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Start date: 2020 × DDC: 600 × Publisher: Amsterdam : Elsevier × WGL Institute: IFWD ×

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Now showing 1 - 4 of 4
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    In situ detection of cracks during laser powder bed fusion using acoustic emission monitoring
    (Amsterdam : Elsevier, 2022) Seleznev, Mikhail; Gustmann, Tobias; Friebel, Judith Miriam; Peuker, Urs Alexander; Kühn, Uta; Hufenbach, Julia Kristin; Biermann, Horst; Weidner, Anja
    Despite rapid development of laser powder bed fusion (L-PBF) and its monitoring techniques, there is still a lack of in situ crack detection methods, among which acoustic emission (AE) is one of the most sensitive. To elaborate on this topic, in situ AE monitoring was applied to L-PBF manufacturing of a high-strength Al92Mn6Ce2 (at. %) alloy and combined with subsequent X-ray computed tomography. By using a structure borne high-frequency sensor, even a simple threshold-based monitoring was able to detect AE activity associated with cracking, which occurred not only during L-PBF itself, but also after the build job was completed, i.e. in the cooling phase. AE data analysis revealed that crack-related signals can easily be separated from the background noise (e.g. inert gas circulation pump) through their specific shape of a waveform, as well as their energy, skewness and kurtosis. Thus, AE was verified to be a promising method for L-PBF monitoring, enabling to detect formation of cracks regardless of their spatial and temporal occurrence.
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    Development and characterization of a metastable Al-Mn-Ce alloy produced by laser powder bed fusion
    (Amsterdam : Elsevier, 2021) Gabrysiak, Katharina; Gustmann, Tobias; Freudenberger, Jens; Neufeld, Kai; Giebeler, Lars; Leyens, Christoph; Kühn, Uta
    Laser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al92Mn6Ce2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al20Mn2Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al92Mn6Ce2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.
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    Tailoring biocompatible Ti-Zr-Nb-Hf-Si metallic glasses based on high-entropy alloys design approach
    (Amsterdam : Elsevier, 2020) Calin, Mariana; Vishnu, Jithin; Thirathipviwat, Pramote; Popa, Monica-Mihaela; Krautz, Maria; Manivasagam, Geetha; Gebert, Annett
    Present work unveils novel magnetic resonance imaging (MRI) compatible glassy Ti-Zr-Nb-Hf-Si alloys designed based on a high entropy alloys approach, by exploring the central region of multi-component alloy phase space. Phase analysis has revealed the amorphous structure of developed alloys, with a higher thermal stability than the conventional metallic glasses. The alloys exhibit excellent corrosion properties in simulated body fluid. Most importantly, the weak paramagnetic nature (ultralow magnetic susceptibility) and superior radiopacity (high X-ray attenuation coefficients) offer compatibility with medical diagnostic imaging systems thereby opening unexplored realms for biomedical applications.
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    Solving the puzzle of hierarchical martensitic microstructures in NiTi by (111)-oriented epitaxial films
    (Amsterdam : Elsevier, 2023) Lünser, Klara; Undisz, Andreas; Wagner, Martin F.-X.; Nielsch, Kornelius; Fähler, Sebastian
    The martensitic microstructure decides on the functional properties of shape memory alloys. However, for the most commonly used alloy, NiTi, it is still unclear how its microstructure is built up because the analysis is hampered by grain boundaries of polycrystalline samples. Here, we eliminate grain boundaries by using epitaxially grown films in (111)B2 orientation. By combining scale-bridging microscopy with integral inverse pole figures, we solve the puzzle of the hierarchical martensitic microstructure. We identify two martensite clusters as building blocks and three kinds of twin boundaries. Nesting them at different length scales explains why habit plane variants with ⟨011⟩B19' twin boundaries and {942} habit planes are dominant; but also some incompatible interfaces occur. Though the observed hierarchical microstructure agrees with the phenomenological theory of martensite, the transformation path decides which microstructure forms. The combination of local and global measurements with theory allows solving the scale bridging 3D puzzle of the martensitic microstructure in NiTi exemplarily for epitaxial films.