Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Eingeladener Vortrag
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The layer-by-layer Additive Manufacturing (AM) by means of Selective Laser Melting (SLM) offers many prospects regarding the design of a part used in aeroplane components and gas turbines. However, structural deviations from the nominal morphology are unavoidable. The cooling of the finished part leads to shrinkage and a high surface roughness is induced by attached powder particles affecting the part volume too.
The integrity and load-bearing capacity of a SLM produced lattice structure (see Fig.1) has been investigated by means of in-situ X-ray computed tomography during compression. The lattice structure was compressed by 10 % in height with an applied maximum force of 5 kN. Additionally, a single strut has been investigated ex-situ as a component of the lattice structure. With the higher resolution achieved on the single strut, the pore distribution (size and location) as well as the surface roughness were assessed. One of the main results coming from the in-situ analysis was that the nodes were identified as the weakest points in the lattice structure.
Collective Orientational Order and Phase Behavior of a Discotic Liquid Crystal under Confinement
(2018)
Discotic liquid crystals (DLCs) are a promising class of soft matter for electronic applications. This is due to their ability to self-organize into columns in a hexagonal columnar mesophase, driven by the overlapping of the π orbitals of their aromatic cores. This leads to a high charge-carrier mobility along the column axis. Previous studies on DLCs showed that their properties, such as phase transition temperatures and enthalpies, are susceptible to nanoconfinement. In this study, 2,3,6,7,10,11 hexakis[hexyloxy] triphenylene (HAT6) was confined into parallel aligned cylindrical nanopores of anodic aluminum oxide (AAO) membranes by melt infiltration. Furthermore, the pore surfaces of a series of membranes were chemically modified, resulting in a more hydrophobic pore surface than the unmodified ones. Collective orientational order and phase behavior of HAT6 confined into modified and unmodified nanopores of AAO were investigated by broadband dielectric spectroscopy and differential scanning calorimetry respectively.
In recent years, substantial efforts have been devoted to investigating nanoscopic confinement of polymers, and its effect on glassy dynamics. Broadband Dielectric Spectroscopy (BDS) was used to study the dynamics of ultra-thin films of PVME/PS 50/50 wt% blend, employing a novel nano-structured capacitor sample arrangement. The investigated system shows a complex dynamic behavior. First, an α-relaxation, related to a bulk-like layer was found. Second, an α’-relaxation was observed, characteristic for dynamically asymmetric blends, where the out of equilibrium dynamics is attributed to weakly-cooperative PVME segments relaxing within a frozen environment of PS segments. Thirdly, for thinnest films, an Arrhenius-like process was dominant in the dielectric spectra, indicating localized fluctuations of the segments. Relaxation rates of this process resembled that of the degenerated α-relaxation of the adsorbed layer, found for pure PVME, thus it was assigned accordingly. For thinnest films, this process undergoes a further confinement, due to the topological constraints, introduced by PS. Such multiple confinement effect has not been reported for ultra-thin films of polymer blends, before this study.
The polymer matrix region near a filler surface, termed as the interface, witnessed increasing interest, due to its possible influence on the macroscopic properties of the nanocomposite. The interphase is expecting to have different segmental dynamic, as compared to the pure matrix, which can percolate into the entire system. Here, the segmental dynamics of epoxy/Boehmite nanocomposite was studied by Broadband Dielectric Spectroscopy. It was found that an artificial relaxation process is present in the nanocomposite, on the contrary to the pure epoxy system. It was assigned to constrained fluctuations of polymer chains in the interfacial region, due to the nanofiller. However, the overall dynamic Tg of the system decreased with increasing filler concentration, indicating higher segmental mobility. This was in accordance with Temperature Modulated DSC investigations of specific heat capacity of the system, which was found to increase with increasing filler concentration, up to 10 wt%, indicating increasing mobility of the polymer matrix segments. Surprisingly, for the highest filler content, the heat capacity decreases, implying a formation of an immobilized rigid amorphous phase in the interfacial region.
In well-annealed thin polymer films, with non-repulsive polymer/substrate interactions, an irreversibly adsorbed layer is expected to form. These adsorbed layers have shown great potential for technological applications. However, their growth kinetics and molecular dynamics are still not fully understood. This is partially due to the hard accessibility of these layers in thin films. Here, the irreversibly adsorbed layers of homopolymer thin films are revealed by solvent-leaching experiments. First, the growth kinetics of these layers is investigated as a function of annealing times and original film thickness. The thickness, topography and quality of the adsorbed layer is controlled with Atomic Force Microscopy (AFM). Secondly, the molecular mobility of the adsorbed layer is investigated with Broadband Dielectric Spectroscopy (BDS). A recently developed nanostructured capacitor is employed to measure the adsorbed layers with a free surface layer. The results are quantitatively compared and discussed with respect to recently published work.
Optimization of laser treatment parameters of Inconel 686 overlay weld on carbon steel 13Mo4-5
(2017)
The work presents the effects of the change of the laser cladding parameters on microstructure, chemical composition and mechanical properties of Inconel 686 overlays (coatings). To obtain the best quality of these coatings the various parameters of laser cladding such as the power density of the laser beam, the laser beam velocity and overlapping ratio of the weld tracks were applied. The substrates were boilers plate made of the 13Mo4-5 steel. Ni - base alloys characterize by the excellent high-temperature corrosion resistance, good strength and good ability to work in aggressive environments. Applied overlays had a proper combination of the metal substrate in particular small amount of Fe. This could be achieved by the reduction of the substrate melting and its dissolution into the overlays. The microstructure, chemical composition of the obtained overlays were investigated by means of a light microscope, a scanning electron microscope (SEM) equipped with the EDS detector. The overlays had cellular-dendritic structure. The variations of the chemical composition (especially Mo, Ni and W ) in the interdendritic and dendritic regions were observed. The interdendritic regions were enriched during solidifications in Mo and W and had lower content of Ni.
Compact nuclear magnetic resonance (NMR) instruments make NMR spectroscopy and relaxometry accessible in industrial and harsh environments for reaction characterization and process control. Robust field integration of NMR systems have to face explosion protection or integration into process control systems with short set-up times. This paves the way for industrial automation in real process environments.
The design of failsafe, temperature and pressure resistant flow through cells along with their NMR-specific requirements is an essential cornerstone to enter industrial production plants and fulfill explosion safety requirements. Additionally, if fast reactions are monitored, suitable mixing devices need to be placed in close vicinity to the measuring volume to mix the reactants properly.
NMR-specific requirements aim at full quantitative pre-magnetization and acquisition with maximum sensitivity while reducing sample transfer times and dwell-times. All parameters are individually dependent on the applied NMR instrument.
Luckily, an increasing number of applications are reported together with an increasing variety of commercial equipment. However, these contributions have to be reviewed thoroughly.
The performance of sample flow cells commonly used in online analytics and especially for low-field NMR spectroscopy was experimentally and theoretically investigated by 1H-NMR experiments and numerical simulations. Especially, the applicability of 3D printed zirconium dioxide for innovative flow cell designs was of interest. Here, we demonstrate and discuss an automated test method to determine the critical parameters of flow through cells for quantitative online NMR spectroscopy. The setup is based on randomized setpoints of flow rates in order to reduce temperature related effects. Five flow cells and tubing were assessed and compared for high-field as well as low-field NMR spectrometers.
An understanding on crystallization behavior and kinetics in glasses is one of the important topics in the glass science and technology. Tsukada et al.1) found an extremely unique and curious phenomenon in the crystallization of multiferroic (ferroelectric and ferroelastic properties) ’-Gd2(MoO4)3 crystals in Gd2O3-MoO3-B2O3 glasses. That is, crystals formed in the crystallization break into small pieces with a triangle prism or pyramidal shape having a length of 50-150 um spontaneously during the crystallization in the inside of an electric furnace, not during the cooling in air after the crystallization. They proposed to call this phenomenon “self-powdering phenomenon”. To the best of our knowledge, such a self-powdering phenomenon has not been observed in the crystallization of any other glasses. To investigate this phenomenon is very important for the glass science and for the preparation of bulk crystallized glasses with ferroelastic crystals. In this work, the preparation of crystallized glasses keeping the original shape is challenged, and the mechanism of self-powdering phenomenon is proposed. Glasses with the compositions of 21Gd2O3-63MoO3-(16-x)B2O3-xTeO2 (mol%) (x=0, 2, 4, 8) such as 21Gd2O3-63MoO3-16B2O3 (GM16B) and 21Gd2O3-63MoO3-8B2O3-8TeO2 (GM8T8B) were prepared using a conventional melt quenching technique. The quenched glasses were heat-treated at some temperatures, and the crystalline phase present in the crystallized samples was identified by X-ray diffraction (XRD) analyses, and the morphology and birefringence of crystals formed were observed using a polarized optical microscope (POM). The densities of GM16B and GM8T8B glasses are 4.76 g/cm3 and 4.91 g/cam3, respectively, and these values are higher than the density of ’-Gd2(MoO4)3 crystal, 4.555 g/cm3. These differences in the density might induce the large stresses in the inside of crystals during the crystal growth. The crystallized glasses of GM16B with ’-Gd2(MoO4)3 crystals do not keep the original glass shape, showing self-powdering phenomenon (breaking into small pieces). However, the crystallized glasses of GM8T8B keep the original glass shape without indicating any self-powdering. It is proposed that the stress at the interface between the glassy phase and ’-Gd2(MoO4)3 crystalline phase might be reduced in GM8T8B glasses containing TeO2 with weak Te-O bonds.
Additive manufacturing (AM) offers an effective solution to the medical sector. It enables the production, on demand, of customised implants which match the patient’s anatomy, with grafts that promote bone growth, as well as surgical guides that help the surgeons. The objective of this project is to provide a comprehensive basis to enable the safe use of medical AM products with traceable and reliable dimensionalmeasurements. This will guarantee the reliability of medical AM products to notified bodies and facilitate acceptance of AM in the medical sector for a better quality of life.
We present an in situ PXRD investigation of the mechanochemical cocrystal formation of pyrazinamide with pimelic acid in two milling jar materials. DFT calculations of the two synthesized polymorphs suggest that the relative stability is based on a conformation change of pyrazinamide in the cocrystal.