPI, 2022) Kühn, Uta; Sander, Jan; Gabrysiak, Katharina Nicole; Giebeler, Lars; Kosiba, Konrad; Pilz, Stefan; Neufeld, Kai; Boehm, Anne Veronika; Hufenbach, Julia Kristin
    A high-performance tool steel with the nominal composition Fe85Cr4Mo8V2C1 (wt%) was processed by three different manufacturing techniques with rising cooling rates: conventional gravity casting, centrifugal casting and an additive manufacturing process, using laser powder bed fusion (LPBF). The resulting material of all processing routes reveals a microstructure, which is composed of martensite, austenite and carbides. However, comparing the size, the morphology and the weight fraction of the present phases, a significant difference of the gravity cast samples is evident, whereas the centrifugal cast material and the LPBF samples show certain commonalities leading finally to similar mechanical properties. This provides the opportunity to roughly estimate the mechanical properties of the material fabricated by LPBF. The major benefit arises from the required small material quantity and the low resources for the preparation of samples by centrifugal casting in comparison to the additive manufacturing process. Concluding, the present findings demonstrate the high attractiveness of centrifugal casting for the effective material screening and hence development of novel alloys adapted to LPBF-processing.