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Directional solidification (DS) is an established manufacturing process to produce highperformance components from metallic materials with optimized properties. Materials for demanding high-temperature applications, for instance in energy generation and aircraft engine technology, can only be successfully produced using methods such as directional solidification.It has been applied on an industrial scale for a considerable amount of time, but advancing this method beyond the current applications is still challenging and almost exclusively limited to post-process characterization of the developed microstructures. For a knowledge-based advancement and a contribution to material innovation, in-situ studies of the DS process are crucial using realistic sample sizes to ensure scalability of the results to industrial sizes. Therefore, a specially designed Flexible Directional Solidification (FlexiDS) device was developed for use at the P07 High Energy Materials Science (HEMS) beamline at PETRA III (Deutsches Elektronen-Synchrotron (DESY); Hamburg, Germany). In general, the process conditions of the crucible-free, inductively heated FlexiDS device can be varied from 6 to 12000 mm/h (vertical withdrawal rate) and from 0 to 35 rpm (axial sample rotation).Moreover, different atmospheres like Ar, N2, vacuum can be used during operation. The device is designed for maximum operation temperatures of 2200 °C. This unique device allows in-situ examination of the directional solidification process and subsequent solid-state reactions by Xray diffraction in the transmission mode. Within this project, different structural intermetallic alloys with liquidus temperatures up to 2000 °C were studied in terms of liquid-solid regions, transformations and decompositions, with varying process conditions.

Lamellar eutectic NiAl–Cr(Mo) alloys show an increased fracture toughness due to different toughening mechanisms. These mechanisms result from the fibrous or lamellar microstructure of the two constituting phases α‐Cr(Mo) and β‐NiAl. However, the fracture toughness of the individual phases and the evolution from early crack growth to the toughening mechanisms have not yet been systematically studied. Herein, bending tests on focused ion beam (FIB)‐notched microcantilever beams are used to characterize the small‐scale fracture properties. The micromechanical investigations reveal that the fracture toughness of the α‐Cr(Mo) phase (7.5−9.1 MPam) is much higher than the fracture toughness of β‐NiAl (2.2−2.9 MPam). Larger cantilevers in the crack arresting orientation show an enhanced fracture toughness with up to 14.4 MPam, which is still lower than the one of macroscopic experiments. This is attributed to the small interaction volume of the crack, which hinders the full exploitation of potential extrinsic toughening mechanisms.

Depending on the process parameters, the directional solidification (DS) of eutectic alloys leads to a fibrous or lamellar microstructure. A physically motivated creep model which was evaluated for a DS-eutectic with a fibrous microstructure is applied to a DS-eutectic with a lamellar microstructure. Creep curves are simulated and compared to experimentally measured ones. It is shown, that the simulation is in good agreement with the experiment.

The directional solidification (DS) of the eutectic alloy NiAl-9Mo (at. %) leads to a formation of single-crystal molybdenumrich fibers embedded in a NiAl matrix and has promising high-temperature properties. Material models describing each phase are necessary to be able to predict the materials behavior of the in-situ composite under several conditions. Using a onedimensional Voigt-Taylor model based on a phenomenological approach, the creep behavior is simulated and the results are compared to experimental data.

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