TY - JOUR A1 - Yilmaz, M. A1 - Wollschläger, Nicole A1 - Esfahani, M. N. A1 - Österle, Werner A1 - Leblebici, Y. A1 - Alaca, B. E. T1 - Superplastic behavior of silica nanowires obtained by direct patterning of silsesquioxane-based precursors N2 - Silica nanowires spanning 10 μm-deep trenches are fabricated from different types of silsesquioxane-based precursors by direct e-beam patterning on silicon followed by release through deep reactive ion etching. Nanowire aspect ratios as large as 150 are achieved with a critical dimension of about 50 nm and nearly rectangular cross-sections. In situ bending tests are carried out inside a scanning electron microscope, where the etch depth of 10 mm provides sufficient space for deformation. Silica NWs are indeed observed to exhibit superplastic behavior without fracture with deflections reaching the full etch depth, about two orders of magnitude larger than the nanowire thickness. A large-deformation elastic bending model is utilized for predicting the deviation from the elastic behavior. The results of forty different tests indicate a critical stress level of 0.1–0.4 GPa for the onset of plasticity. The study hints at the possibility of fabricating silica nanowires in a monolithic Fashion through direct e-beam patterning of silsesquioxane-based resins. The fabrication technology is compatible with semiconductor manufacturing and provides silica nanowires with a very good structural integrity. KW - Silica nanowires KW - HSQ KW - Superplasticity KW - In situ bending tests PY - 2017 DO - https://doi.org/10.1088/1361-6528/aa5b80 SN - 0957-4484 SN - 1361-6528 VL - 28 IS - 11 SP - Article 115302, 1 EP - 10 AN - OPUS4-39166 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Konnertz, Nora A1 - Ding, Yi A1 - Harrison, W.J. A1 - Budd, P.M. A1 - Schönhals, Andreas A1 - Böhning, Martin T1 - Molecular mobility and gas transport properties of nanocomposites based on PIM-1 and polyhedral oligomeric phenethyl-silsesquioxanes (POSS) N2 - Polymers with intrinsic microporosity (PIMs) are of great interest in the field of gas separation membranes. Already the first synthesized PIM-1 shows extraordinary permeability and selectivity. Unfortunately, PIM-1 is susceptible to physical aging and thus gradually loses its outstanding properties. In this study a polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) was used as a nanofiller (0–40 wt%) in the PIM-1 matrix to potentially improve the gas transport properties and prevent physical aging. The molecular mobility of the solution-cast nanocomposite films was analyzed by Broadband Dielectric Spectroscopy (BDS). Furthermore, gas permeability was determined with the time lag method (0–20 bar upstream pressure) at 35 °C for N2, O2, CH4 and CO2. KW - Broadband Dielectric Spectroscopy KW - Gas separation KW - Gas permeation KW - Polymers of intrinsic microporosity KW - Nanocomposite KW - POSS KW - PIM-1 PY - 2017 DO - https://doi.org/10.1016/j.memsci.2017.02.007 SN - 0376-7388 SN - 1873-3123 VL - 529 SP - 274 EP - 285 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-39169 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Selleng, Christian A1 - Meng, Birgit A1 - Gröger, K. A1 - Fontana, Patrick T1 - Einflussgrößen auf die Wirksamkeit einer Wärmebehandlung von Ultrahochfestem Beton (UHFB) T1 - Influencing factors for the effectivity of heat treatment of ultrahigh performance concrete (UHPC) N2 - Mittels Wärmebehandlung lassen sich die hervorragenden Eigenschaften von UHFB nochmals verbessern. Die für eine optimale Umsetzung relevanten Randbedingungen werden aktuell in der Fachwelt diskutiert. In dieser Veröffentlichung werden die Ergebnisse eines Forschungsprojekts vorgestellt, das die Wirkung verschiedener Einflussgrößen bei der Wärmebehandlung auf die Eigenschaften von UHFB zum Thema hatte. Dabei wurden die Art des Schutzes gegen das Austrocknen, die Vorlagerungszeit und die Haltezeit variiert. Um die zugrunde liegenden Prozesse zu verstehen, wurde der Phasenbestand mittels Röntgendiffraktometrie untersucht. Die höchsten Druckfestigkeiten des UHFB ließen sich bei einer Wärmebehandlung mit Wasserlagerung erzielen, da hierbei eine weitere Hydratation begünstigt wird. Vergleichsweise niedriger waren die Steigerungen bei einer Behandlung mit Schutz vor Austrocknung, während eine ungeschützte Behandlung zu deutlich geringeren Festigkeiten führte. Die Vorlagerungszeit beträgt im Idealfall einige Tage, um die Ausbildung eines offenbar günstigen Ausgangsgefüges sicherzustellen. Die Haltezeit sollte möglichst ausgedehnt sein, weil die Hydratation entsprechend lange gefördert wird. Im oberflächennahen Bereich war unter bestimmten Bedingungen eine Zonierung zu beobachten, deren Ursachen und Folgen, insbesondere in Bezug auf die Dauerhaftigkeit, weitere Forschung erfordern. KW - Ultra-Hochleistungsbeton KW - Wärmebehandlung KW - Behandlungsparameter KW - Vorlagerungszeit KW - Haltezeit KW - Festigkeitssteigerung KW - Zonierung KW - Ettringit PY - 2017 DO - https://doi.org/10.1002/best.201600059 SN - 0005-9900 VL - 112 IS - 1 SP - 12 EP - 21 PB - Ernst & Sohn AN - OPUS4-39171 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nolze, Gert A1 - Winkelmann, Aimo T1 - Crystallometric and projective properties of Kikuchi diffraction patterns N2 - Kikuchi diffraction patterns can provide fundamental information about the lattice metric of a crystalline phase. In order to improve the possible precision and accuracy of lattice parameter determination from the features observed in Kikuchi patterns, some useful fundamental relationships of geometric crystal-lography are reviewed, which hold true independently of the actual crystal symmetry. The Kikuchi band positions and intersections and the Kikuchi band widths are highly interrelated, which is illustrated by the fact that all lattice plane trace positions of the crystal are predetermined by the definition of only four traces. If, additionally, the projection centre of the gnomonic projection is known, the lattice parameter ratios and the angles between the basis vectors are fixed. A further definition of one specific Kikuchi band width is sufficient to set the absolute sizes of all lattice parameters and to predict the widths of all Kikuchi bands. The mathematical properties of the gnomonic projection turn out to be central to an improved interpretation of Kikuchi pattern data, emphasizing the importance of the exact knowledge of the projection centre. KW - EBSD KW - Crystallography KW - Kikuchi patterns KW - Projective geometry PY - 2017 DO - https://doi.org/10.1107/S1600576716017477 SN - 1600-5767 VL - 50 IS - Part 1 SP - 102 EP - 119 PB - International Union of Crystallography AN - OPUS4-39061 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madia, Mauro A1 - Schork, B. A1 - Bernhard, J. A1 - Kaffenberger, M. T1 - Multiple crack initiation and propagation in weldments under fatigue loading N2 - The work aims at addressing the modelling and implementation of criteria for multiple crack propagation, including interaction and coalescence, for a more reliable fracture mechanics-based prediction of stress-life curves for weldments. A large experimental work is presented in which micro-cracks have been made visible by heat-tinting at successive stages of fatigue life of the welded specimens. Here the correlation between the number of initiation sites and the applied stress level has been also investigated. The criteria have been implemented in in-house software, which allows multiple fatigue crack propagation, and validated against selected experimental tests. The results have shown that the modelling of multiple crack propagation and interaction is crucial for the prediction of the fatigue strength of weldments, both in finite and infinite life regime. T2 - FDMD 2017 CY - Lecco, Italy DA - 19.09.2017 KW - Weldments KW - Fatigue strength KW - Multiple crack propagation PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-438593 DO - https://doi.org/10.1016/j.prostr.2017.11.108 SN - 2452-3216 VL - 7 SP - 423 EP - 430 PB - Elsevier B.V. AN - OPUS4-43859 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lüchtenborg, Jörg A1 - Mühler, T. A1 - Léonard, Fabien A1 - Günster, Jens T1 - Laser-induced slip casting (LIS) – a new additive manufacturing process for dense ceramics demonstrated with Si3N4 N2 - Up to now, there exists a lack of methods for the additive manufacturing of voluminous ceramic parts with properties comparable to those of conventionally manufactured ones. A high density after sintering is needed to reach the superior properties of ceramic materials. We have developed a new additive manufacturing method, Laser-Induced Slip casting (LIS), to generate ceramic green bodies with high particle packing density and with virtually no restriction in the particle size of the feedstock, especially in terms of small particles. This is achieved by laser-induced local drying of slurries, with the process resembling many features of the well-established stereolithography, but without the excessive use of polymeric material. Thus, unlike the stereolithography process, the resulting green bodies can be processed like traditionally produced ceramic parts. This method allows large and dense additive-manufactured parts to be obtained from conventional water-based ceramic slurries. As an example, we will demonstrate the application of this novel technique with Si3N4. KW - Additive manufacturing KW - Ceramics PY - 2017 DO - https://doi.org/10.4416/JCST2017-00091 SN - 2190-9385 VL - 8 IS - 4 SP - 531 EP - 540 PB - Göller Verlag CY - Baden-Baden AN - OPUS4-43738 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Häusler, Ines T1 - Volume fraction determination of discretely oriented disc-shaped precipitates in transmission mode T1 - Bestimmung des Volumenanteils von diskret orientierten kreisscheibenförmigen Ausscheidungen im Transmissionsmodus N2 - In der vorliegenden Arbeit wurde eine Formel zur Berechnung des Volumenantei ls dis­ kret orientierter scheibenförmiger Phasen für die Untersuchung im Transmissionsmodus hergeleitet, validiert und mit bereits veröffent­ lichen Formeln verglichen. Bei diesem Ver­ gleich konnte gezeigt werden,dass die in zahl­ reichen Veröffentlichungen benutzte Formel von E. E. Underwood für die Volumenanteils­ bestimmungbeidiskret orientierten Ausschei­ dungsphasen nicht benutzt werden sollte, da sie den Volumenanteil deutlich unterschätzt. Die Ursache liegt in der von E.E. Underwood getroffenen Annahme, dass die kreisförmigen Scheiben regellos angeordnet und nicht aus­ gerichtet sind, was in Al-Legierungen in der Regel nicht der Fall ist. KW - Material KW - TEM KW - Volumenbruchteil KW - Al-Cu-Li-Legierung KW - Ausscheidungen PY - 2017 DO - https://doi.org/10.3139/147.110471 SN - 0032-678X SN - 2195-8599 VL - 54 IS - 12 SP - 816 EP - 837 PB - Carl Hanser AN - OPUS4-43722 LA - mul AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gook, S. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Hybrid laser arc welding of high grade X80 and X120 pipeline steels N2 - The aim of the present work was to investigate the possibilities of hybrid laser arc welding regarding reliable production of longitudinal welds of high strength pipe steels X80 and X120 and to evaluate achievable mechanical properties of laser hybrid welds. The study focused on weld toughness examination in low temperature range up to -60 °C. SЮТЭКЛХО ПТХХОЫ ЦКЭОЫТКХЬ were identified in the context of this task. It could be shown that metal cored electrodes guaranteed sufficient Charpy impact toughness at low temperature for both investigated materials. Modern arc welding technologies such as modified pulsed spray arc were used to promote deeper Penetration of the filler material into the narrow laser welding gap. Edge preparation with a 14 mm deep root face was considered as optimum, because no penetration of the filler material could be detected beyond this depth limit and therefore any metallurgical influences on the weld metal properties through the welding wire could be excluded. KW - High strength steel KW - Longitudinal weld KW - Modified spray arc KW - Pipeline KW - Hybrid laser arc welding PY - 2017 SN - 2499-9733 SN - 2305-414Х VL - 1 IS - 22 SP - 21 EP - 35 AN - OPUS4-44343 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marko, A. A1 - Graf, B. A1 - Gook, S. A1 - Rethmeier, Michael T1 - Application of D-optimum experimental designs in consideration of restrictions for laser metal deposition N2 - The process of laser metal deposition can be applied in many ways. Mostly, it is relevant to coating, for repair welding and for additive manufacturing. To increase the effectiveness and the productiveness, a good process understanding is necessary. Statistical test planning is effectual and often used for this purpose. For financial and temporal reasons, a restriction of the test space is reasonable. In this case, it is recommended to use a D-optimal experimental design which is practically applied to extend existing test plans or if process Limits are known. This paper investigates the applicability of a D-optimum experimental design for the laser metal deposition. The results are compared to the current results of a full factorial test plan. Known restrictions are used for the limitation of the test space. Ti6Al4 is utilized as Substrate material and powder. Comparable results of the D-optimal experimental design and of the full factorial test plan can be demonstrated. However, 80 % of time can be saved by the experimental procedure. For this reason, the application of D-optimal experimental design for laser metal deposition is recommend. KW - Design of experiments KW - Repair welding KW - Additive manufacturing KW - Cladding parameter KW - Laser metal deposition KW - Laser cladding PY - 2017 SN - 2499-9733 SN - 2305-414Х VL - 3 IS - 24 SP - 46 EP - 60 AN - OPUS4-44344 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Martynenko, Irina ED - Baimuratov, A. S. ED - Osipova, V. A. ED - Kuznetsova, V. A. ED - Purcell-Milton, F. ED - Rukhlenko, I. D. ED - Fedorov, A. V. ED - Gun'ko, Y. K. ED - Baranov, A. V. T1 - Excitation energy dependence of the photoluminescence quantum yield of core/shell CdSe/CdS quantum dots and correlation with circular dichroism N2 - Quantum dot (QD) based nanomaterials are very promising materials for the fabrication of optoelectronic devices like solar cells, light emitting diodes (LEDs), and photodetectors as well as as reporters for chemo- and biosensing and bioimaging. Many of These applications involve the monitoring of changes in photoluminescence intensity and energy transfer processes which can strongly depend on excitation wavelength or energy. In this work, we analyzed the excitation energy dependence (EED) of the photoluminescence quantum yields (PL QYs) and decay kinetics and the circular dichroism (CD) spectra of CdSe/CdS core/shell QDs with different thicknesses of the surface passivation shell. Our results demonstrate a strong correlation between the spectral position of local maxima observed in the EED of PL QY and the zero-crossing points of the CD profiles. Theoretical analysis of the energy band structure of the QDs with effective mass approximation suggests that these structures could correspond to exciton energy levels. This underlines the potential of CD spectroscopy for the study of electronic energy structure of chiroptically active nanocrystals which reveal quantum confinement effects. KW - Fluorescence KW - Semiconductor KW - Nanoparticle KW - Surface chemistry KW - Quantum yield KW - Lifetime KW - Nanocrystal KW - Cysteine KW - Thiol KW - Ligand KW - Quantum dot KW - CdSe KW - Exciton KW - Circular dichroism KW - Theory KW - Excitation spectra KW - Excitation energy dependence PY - 2017 DO - https://doi.org/10.1021/acs.chemmater.7b04478 SN - 0897-4756 SN - 1520-5002 VL - 30 IS - 2 SP - 465 EP - 471 PB - ACS Publications AN - OPUS4-44034 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -