TY - JOUR A1 - Bachmann, F. A1 - Bente, Klaas A1 - Codutti, A. A1 - Faivre, D. T1 - Using Shape Diversity on the Way to Structure-Function Designs for Magnetic Micropropellers N2 - Synthetic microswimmers mimicking biological movements at the microscale have been developed in recent years. Actuating helical magnetic materials with a homogeneous rotating magnetic field is one of the most widespread techniques for propulsion at the microscale, partly because the actuation strategy revolves around a simple linear relationship between the actuating field frequency and the propeller velocity. However, full control of the swimmers’ motion has remained a challenge. Increasing the controllability of micropropellers is crucial to achieve complex actuation schemes that, in turn, are directly relevant for numerous applications. However, the simplicity of the linear relationship limits the possibilities and flexibilities of swarm control. Using a pool of randomly shaped magnetic microswimmers, we show that the complexity of shape can advantageously be translated into enhanced control. In particular, directional reversal of sorted micropropellers is controlled by the frequency of the actuating field. This directionality change is linked to the balance between magnetic and hydrodynamic forces. We further show an example of how this behavior can experimentally lead to simple and effective sorting of individual swimmers from a group. The ability of these propellers to reverse swimming direction solely by frequency increases the control possibilities and is an example for propeller designs, where the complexity needed for many applications is embedded directly in the propeller geometry rather than external factors such as actuation sequences. KW - Active Matter KW - Low Reynolds number swimmers KW - Actuating materials KW - Microstructure KW - Swarming PY - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.11.034039 VL - 11 IS - 3 SP - 034039 PB - American Physical Society AN - OPUS4-47731 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frei, J. A1 - Alexandrov, B. A1 - Rethmeier, Michael T1 - Low heat input gas metal arc welding for dissimilar metal weld overlays part III: hydrogen-assisted cracking susceptibility N2 - Dissimilar metal weld overlays of nickel-base alloys on low-alloy steel components are commonly used in the oil and gas, petrochemical, and power generation industries to provide corrosion and oxidation resistance in a wide range of service Environments and temperatures. Traditionally, dissimilar weld overlays are produced using cold or hot wire gas tungsten arc welding. This study aims to identify and evaluate potential advantages of low heat input gas metal arc welding processes over the conventional gas tungsten arc welding in the production of such overlays. Parts I and II of this publication series described characteristics of the heat-affected zone and the transition zone region of alloy 625 on grade 22 steel overlays. These results indicate a good resistance against hydrogen-assisted cracking, which is being verified within this third part of the publication series. To determine the hydrogen-assisted cracking susceptibility, welded samples are tested using the delayed hydrogen-assisted cracking test. Fractography is performed using scanning electron microscopy along with energy dispersive spectroscopy. The results confirm the suitability and efficiency of low heat input gas metal arc welding for dissimilar weld overlays. Variation of the postweld heat treatment procedure bears potential for improvement in this respect. KW - Low heat input GMA welding KW - Dissimilar metal weld overlays KW - Coarse-grained heat-affected zone KW - Grain size KW - Microstructure KW - Fusion zone KW - Nickel alloys PY - 2019 U6 - https://doi.org/10.1007/s40194-018-0674-7 VL - 63 IS - 3 SP - 591 EP - 598 PB - Springer AN - OPUS4-48096 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -