Influence of annealing temperature on the mechanical properties of carbon supersaturated TaW coatings

The combination of ceramic hardness with metallic toughness is a major challenge in the development of protective coatings. The relative new concept of high entropy alloys (HEAs) can be a promising pathway to achieve new high-performance materials While HEA thin films have been studied to some extent by experimental and computational materials science, there is only limited information available about the influence of carbon on HEA thin films, especially when prepared with physical vapor deposition techniques. We have recently studied the properties of CrNbTaTiW thin films and observed a combination of high hardness and crack resistance for Ta and W-rich compositions when small amounts of carbon (\u3c 10 at%) is added [1]. To increase our understanding of the properties of these multicomponent HEA films, we have studied the influence of temperature and carbon on the structure and properties alloys in the ternary TaW-C system. The Ta-W-C thin films were deposited by non-reactive magnetron sputtering from elemental targets. The material properties were strongly depending on the carbon content. The TaW films crystallise in a bcc structure with a strong (110) texture with coherent grain boundaries. TEM analysis revealed that the films exhibit coherent grain boundaries with specific crystallographic directions. The addition of 8 at.% led to the formation of a metastable bcc supersaturated solid-solution without the formation of carbide precipitates. The main effect of the carbon addition was agrain refinement reducing the column width, which resulted in an increase in hardness from 14 to 16 GPa while the reduced E-modulus was unaffected. The enhanced hardness will be discussed in terms of solid solution hardening and grain refinement strengthening. The films were also annealed up to 900 °C to investigate the thermal stability. The TaW(C) remained in the bcc structure and no carbide formation was observed. Furthermore, the annealing had an age-hardening effect leading to a peak hardness of 26 GPa. These results indicate that TaW-C alloys are suitable for future high temperature application. [1] S. Fritze, P. Malinovskis, L. Riekehr, L. von Fieandt, E. Lewin, U. Jansson, Hard and crack resistant carbon supersaturated refractory multicomponent nanostructured coatings, Sci. Rep. (2018) 1–8

Research-Data Management Planning in the German Mathematical Community

In this paper we discuss the notion of research data for the field of mathematics and report on the status quo of research-data management and planning. A number of decentralized approaches are presented and compared to needs and challenges faced in three use cases from different mathematical subdisciplines. We highlight the importance of tailoring research-data management plans to mathematicians' research processes and discuss their usage all along the data life cycle

Wege zu neuartigen anorganisch-organischen Hybridmaterialien durch Anwendung von neuen B–C Kupplungsstrategien

π-Conjugated oligomers and polymers with tricoordinate boron centers incorporated into the main chain have attracted considerable attention as the interaction of the vacant p orbital on boron with an adjacent π system of the chain leads to conjugated materials with intriguing optical and electronic properties. This enables applicability in organic electronics and optoelectronics (OLEDs, OFETs, photovoltaics) or as sensory materials. The potential of our B–C coupling protocol using metal-free catalytic Si/B exchange condensation is demonstrated by the synthesis of a series of π-conjugated monodisperse (het)aryl oligoboranes. Variation of the (het)aryl moieties allowed for tunability of the optoelectronic properties of the materials. Additionally, catalytic C–C cross-coupling strategies were applied to synthesize oligofuryl-based mono- and bisboranes, as well as polymers. These studies led to very robust and highly emissive compounds (f up to 97 %), which allow for tuning of their emission color from blue to orange. Furthermore, this work includes investigations of reaction routes to a kinetically stabilized tetraoxaporphyrinogen. Being a key aspect of this work, a full investigation of the mechanism of the catalytic Si/B exchange was carried out. Additionally, this work presents the use of borenium cations to perform B–C coupling via intermolecular electrophilic borylation. Similar to the Si/B exchange, this route is capable of giving access to diaryl(bromo)boranes.π-konjugierte Oligomere und Polymere mit dreifach koordinierten Bor-Zentren, die in die Hauptkette eingebaut sind, haben große Aufmerksamkeit erregt, da die Wechselwirkung des vakanten p-Orbitals am Bor mit dem π-System der Kette zu konjugierten Materialien mit faszinierenden optischen und elektronischen Eigenschaften führt. Dies ermöglicht die Anwendbarkeit in organischer Elektronik und Optoelektronik (OLEDs, OFETs, Photovoltaik) oder als sensorische Materialien. Das Potenzial unseres B–C-Kupplungsprotokolls unter Verwendung der metallfreien katalytischen Si/B-Austauschskondensation wird durch die Synthese einer Reihe von π-konjugierten monodispersen (Het)aryl-Oligoboranen demonstriert. Durch Variation der (Het)aryl-Anteile konnten die optoelektronischen Eigenschaften der Materialien eingestellt werden. Zusätzlich wurden katalytische C–C-Kreuzkupplungsstrategien angewandt, um Oligofuryl-basierte Mono- und Bisborane sowie Polymere zu synthetisieren. Diese Untersuchungen führten zu sehr robusten und stark emittierenden Verbindungen (f bis zu 97 %), die die Einstellung ihrer Emissionsfarbe von blau bis orange ermöglichen. Weiterhin beinhaltet diese Arbeit Untersuchungen von Reaktionswegen zu einem kinetisch stabilisierten Tetraoxaporphyrinogen. Als ein Schlüsselaspekt dieser Arbeit wurde eine vollständige Untersuchung des Mechanismus des katalytischen Si/B-Austauschs durchgeführt. Zusätzlich wird in dieser Arbeit die Verwendung von Borenium-Kationen zur Durchführung von B–C-Kupplungen über intermolekulare elektrophile Borylierungen vorgestellt. Ähnlich wie beim Si/B-Austausch kann dieser Weg genutzt werden, um Zugang zu Diaryl(bromo)boranen zu geben

ABA Type Amphiphiles with Poly(2-benzhydryl-2-oxazine) Moieties : Synthesis, Characterization and Inverse Thermogelation

Thermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2- benzhydryl-2-oxazine) (pBhOzi) repeating units are described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2-methyl-2-oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx-b-pBhOzi-b-pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2-benzhydryl-2-oxazoline) block (pMeOx-b-pBhOx-b-pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.%. For 25 wt.% pMeOx-b-pBhOzi-b-pMeOx, a surprisingly high storage modulus of approximate to 22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self-assemblies of pMeOx-b-pBhOzi-b-pMeOx and pMeOx-b-pBhOx-b-pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx-b-pBhOzi-b-pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2-oxazoline) and poly(2-oxazine)-based self-assemblies, but additional studies will be needed to unravel the exact mechanism.Peer reviewe

Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings

Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase forma-tion, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were inves-tigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 degrees C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 degrees C exhibited a single NaCl-type multicom-ponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 degrees C, or exposed to UHV annealing at 1000 degrees C, however, revealed the decom-position of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in appli-cations at elevated temperatures