de Wild, Michael

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de Wild
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Michael
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de Wild, Michael

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2012 - 20142
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Item-Typ: Publikation × Hochschule: Hochschule für Life Sciences × Institut: Institut für Medizintechnik und Medizininformatik × Thema: NiTi × Thema: Selective laser melting ×

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    Publikation
    Microstructure of selective laser melted nickel–titanium
    (Elsevier, 2014) Bormann, Therese; Müller, Bert; Schinhammer, Michael; Kessler, Anja; Thalmann, Peter; de Wild, Michael [in: Materials Characterization]
    In selective laser melting, the layer-wise local melting of metallic powder by means of a scanning focused laser beam leads to anisotropic microstructures, which reflect the pathway of the laser beam. We studied the impact of laser power, scanning speed, and laser path onto the microstructure of NiTi cylinders. Here, we varied the laser power from 56 to 100 W and the scanning speed from about 100 to 300 mm/s. In increasing the laser power, the grain width and length increased from (33 ± 7) to (90 ± 15) μm and from (60 ± 20) to (600 ± 200) μm, respectively. Also, the grain size distribution changed from uni- to bimodal. Ostwald-ripening of the crystallites explains the distinct bimodal size distributions. Decreasing the scanning speed did not alter the microstructure but led to increased phase transformation temperatures of up to 40 K. This was experimentally determined using differential scanning calorimetry and explained as a result of preferential nickel evaporation during the fabrication process. During selective laser melting of the NiTi shape memory alloy, the control of scanning speed allows restricted changes of the transformation temperatures, whereas controlling the laser power and scanning path enables us to tailor the microstructure, i.e. the crystallite shapes and arrangement, the extent of the preferred crystallographic orientation and the grain size distribution.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild nicht verfügbar
    Publikation
    Tailoring selective laser melting process parameters for NiTi implants
    (Springer, 12/2012) Bormann, Therese; Schumacher, Ralf; Müller, Bert; Mertmann, Matthias; de Wild, Michael [in: Journal of Materials Engineering and Performance]
    Complex-shaped NiTi constructions become more and more essential for biomedical applications especially for dental or cranio-maxillofacial implants. The additive manufacturing method of selective laser melting allows realizing complex-shaped elements with predefined porosity and three-dimensional micro-architecture directly out of the design data. We demonstrate that the intentional modification of the applied energy during the SLM-process allows tailoring the transformation temperatures of NiTi entities within the entire construction. Differential scanning calorimetry, x-ray diffraction, and metallographic analysis were employed for the thermal and structural characterizations. In particular, the phase transformation temperatures, the related crystallographic phases, and the formed microstructures of SLM constructions were determined for a series of SLM-processing parameters. The SLM-NiTi exhibits pseudoelastic behavior. In this manner, the properties of NiTi implants can be tailored to build smart implants with pre-defined microarchitecture and advanced performance.
    01A - Beitrag in wissenschaftlicher Zeitschrift