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Refractory high-entropy alloys (RHEAs) are potential candidate materials for use in next-generation nuclear reactors due to their excellent mechanical performance at high temperatures. Here, we investigate the microstructure and mechanical properties of the nanocrystalline RHEA TiZrNbHfTa before and after irradiation with He2+ ions to determine radiation-induced property changes. Using nanoindentation and in situ microtensile testing we find only small changes in hardness after irradiation but a significant increase in yield and ultimate tensile strength without loss in ductility. This is associated with radiation hardening and a shift from shear localization failure with smooth fracture surfaces to a fracture morphology consisting of fine dimples and intergranular failure characteristics. Overall, the material shows excellent damage-tolerant properties with good combinations of strength and ductility both prior to and after ion irradiation.

The feasibility of engineering bimodal grain size distributions to achieve superior mechanical properties was explored in two face-centered cubic compositionally complex alloys, namely CrMnFeCoNi and its high-performance subvariant CrCoNi. Therefore both alloys were processed down to the nanocrystalline grain size regime by utilizing high-pressure torsion and subsequently annealed at intermediate temperatures. Especially the CrCoNi alloy is prone to formation of bimodal microstructures and for an annealing treatment at 500 °C for 100 h an excellent combination of ultra-high tensile strength, exceeding 1500 MPa, and decent ductility with elongations to failure of 10% could be achieved.

A CrMnFeCoNi high-entropy alloy was investigated by nanoindentation from room temperature to 400 °C in the nanocrystalline state and cast plus homogenized coarse-grained state. In the latter case a 〈100〉-orientated grain was selected by electron back scatter diffraction for nanoindentation. It was found that hardness decreases more strongly with increasing temperature than Young’s modulus, especially for the coarse-grained state. The modulus of the nanocrystalline state was slightly higher than that of the coarse-grained one. For the coarse-grained sample a strong thermally activated deformation behavior was found up to 100–150 °C, followed by a diminishing thermally activated contribution at higher testing temperatures. For the nanocrystalline state, different temperature dependent deformation mechanisms are proposed. At low temperatures, the governing processes appear to be similar to those in the coarse-grained sample, but with increasing temperature, dislocation-grain boundary interactions likely become more dominant. Finally, at 400 °C, decomposition of the nanocrystalline alloy causes a further reduction in thermal activation. This is rationalized by a reduction of the deformation controlling internal length scale by precipitate formation in conjunction with a diffusional contribution.

The equiatomic high-entropy alloy (HEA), CrMnFeCoNi, has recently been shown to be microstructurally unstable, resulting in a multi-phase microstructure after intermediate-temperature annealing treatments. The decomposition occurs rapidly in the nanocrystalline (NC) state and after longer annealing times in coarse-grained states. To characterize the mechanical properties of differently annealed NC states containing multiple phases, nanoindentation was used. The results revealed besides drastic changes in hardness, also for the first time significant changes in the Young's modulus and strain rate sensitivity. Nanoindentation of NC HEAs is, therefore, a useful complementary screening tool with high potential as a high throughput approach to detect phase decomposition, which can also be used to qualitatively predict the long-term stability of single-phase HEAs. Keywords: Nanoindentation, High-entropy alloys, Severe plastic deformation, High-pressure torsion, Phase stability, Nanocrystalline

Nachdem die Gehaltsunterschiede zwischen deutschen Altenpflegefachkraften und lu-xemburgischen Aides-Soignants ausfuhrlich dargestellt wurden, sollen in diesem Kapitel die Struktur sowie die Rahmenbedingungen in der luxemburgischen Altenpflege aufge-zeigt werden. Innerhalb des letzten Jahrzehnts prasentierte sich Luxemburg als der gros-te Wachstumsmarkt in der Grosregion SaarLorLux. Diese Entwicklung schliest auch die Altenpflege mit ein. So ist in Luxemburg „[…] die Beschaftigtenzahl […] im Jahr 2011 mehr als doppelt so hoch wie noch zwolf Jahre zuvor.

Die vorliegende Untersuchung hat zum Ziel, das Erleben der Statuspassage deutscher Altenpflegefachkrafte in Luxemburg zu eruieren. Sie soll also ein Phanomen, uber das noch wenig bekannt ist, beschreiben und analysieren, womit diese Arbeit dem deskriptiv-analytischen Design zuzuordnen ist (vgl. Mayer 2011: 125).

In Deutschland gibt es uber 13.030 Pflegeheime (Stand: 31.12.2013, vgl. Statistisches Bundesamt 2015), davon 492 in Rheinland-Pfalz (vgl. Statistisches Landesamt RLP 2015: 18) und 131 im Saarland (vgl. Pflegegesellschaft Saarland 2015). Die vollstationare Pflege in Form von Pflege- oder Altenheimen stellt nach der hauslichen Pflege die hau-figste Versorgungsform fur altere Menschen dar (vgl. Jacobs et al. 2015: 19). Die Ten-denz ist steigend: So wird von einem Zuwachs an Pflegeheimen um 29 % im Zeitraum von 2005 bis 2011 berichtet (vgl. ebd.).

Die beschriebene Situation der Nicht-Anerkennung von Altenpflegefachkraften mit drei-jahrigem deutschem Altenpflegeexamen als ebensolche Pflegefachkrafte in Luxemburg ist nur in zweiter Linie Folge der EU-Richtlinie 2006/36/EG. In erster Linie kommt diese unbefriedigende Situation durch das Fehlen einer einheitlichen Pflegeausbildung in Deutschland zustande, wie sie die generalistische Pflegeausbildung fruhestens 2018 – eher spater – bieten soll. Das heist auch, dass entsprechende Absolventen einer solchen generalistischen Ausbildung fruhestens im Jahr 2021 ins Berufsleben einsteigen konnten.

Acta materialia 142, 201 - 212 (2018). doi:10.1016/j.actamat.2017.09.035, An equiatomic, single-phase TiZrNbHfTa high-entropy alloy was subjected to high-pressure torsion,leading to a grain size below 100 nm. Introducing a nanocrystalline microstructure to the material shouldhelp to accelerate a possible phase decomposition of the material by having a high amount of fastdiffusion pathways and possible nucleation sites in the form of grain boundaries. In order to test thematerials thermodynamic stability the nanocrystalline high-entropy alloy. was subjected to various heattreatments for temperatures between 300 C and 1100 C. Isochronal heat treatments (1 h) resulted in ahardness increase from 420 HV1 for the as-processed state to 530 HV1 for an annealing temperature of500 C, while for temperatures of 700 C and higher a softening compared to the as-processed stateoccurred. In order to clarify this unexpected annealing response, analysis of selected microstructuralstates was performed utilizing electron microscopy, x-ray diffraction as well as mechanical testing to gainfurther information on microstructure-property relationships. Complementary, thermodynamic simulationswere performed via the Calphad approach and compared to the experimental results. A phasedecomposition of the originally equimolar single-phase high-entropy alloy into a NbTa-rich bodycenteredcubic phase and ZrHf-rich phases, which occurred in two different crystal structures dependingon the annealing temperature, was the main reason for the property changes. The obtained results notonly give valuable new insights into the phase stability of the TiZrNbHfTa alloy, but also demonstrate theimpact of the newly forming phases in regards to mechanical properties and its implication for a possiblepractical application of this alloy., Published by Elsevier Science, Amsterdam [u.a.]

Materials 11(5), 662 (2018). doi:10.3390/ma11050662, An equiatomic CrCoNi medium-entropy alloy was subjected to high-pressure torsion.This process led to a refinement of the microstructure to a grain size of about 50 nm, combined witha strong increase in the materials hardness. Subsequently, the thermodynamic stability of the mediumentropy alloy was evaluated by isothermal and isochronal heat treatments. Annealed sampleswere investigated by scanning and transmission electron microscopy as well as X-ray diffraction,and were subjected to tensile tests to establish microstructure-property relationships. Furthermore,a comparison of mechanical properties with a grade 316L stainless steel was performed in order toevaluate if the CrCoNi alloy is competitive with commercially available structural materials in thenanocrystalline state. A minority phase embedded in the face-centered cubic matrix of the CrCoNialloy could be observed in multiple annealed states, as well as the as-received and high-pressuretorsion processed material. For 200 h of annealing at 500 C, it was determined that the minorityphase has a hexagonal-closed-packed crystal structure. A possible explanation for the formation ofthe phase is a preferential segregation of Co to stacking faults., Published by MDPI, Basel

In contrast to the general notion about the annealing behavior of coarse grained materials, hardening phenomena in nanocrystalline materials can occur. Although the phenomena have already been recognized several years ago, the mechanisms behind are still controversially discussed. For example, the influence of solutes segregated to grain boundaries on the strengthening mechanism is unclear. We present a combination of atom probe tomography and mechanical data to reveal the role of segregations to the strengthening. The results show that despite large modifications of the boundary chemistry the mechanical behavior remains widely unaffected. Additionally, it will be shown that hardening upon annealing can only occur below a material-specific grain size threshold value.